Encyclopedia of Smart Materials (Vols 1 and 2) - M. Schwartz (2002) WW Part 13 pdf

creases during constrained heating It has been also found that the stress is affected by many other parameters, including the thermomechanical history and the prestrain (69,86) Depending on the magnitude of the prestrain, either a plastic upper limit or an elastic upper limit to σr exists At lower prestrains, the stress increases during heating until the reverse transformation is completed The upper stress limit in this case is given by the strain divided by Young’s modulus When the prestrain is sufficiently high, the stress increases during heating until plastic yield occurs at a temperature Md So, the upper stress limit in this case is the plastic yield stress σy Evidently, in cyclic actuation, the maximum temperature should be kept below Md In all cases discussed, a constraint prevents the SMA element from returning to the hot shape when heated Thus, a more specific name would be “hot shape” recovery stress It has been found in trained Cu-based SMA-elements that stresses can also be generated when the TWME is impeded during cooling (69,83) Because the constraint in this case prevents the sample from returning to the cold shape when cooled, the generated stress was called “cold shape” recovery stress to contrast with “hot shape” recovery stress Practical applications have not been reported so far Quantitative comprehension of recovery stress generation presented in the literature is far below the comprehension of the other functional properties of shape-memory alloys Therefore, recovery stress generation was discussed a bit more extensively than other functional properties Considering the substantial research efforts in developing hybrid composites that have embedded shape-memory elements, substantial progress in quantitatively understanding recovery stress generation can be expected in the near future Work Output One- and two-way memory effects can be used for free recovery applications in which the single function of the SMA element is to cause motions without any biasing stress Under constant strains, shape-memory elements can generate substantial recovery stresses Between these two extremes of free recovery and completely constrained recovery, shape-memory components can yield a wide variety of combinations of strains and stresses As shown in Figure 6 The work output The sample is deformed perature at a below Mf (A→B), followed by unloading ( loading again using a bias weight W (C→D) Shape re curs under an opposing force W during heating to a te above Af (D→E) So work is done [from (69)] Fig 6, a shape-memory element can be deform force in the martensitic condition or during the transformation and can exert a substantially hig as it reverts to the hot shape when heated So, to 5 J/g is done during heating This concept can in thermal actuators in which the SMA elemen vated by an increase in the environmental tem or in electrical actuators in which the SMA elem general activated by direct Joule heating The wor to deform the SMA element is much lower than that can be obtained during heating This has bee sis of many prototypes of heat engines that con into useful work [see (117)] SMA actuators offer distinct advantages c other types of actuators (118) The main advanta by far SMA actuators offer the highest work an to-weight ratios of all available actuating techn low levels of weight (119) These high-work and hi densities enable a whole class of applications (e field of micro actuation) that are impossible to r using other actuating technologies (120–123) SM tors can be reduced mostly to a single SMA elemen auxiliary parts, resulting in simple compact an devices Several important drawbacks that limit the us actuators to specific niches should also be consid conversion of heat into mechanical energy via SM tors was studied extensively 15 to 25 years ag thermodynamic calculations showed that the m theoretical efficiency of an SMA actuator is less (124) In practice, the conversion of heat into m work is less efficient, and the result is that real ef even one order of magnitude smaller than the th value Another drawback is that the SMA actua be heated and cooled The low cooling rate, especia the use of SMA actuators to relatively low-frequ plications It was discussed before that stresses i Cu-based SMA elements can also be generated superelastic loading and unloading, as explained before A detailed analysis can be found in (125,126) BIBLIOGRAPHY 1 L Delaey, M Chandrasekaran, M Andrade, and J Van Humbeeck, Proc Int Conf Solid-Solid Phase Transform pp 1429–1453 2 T Maki, and T Tamura, Proc ICOMAT-86, 1986, pp 963– 970 3 J Van Humbeeck, M Chandrasekaran and R Stalmans, Proc ICOMAT-92, Monterey, CA, 1993, pp 1015–1025 4 Q Gu, J Van Humbeeck, and L Delaey, transformation and shape memory effect in Fe-Mn-Si alloys, J Phys IV Col C3 4: C3-135–140 (1994) 5 J Van Humbeeck, Trans ASME 121: 98–101 (1999) 6 T Maki, in Shape Memory Materials, K Otsuka, and C.M Wayman eds., Cambridge University Press, 1998, Chap 5 7 A Sato, K Sama, E Chishima, and T Mori, J Phys 12(C4): 797–802 (1982) 8 A Sato, E Chishima, K Soma, and T Mori, Acta Metall 30: 1177–1183 (1982) 9 J.S Robinson and P.G McGormick, Mater Sci Forum 56: 649–653 (1990) 10 A Sato, MRS Int Mtee Adv Mater 1989, pp 431–445 11 M Murakami, H Otsuka, H.G Suzuki, and S Matsuda Proc Int Conf Martensitic Transform (ICOMAT-86), 1986, pp 985–990 12 D.Z Liu, W.X Liu, and F.Y Gong, J Phys IV, Suppl J Phys III 5: (1995), ICOMAT-95 Proc., pp 1241–1246 13 J Van Humbeeck and L Delaey, The Martensitic Transformation in Science and Technology, E Hornbogen and N Jost, eds., DGM Verlag, Oberursel, Germany, 1989, pp 15–25 14 T Tadaki, in Shape Memory Materials, K Otsuka, and C.M Wayman, eds., Cambridge University Press, 1998 15 M Ahlers, Progress in Materials Science, Vol 30, J.W Christian, P Haasen, and T.B Massalski, eds., 1986, pp 135– 186 16 S.K Wu and H Ming, in Engineering Aspects of Shape Memory Alloys, T Duerig et al., eds., Butterworth Scientific, U.K., 1990, pp 69–88 17 R Rapacioli and M Chandrasekaran, Proc Int Conf Martensitic Transform Cambridge, MA, 1979, pp 596–601 18 R Rapacioli and M Ahlers, Acta Metall 27: 777–784 (1979) 24 M Chandrasekaran, E Cesari, and J Van Humb Int Conf Martensitic Transform ICOMAT-92, Mon of Advanced Studies, 1993, pp 575–580 25 J Van Humbeeck, L Delaey, and T Suzuki, Scri 18: 893–903 (1984) 26 F.C Lovey et al., “The influence of γ -phase precipit martensitic transformation in Cu-Zn-Al alloys”, Conf Martensitic Transform, Sydney, 1990, 56– 498 27 R Elst, J Van Humbeeck, and L Delaey, Mater S 4: pp 644–648 (1988) 28 R Elst, J Van Humbeeck, and L Delaey, Acta Me 1729 (1988) 29 E Hornbogen, Acta Metall 33: 595–601 (1985) 30 D.N Adnyana, Proc Int Conf Martensitic Transf pp 774–779 31 Z Nishiyama, Martensitic Transformation Acad 1978 32 R Elst, J Van Humbeeck, and L Delaey, Proc Martensitic Transform, 1986, pp 891–895 33 W Jianxin, J Bohong, and T.Y Hsu, Acta Metall 1526 (1988) 34 J.V Wood and P.H Shingu, Met Trans A 15A (1984) 35 K Mukunthan and L.C Brown, Met Trans A 1 2929 (1988) 36 A.Q Khan and L Delaey, Zeit fur Met 60: 949–9 ¨ 37 T Saburi, MRS Int Meet Adv Mater 1989, Vol 9 38 T Saburi, in Shape Memory Materials, K O C.M Wayman, eds., Cambridge University P Chap 3 39 T Todoriki and H Tamura, Trans Jpn Inst Met (1987) 40 D Treppman, E Hornbogen, and D Wur Proc ICOMAT-95, pp 569–574 42 M Nishida, C.M Wayman, and T Honma, Met T 1505–1515 (1986) 43 C.M Wayman, Proc Int Conf Martensitics Trans pp 645–652 44 K.H Eckelmeyer, Scripta Met 10: 667–672 (1976 45 T Honma, M Matsumoto, Y Shugo, and I Yama ICOMAT-79, pp 259–264 46 P Huisman-Kleinherenbrink, Ph D Thesis, Un Twente (NL), 1991 47 V.N Kachin, “Martensitic transformation and sha effect in B2 intermetallic compounds of Ti”, Rev 24: 733—739 (1989) ICOMAT-95 Proc Part I and II, Lausanne, 1995, pp 1017– 1022 56 H Sasano and T Suzuki, 5th Proc Int Conf Titanium, 1984, Vol 3, pp 1667–1674 57 T Hamada, T Sodeoka, and M Miyagi, Proc Int Conf Titanium, 1988, Vol 2, pp 877–882 58 T Sugimoto, M Ikeda, S Komatsu, K Sugimoto, and K Kamei, Proc Int Conf Titanium, 1988, Vol 2, pp 1069–1074 59 T.W Duerig, J Abrecht, D Richter, and P Fisher, Acta Met 30: 2161–2172 (1982) 60 T Sohmura and H Kimura, Proc ICOMAT-86, pp 1065– 1070 61 S.G Fedotov, T.V Chelidze, Y.K Kovernistyy, and V.V Sanadze, Phys Met Metall 62: 109–112 (1986) 62 Europa¨sche Patentanmeldung 0062365, anmeldetag 11, 03, ı 1982 63 C.Y Lei, M.H Wu, L McD Schetky, and C.J Burstone, Proc Wayman Symp., May 1996, pp 413–418 64 T Kakeshita and K Shimizu, Trans Mater Res Soc Jpn 18B: 981–984 (1994) 65 T Kakeshita, T Saburi, and K Shimizu, MRS Symp., Boston, 1997, Vol 459, pp 269–279 66 V.A Chernenko, A Amengual, E Cesari, V.V Kokorin, and I.K Zasimchuk, ESOMAT-94 Proc., Barcelona, 1994, J Phys IV Vol 5; C2, pp 95–98 67 V.A Chernenko, E Cesari, V.V Kokorin, and I.N Vitenko, Scripta Met Mater 33: 1239–1244 (1995) 68 M Cohen, G.B Olson, and P.C Clapp, phase transformations, Proc ICOMAT-79, Cambridge, pp 1–11 69 R Stalmans, Doctorate Thesis, Catholic University of Leuven, Department of Materials Science, Heverlee, 1993 70 A.B Greninger and V.G Mooradian, Trans Met Soc 128: AIME, 337 (1938) 71 L Delaey, in Materials Science and Technology, Vol 5: Phase transformations in Materials, P Haasen, ed., VCH Verlagsgesellschaft, Weinheim, 1991, pp 339–404 72 W.J Buehler, J.W Gilfrich, and R.C Wiley, J Appl Phys 34: 1616 (1963) 73 J Perkins and D Hodgson, in Engineering Aspects of Shape Memory Alloys, T.W Duerig, K.-N Melton, D St¨ ckel, and o C M Wayman, eds., Butterworth-Heinemann, London, 1990, pp 195–206 74 H Tas, L Delaey, and A Deruyttere, J Less-Common Met 28: 141–151 (1972) 75 L Contardo and G Gu´ nin, Acta Metall Mater 38: 1267– e 1272 (1990) 76 G Gu´ nin, in The Martensitic Transformation in Science and e 83 R Stalmans, J Van Humbeeck, and L Delaey, Ma JIM 33: 289–293 (1992) 84 R Stalmans, J Van Humbeeck, and L Delaey, Scri 31: 1573–1576 (1994) 85 M Sade, A Hazarabedian, A Uribarri, and F.C L Int Conf Solid Phase Transform., Cambridge, 198 281 86 J Van Humbeeck and R Stalmans, in Shap Materials, K Otsuka and C.M Wayman, eds., C University Press, Cambridge, 1998, pp 149–183 87 T Saburi, in Shape Memory Materials, K Otsuka Wayman, eds., Cambridge University Press, C 1998, pp 49–96 88 R Kainuma and M Matsumoto, Scripta Metall 2 (1988) 89 K Otsuka and K Shimizu, Int Met Rev 3 (1986) 90 T.W Duerig and R Zadno, in Engineering Aspect Memory Alloys, T.W Duerig, K.N Melton, D St C.M Wayman, eds., Butterworth-Heinemann, Lon pp 369–393 91 S.M Russell, D.E Hodgson, and F Basin, Proc 2nd Shape Memory Superelastic Technol., SMST, Sa 1997, pp 429–436 92 C.S Zhang, Y.Q Wang, J.X Cheng, and C.L Zha Int Conf Shape Memory Superelastic Technol., 1994, pp 383–388 93 T.W Duerig, A.R Pelton, and D St¨ ckel, Metall 5 o (1996) 94 K.N Melton, in Shape Memory Materials ’94, C T Hailing, eds., International Academic, Beijing 523–529 95 Proc.1st Int Conf Shape Memory Superelastic MIAS, Monterey, 1994, pp 341–400 96 O Mercier and E Torok, J Phys C4: 267–272 (19 97 G.R Zadno and T.W Duerig, in Engineering Aspec Memory Alloys, T.W Duerig, K.N Melton, D St C.M Wayman, eds., Butterworth-Heinemann, Lon pp 414–419 98 K Otsuka and C.M Wayman, eds., Shape Memory Cambridge University press, Cambridge, 1998, p 99 P Sittner, D Vokoun, G.N Dayananda, and R Mater Sci Eng 286: 298–311 (2000) 100 J.L Proft and T.W Duerig, in Engineering Aspect Memory Alloys, T.W Duerig, K.N Melton, D S C.M Wayman, eds., Butterworth-Heinemann Lon pp.115–129 101 M Kapgan and K N Melton, in Engineering Aspec Memory Alloys, T.W Duerig, K.N Melton, D St 1987, pp 397–405 107 K Madangopal, S Banerjee, and M.K Asundi, in Shape Memory Alloy ’86, Chu Yougi, T Y Hsu, and T Ko, eds., China Academic, Beijing, 1987, pp 181–186 108 K Madangopal, R Ganesh Krishnan, and S Banerjee, Scripta Metall 22: 1593–1598 (1988) 109 Y Furuya, H Shimada, Y Tanahashi, M Matsumoto, and T Honma, Scripta Metall 22: 751–755 (1988) 110 T.W Duerig and K.N Melton, MRS Int Meet Adv Maters., 1989, Vol 9, pp 581–597 111 E Cydzik, in Engineering Aspects of Shape Memory Alloys, T.W Duerig, K.N Melton, D St¨ ckel, and C.M Wayman, o eds., Butterworth-Heinemann, London, 1990, pp 149– 157 112 H Tobushi, P.H Lin, K Tanaka, C Lexcellent, and A Ikai, Proc 1st Int Conf Shape Memory Superelastic Technol., MIAS, Monterey, 1994, pp 163–168 113 R Stalmans, L Delaey, and J Van Humbeeck, Mater Res Soc Symp Proc.: Mater Smart Syst II, Pittsburgh, 1987, Vol 459, pp 119–130 114 D Vokoun and R Stalmans, SPIE 3667: 825–835 (1999) 115 Y Zheng, L Cui, D Zhu, and D Yang, Mater Lett 43: 91–96 (2000) 116 M Piao, K Otsuka, S Miyazaki, and H Horikawa, Mat Trans JIM 14: 919–929 (1993) 117 R.M Banks and M.C Fleming, J Phys Colloque C-4: 833– 838 (1982) 118 J Van Humbeeck, R Stalmans, and P A Besselink, in Metals as Biomaterials, J Helsen and H Breme, eds., Wiley, 1998, pp 73–100 119 K Ikuta, Proc IEEE Workshop, 1990, 2156–2161 120 Y Bellouard, T Lehnert, T Sidler, R Gotthardt, and R Clavel, MRS Symp., Mater Smart Syst III, Vol 604, pp 177–182 121 Y Bellouard, Th` se, Nr 2308 (2000), Lausanne EPFL e 122 D Reynaerts, J Peirs, and H Van Brussel, Proc 2nd Int Conf SMST, Asilomar, 1997, pp 533–538 123 A.D Johnson and J.D Bush, Proc 1st Int Conf SMST, Asilomar, 1994, pp 299–304 124 P Wollants, M De Bonte, L Delaey, and J Roos, Z Metallk 74: 146–151 (1979) 125 J Van Humbeeck, Mater Sci Eng A 273–275: 134–148 (1999) 126 J Van Humbeeck, Chapter 3, pp 46–60 in “Shape Memory Implants” ed by L’ Hacine Yahia, Springer-Verlag 2000, ISBN 3-540-67229-X 127 C Baber, Metal Science Journal, 1971, Vol 6, pp 92– 100 different length scales The crystallographic s are responsible for shape-memory behavior tak unit cells of atomic dimension Here, however, croscopic length scales are not the focus, rather, cle considers the macroscopic scale modeling th for the engineering assessment of thermomech sponse (stress–strain–temperature) and energy (including damping) for devices such as connecto tors, vibration absorbers, and biomedical stents T scale is useful for primary design evaluation su dicting triggering forces and determining range Since the shape-memory material is typically inc into a larger engineered device or structure, ther need for detailed computational simulation of th as a whole BASIC MATERIAL BEHAVIOR AND MODELING IS The term shape-memory material (SMM) is me compass a wide class of metallic alloys with the feature that they exhibit, at the macroscopic sc peculiar and useful functional properties such doelasticity and shape memory Nickel-titanium perhaps the best known and most widely used terial SMM functional properties derive from tra tions between two different solid phases: austeni martensite (M) Aspects of the A ↔ M phase tra tion are essential for model development and i tation In addition, certain intermediate phases occur, but these are neglected here because thei the macroscopic response is small in comparison The A ↔ M transformation can be induced ety of energy inputs (mechanical, thermal, mag trasonic, etc.), and it is influenced by grain bo dislocations, inclusions, and other material def article considers the standard thermomechanic namely the A ↔ M transformation that is induc perature T and stress σ In general, austenite is high temperatures and low stress, whereas mar favored at low temperatures and high stress We boldface σ (and ε) to denote a general stress and s sors with components σi j (and εi j ) Models invo a single stress component σ will be developed m those involving the tensor σ Austenite is of higher crystallographic symme can transform into one or more martensite var differ mainly by their orientation relation to the parent By contrast, all martensite variants tend to transform into a single common austenite crystal structure The transformation from the A structure to that of a particular M variant is characterized by a crystallographic transformation strain Typically, an A material region transforms into a martensitic microstructure with several variants that combine in complicated twin arrangements and plate morphologies These microstructures provide a local transformation strain γ ∗ This in turn gives a macroscopic transformation strain ε∗ at the engineering scale This ε∗ gives a potentially large strain in stress-induced A → M transformations It is negligible in cooling-induced A → M transformations because the resulting microstructures involve so-called self-accommodated martensite with local strains γ ∗ that cancel each other Since the phase transformations can be activated under very different conditions to obtain different effects, to have a picture of SMMs behavior, it is necessary to see how stress and temperature differ with respect to A ↔ M transformation Figure 1 shows a stress and temperature phase diagram of a single austenite phase A and two families of martensite variants M+ and M− The curves in this diagram show the relation between stress and temperature levels at which various phase transformations begin and end This partitions the (σ, T )-plane into three single phase regions, three double phase regions, and a triple phase region Purely Thermal Transformation In the absence of stress, austenite is stable at high temperatures, and martensite is stable at low temperatures Stress-free cooling of austenite gives A → M conversion beginning and concluding at temperatures Ms and M f , respectively (M f < Ms ) The resulting microstructure is an unbiased martensite with a fine-scale arrangement of variant twins with opposing local transformation strains γ ∗ Austenite is not present at temperatures be Nonzero stress at these low temperatures cause martensite variants to be relatively more favo favoritism correlates with the value of the tra tion work σ · γ ∗ = σi j γi∗ In the important speci j uniaxial tension/compression, the variants favor sion are those for which γ ∗ projects onto the tensi a positive quantity It is convenient to group all of ants favored in tension into an M+ variant famil variants favored in compression into an M− var ily Unbiassed martensite involves a mixture of and M− Sufficiently high tensile loading at temp below M f causes movement of the internal bo separating the martensite plates, which can b as a conversion from the M− family into the M This M − → M+ transformation yields biased m namely ε∗ = 0 Unloading does not cause the reve formation (M + → M−) so long as the load doe come compressive Hence the transformation st like a conventional plastic strain upon unloadin The M− ↔ M+ transformation is referred to a tation As a result, a plasticlike reorientation p observed on the isothermal stress–strain curve, tensile reorientation beginning and concluding a σs+ and σ + (σ + > σs+ > 0) These reorientation str f f relatively insensitive to temperature changes (t be a mild increase in σs+ and σ + with a tem f σ Pseudoelasticity σ A →M T Af σ Ms Mf As A← → M − M+ M A← M Fast ε T Purely thermal transformations M← A where the various phase transformations can occur Each curve represents the (σ, T )-points at which a transformation can either be activated or else completed Hence there are two curves (start and finish) for each transformation The figure shows a sketch of a phase diagram that can arise when the SMM is modeled as a mixture of austenite A and two martensite variants M+ , M− Such a diagram can be viewed as an unfolding of a conventional phase diagram triple point so as to include the effects of phase mixing and transformational hysteresis Fast ε Low temperature reorientation Figure 2 Sketch of the macroscopic effects of the var transformations in the stress–strain–temperature (σ (left) Effect of the loading rate on the pseudoelastic faster loads give rise to greater hardening and temper ations (right, where t denotes time) spectively During A → M the material self-hea temperature rise works against the transforma versely during M → A the sample self-cools) T involve a number of consequences: different onse for transformation plateaus, plateau steepening, ation in the shape of internal loops (Fig 2) T of this effect is governed by the heat exchange environment: high rates of loading can cause s departure from isothermal behavior High rates can occur in both actuator and damping shape-m vices doelastic plateau so as to distinguish it from the reorientation plateau observed at the lower temperatures For T > A f , the start and finish stresses for pseudoelasticity are greater than the M− → M+ reorientation stresses σs+ and σ + They are also highly temperature sensitive, inf creasing with temperature at an approximately constant rate However, if the temperature is close to M f , then little distinction can be made between pseudoelasticity and reorientation because the loading plateau stresses match the reorientation values σs+ and σ + Unloading activates f the M+ → A transformation if T > As , resulting in an unloading plateau below the A → M+ loading plateau The unloading plateau rejoins the loading curve if M+ → A goes to completion (T > A f ), and so defines a hysteresis loop (Fig 2) At temperatures As < T < A f , the M+ → A unloading conversion does not go to completion and the unloading plateau intersects the strain axis before reaching the origin of the stress-strain diagram If T < As , then the M+ → A transformation is not even activated upon unloading Thus, in all cases where T < A f , there is some residual strain due to the presence of M+ martensite when unloading is complete In uniaxial loading, significant differences in th strain behavior have been observed between te compression This is due to the different micros that the formed In particular, the behavior of the ant family in tension is not the symmetric ima behavior of the M− variant family in compress a phenomenon is modeled by a phase diagram t symmetric with respects to σ Shape-Memory Effect Three-Dimensional States At all temperatures, where T < A f , after sufficiently high load causing either A → M+ or M− → M+ transformation, residual strain is present after unloading due to the presence of biased martensite Unlike conventional plastic flow in metals (generated by dislocations) the SMM plasticlike residual strain is recovered by heating above A f , because this converts martensite to austenite Since this austenite converts to unbiased martensite upon any later stressfree cooling, the residual plastic strain does not return (unless there is further loading/unloading) This heating/cooling elimination of an apparently “plastic” strain due to previous loading/unloading is the shape-memory effect While the preceding discussion has covered the basic aspects of the material behavior that macroscopic models should reproduce, SMM is often employed in situations involving further effects that are important objectives for useful modeling The most important of these are briefly described next In the three-dimensional case involving tensor than scalar σ , the experimental behavior is les derstood, and complex multivariant structures expected in most cases A key issue in three-dim modeling is the proper constitutive description of priate local transformation strain that transcend of information about the actual multivariant m ture In view of the correlation of variant favori the transformation work σ · γ ∗ = σi j γi∗ , some so j iality relations between stress and transformat are conjectured at modeling scales appropriate t variant microstructure These difficulties are com under nonproportional loading, since the trans strain then evolves as a consequence of both pse A ↔ M processes and M ↔ M reorientation o variants Response to Complex Loading Paths At constant temperature, loading reversals that interrupt A → M and M → A before completion lead to internal Tension/Compression Asymmetries STATE OF THE ART AND HISTORICAL DEVELOPM Modeling of the macroscopic behavior of SMM the subject of much activity since the beginni 1980s, attracting the interest of engineers, appli maticians, and materials scientists This sectio the state of the art on the basis of the huge The discussion of the previous section makes clear that the behavior of SMM observable at the macroscopic scale is the effect of several complex microstructural phenomena This section is organized, as in the list below, with respect to contributions that include an explicit model for such microstructural phenomena and others that do not Although certain models that will be discussed can be viewed as spanning more than one such approach, the classification given below aids in organizing the numerous modeling approaches that have been proposed Approaches modeling one or more microstructural phenomena Lattice cell mechanics Interface nucleation and propagation Micromechanics Approaches modeling directly the macroscopic behavior Models without internal variables Hysteresis models Models with internal variables Approaches Modeling One or More Microstructural Phenomena Models included in this group are grounded in theories that analyze the material at a scale in which the multiphase nature of the material is rendered explicit and one or more effects of phase transformations can be described by some direct microstructural model Macroscopic behavior is then recovered by some kind of averaging procedure In a continuum setting, this implies that each point belongs to one phase and the first spatial derivatives of the displacement and temperature fields can be discontinuous Lattice Cell Mechanics In this approach, the macroscopic response of the material is determined by studying the behavior of a collection of lattice cells that can be in a particular phase or phase variant In response to loads and temperature changes at the system boundary, cell transitions between different phases can take place Two approaches for the transition kinetics can be broadly identified: statistical mechanics and strain energy minimization The statistical mechanics approach has roots in Muller and Wilmanski (1) and has been further developed by Achenbach (2) The cellular array is grouped as a stack of layered aggregates of cells that can be found in one of the ences among the ordinates of the various minima repres ergy barriers that cells have to overcome to undergo ph formations The right graph shows the effect of a mech P that lowers the right minumum and causes the M+ p the energetical favorite three phases: austenite A and two martensite M+ , M− ; each characterized by a different cell len are in random thermal motion, and thermal flu permit them to transform from one phase to anot transitions lead to variations in the stack com that are monitored by the phase fractions ξA ξ − A three-well potential energy φ whose mi each associated with one phase is the basic tive ingredient from which all material param derived by statistical arguments (Fig 3) Ma strain and temperature are obtained respectiv the normalized length of the whole layer aggre from a measure of the thermal fluctuation T fraction evolution is governed by a system of differential equations expressing the transit balance between layers on the basis of the prob overcoming the energy barriers that separate th of φ This finally provides a complete model for stress pseudoelasticity and reorientation A second approach for the description of the tr between lattice cells is based on strain energy m tion A model developed by Morris and his coll (3) involves a multidimensional lattice of cells responding multidimensional transformation st each cell The total free energy is the sum of a tem dependent chemical free energy and a strain-d elastic strain energy The strain energy contri highly dependent on cell location and choice of tra tion variant, due to the constraint of surrounding computation is based on isotropic elasticity, and t lying mathematical technique developed by Khac requires equality of elastic constants in all phas given change in temperature, the overall transf process is simulated by a stepwise energy mini At each step, the particular cell that transforms i as the one that most lowers the energy, and such mations continue so long as the overall energy is Complex microstructures and internal stress sta These complex states are the main focus of such m as opposed to providing a macroscopic model fo stress–strain–temperature behavior faces across which the strain is discontinuous so as to avoid unstable branches The connection to stress-induced phase transformation follows by placing the distinct stable branches of the stress–strain curve into correspondence with distinct material phases Avoidance of the unstable branches is then formally similar to spinodal decomposition One outgrowth of this work has focused on putting the crystallographic theory of martensite on a rigorous mathematical foundation so as to predict microstructure without invoking the approximations inherent in the linear theory of elasticity (5–7) The fundamental nature of much of the work cited immediately above renders it outside the scope of this modeling survey However, under suitable interpretation, certain treatments of this type do provide a macroscopic model for the thermomechanical behavior of shape-memory materials In particular, SMM uniaxial response follows from a thermoelastic free-energy density with either two or three minima that each define a distinct phase Boundary value problems give solutions in which the continuum is subdivided via phase boundary interfaces into different phase regions Phase transformation proceeds from the nucleation of new interfaces or from the propagation of the existing ones (8) The jump in the Gibbs free energy across the interface follows from the Eshelby energy-momentum tensor in the form of a generally nonzero driving traction Phase boundary movement gives either energy dissipation or energy accumulation as determined by the direction of interface motion Standard boundary value problems do not have a unique solution when phase boundaries are present unless the constitutive theory is augmented with both interface nucleation criteria and interface kinetic motion criteria These typically depend on the driving traction, and they can be formulated so that the overall load– displacement–temperature relation reproduces pseudoelastic and reorientation behavior Kinetic criteria can be derived, for example, similarly to that of Achenbach and Muller, so as to involve a probability of overcoming the energy barriers between phases on the basis of thermal fluctuation Quasi-static and fully dynamic treatments follow for isothermal, adiabatic, and heat conducting cases The kinetic motion criteria can be extracted from more refined theories in which the phase boundaries are regarded as transition zones exhibiting additional physical effects (9) Micromechanics In the models of this group each macroscopic point is put in correspondence with a representative volume element (RVE) of a multiphase material in which some regions are subjected to local trans strains due to the different crystal structure of t (Fig 4) Under proper boundary conditions, a bound problem on the RVE that models the effects of transformations is obtained Local quantities a averaged over the RVE, giving macroscopic quan generally retain a dependence on the microstruc tures through some overall descriptor α (usually fractions ξ ) The resulting equations for the ma behavior fit into the framework of internal vari els, as described later in this section Constitut dients are a macroscopic free-energy function of kinetic rate equations for the microstructura tors α The free energy provides, via partial d tion with respect to stress (or strain), equations (or stress) while derivatives with respect to α eralized forces that drive the phase transforma free-energy functions are structured as the sum tic strain energy and a chemical a free energy chemical contribution is specified mainly by stan modynamic expressions, the elastic term varies ably among such models as it follows from diff cromechanic assumptions on the accommodatio due to phase interaction (10) Kinetic equation rived from phase transformation criteria statin transformations occur when the generalized driv meet experimentally determined threshold valu Patoor, Eberhardt, and Berveiller initiated approach in 1987 by combining ideas from tra tion plasticity, continuum micromechanics, and graphic theories of martensitic transformation ( recent formulation, their model considers, at t crystal level, a linear elastic RVE consisting of a ite matrix with inclusions of 24 martensite vari exhibiting a local transformation strain comput the lattice parameters Each variant is assume mixed with austenite, in a well-defined cluster action energy describing the accommodation betw of variants is then computed using the interfac tor method of Hill The minimization of this in energy determines the cluster orientation and all free energy finally depends only on the var tions At the polycrystalline level, a second RVE of nontextured assemblies of spherical grains ered and a self-consistent approach is used to d martensite phase The phase interaction energy is computed using Mori-Tanaka theory by considering martensite grains as randomly dispersed spherical inclusions within the matrix of austenite grains While martensite is considered as a single phase without explicitly accounting for the different variant orientations, neglect of the multivariant structure is overcome by proposing a direct relation between the local transformation strain and the average stress in the matrix so as to simulate the biasing effect of stress in the variant selection process The local transformation strain is therefore not strictly crystallographic, and the resulting description is in terms of an equivalent transformation strain Reorientation effects are taken into account by introducing a second martensite fraction Issues related to nonproportional loading are also discussed (12) Starting in the early 1990s, Levitas developed models from a somewhat different viewpoint (13) The SMM is modeled as a dissipative material already at the microscale where, due to the phase transformations, relevant field quantities vary between two values reflecting an underlying two-phase model for the microstructure A firstaveraging procedure is performed over an internal time scale representative of the transformation duration in order to obtain an average dissipation rate and driving force Different energetic transformation criteria are given: an overall nucleation criterion results after integration over the RVE while a criterion for interface propagation is given after integration over the propagating interface An extremum principle with respect to the variation of the RVE boundary conditions is invoked to determine the evolution of the microstructural parameters Goo and Lexcellent (14) proposed a model for single crystals based on a free-energy function and a dissipation rate function The free-energy function is derived by a self-consistent evaluation of internal stresses among the phases The model allows for nonisothermal behavior, reorientation, and two-way shape-memory effect The influence of the interaction energy on the macroscopic modeling is examined, and the comparisons with experimental data under uniaxial stress show good agreement with the modeling prediction The analysis of Lu and Weng (15) treats each grain as a mixture of austenite and a single martensite variant whose local transformation strain is computed from lattice parameters The particular variant is selected in analogy with the Patel-Cohen criterion on maximum transformation work Polycrystals are then modeled by an assembly of be of spherical shape This idealization is shown ful in modeling thermally activated transforma low-temperature reorientation The model capt the tension/compression asymmetry and the dif sponse observed experimentally when the loadi tion varies with respect to crystal axes The m been extended to cover penny-shaped inclusions crystalline behavior by studying an assembly o tured spherical grains homogenized by a self-c method Summarizing, micromechanic approaches in several features into the modeling, including t of a multiple-variant microstructure and the ef polycrystalline texture This permits explanation macroscopically observed behaviors, though ce tailed issues remain under discussion Such issue the determination of the number of variants and eling of their arrangement (17), as well as the m nonproportional multi-axial loading; for recent ex tal studies, see (18,19) Approaches Modeling Directly the Macroscopic Be Direct modeling will be understood as including where each point of the material, instead of be identifiably distinct phase, is representative of mixture whose microstructural features are des one or more descriptive variables In a continuum the associated strain and temperature gradient continuous Models without Internal Variables In such m material behavior is described by strain, stress ature, and entropy without the introduction of q representing the phase mixture Constitutive inf is provided by a free-energy function whose parti tives provide constitutive equations for strain ( and entropy In 1980, Falk proposed a Landau-Devonsh of free-energy function based on the analogy SMM uniaxial stress–strain curves and the elec magnetization curves of ferromagnetic mater Nonmonotone stress–strain curves are obtained unstable negative slope part is interpreted as t rence of the phase transition The actual pattern during transformation is assumed to proceed at stress The particular form of the Landau-Devons energy accounts for the temperature dependen fossil fuels waste gases Recovery Human ecosystem Natural ecosystem Figure 1 Re-circulation based society input from nature (fossil energy, raw materials) as well as its output into nature’s ecosystem (exhaust gases, exhaust heat, waste materials), and makes efforts to recirculate and regenerate the input from nature within the human ecosystem In other words, when manufacturing goods for a recirculation-based society, it is very important to think about the total energy balance and the material balance In practice, it is necessary to reduce the output by reducing the input, and in addition, synthesize new materials from materials and energy that have the possibility of producing fresh output We must, therefore, change our attitude from recycling to recirculation Manufacturing of Goods with Consideration for the Earth Although manufacturing of goods with an awareness of a recirculation-based society is unavoidable, it is doubtful whether goods manufactured based on such a concept would be accepted by the world Let us consider an extreme example An electric refrigerator not only consumes electricity but also the refrigerating agent, which is Freon gas and a burden to the earth’s environment In order to lower the input and output, should we then stop using electric refrigerators and return to the earlier era of ice-boxes for refrigeration? Most people would answer no It is not easy to abandon a convenience once it has been experienced Furthermore, denial of the existence of electric refrigerators means also denial of large businesses that sell refrigerated foods like department stores, supermarkets, and convenience stores The invention of the electric refrigerator brought great changes to the social system As long as irreversibility of life values exists, we cannot easily return to the “good old age.” If we reach an ultimate state where there is no alternative but to return to the past such a reversal would probably be at the expense of unprecedented patience and great pain Conversely, if it were easy to return to a former way of living, environmental problems would not occur, there might not be the need t new materials Our inability to return to a forme efficient way of living is why we need to address th issue of environmental pollution and set guideline materials: Most important, the manufactures need to more conscious of the earth The goods they should be useful, convenient, or improvements o goods that are necessary to people Of course, as mental problems become more severe, the balance people and the earth will shift, and without dou emphasis will start to be placed on earth friend rials and manufacturing Materials and goods without consideration of their value or usefulne ple would cease to exist Taking this argument fr ferent perspective, no one could argue that the turing of goods does not exploit something (input earth and then discharge some waste to the earth which is produced as the input from the earth is c into goods with functions that have some value (Fig 2) We could express this relation of the dev of goods as, Value = P , I+O where P is the performance of the material, I the input and output of the material when manu used, and scrapped In general, if the value for people is less than o is no merit to developing the material or goods ment should aim to raise this value to five, ten the hundreds Attain entirely new approaches, necessary, disregarding any current concepts N think specifically about materials that could be d using the P/(I + O) valuation concept Earth Figure 2 A new value for the manufacturing 1973, when the industrial energy consumption in 1997 was 104%, today dwellings consume energ as 217%, and this figure has been rapidly climbin energy increases have occurred even though much has been made in the development of low-energy tion type of appliances The technological solution to this problem w have a self-monitoring and self-regulating the i mate (humidity, in particular) by materials of th the floor, walls, and ceiling materials—that ha value At the same time, it is necessary to exa methods of synthesizing these materials from th tive of not using even more energy and natural for the synthesis—that is, to maintain a low (I + If such materials could be developed, indoor clima could made effective even in the most airtight insulated homes Such materials would possess h as those to society with due consideration to hu the earth SMART MATERIALS FOR THE LIVING ENVIRONMENT Foremost among materials for maintaining a comfortable living space, while reducing the burden on the earth’s environment, is the development of high heat insulation houses Of course, this is not a consideration in hot and humid regions with monsoon climates Primarily, there is the case of Japanese dwellings Japan, which is located in a monsoon zone, has a relatively distinct climate compared to other developed nations In this unique hot and humid climate, much damage is caused by the high humidity Although the humidity itself is lower than that of say, London, Paris, or San Francisco, Japan is at the top with regard to humidityrelated damage to houses This is due to the fact that fungi and bacilli that affect human health and cause damage to houses are able to breed rapidly under the warm and humid Japanese climate To counter these adverse influences, elevated houses emerged in Japan as far back as the nineth century Elevated floors allow for underfloor ventilation The materials used for construction were paper, wood, and soil Some 50 years ago airtight houses were introduced in Japan following examples in Europe and America A new apartment house building trend then took root in Japan However, it has turned out that the Western airtight dwellings were unsuited to a humid climate, and thus uncomfortable for living The search for comfort led to the introduction of various indoor implements—electric fans, followed by coolers and air conditioners Then the first oil CLIMATE CONTROL BY POROUS BODIES The humidity range in which a person feels co is said to be 40% to 70% It has been reporte maintaining humidity within this range, allerg such as mites, as well as the breeding of wood-e teria, molds, and the like, that cause degradatio in wooden houses, could be restricted (7) This range is also thought to be effective in curbing t of viruses and even the accumulation of static e Chemical and physical methods of humidity regu available, but here, let us think about a safe meth is humidity regulation by porous bodies The target material would be one that does n the water vapor when the humidity is less than if the humidity rises higher, it should work to humidity by rapidly absorbing the water vapor atmosphere Then, as the humidity starts to fal terial should act to increase the humidity rapi preferred 40% to 70% In other words, the water sorption isotherm of the material should be ste 40% to 70% humidity range (Fig 4) So these humidity-regulating porous materia be capable of making the water vapor in the at to condense within the capillary pores that exis surface when the humidity is high Conversely, humidity is low, they should function to vap Energy-saving and comfortable life!! Using much electricity Leave it to me !! Extractor fan Air-conditioner Drier Electric fan Figure 3 Earth and people conscious materials for the living environment condensed water The relation between the vapor pressure, P/P0 , required for capillary condensation and pore size, with curvature radii r1 , r2 , is expressed by Kelvin’s equation of capillary condensation: ln P P0 =− γV cos θ/RT 1 1 + r1 r2 Here, r1 and r2 are the radii of curvature of the pores in two perpendicular directions, γ is the surface tension of the condensate, V is the molecular volume of the condensate, and θ the contact angle of the condensate within the pore Calculations based on this equation, corrected for the preexistence of a certain thickness of the adsorbed layer prior to capillary condensation (8), yield pore radii values of 3.2 nm for 40% relative humidity and 7.4 nm for 70% humidity High-humidity regulating performance can be expected from materials synthesized with their p being controlled to be within this range USING THE GREATNESS OF NATURE WISELY Utilizing Soil There are many possibilities of synthesizing po terials with humidity-regulating properties For taking petroleum as the starting material, the could be done by chemical polymerization or bi methods However, the use of these methods difficult to lower the input and output of the sy material For this reason, we should select “soi starting material Natural soil is a material cont cipient micropores that can be effective in impa midity regulating performance Even after its u Adsorption vol 0 0.01 1 Pore diameter (µm) Low Figure 5 Examples for the pore size distribution of soil after dry-pressed under 30 MPa (solid line) and 20 ken line) 0 20 40 60 80 100 Relative humidity (%) Figure 4 Property for the humidity-regulating porous materials human ecosystem is over, soil will not inflict a large burden on the natural ecosystem Soil appeared some 400 million years ago at a time when plenty of oxygen was supplied by the atmosphere The composition of soil is almost the same today The excess oxygen was decomposed in the stratosphere to form the ozone layer The ozone layer has prevented strong ultraviolet rays from pouring onto the surface of the earth, and allowed the movement of animals and plants from the sea to land to begin With the help of this organic matter, the land of stone and sand turned into a land of green, and soil appeared for from the weathering and decomposition of rocks (9) Were it not for soil, the perfect recirculation performance of the current natural ecosystem would not exist So one cannot ignore the benefits obtained from soil for the existence of humankind Humankind is, of course, indebted to soil with regard to food crops, but more so, it was through the aid of earthen dwellings that humankind was able to survive the glacial era without running out of seed Soil contains numerous pores, both large and small These pores collect air, water, and many nutrients, allowing soil to carry out its functions For example, a survey of the virgin forests of the Shiga plateau (Japan) has shown that in a 1 m by 1 m by 15 cm volume of soil, there are 360 living creatures such as centipedes and earthworms ranging about 2 cm in size, then some 2 mm in size thread earthworms, beach fleas amounting to 2.3 million in count, and finally any number of protozoan, mold, and bacteria of more than 10 trillion in count (10) Figure 5 pore size distribution of common earth (soil) It is the 10 nm (0.01 µm) pores considered suitable for regulation are incipient in the material It is also the cohesive structure in the neighborhood of 10 not collapse easily even under pressure Howe any kinds of soil if lost for some reason or the o not be regenerated for an extremely long time more, because of its complex structure, soil is a that has not been successfully synthesized artific now Humankind has utilized earth very cleverly struction material in many ways In its natura has been used for cave-type and pit-type dwel has been processed and used to obtain variou construction materials such as sun-dried bricks it was used as Tataki, or earthen walls The hum ulation and thermal insulation properties arisin innumerable pores in soil were utilized in Ja period to build earthen storehouses that protec from wind, fire, and water The technology o lization was even raised to an artistic level, seen from the Nurikabe walls of the Edo era O soil materials have served their purpose in th ecosystem, they can be returned to the natur tem Therefore, soil is an extremely rare mat can cross the system boundary zone freely Unfo the use of earth as soil, is usually not the possib rent construction practice If, for example, soil its natural state for the flooring of today’s air heat-insulated dwellings, the house would beco and the health of the inhabitants may be affected In addition, there are problems regarding stren bility, and workability Property of ceramics -culture of stone- High strength high density > 1000 °C 2 Calcination Ceramics Figure 6 A culture of soil in human history Solidified ceramics such as bricks, blocks, and tiles made their appearance early in history in order to solve these problems However, ceramics, which could be considered to have been developed in the Stone Age, are produced through high-temperature reactions For this reason, it is difficult to say that ceramics maintain the inherent properties and performance of soil In order to sustain the inherent properties and performance of soil (pore size distribution), the temperature of manufacture of earthen products must be lower than 500◦ C In the case of earth/organic material composites, an even lower temperature is desirable The new technology of solidifying soil by hydrothermal treatment is a low-temperature process developed to obtain a material with properties and performance between those of soil and ceramics (6) Hydrothermal Processing The largest application of hydrothermal processing is in the field of building materials manufacture It was developed in Europe and has over 100 years of history as represented by sand lime bricks (11,12) Usually, the process involves mixing quartz (SiO2 ) with about 10% lime (Ca(OH)2 ) and exposing the mixture to saturated steam at about 200◦ C This results in the formation of acicular calcium silicate hydrates (Fig 7) (13) It is believed that strength development is obtained because these hydrates (tobermorite, xonotolite, etc.) are entwined with each other in the solidified bodies From the point of view of energy consumption, this method of synthesis is an extremely high efficiency process Numerous studies have been made regarding the reactions involved during synthesis by hydrothermal treatment and regarding the behavior of Figure 7 Calcium silicate hydrates, the most impor ing materials in the hydrothermally solidified buildin (photo: tobermorite in autoclaved sand lime brick) calcium silicate hydrate materials, mainly in t SiO2 –H2 O system (14–16) Although many of th deal with the purity of the starting materials, erally accepted that it is desirable to use SiO2 w purity (12) Almost no studies seem to have be with significantly altered SiO2 compositions M al (17,18) have studied the effects of Al2 O3 sou tions to the CaO–SiO2 –H2 O system and the rep of Si by Al in tobermorite (Ca5 (Si6 O18 H2 )· 4H2 O) the addition of Al2 O3 in this study was up to Al/(A 0.16, which corresponds to the solid solution lim tobermorite (19,20) An investigation by Kalo reported that when kaolinite is used as the A hydrogarnet forms in the range Al/(Al + Si) = 0 (20) Generally, this hydrogarnet has a cubic and contains Ca3 Al2 Si3 O12 –Ca3 Al2 H12 O12 in solid (21,22) In a recent study of metakaolin–quartz ries slurries, the effect of amount of metakaolin and of quartz grain size on hydrogarnet forma been clarified (23–25) These reports indicate tha creasing Al/(Al + Si) ratio in the CaO–SiO2 –Al system, hydrogarnet forms in addition to calcium hydrates such as C–S–H (calcium silicate hydr and tobermorite, and that the hydrogarnet bec main phase for Al/(Al + Si) ratios higher than a However, in the composition range over which h net is the main phase formed, not much study have been carried out on the strength developm drothermally synthesized bodies Investigations relationship between strength development and crostructural changes that accompany the format drogarnet cannot be found either This is probabl of the fact that it was thought that formation of h net causes strength deterioration in calcium silic rials (26) Because of this belief, avoiding the for hydrogarnet has been an important direction of up to now SiO2 (quartz) Al2O3 Al2Si2O5(OH)4 (Kaolinite) 0 Figure 8 Experimental compositions (mass ratio) in the CaO– SiO2 –Al2O3 system Hatched area was mainly discussed in the past An approach completely different from current directions of research is required here Soil, which usually consists of minerals such as quartz, feldspar, and kaolinite (Al2 (Si2 O5 )(OH)4 ), contains besides SiO2 a considerable amount of Al2 O3 (about 30%) For this reason, it is unsuitable as the raw material for calcium silicate hydrate formation In order to produce solidified materials with soil as the starting material, sufficient strength development would be required in solidified bodies that contain hydrogarnet as the main phase Hydrothermal Solidification of Kaolinite An example of a solidification experiment using nearly pure quartz (Indian quartz), kaolinite (Georgia kaolin—a clay mineral without micropores), and lime (CaO) is outlined here In this experiment, the mass ratio of quartz, kaolinite, and lime were varied (Fig 8, Table 1) So that kaolinite : quartz + kaolinite K = 0, 0.1, 0.5, 0.9, 1.0, (Q + K) and lime = 0.21 quartz + kaolinite After weighing the materials, the lime was slaked and a further 10% of water was added and mixed to allow for easy forming The specimens were obtained by uniaxial Table 1 Compositions of the Experimental Mixtures K/(Q + K) (mass ratio) 0.0 0.1 0.5 0.9 1.0 Al/(Si + Al) (atomic ratio) Ca/Al (atomic ratio) Ca/(Si + Al) (atomic ratio) 0.00 0.05 0.24 0.45 0.50 0.23 0.24 0.31 0.45 0.50 0.23 0.23 0.24 0.24 0.25 0 10 Curing time (h) 20 Figure 9 Generation of the flexural strength and along with the hydrothermal processing press forming of this mixture at 30 MPa The pre specimens were cured under saturated steam pr 200◦ C for 2 to 20 hours (The compositional ran specimens was Ca/(Si + Al) = 0.23 to 0.25, AI/(S 0.0 to 0.50 The variation in the phases formed with treatm is shown in Fig 9, together with the strength ment characteristics It is recognized that in all s hydrothermal treatment results in increased strengths It is also clear that hydrothermal sol is possible even in those specimens with Al/(S 0.24 to 0.50 where hydrogarnet is the main phas In the case of specimens with AI/(Si + Al) = 0 and correspond to compositions investigated frequen past, mainly calcium silicate hydrates are forme maximum flexural strength of about 30 MPa is in 2 hours of treatment Longer treatment tim decreased strength, particularly for the specim Al/(Si + Al) = 0 In kaolinite-rich specimens with Al/(Si + Al) 0.50, flexural strength reaches approximately 15 in 2 hours along with the formation of hydrogarn treatment times lead to only slight strength incre flexural strength is maximum for specimens wit Al) = 0.05, and becomes lower for larger Al/(Si + A However, the rate of decrease in strength becom with increasing Al/(Si + Al) value In the specim Al/(Si + Al) = 0.24 to 0.50, the decrease in maxi ural strength with increase in Al content is clear than in those with Al/(Si + Al) < 0.24 These results are extremely significant: 1 By making hydrogarnet as the main phase, strength allowing the synthesized bodies lized as building materials is obtained, alt strength may be somewhat lower than tho ventional calcium silicate hydrate materia 2 Although the strength decreases with i amounts of kaolinite, it is possible to Rea 0.24 0.45 0.50 0 0 10 Curing time (h) 20 Figure 10 Influence of the starting materials on the reaction rates of Ca source with processing time strength decrease to acceptable levels by making hydrogarnet as the main phase As a result, in actual practice, variations in composition of natural soil will not significantly affect the final physical properties of the synthesized material In other words, this means that the range of starting materials that can be used is wide Unfortunately, the mechanism of strength development by hydrogarnet formation still remains unclarified although there is a possibility that this is related to the reaction scenario of Ca as explained below In the case of specimens with Al/(Si + Al) ratios lower than 0.24, almost 100% of the calcium is consumed within the first two hours of reaction (Fig 10) For specimens with Al/(Si + Al) = 0.24 to 0.50, calcium is consumed rapidly during the first two hours, but since little or no further calcium consumption occurs, after that, the reaction ratio stagnates in the range 50% to 75% This low reaction ratio may be one of the factors influencing strength development by hydrogarnet formation Some interesting results are provided by microstructural evaluation (Fig 11) For Al/(Si + Al) = 0 and 0.05, acicular and platelike reaction products (identified by XRD to be C–S–H, tobermorite) can be observed to fill up the interparticle spaces after two hours of treatment In contrast, for Al/(Si + Al) = 0.45 and 0.50, only platelike kaolinite particles are recognizable, and hydrogarnet cannot be observed despite the fact that its existence has been confirmed by XRD Hydrogarnet crystals in sizes ranging from a few µm to some tens of µm have been reported to have been observed in hydrothermally synthesized bodies using slag as the starting material (27) and in slurries (23–25) In the current specimens, however, such hydrogarnet crystals could not be recognized, even through TEM observation This indicates the possibility strength increase (28,29) When the treatment t creased to five hours or more in Al/(Si + Al) = 0, in the neighborhood of 0.01 µm formed by two hydrothermal treatment shifts toward coarser s pore-coarsening phenomenon is due to the format rolite (28), and it appears to be connected to the strength reduction The behavior of specimens with Al/(Si + Al) = 0.50 differs greatly from that of those with Al/(S 0 and 0.05 For Al/(Si + Al) = 0.45 and 0.50, the distribution in the press-formed state does not s hydrothermal treatment time, but the number of crease as the treatment time increases As a res around 0.04 µm are formed Another characterist compositions is that the pore volume hardly cha ing this time From the preceding results, it is clear that the in pore size distribution of specimens with Al/(S 0.45 and 0.50, where hydrogarnet is the ma formed, are different from those with Al/(Si + Al 0.05 in which pores are filled up by the calcium si drates formed The formation of hydrogarnet and development without alteration of the pore sizes at the time of press-forming suggests that the structure may be one that corresponds to that Fig 13 It is envisaged that ultra-fine hydrogar cles grow densely and in situ from the surface ite particles inward (forming 0.04 µm pores) Thr solidification mechanism, bonding of the kaolinite occurs with almost no alteration to the pore size at the time of press forming The reason for the a hydrogarnet formed reaching a near-saturation l two hours of hydrothermal treatment may be th action has become diffusion controlled because of nite particles being covered by the hydrogarnet l In similar experiments using silica sand contai purity clay minerals as the starting material, it found that although the type of phases formed d drothermal treatment change greatly with the t temperature and time, the strength of the solidifi rial is strongly influenced not by the type but by th of formed phases (Fig 14) (30) On the other ha been clearly shown that the strength of bodies f extrusion and casting processes, which require tion of large amounts of water (binder) to the r rial, is much lower than that of bodies formed ial pressing (dry pressing) Although the detaile nism of strength development by hydrothermal t (c) (d) (e) (f) (g) (h) Figure 11 SEM photographs of the fracture surface of the specimens (Al/(Al + Si) = 0 (a, b), 0.05 (c, d), 0.45 (e, f), and 0.50 for 2 hours (a, c, e, g) and 20 hours (b, d, f, h) 1022 (c) (d) Figure 12 Pore size distributions of the specimen with processing time, a = Al/(Al + Si) of 0, b = 0.05, C = 0.45, and d = 0.50 drogarnet under higher Al/(Al + Si) Mixing of soil needs further investigations, it is believed that the strength development is attained through ultra-fine particles becoming uniformly dispersed within the densified body, that is, through a mechanism similar to the that of strength development in DSP (densified system particles— containing homogeneously arranged ultra-fine particles) (31–33) As described previously, sufficient strength development is obtained through hydrothermal treatment of bodies that have been press-formed from a mixture of lime and the starting material, kaolinite The strength is believed to be attained not by the filling up of the pores in the material but by the formation and dispersion of ultra-fine hydrogarnet particles within the press-formed, dense body This solidification mechanism allows strength to be attained without destroying the agglomerated micropore structure This is important from the point of view of the humidity regulation performance of the solidified bodies Form 150 °C Autoclaving Earth c Figure 15 Actual processing of the earth ceramics m PERFORMANCE OF THE HYDROTHERMALLY SOLIDIFIED SOIL BODIES Earth Ceramics Curing temp (°C) Flexural strength / MPa 30 160 170 180 20 10 0 0 20 40 Amount of phases forme / mass % 60 Figure 14 Examples for the generation of the flexural strength with amount of formed phases under the various curing time The phases formed change with curing time and temperature However, the strength seems to be controlled by the amount of the formed phases independently The industrial method of synthesizing hydrothe lidified soil bodies is illustrated in Fig 15 A little water are added to the soil and mixed well Since ment temperature is low, straw or other organic can be added if necessary in order to obtain highe or to enhance the finish The mixture is then dr into tiles and then cured for a few hours at abou saturated steam pressure to obtain solidified bod Among those industrial ceramics that utiliz amounts of energy (34) for their manufacture, cer are considered to consume relatively little energ ergy required for synthesizing earth ceramics is e being about 2.7 GJ/m3 (35), which is only 1/6th t energy needed for ceramic tiles (Fig 16) Since there is little limitation with regard to th materials and the energy required for synthesis i can be concluded from the point of view of natur tem that earth ceramics are materials with very put and output Pore sizes in earth ceramics are concentrated gions: at around 0.05 µm corresponding to the in at the time of press forming, and at around 0.01 µ reflecting the agglomerated structure of soil Thi 1/10,000th of the pore diameters usually found in 2.6 2.7 2 1 0 Flexural strength [ MPa ⋅ m3/GJ ] Hydrothermally solidified soil 0 (Earth ceramics) 10 20 30 40 Manufacturing energy [GJ / m3] and pottery (Fig 17) The amount of water vapor absorbed at equilibrium when the relative humidity is varied from 40% to 80% at 25◦ C is shown in Fig 18 Although the response in the case of earth ceramics is somewhat slower, it can be seen that they exhibit humidity absorbency properties as good as, or better than, that of wood because of the presence of micropores in the starting material (soil) Living in a House of Soil Earth ceramic tiles (size: 200 × 200 mm) were used as the flooring material for the living room of a highly airtight Earth ceramics 0.118 cm3/g Figure 16 Energy consumpt materials on processing and heat-insulated apartment (Fig 19), and the in temperature and humidity were measured A ment in the same apartment complex with acry flooring was used for comparison (reference ap the floor plan and family makeup being the sam apartments The measurements during the winte (December to June) are shown in Fig 20 The r earth ceramic flooring exhibits very stable tem variation Since there were differences in the hea tems of the two apartments, the measurements ried out after the heaters were switched off for (Table 2) The high heat insulation performance of ramics was confirmed by the fact that the avera decrease in temperature (because of the difference indoor and outdoor temperatures) in the earth floor apartment was 1.3◦ C compared to 5.7◦ C for ence apartment In the former apartment the hum also unaffected by the outdoor atmosphere and Concrete brick 0.102 cm3/g 200 Moisture absorption (g/m2) Pottery 0.068 cm3/g 180 160 140 120 0.1 1 10 Pore diameter (µm) 100 Figure 17 Pore size distribution of the earth ceramics Wood (ceda 80 Plaster boa 60 40 20 0 0.01 Earth ceram 100 0 2 4 6 Curing time (days) 8 Figure 18 Variation of the moisture absorption cap time at 25◦ C when specimens (earth ceramics, wood, a board) were kept under relative humidity from 40% o librium condition to 80% Figure 19 Photo for the application of the earth ceramics flooring in the room 30 Earth ceramics floor Carpet floor Open air Temperature (°C) 25 20 15 10 stable In highly airtight and heat-insulated ho relative humidity increases as the temperature superior ability of earth ceramics for self-regulat midity is evident from the fact that the increas tive humidity was 1.6%/◦ C in the reference apart only 0.1%◦ /C in the earth ceramic floor apartment The variations of temperature and humidity me 6 am, 12 noon, and at 8 pm during one winter m shown in Fig 21 The temperature and humid earth ceramic flooring were within the range 1 and 40% to 50%, respectively This shows that stable and comfortable living environment can be by the use of earth ceramics The nighttime tem in the earth ceramic floor apartment were abo five degrees lower compared to the reference a but there was little recognizable difference in tive temperature felt by the human body This because the air temperatures near the ceiling, intermediate locations were about the same, the ture difference being only about 0.5 to 1.0◦ C The measurements were continued for on was found that compared to the reference apart 100 1/31/97 18:00 12:00 6:00 1/30/97 18:00 12:00 1/29/97 0 6:00 5 Earth ceram Carpet floor 80 Earth ceramics floor Carpet floor Open air 80 Relative humidity (%) Relative humidity (%) 100 60 40 60 40 1/31/97 18 : 00 12 : 00 6 : 00 1/30/97 18 : 00 12 : 00 6 : 00 20 1/29/97 20 Figure 20 (a) Example of the variation of the temperature when the earth ceramics or carpet was used on the floor in winter (b) Example of the variation of the relative humidity when earth ceramics or carpet was used on the floor in winter 0 5 10 15 20 Temperature (°C) 25 Figure 21 Variations of temperature and relative hu ing one winter month when the earth ceramics or carpe on the floor throughout the year in the earth ceramic flooring apartment In particular, the humidity was within the 40% to 70% RH range, which is the normal range of comfort for humans Therefore, the use of humidifiers or dehumidifiers was not necessary, and the period of air-conditioner operation was short, resulting in low use of fossil energy The amount of energy utilized for living (electricity, gas, water) in the apartment before and after the earth ceramic floor was installed is shown in Fig 22 converted into an equivalent amount of CO2 After remodeling, the amount of electricity thought to have been used for air-conditioning dropped sharply, and the seasonal fluctuation of energy consumption was controlled On average, there was a 17% reduction of energy consumption that year This energy consumption refers to the entire quantity required for living in the apartment (floor area = 72 m2 ) The energy Electricity Gas Water Jan 69.1 43.7 Feb 47.0 50.4 39.9 Mar 44.0 46.6 Apr 40.4 39.9 May 31.5 36.8 Jun Jul 44.9 36.0 31.4 Aug 35.2 30.8 32.8 Sep Non measured 41.0 Oct 41.0 Nov 65.7 32.8 Non measured Dec (re-modeling) 45.9 80 (kgc) 60 43.8 38.0 Mean 40 20 1996 (Carpet floor) 20 40 60 80 (kgc) 1997 (Earth ceramics floor) Figure 22 Amount of energy utilized for living (electricity, gas and water) before (carpet) and after the use of the Earth Ceramics floor is due to the good humidity regulation characte the material or whether it is the result of chang pH of the surface by humidity absorption NEW FUNCTIONAL MATERIALS It is thought that hydrothermally solidified soil attain strength through the ultra-fine hydroga ticles becoming uniformly dispersed within the press-formed body, similar to DSP materials T of material synthesis holds many possibilities as cess for producing new functional materials Such ities need to be investigated through further exp For example, another functional material could b place of the ultra-fine dispersed particles From the point of view of humidity regula author has investigated here only the process thermal synthesis There are many other p possibilities of using low-energy processes for p new materials One is the use of natural porous m Sepiolite (Mg5 Si8 O20 (OH)2 · 8H2 O) contains micr about 1 nm and mesopores that are a few nm in s phane (1–2SiO2 · Al2 O3 · nH2 O) is an amorphous s alumino-silicate formed during the weathering o glass, which is the major constituent of volcanic widely distributed in nature in the form of hollow of 3–5 nm in diameter (36, 37) As shown in the wa absorption/desorption isotherms of Fig 23, both and allophene exhibit high humidity absorption/d ability Even at relative humidities less than 4 show this high ability This is thought to result disordered surface structure and micropores sma 1 nm formed by the adsorbates By adding a small of binder to allophane-rich soil (Kanuma-soil/Jap forming the material to shape and firing at about is possible to obtain a solidified material that has midity regulation ability (trade name: Eco-carat) midity absorption/desorption characteristics of at 40% to 80% RH is shown in Fig 24 Althou is limitation in the choice of material, the micro ume of Eco-carat is around three times that of ramics, and it shows extremely high humidity r performance However, since these micropores d at about 1000◦ C because of phase changes, it is sible to raise the firing temperature With this firing temperature, one cannot expect sufficient to develop by the characteristic sintering mech M 5 ACKNOWLEDGMENT 0 0 20 40 60 Relative humidity (%) 80 100 Figure 23 Water vapor absorption/desorption isotherms of sepiolite, allophane, and plasterboard ceramics But because of the high humidity regulation performance, sufficient performance is obtained even if thin material is used In actual practice, the material has been laid on interior walls to good effect CONCLUSIONS The present age is one in which ignoring the global environment will have serious consequences for humankind In maintaining, as far as possible, the inherent highly advanced properties and abilities of nature, it is important to develop technologies that convert, using the least amount of energy possible, these gifts of nature into forms that can be utilized in the human ecosystem Earth ceramics can 200 Moisture content (g /m2) Absorption Desorption Eco - karat 150 Earth ceramics Wood(cedar) 100 50 0 0 12 24 36 48 Time (h) Figure 24 Humidity absorption/desorption characteristics of Eco-carat at 40% to 80% RH The author would like to thank Dr H Maenami a Watanabe, INAX Corp Japan and Prof Dr T Univ of East Asia for the helpful discussions BIBLIOGRAPHY 1 D.H Meadows, D.L Meadows, and J Randers, B limits, Chelasea Green Publishing Company, Verm pp 104–140 2 L.R Brown and H Kane, Full House, W.W Norton & New York, 1994, pp 35–106 3 E.U Weizsacker, Erdpolitik, Wissenschaftliche lschaft, Darmstadt, Germany, 1989, pp 68–121 4 J Tibbetts, Green House, Environmental Health Pe 104(10): 1036–1039 (1996) 5 H Komine, Effects from house air quality on heal of Housing Research Foundation, 23: 5–17 (1997) 6 ’99 Handbook of Energy and Economic Statistics in Energy data and Modeling Center, 1999, pp 32–33 7 T Uemura, J Kohara and S Tokoro, Materials and of the Wall for Humidity Controll (in Japanese), Sho Japan, 1991, pp 18–20 8 C Arai, T Mizutani, Y Murase, T Hanakawa, an Measurement of Pore Distribution by Water Vapo tion, Soc Powder Tech Japan, 20(3): 115–121 (198 9 V.G Carter and T Dale, Topsoil and Civilization, of Oklahoma Press, Norman, OK, 1974, pp 10–31 10 S Iwata, Ecological Life (in Japanese), Ienohika Japan, 1991, pp 12–13 11 G.E Bessey, The History and Present Day Deve the Autoclaved Calcium Silicate Building Produ tries, Society of Chemical Industry, pp 3–6, Lo 1965 12 G.E Bessey, Sand-Lime Brick, National Buildi Special Report No 3, 1–21 (1948) 13 P.D Rademaker, H Hibino, T Mitsuda, Electron M of Calcium Hydrates, Annual Report of the Ceramic Lab Nagoya Institute of Technology, 1: 33 (1991) 14 H.F.W Taylor, The Chemistry of Cements, Acade New York, 1964, pp 168–232 15 S Sohmiya, Handbook for Hydrothermal S Japanese), Gihodoh, Japan, 1997, pp 292–320 16 F.H Wittmann, Advances in Autoclaved Aerated A.A Balkema, Rotterdam, 1992, pp 11–34 107: 605–18 (1984) 22 J.L Larosa-Thompson and M.W Grutzeck, C-S-H, Tobermorite and Coexisting Phases in the System CaO-Al2O3SiO2-H2O, World Cem., 27(1): 69–74 (1996) 23 D.S Klimesch and A Ray, Hydrogarnet Formation during Autoclaving at 180◦ C in Unstirred Metakaolin—Lime—Quartz Slurries, Cem Concr Res., 28(8): 1109–17 (1998) 24 D.S Klimesch and A Ray, Effects of Quartz Particle Size on Hydrogarnet Formation during Autoclaving at 180◦ C in the CaO-Al2O3-SiO2-H2O System, Cem Concr Res., 28(9): 1309– 16 (1998) 25 D.S Klimesch and A Ray, Effects of Quartz Particle Size and Kaolin on Hydrogarnet Formation durong Autoclaving, Cem Concr Res., 28(9): 1317–23 (1998) 26 I Stebnicka-Kalicka, Application of Thermal Analysis to the Invastigation of Phase Composition of Autoclaved Cement Pastes and Mortars, Therm Anal 1: 369–74 (1980) 27 S.A Abo-El-Enein, N.A Gabar, and R.Sh Mikhail, Morphology and Microstructure of Autoclaved Clinker and Slag-Lime Pastes in Presence and in Absence of Silica Sand, Cem Concr Res., 7(3): 231–38 (1977) 28 N Isu, S Teramura, H Ishida, and T Mitsuda, Influence of Quartz Particle Size on the Chemical and Mechanical Properties of Autoclaved Aerated Concrete (II) Fracture Toughness, Strength and Micropore, Cem Concr Res., 25(2): 249–54 (1995) 29 T Mitsuda, K Sasaki, and H Ishida, Phase Evolution During Autoclaving Process of Aerated Concrete, J Am Ceram Soc., 75(7): 1853–63 (1992) 30 O Watanabe, K Kitamura, H Maenami, and H Ishida, Hydrotheraml Reaction of Silica Sand Complex with Lime, J Am Ceram Soc., (2000) in press 31 L Hjorth, Microsilica in Concrete, Nordic Concr Res., 1: 1– 18 (1982) 32 L Hjorth, Development and Application of High-density Cement Based Materials, Phil Trans R Lond., A310, 167/73 (1983) 33 S Brunauer, J Skalny, I Odler, and M Yudenfreund, Hardend Portland Cement Pastes of Low Porosity, Cem Concr Res., 3: 279–93 (1973) 34 M.F Ashby, Materials Selection in Mechanical Design, Pergamon Press, New York, 1992, p 245 35 H Shin and T Kurushima, Thermodynamic Consideration on Energy Consumption for Processing of Ceramics, Bull Ceram Soc Japan, 32(12): 981–84 (1997) 36 G.W Brindley and G Brown, Crystal Structures of Clay Minerals and their X-Ray Identification, Mineralogical Soc Monograph, 5: 104–109, 405–407 (1980) 37 B Velde, Development in Sedimentology, Elsevier, New York, 1985, pp 225–56 actuators are attached directly to the structure used to modify its structural vibration characteris tial and temporal) in order to minimize the sound (1) In ASAC, the actuators tend to be compact cover only a very small portion of the structure fect is achieved because of the distributed elastic of the structure This technique has worked well f ber of applications, usually where the structure h sonable mobility and a low modal density of res some applications, however, the structure is quite or stiff (e.g., an electrical transformer casing), extremely difficult to elicit the necessary contro sponse with practical control actuators In this a discuss a variant of the ASAC approach in which trol inputs come from a smart or active skin that or most of the vibrating surface A schematic of t skin approach is shown in Fig 1 The objective of the smart skin is to locally ch radiation impedance (the resistive component) of ture in order to control the total radiated power in to the conventional ASAC, which alters the dyn sponse of the host structure The sound radiati are directly coupled to the normal displacement smart skin Thus modification of the transfer fun tween the structural displacement ws and the sm displacement wsk will lead to a change in sound r This modification can occur via a decrease in the a of wsk , thus decreasing the sound levels, or via in the amplitude distribution of wsk , causing th skin surface to be an inefficient sound radiation extended area Since it does not drive the host s Sound radiati Normal skin vibration wsk ws Normal structural vibratio Structure S Figure 1 Concept of a smart skin for sound radiatio ... Properties of Some Piezoelectric Materials a Tc (◦ C) εX 33 εX 11 d 31 α-Quartzab — 13 0 315 220 560 420 12 10 665 494 4.6 19 00 12 00 2800 225 400 29 43 203 — 16 00 11 30 — — 600 85 53 — — −79 ? ?11 9 −234 ? ?11 ... view of Eq (6), the reversible contribution is 200 0.0 Equations (7), ( 21) , ( 22) (7), (11 )1 , ( 21) , ( 22) (7), ( 21) , ( 22), (29) (7), (11 )1 , ( 21) , ( 22), (29) (7), ( 21) , ( 22), (29), (30) (7), (11 )1. .. 283– 318 (19 80) 10 11 12 13 14 M Achenbach, Int J Plast 5: 3 71? ??398 (19 89) P Xu and J.W Morris, Metall Trans A24: 12 81? ? ?12 94 (19 93) J.L Ericksen, J Elast 3–4: 19 1–2 01 (19 75) J.G Ball and R.D James,