Mechanical Engineer''''s Reference Book 2011 Part 7 ppt

7/92 Materials, properties and selection ducts, a number of neutrons which serve to carry on the chain reaction, other particles and energy including y-radiation. Fissile materials include U-235 (a constituent of natural uranium), U-233 (a product of neutron capture by thorium) and plutonium (a product of neutron capture by U-238, the major constituent of natural uranium). They constitute the fuel in nuclear reactors. ‘Fertile’ metals include U-238 and thorium. They are incorporated into nuclear reactor fuel or used separately in ‘blankets’ to absorb neutrons and produce additional fissile material. ‘Canning’ metals are used to contain nuclear fuel in a reactor, maintain its integrity and dimensions, protect it from attack by the coolant, retain fission products so that they do not contaminate the coolant (and, through it, the environment), transfer the heat produced efficiently and absorb a minimum proportion of neutrons. Canning and core structural materials now in use include stainless steel for sodium-cooled and high-temperature gas-cooled reactors, magnesium alloy for the original ‘magnox’ reactors, zirconium for pressurized water and boiling water-cooled power reactors and aluminium for water-cooled research reactors. Zirconium6* occurs naturally together with hafnium, which has high neutron-absorbing properties. These must be sepa- rated by a complex chemical process before they can be used in water reactors: zirconium as a core structural material, hafnium as a control rod material. Both have excellent resistance to pressurized water attack if they are suitably alloyed and satisfactorily pure. Beryllium combines a very low nuclear capture cross section with good strength and hardness at moderately high temperatures. It appeared to have great promise as a canning and core structural material but the promise has not been fulfilled mainly because of its lack of ductility and resistance to environmental attack and partly because of doubts concerning the effect of helium, which is produced when beryllium is irradiated by neutrons. The applications of alloys based on beryllium are confined to those such as spacecraft, where its high specific strength outweighs its high cost and hazard to health. (Its oxide causes ‘beryllicosis’, similar to silicosis but more virulent when ingested by breathing.) 7.4.9.4 Metals used in integrated circuits Silicon and germanium. which when pure are very poor electronic conductors of electricity, can be transformed by ‘doping’. Introducing into the lattice pentavalent elements, phosphorus, arsenic or antimony creates free electrons and gives rise to negative or n-type conductivity. Introducing trivalent elements boron or aluminium reduces the number of electrons to form ‘holes’ and gives rise to positive or p-type conductivity. Junctions between regions of these two conductivity types are called p-n junctions. These are at the heart of most semiconductor devices: diodes, transistors, solar cells, thy- ristors, light-emitting diodes, semiconducting. lasers, etc. By taking a slice of highly pure single-crystal silicon, diffusing into it p- and n-type atoms in a geometrical pattern controlled photographically and then insulating or interconnecting regions by metallization, circuits with millions of components can be formed on one silicon chip. Highly pure, zone-refined single-crystal silicon has com- pletely superseded germanium for the manufacture of transistors and silicon integrated circuits. The quantity used is small, amounting only to tens of tons per annum, but its technological importance is enormous. 7.5 Composites 7.5.1 Introduction A composite is a combination of two or more constituents to form a material with one or more significant properties superior to those of its components. Combination is on a macroscopic scale in distinction to alloys or compounds which are microscopic combinations of metals, polymers or ceramics. Those properties that may be improved include: Specific gravity Elasticity and/or rigidity modulus Yield and ultimate strength and, in the cases of ceramics and concrete, toughness Fatigue strength Creep strength Environmental resistance Hardness and wear resistance Thermal conductivity or thermal insulation Damping capacity and acoustical insulation Electrical conductivity Aesthetics (attractiveness to sight, touch or hearing) cost Not all these properties can (or should) be improved at the same time, but the consideration which governs the choice of a composite is that a critical property has been adequately improved, while deterioration in other properties has not been significant. Usually (but not invariably) a composite consists of a matrix which is relatively soft and ductile containing a filler which is harder but may have low tensile ductility. The use of composites has persisted ever since tools of wood or bone (which are naturally occurring composites) were used by primitive hu- mans. The earliest human-made composite was probably straw-reinforced mud for building. The Egyptians invented plywood, an early example of the improvement (which con- tinues to the present day) of the natural composite, wood. There are two ways of classifying composites: according to either the material of the matrix or the geometrical distribu- tion of the components. Composites classified according to geometry include: Particulate composites which are distributions of powder in a matrix; Laminar composites which comprise layers of two or more materials: Fibrous composites which comprise a matrix that is usually relatively soft and ductile surrounding a network of fibres which are usually stronger but may be brittle relative to the matrix. The fibres may be short and their orientation effectively random or they may be long and carefully aligned. Composites with long fibre reinforcement are known as ‘Filamentary Composites’ and the fibres may be aligned on one, two or three directions. Composites classified according to matrix include: Fibre-reinforced or powder-filled polymers Concrete, reinforced concrete and prestressed concrete Wood and resin-impregnated wood Metal matrix composites Fibre-reinforced ceramics and glasses Carbon fibre-reinforced carbon Of these, reinforced concrete probably has the greatest indus- trial importance but fibre-reinforced polymers have the greatest technological and engineering interest and the major part of this section will be devoted to them. Some other classes of composite will be described briefly and their properties and applications outlined. Table 7.47 Properties of fibres and whiskers appropriate for use in composites Type of filament Density Elasticity Tensile Specific Specific Elongation, Type of composites used in: modulus E strength, cr,, strength, crJp stiffness, E/p E Fibre Whisker (kgm-3) (GPa) (MPa) (km) (mn) ("/.) - Asbestos Boron Carbon Cellulose Glass Kevlar Nylon Polypropylene Steel Alumina Chrysotile Crocidolite Boron carbide High modulus Low modulus Carbon Copper E Alkali resistant Iron High modulus Low modulus Nickel Silicon carbide High tensile Stainless ~ 3880 2550 3370 2520 2470 1900 1900 1630 1200 8740 2500 2700 7680 1440 1140 8790 1140 900 3120 7860 7860 380 164 196 390 450 340 235 980 10 124 86 75 200 133 69 215 >4 >8 840 200 160 18 000 1 000 3 500 3 400 6 700 3500 2350 21 000 400 3 000 3 200 2 500 13 000 2 900 2 900 3 900 850 400 11 000 2 000 1 700 4.5 0.4 1.1 1.35 2.70 1.8 1.37 13.00 0.33 0.34 1.37 0.95 1.70 2.01 2.63 0.44 0.75 6.44 3.50 0.25 0.22 9.8 6.5 6 15 18 18 12 60 0.8 1.4 3.4 3 2.6 9 6 2.4 0.35 0.9 27 3.1 2.5 2.5 2.5 0.5 1.0 15 4.8 3.6 2.1 4 13.5 18 3 3.5 Metal matrix Previously cement Polymer matrix Metal matrix Polymer Polymer, metal and ceramic matrix Concrete matrix Polymer matrix Polymer matrix Polymer and concrete matrix Polymer matrix Polymer matrix Polymer matrix Polymer matrix Concrete matrix Concrete matrix Polymer and metal matrix Concrete matrix Polymer matrix Composites 7/95 these criteria have been met it should set as quickly as possible to a strong and heat- and environment-resisting solid. Polymers share with concretes the advantage over other possible matrix materials that they fulfil these requirements at a relatively low processing temperature. There are two classes: thermosetting and thermoplastic polymers (see Section 7.4). Thermosetting resins compounded with a hardener may be infiltrated between fibres while liquid and allowed to harden at room or elevated temperature. They include unsaturated polyesters, which are relatively cheap and easy to work but do not bond well to fibres and have a relatively high shrinkage. These are used for large and comparatively low-duty composites, usually with glass reinforcement. Epoxide resins are the most extensively used matrix materials for high-duty carbon? boron and aramid fibres. They perform excellently at temperatures up to the region of 1.60-200°C. Thermosetting resins which have been used as matrices operating at higher temperatures include phenolics, phenol arakyls and the recently developed polyphenylene quinoxia- line. Resins which are beginning to replace epoxides for high-temperature service with carbon reinforcement are bis- rnaleides (BMI) and polyimides (PI) which have continuous service capabilities of 200°C and 300°C respectively. (Some polyimides have survived short exposures to 760°C.) These polymers are, however, difficult to handle and polyimides in particular are expensive and require high cure temperatures, Thermoplastic matrix materials are tougher than thermosets, have an indefinite sheif life. the semi-finished composite can be hot formed and in some cases have better high- temperature and solvent resistance. However, the molten polymer has a highe.r viscosity than an uncured thermoset, fabrication temperatures are high and some are expensive. Many thermoplastics havc been used, ranging from the cheapest (nylon) to the highly expensive polyamide imide @AI) and polyether-ether ketone PEEK. PEEK composites have a maximum service temperature of 250°C. a work of fracture up to thirteen times that of epoxide composites and significantly better fatigue resistance. but are expensive. 7.5.4 Manufacturing procedures for filamentary polymer composites Filamentary composites are manufactured by ‘lay-up’, a term used for positioning the fibres and matrix to form the shape of the final component. Lay-up may be accomplished by ‘pultrusion’, ‘winding’ or ‘laying’, ‘tow’, ‘tape’, ‘cloth’ or ‘mat’. In none of these forms are the fibres twisted to form a yarn. All forms oE sub-assemblies can be obtained as ‘prepregs’ satu- rated with the resin which is later to form the matrix. Headstock Figure 7.57 Gantry type five-axis filament winding machine. (Reproduced by permission of Metals and Materials) In pultrusion (see Figure 7.56) the reinforcing fibres are used to pull the material through a die. In winding, impregnated single filaments, rovings or tapes are wound onto a former or mandrel. Figure 7.57 shows a winding machine which may be computer controlled to produce any convex shape from which the mandrel can be removed. Filaments may be orientated according to the pattern of stresses that are to be withstood. Cloth winding or laying utilizes pre-impregnated cloth which is deposited in the desired form and orientation. The bidirec- tionality and convolutions of the fibres in cloth make for lower precision in strength and stiffness. Cloth laying is therefore often used for filling where strength and stiffness are not critical. Moulding can start with a deposition of pre-cut layers of prepreg fibres which are compressed at elevated temperature to form the final laminate. Continuous iamination is the application of pressure by rolling to bond layers of prepreg cloth or mats. 7.5.5 Properties of filamentary polymer composites Filamentary polymer composites consist, in principle, of ‘laminae’ which are assembled into ‘laminates’. A ‘lamina’ is a flat or curved assembly of unidirectional fibres in a matrix. It is Primary carding Caterpiiler and squeeze-out haul-off Hot curing and Fibre let-off / Resin impregnation Figure 7.56 of Metals and Materials) Pultrusior process in which the reinforcing fibres are used to pull the material through the die. (Reproduced by permission 7/96 Materials, properties and selection Table 7.48 Properties of 60% fibre plies in epoxide laminates Property E glass S glass Kevlar 49 HT-CFR P HM-CFRP Boron Elastic modulus (GPa) El1 E22 GI2 VI2 Strengths (MPa) UlT -2T UlC -2c 712 ILSS Strains to failure E11 E22 EllC E22C Thermophysical SG q, X 10-6K-1 al, X K-' kl, Wm-' K-' k2, Wm-' K-' Specific heat, J kg-' K-' 37-50 12-16 4.5-6 0.20 1100-1200 40 620-1000 140-220 50-70 60 2-3 0.4 1.4 1.1 1.9-2.1 6.3 30 1.26 0.59 840 55 16 7.6 0.26 1600-2000 40 690-1000 140-220 80 80 2.9 0.3 1.3 1.9 2.0 3.5 29 1.58 0.57 840 77-82 5.1-5.5 1.8-2.1 0.31 1300-2000 20-40 235-280 140 40 60 1.8 0.5 2.0 2.5 1.35-1.38 -4 to -4.7 60-87 1.7-3.2 0.15-0.35 1260 140-207 9.8-10.0 5-5.4 0.25-0.34 1240-2300 1200-1580 170 80 90-100 41-59 1.1-1.3 0.5-0.6 1.6 0.9-1.3 1.5-1.6 +0.4 25 10-17 0.7 840 220-324 6.2-6.9 4.8 0.20-0.25 783-1435 21 620 170 60-70 60-90 0.5-0.6 <0.7 2.8 - 1.63 -0.43 to -0.8 27-32 48-130 0.8-1.0 840 210 19 4.8 0.25 1240 70 3300 280 90 90 0.6 0.4 1.6 1.5 2.2 4.5 23 - - 1260 Reproduced by courtesy of Metals and Marerials. from a paper by R. Davidson. highly anisotropic, having low stiffness and strength trans- versely (see Table 7.48). Laminae of varying orientations are therefore superimposed in a stack to form a 'laminate' with directional properties tailored to match the stress. Laminates are therefore essen- tially two-dimensional structures (the 'dimensions' may be curved when the component is a cylinder or sphere) and the mechanical properties in any of the principal directions of a laminate are inferior to those in the principal direction of one of the constituent laminae. Additionally, the thermal stresses which arise on cooling from the curing temperature may impair strength. Three-dimensional reinforcement such as is employed in carboqkarbon composites (see Sections 7.5.8 and 7.5.11) is not normally applied to laminated plastics and shear and transverse tensile stresses can result in delamination. The matrix supports, protects, distributes load among and transmits load between the fibres. If a fibre should break the matrix, stressed in shear, transmits load from one broken end to the other and to adjacent fibres. Because boron or graphite fibres in a polymer matrix provide by far the greater proportion of strength and stiffness, composites with these fibres can, in most cases, be considered to be linear elastic materials. In composites with glass or aramid fibres the lower modulus results in the matrix bearing a higher proportion of the load and the stress strain relation may depart from linearity. Elastic and physical properties may, in the case of hi h strength are more difficult to calculate because the secondary stresses induced in a composite may exceed the transverse shear strengths and may themselves cause failure. composites, be calculated from classical theory.6 F- Strengths The parameters which must be taken into account in design include: Elastic properties: Longitudinal Stiffness Ell. Transverse Stiffness EZ2, In-Plane Shear Modulus GI2, Poisson's ratio VI?. Strength properties: Longitudinal Tensile Strength (T~.~, Transverse Tensile Strength uxr, Longitudinal Compress- ive Strength (T~,~. Transverse Compressive Strength qC, Yield Strength uj, In-plane Shear Strength Physical properties: Specific Gravity SG, Longitudinal Thermal Expansion Coefficient al, Transverse Thermal Expansion Coefficient (Y~, Longitildinal Thermal Conduc- tivity kl, Transverse Thermal Conductivity k2. The Specific Strengths and Moduli of Fibrous Composites and other engineering materials are illustrated diagramatically in Figure 7.58. (In this figure specific properties are derived by dividing the modulus or strength by the density and a gravita- tional term of 9.81.) The fatigue processes which occur in composites differ fundamentally from those in metals, and, providing that they are well understood, offer very significant advantages to the designer. High-modulus fibres such as carbon and boron confer excellent tensioqhension fatigue properties, the fatigue stress at lo7 cycles of longitudinal boron epoxy being only 15% less than the tensile stress. This is because the high-modulus fibres limit the stress in the lower-modulus matrix and so protect it from fatigue damage. However, in those plies in which fibres are orientated transverse to the principal cycle stress the matrix is subjected to transverse tensile and shear stresses which cause cracking Composites 7/97 Specific modulus lx TO3 K ml 1 2 5 10 20 50 0.1 I I I I I I, I1, 1 I I 1 11 31, 1 II I Moulding compounds Matrix resins @13 Design area for CFRP laminates 0 1 Carbon fibre -intermediate modulus 2 Carbon fibre -high tensile 3 Carbon fibre -high modulus 4 Carbon fibre -ultra high modulus 5 Boronfibre 7 S glass 9 E glass 10 Silicon carbide whiskers 11 Kevlar - 49 aramid fibre 12 Woven fabric CFRP 13 45 DEG glass fibre laminate 14 Woven fabric KRP X 1 Titanium alloy 2 Maraging steel H.11 3 Aluminium-lithium alloy 4 Aluminium alloy - 7000 5 Aluminium alloy - 2000 6 Stainless steel -martensitic 7 Stainless steel -austenitic 8 Aluminium-magnesium alloy 0 1 Nylodglassfibre 2 Nylon/carbon fibre 3 Polyphenylene sulphidekarbon fibre 1 Epoxide resin 2 Nylon 3 Polyphenylene sulphide 0 Unidirectional composite in fibre direction (0") Unidirectional composite in @ transverse direction (90") (Average values only -check individual value at source) Figure 7.58 Specific strengths and moduli of composites and competing materials. (Reproduced by permission of Metais and Materials) 7/98 Materials, properties and selection n m .c t10 - 0’ U Proportion of 0’ fibres - - ’ I I I I I I I I I J Mean stress (MN m-’) Proportion of 0” fibres i30 b “0 c e t: \ . 100 EO 60 40 20 0 20 40 60 80 100 Compressive strength (%) Tensile strength (56) Mean stress Figure 7.59 Demission of Metals and Materials) Maximum and minimum stress in fatigue cycling causing failure at lo6 cycles in various CFRP laminates. (Reproduced by parallel to the plies and delamination. The effect of fibre orientation on CFRP laminates is shown in Figure 7.59. Only glass composites have a steep S-N slope, presumably caused by the diffusion of moisture which causes cracks to initiate in the glass fibres. Even so, the specific fatigue resistance of longitudinal fibreglass is far superior to that of any metal. A further advantage of composites subjected to fatigue is that, whereas in metal fatigue there is, during the greater part of the life of a component, no superficial evidence of deterioration, there is in filamentary reinforced plastics a slow and progressive deterioration revealed at an early stage by a decrease in modulus or an increase in cracking in specific plies which is easily detectable by non-destructive examination. This reduction in modulus could, if allowed to continue, lead to failure by buckling, but both because of the higher specific fatigue strength and because of the more obvious incidence of failure, catastrophic fatigue failures in filamentary composites are much less likely than in metals. The assessment of the influences of impact on filamentary composites is more complex than metals because of their anisotropy and large number of failure mechanisms. Where, for example, in a jet engine a titanium blade will shear undamaged through the body of an intruding bird, a composite blade of equivalent strength will shatter. It can be stated that, in terms of impact strength. for composites the common fibres may be ranked in order of superiority: 1. Kevlar 29, Glass 2. Kevlar 49, boron 3. High-tensile carbon 4. High-modulus carbon The resistance to attack of polymers depends on the specific polymer and its environment. Traditional matrices based on polyesters, vinyl esters and epoxides perform very successfully in atmosphere, soil and many items of chemical plant. Protec- tion may, however, be needed against degradation by ultravio- let radiation from sunlight. Some polymers, including fluor- oplastics PTFE and PDF and polyether ether ketone PEEK have exceptional resistance to radiation damage and may be used as matrices and as coatings. Composites 9/99 shaped by melt fabrication techniques. injection moulding, extrusion, blow moulding and thermoforming. The material is melted or plasticized by heating, shaped in the plasticized condition and cooled to resolidify. Reinforced thermosets may be made to flow in the pre-cured state and cured or cross linked to an infusible mass in the hot mould. 'Commodity' thermoplastics, polyolefins, polystyrene, poly- vinyl chloride. etc. are utilized mainly in the non-reinforced form but are marketed in the fibre-reinforced form. A much higher proportion of engineering thermoplastics, polyamides. polyacetyls and thermoplastic polyesters are reinforced, usually with short glass fibre and the specialized high- performance thermoplastics such as polysulphones are also reinforced, often with short carbon fibre. Short glass-fibre reinforcement is used for thermosets such as phenolic. amino and melamine formaldehyde resins which may be injection moulded, although the curing time lengthens the manufacturing cycle. An important class of composite are the long fibre-reinforced sheet-moulding compounds (SMC) and the dough-moulding compounds (DMC) based on unsaturated polyester, vinyl ester and epoxide resins. These materials aie normally compression moulded (see Figure 7.60) and have to compete with steel pressings. Similar composites are based on the thermoplastics which are produced as sheets that are heated and then pressed between cold dies. Two materials are used for discontinuous fibie reinforcement: short and long staple glass fibre, and short staple carbon fibre. Aramid fibres have the required properties but polymers compounded with them are not yet obtainable commercially. Discontinuous fibre-reinforced plastics cost less to fabricate than the corresponding filamentary reinforced materials but their mechanical properties are significantly inferior. This is because the rule of mixture that is obeyed precisely so far as modulus is concerned. and approximately so far as yield strength and UTS is concerned, for high-modulus continuous fibres is no longer obeyed for discontinuous fibres. The strength of short fibre-reinforced polymers is controlled by a complex series of interactions between the fibres and the matrix. The fibre/matrix interface is usually the weakest link. In aligned fibres the end becomes debonded at quite low loads and the debonding spreads along the fibre as the load increases. Debonding reduces the stiffening efficiency of the fibre and constitutes a microcrack which may extend into the matrix. The mechanical strengths of typical short and woven fibre- reinforced thermosets are listed in Table 7.49. Table 7.50 details the mechanicai properties of short fibre-reinforced 7.5.6 A~~~~~a~~ons of filamentary polymer composites The cost of GFRP is of a similar order to steel and aluminium or timber and where its lightness and corrosion resistance are advantageous, and its fabrication methods suitable for the specific component, it is used. Applications include small boats (and not so small minesweepers), roofing and cladding for buildings and many components for road and rail trans- port. Other uses of GFR.P are promoted by one or more specific property parameters. It is, for example, displacing steel for vehicle leaf springs 'on account of its lightness and fatigue resistance. It is replacing porcelain and glass for electrically insulating components on account of its strength and insulating properties. It is replacing steel for aqueous liquid vats, tanks and pipes because of its lightness, strength and corrosion resistance. High-performance composites are used in aerospace or sport. where the requirement for the specific stiffness and/or specific strength justifies the increased cost. The aerospace applications of CFRP include the basic structures of spacecraft and commenced with ancillary fittings, floors and furniture of aircraft, but is now extending to major structural items such as stabilizers, tailplanes and fins. Future fighter aircraft will probably contain a high proportion of CFRP and will benefit from a reduced sensitivity to radar. High-performance sports goods are also increasingly made of CFRP because the reward of coming first in a race (or a fishing contest) far outweighs the additional cost of a CFRP racing-car skin or a CFRP fishing rod compared with any conceivable alternative material: except possibly boron-fibre (BF) reinforced composites. The icombination of a specific tensile strength around 0.8 and modulus around 105 GPa m3 kg-' can only be obtained from BF-reinforced plastics. Boron fibres may be used by themselves or as a bybrid composite, part BF, part CF for horizontal and vertical stabilizers, control surfaces, wing skins, flaps, slats, tail surfaces, spars, stringers, fuselage- reinforcement tubes, spoilers, airhole flaps, doors, hatches. landing-gear struts, helicopter rotor shafts and blades for military and civil airplanes and space shuttles. The use of such materials (including aluminium matrix composites) can reduce weight by from 12% to 45% I almost double service life, and decrease fuel usage and maintenance by about 10%. BF- reinforced composites are also used for the pickup arms for high-fi record-playing decks where specific stiffness is para- mount. The relative cost of glass, carbon, hybrid and boron- reinforced plastics is 1, 10, 20 and 30, but the cost of the high-strength high-modulus fibres is reducing with time. The use of 'aramid' para-orientated aromatic polyamids fibres has been restricted because their relatively low moduli (58.9-127.5 GPa) makes it difficult to take advantage of their high UTS, (up to 2.64 GPa) in designs which may be buckling critical. They have been used for golf shafts, tennis racquets and boat hulls, Kevllar T950 for tyrcs and Kevlar T956 for other riibjer components. 7.5.7 Discontinuous fibre-reinforced polymer composites 7.5.7.1 General Discontinuous fibres of an average length in the region of 380 pm may be incorporated in proportions up to about 25% by volume in mouldable polymers to enhance their stiffness, strength, dimensional stability and elevated temperature performance. Reinforced thermoplastic materials (RTP) may be Figure 7.60 Press moulding arrangement for discontinuous fibre reinforced plastics. (Reproduced by permission of Merals and Materials) 7/100 Materials, properties and selection Table 7.49 Properties of short fibre and woven fibre reinforced thermosets Property BMC SMCb Glass fibre Glass fibre Woven CF Woven Kevlar polyester epoxide epoxide epoxide Stiffness (GPa) Ell, E22 v12 Strengths (MPa) UlC9 u2c ai TILS Izod impact, J m-' SG q, cu2 X K-' kl, k2 Wm-' K-' Specific heat, J kg-' "C-' ulT~ (T?T 11 0.11 12-13 0.11 17-2 1 0.11-0.12 23-26 0.12-0.16 70 0.08 31 - 60-69 138 103 13.8 430-640 1.65-1 .SO 18-3 1 0.1-0.23 75-120 179-193 138-172 17-28 640-850 1.7 22-36 0.6-0.22 303 276 214 24 750-960 1.7-1.8 10-16 0.164.20 379-517 345-413 517-624 28 1600 1.8-1.9 10.6 0.16-0.33 586-620 690 841-1034 55-67 517 83 345 55 1.59 3 1.33 0 850 850 850 850 1260 ~~ a 15-25% glass 3MO% glass. Reproduced by courtesy of Metals and Mafenals, from a paper by R. Davidson Table 7.50 Mechanical properties of short fibre reinforced thermoplastics IB Polymer 2B 9 10 I1 12 13 Glass fibre Water Flexural UTS Tensile Notched (W%) (V%) (max) ("/.I (J m-') content absorption modulus (MPa) elongation Izod impact ("/.I 1. Polyethylene (HD) 2. Polyethylene (HD) 3. Polypropylene 4. Polypropylene 5. Polypropylene 6. Nylon 6 7. Nylon 6.6 8. Nylon 6.6 9. Nylon 6.10 (chemically coupled) (chemically coupled) 10. Nylon 11 11. Acetal homopolymer 12. Acetal co-polymer 13. Acetal 14. Polystyrene 15. SAN 16. ABS 17. Modified PPO 18. PETP 19. PBTP 20. Polysulphone 21. Polyethersulphone 22. PPS 23. Polycarbonate 24. Polycarbonate 25. Polycarbonate (chemically coupled) 20 9 0.1 40 20 0.3 20 8 0.02 20 8 0.02 40 19 0.09 40 23 4.6 20 10 5.6 40 23 3.0 40 22 1.8 30 15 0.4 20 12 1.0 30 19 1.8 30 19 0.9 40 22 0.1 40 22 0.28 40 22 0.5 40 22 0.09 30 18 0.24 40 26 0.4 40 26 0.6 40 26 - 40 26 0.06 20 10 0.19 30 17 0.18 40 24 0.16 4.0 55 7.5 80 4.0 63 4.0 79 7.0 103 10.5 180 9.0 130 15 210 9.0 210 3.2 95 4.3 60 9.0 90 2.5 2.5 2.5 50 70 75 90 100 150 100 4 4 2.5 3.5 2.5 2.5 5 136 170 - 40 40 95 60 60 70 80 85 155 100 80 80 180 190 200 9.7 11.3 13.4 7.6 110 8.6 135 8.3 130 9.6 150 11.0 138 11.0 205 12.5 160 135 103 128 2.5 2.5 3.5 3.5 4 4 2 3 6 - 5 4 Carbon fibre filled materials 26. Nylon 6.6 27. PETP 28. Polysulphone 29. PPS 30 21 2.4 20.0 240 3.5 75 30 24 0.3 13.8 138 2.5 60 30 24 0.4 14.0 158 2.5 60 30 24 0.1 16.9 186 2.5 55 Reproduced by permission of North-Holland Publishing Co. Composites 71101 thermoplastics which includes some carbon fibre-reinforced materials. The superiority of filamentary reinforcement is evident. Short fibre reinforcement shows to even less advantage in fatigue, creep and impact loading and is not to be recommended for highly stressed parts. Short fibre reinforcement is, however, much cheaper than filamentary reinforcement and is used extensively for a great variety of domestic, architectural. engineering, electrical and automotive components. 7.5.8 Carbon-carbon composites Carbon-carbon composites retain their strength to a higher temperature than any competitive material (see Figure 7.61). They are unique in that the matrix is identical in composition to that of the reinforcing fibres. They differ from the polymer composites already described in that the matrix which can exist in any number of quasi-crystalline forms from 'glassy' or amorphous carbon to graphite has low strength and negligible ductility. While. therefore, single and bidirectionally reinforced carbon-carbon composites are manufactured the need to avoid delamination has promoted three-directional reinforcement. Complex weaving equipment has been developed to achieve multilayer locking by means of structures such as are shown in Figure 7.62. Even more complex patterns are employed. As an alternative to three- (or eleven-) directional weaving, the directional reinforcement may be produced by fabric piercing. Arrays of layers of two-directional iabric are pierced with metal rods or needles. The metal needles are withdrawn and replaced by yarns or by precured resin yarn rods. Fabric piercing is versatile and can produce a higher overall fibre volume and a higher preform density than weaving. Other techniques for producing multi-directional structures involve the assembly of rods coilsisting of yarns pre-rigidized with phenolic resins by pultrusion. These can be used to form '4D' tetrahedral structures or by incorporating a filament winding operation into a cylindrical structure. Densification of the structure with carbon is achieved by impregnation with 0.5 r I 1 ,Titanium 35% SIC fibres (0" only) 11 Columbium (Niobium) C129Y \ 400 800 1200 1600 Temperature (K) Figure 7.61 Strength-to-density ratio for several classes of high temperature materials with respect to temperature. (Reproduced by permission of Metak and Materials) X' 'Y Figure 7.62 Three-dimensional orthogonal weaves for carbon carbon composites. (Reproduced by courtesy of North-Holland Publishing Company) pitch, a thermosetting phenol or furfural type resin or by depositing carbon from a hydrocarbon (CVD process). The preform may be impregnated with liquid by a vacuum process, carbonized at 655-1105°C at low pressure and then graphitized within the range 2000-2750°C. The cycle is repeated until the desired density is achieved. Alternatively, the preform may be impregnated with pitch, carbonized and then graphitized at high pressure in a HIPIC furnace: and the cycle repeated as required. In this process the workpiece must be isolated from the pressure vessel in a fxnace of the type shown in Figure 7.63. Impregnation by carbon by the CVD process is carried out by feeding hydrocarbon gas through and into the pores of the preform, isothermally, under a thermal gradient or under differential pressure. Carbon is deposited at 1155°C and in this case, as in impregnation with a thermosetting resin. a carbon rather than a graphite matrix is formed. The tensile properties of carbon-carbon composites with various matrices are listed in Table 7.51. The application of carbon-carbon composites has so far been restricted by high cost and their susceptibility to oxidation at temperatures above 400°C. Coatings to protect against oxidation are under development. Their most important application has been as rocket nozzles, thrust chambers, ramjet combustion lines and heat shieids for space vehicles. They are used commercially for aircraft brake systems for Concorde and military aircraft as well as for hot pressing moulds. They can also be employed for very high-temperature heat shields and elements for vacuum furnaces. Their high-temperature strength will favour a large number of uses if their cost is- reduced. 7.5.9 Fibre-reinforced metals The potential of fibre-reinforced metals is so great that they have been declared a strategic material in the United States. [...]... 3.18 3.18 4 .75 4 .75 to 12 .7 4 .75 to 9.53 Ureas and melamines Cellulose-filled Fabric-filled Mineral-filled 0.89 1. 27 1.02 1.58 3.18 2.36 2.54 3. 17 4 .75 3.18 to 4 .75 3.18 to 4 .75 4 .75 to 9.53 Thermoplastic Acrylics Cellulose acetate Cellulose acetate butyrate Ethyl cellulose Polyamide Polyet hylene Polystyrene Pol yvin yls 0.64 0.64 0.64 0.89 0.38 0.89 0 .76 1.36 0.89 1. 27 1. 27 1. 27 0.64 1. 27 1. 27 1.58 2.36... choice is made Polymers 71 1 19 7 Pol Poly Methyl rnethacrilate General- purpose I 1 1 1 I I 1 1 Cellulose acetute Cellirlose PVC Fle.\-ib/r tiitrate 63-105 83- 11s 74 -140 1.0-4.5 0 .70 - 1.3 17- 62 60-133 68 112-190 IO - 140 2.5 3.0 22-25 - 56 55-85 1 40-60 I 29 -77 I 35 -70 I 7- 26 MI00 35 - 84 I M70- 100 I R54- 125 I M25-50 1 S A -75 96 IO - 55 2800 - 3500 5900-9000 9000-2500 4200 -70 00 1200-1400 2800 - 3200... Compressive Rolling shear Working R = -1 R=I (MPa) 39.25 34.43 30.21 4 .71 32. 87 28.84 25.30 3.94 16.69 16.69 16.69 2.11 39.25 34.43 30.21 4 .71 (MPa) (MP4 (MPa) 1.15 9.92 0 .70 ' 0. 97 8.25 0.59 0. 47 3.81 0.32 1.15 9.92 0 .70 (MPa) (MP4 Douglas Fir laminae, values corrected to 8% moisture, 49°C except R = -1 (room temperature) Polymers 71 1 07 Table 7. 56 Mechanical lproperties of Permali impregnated compressed wood... 0. 17 1 60-80 0.16-0.25 I 0.16-0.2 10.26-0.32 10.13-0.21 0.125 - 0.lf 70 75 80-190 130- 160 50- 180 1015 10'3 1013 1012- 10'" 1012- 109- 1 0 ' 3 200 - 280 200 200 100-240 120-240 120- 160 2.45 - 3.1 3.3 - 3.9 3.3 -4.5 3.5 - 7. 5 6 .7 7.3 - 5-9 6.2 3.3 - 3.45 1011- 2.4-2 .7 I - I/ 2.4-3.8 I f 0.001-0.003 0.0 07- 0.015 1 I 1 1 I I 0.000 07 0.004-0.014 10.003-0.008 1 25-40 50-85 1.04-1.11 11.2-1.33 11.04-1. 07. .. measurable 5000-12 000 70 00-9000 230 30-120 41 -70 103 70 -1 15 Not measurable 0.6-0.9 70 00-11 000 6900-12 400 100-9200 0.1-0.3 RM 120 35-138 105-150 Not measurable 17 000 13 000-18 000 0.34.9 40-90 70 -120 0.5-1 70 00-10 000 9000-11 000 0.12-0.28 RM 115 Max continuous service temp no load Deflection 0.45 MNm-’ temp 1.8 MNm-’ Thermal conductivity Thermal expansion 100-150 175 -290 100 150-205 75 75 130-190 0.16-0.3... 15- 17 130-145 0.28-0.14 22-36 - 100-160 5-13 4-6 56-160 5 -7. 1 4.5-6.6 109-10** 110-120 6-9 7- 9 0.04-0.08 0.025-0.045 110-114 2 x io9 70 -120 10-11 7 0.2 0.014 180 10~O-10~~ 1 0 ~ - 1 0 ~ ~ 120-180 120-160 7- 9 7- 9.5 6-8.5 6.5 -7 0.25-0.45 0.25-0.43 0.25-0.4 0.2-0.3 80-130 80-150 Specific gravity Mould shrinkage Water absorption Refractive index 1.3-1.5 0.4-0.9 1 Opaque 1 .7- 2 0.15-0.3 0.03-1.20 Opaque 1. 47- 1.55... fibres Alumina fibres Boron fibres Ultrahligh modulus graphite fibres Silicon carbide particles Silicori carbide monofilament fibres 0 60 50 50 45 40 35 Tensile strength (MPa) Longitudinal Transverse Longitudinal Transverse 70 1 47 203 203 350 1 47 2 17 70 10.5 154 126 35 1 47 188 280-490 1260 1050 1530 630 560 175 0 280-490 35 175 105 35 560 420 Reproduced by courtesy of Metals Engineering Apply aluminium foil... OC-C, figure 7. 89 Structure of typical aromatic polyamide H2, CONH-CpH2,NH nylon m+2, p Figure 7. 86 Formation reaction for polyamides + nH2O Table 7. 61 Properties and an indication of price of typical engineering thermoplastics I Polvnmidr Aertd w s m Poiveorhnnorc Polyeaor rerim 40% gi"rs 170 300 25 HM71 88 RM71 140 60 4-6 1-6 1-6 R llS , 142 L 109 R 124 R 11 2 I 70 M Io5 2 17 142 u8 ) I1 0 1 37 0 24 0.23... 0.23 I 8.5 1 37 0.16 89 44 - 80 67 25 49 28 1 2 x IO" 7. 5x 10'2 10 17 10" in" 2 x IO" 170 195 212 I50 177 3 39 265 3.15 3 36 26 4 31 1 0.002 I 0.0025 I 0.ow4 I 0,0020 38 I I water abramtion 1.5 1.8 Refractive Translucent Tmnrluvcnl index ' I 0.2s 09 Approximate mid-1991 prices, f per kilo per tonnc Opaque 0.18 Opaque Opaque 0.12-0l9 I 54 - 1.6 224 250 290 285 - 29s 02 - 08 224 05 - 0 7 0.I 03... usually carried out by a vacuumforming process (Figure 7. 75) but polymers which are more difficult to deform such as polymethyl methacrylate and unplasticized PVC may require mechanical pressure or positive air pressure (Figures 7. 75(d) and (e)) Figure 7. 75 Shaping of sheet in the rubbery phase (a) Application of vacuum; (b) and (c) air pressure; (d) mechanical pressure; (e) combination of methods (vacuum . 3880 2550 3 370 2520 2 470 1900 1900 1630 1200 874 0 2500 270 0 76 80 1440 1140 879 0 1140 900 3120 78 60 78 60 380 164 196 390 450 340 235 980 10 124 86 75 200 133 69. 17- 2 1 0.11-0.12 23-26 0.12-0.16 70 0.08 31 - 60-69 138 103 13.8 430-640 1.65-1 .SO 18-3 1 0.1-0.23 75 -120 179 -193 138- 172 17- 28 640-850 1 .7 22-36 0.6-0.22 303 276 . 1200-1580 170 80 90-100 41-59 1.1-1.3 0.5-0.6 1.6 0.9-1.3 1.5-1.6 +0.4 25 10- 17 0 .7 840 220-324 6.2-6.9 4.8 0.20-0.25 78 3-1435 21 620 170 60 -70 60-90 0.5-0.6 <0 .7 2.8