Mechanical properties of polymers, composites-Nielsen 2010 Part 7 docx

... Inc.Cottrell, A.H. (19 57) The Properties of Materials at High Rates of Strain. Institute of Mechanical Engineering, London, UK.Courtney, T.H. (1990) Mechanical Behavior of Materials, John Wiley, ... John Wiley, New York.Frenkel, J. (1926) Z Phys. vol. 37, p 572 .Gilman, J.J. and Johnston, W.G. (19 57) Dislocations and Mechanical Properties of Crystals. In: J.C. Fisher, W.G. Johnston, R. Thomson ... Inc.givenbyEq.(6.5)foracubiclattice.Slipis,therefore,morelikelytooccurbytheexchangeofbonds,thanthecompleteshearofatomicplanesovereachother,assuggestedbyFig.6.1.ThereadershouldexamineEqs(6.8a)and(6.8b)carefullysincethedependenceofthelatticefrictionstress,f,onlatticeparametersaandbhassomeimportantimplications.Itshouldbereadilyapparentthatthefrictionstressisminimizedonplaneswithlargeverticalspacings,a,andsmallhorizontalspacings,b.Dislocationmotionis,therefore,mostlikelytooccuronclose-packedplaneswhichgenerallyhavethelargestvaluesofaandthesmallestvaluesofb.Dislocationmotionisalsomostlikelytooccuralongclose-packeddirectionswithsmallvaluesofb.Hence,close-packedmaterialsaremorelikelytobeductile,whilelessclose-packedmaterialssuchasceramicsaremorelikelytobebrittle.Wearenowpreparedtotackletheproblemofdislocationmotionincrystallinematerials.First,wewillconsiderthemovementofedgedisloca-tionsonclose-packedplanesinclose-packeddirections.Suchmovementisgenerallydescribedasconservativemotionsincethetotalnumberofatomsontheslipplaneisconserved,i.e.,constant.However,wewillalsoconsiderthenonconservativemotionofedgedislocationswhichisoftendescribedasFIGURE6.8Schematicof(a)wideand(b)narrowdislocations.(FromCottrell,19 57. Reprinted with permission from Institute of Mechanical Engineering.)Copyright © 2003 Marcel Dekker, Inc.FIGURE 6.5 Structure of a screw dislocation: (a) displacement of upper half of crystal...

... area(1.28 cmdiameter)(%) 70 75 -T6 505 570 11 — 70 75 -T73 415 505 11 — 71 78 -T6 540 605 11 —PlasticsACBS Medium impact — 46 6–14 —Acetal Homopolymer — 69 25 75 —Poly(tetrafluorethylene) ... Inc.5.2PHYSICALBASISFORPLASTICITY5.2.1PlasticityinCeramicsMostceramicsonlyundergoonlyelasticdeformationpriortotheonsetofcatastrophicfailureatroomtemperature.Hence,mostreportsonthemechanicalpropertiesofceramicsareoftenlimitedtoelasticproperties.Furthermore,mostceramistsreportflexuralpropertiesobtainedunderthree-orfour-pointbending.TypicalstrengthpropertiesofselectedceramicmaterialsarepresentedinTable5.1.Notethatceramicsarestronger(almost15 ... Inc.LeChateliereffect,inhonorofthetwoFrenchmenwhofirstreportedit(PortevinandLeChatelier,1923).Theserrationsarecausedbythepinningandunpinningofgroupsofdislocationsfromsolutesthatdiffusetowardsitasitmovesthroughalattice.Themechanismsisparticularlyeffectiveatparticularparametricrangesofstrain-rateandtemperature(Cottrell,1958).Finallyinthissection,itisimportanttodiscusstheso-calledanom-alousyieldphenomenathathasbeenreportedinsomeplaincarbonsteels(Fig.5 .7) .Thestress–strainplotsforsuchmaterialshavebeenobservedtoexhibit...

... Nz=ðhzL), we mayrewrite Eq. (7. 6) as ¼Xhi¼1bxiN 7: 7ÞAssuming that the average displacement of each dislocation isx, Eq. (7. 7) may now be written as ¼ bx 7: 8ÞThe shear strain rate,_, ... Inc.partialdislocationsisconfinedtoplanescontainingthestackingfaults,materialswithlowerstackingfaultenergies(wideseparationsofpartials)tendtoexhibithigherlevelsofstrainhardening(Table7.3). 7. 8.6SuperdislocationsSofar,ourdiscussionhasfocusedondislocationmotionindisorderedstructuresinwhichthesoluteatomscanoccupyanypositionwithinthecrystalstructure.However,insomeintermetallicsystems(intermetallicsarecompoundsbetweenmetalsandmetals),orderedcrystalstructuresareformedinwhichtheatomsmustoccupyspecificsiteswithinthecrystalstructure.Oneexampleofanorderedf.c.c.structureistheNi3AlcrystalshowninFig .7. 23.Thenickelandaluminumatomsoccupyspecificposi-tionsinthestructure,whichmustberetainedafterdislocationglidethrough{111}planes.However,themovementofasingledislocationontheglideplanedisturbstheorderedarrangementofatoms,givingrisetoanenerge-ticallyunfavorablearrangementofatoms,Fig .7. 24(a).A ... differentiating Eqs (7. 16) and (7. 17) givesdd¼ðmÞ2 7: 18ÞPlots of shear stress versus shear strain will, therefore, be expected to exhibitstress levels that are a factor of ðmÞ2greater...

... The mechanical properties of compatible blends resemblethose of random copolymers, having a single T^ value and modulus tran-sition zone. TK varies rather regularly with composition, often ... effect of any change in £()jrCopolymers and plasticized materials often show another effect—abroadening of the transition region with a decrease in the slope of themodulus curve in the region of ... Polymer mixtures of different chemical compositiontend to be insoluble in each other, and this tendency for phase separationis another cause of the broadening of the transition region ( 87) . If themolecules...

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... theory 2 97 IK. Theories of Yielding and Cold- Drawing 299IV. Impact Strength and Tearing 3 07 A. Nature of impact tesfs 3 07 B. Effect of notched 308C. Effects of temperature 310D. Effects of orientation ... Effect of hydrostatic pressure 2t?3H. Effect of molecular weight and branching 265I. Effect of cross-linking 268J. Relationships and inlcraclJQrtS 277 K. Effect of erysNsllinity 280U. Hffects of ... Dynamical Mechanical Properties I- Introduction and InstrumentsH. Temperature and Frequency EffectsLibrary of Congress Cataloging-In-Publitation DateNielsen. Lawrence E. Mechanical properties of...

... tests, a number of general reference books have been published on testing and on the mechanical properties of poly-mers and viscoelastic materials (2 -7) . Unfortunately, a great variety of units ... types of apparatus arc capable of covering the range from a small . fraction of a cycle per second up to millions of cycles per second. Most instruments measure either shear or tensile properties, ... is the frequency of the oscillations in radians per second. Note that the real part of the complex viscosity is an energy-dissipation term, just as is.the imaginary part of the complex modulus....

... Kupluil. Kolloitl '/ 1 57. 27 ( 113. E. Ho urul T. Iliilakfyamn. 7. Polymer Sn. [Phyx,). 12. 1 477 (1 974 ). 114. W, O, Slran.nK 7. puiymei .SV/ CZO. I I 7 ( 1 % 7 ) . . 115. Ci. (iec, P, ... Behavior of High Polymers. Intersaence, New York. 1948. 3. J I), Ferry. Viscoelastic properties of Polymers, 3rd ed., Wiley. New York, 1980. 4. I , n, Nielsen. Mechanical Properties of Polymers. ... Nature of / the Glassy State. Ann. N.Y. Acad. Sci., 279 (1 976 ). 46. R. F. Landel and R. F. Fedors, Mechanical Behavior of Materials, Vol. Ill, Society of Materials Science, Kyoto, Japan, 1 972 ,...

... the dimensional stability of amaterial, and because the tests can be of long duration, such tests are of great practical importance. Creep measurements, especially, are of interestto engineers ... creep of rigid materials, the difficulty arises from the ne-cessity to measure accurately very small deformations and deformationrates. In the case of the stress relaxation of rigid polymers, ... model, the change of the elongation of the spring iscompensated by an equal change in the dashpot, but the net rate of changeis zero; that is.Figure 1 Stress relaxation of a Maxwell model...

... makereptation difficult. ,IX. EFFECT OF PLASTICIZERS ON MELTVISCOSITYPlasticizer or liquid diluents greatly reduce the melt viscosity of polymers(28. 170 - 177 ). Small amounts of liquids at temperatures ... (1 67) . Bueche (163) has attempted to explain theoreti-cally the effect of branching on viscosity. The important factor is the ratio of the mean-square radius of the branched molecules to that of ... fixedwhereBueche (16, 172 ) proposed that the viscosity is proportional to the fourthpower of the polymer concentration and a complex function of the freevolume of the mixture. Kraus and Gruver ( 170 ) find...