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Literature survey Carbon matrices
LRerature survey Prepared by M.R. Alexander, J. Collins, J.D. Hague and A.J, Hosty, University of Sheffield, UK CARBON MA TRICES
CERAMIC MA TRICES
Energy toughness parameters for a 21) carbon fibre reinforced carbon composite R'Milli, M., Rouby, D., Fantozzi, G. and Lamicq, P. Composites Science and Technology Vo137 ?Cos1-3 (1990) pp 207-221 Studies to characterize the fracture behaviour of a 2D carbon-carbon composite laminate are described. The material was produced by chemical vapour deposition at the Socitt6 Europtenne de Propulsion (SEP) in France. The authors describe several techniques for the determination of R-curves and discuss them in terms of linear elastic fracture mechanics and also in the context of a nonlinear scheme, taking into account the nonelastic behaviour. The fracture behaviour was analysed for two orientations: interlaminar cracking in compact tension, and edgewise cracking in which the notch plane and tip are perpendicular to the cloth plane. The results of this study show that for these materials the non-linear analysis is more accurate and that the measured R-curves depend neither on the notch depth nor on specimen dimensions.
Characterisation of rapidly solidified ceramic-titanium alloy powders Adams, M.L., Kampe, S.L. and Christodoulou, L. International Journal of Powder Metallurgy Vo126 No 2 (1990) pp 105-114 Induction cast (XD) titanium aluminate compositions containing particulate TiB 2 reinforcement were rapidly solidified to produce a composite powder. One alloy was atomized using a centrifugal atomization process. A second alloy was atomized via the plasma rotating electrode process (PREP). Scanning electron microscopy and X-ray diffraction techniques were used to characterize the powders prior to and after heat treatments. Results showed that atomization of TiB 2reinforced titanium aluminide produced a powder containing intrinsic TiB2 reinforcement of both a particulate and flake morphology. Heat treatment was found to coarsen the network of boride flakes to a spheroidal or particulate morphology.
Phthalonitrile as a carbon source Keller, T.M. Polymer Communications Vol 31 No6 (1990) pp 229-231 4, 4'-bis(3,4-dicyanophenoxy) biphenyl was cured with small quantities of aromatic amine to produce a thermosetting polymer resin. The polymer and its subsequent pyrolysate were found to exhibit favourable properties for the production of pore-free glassy carbon. Visually void-free pyrolysed samples were readily obtained. However, microscope examination revealed a microporous microstructure. The pyrolysis behaviour was attributed to the heterocyclic cross-links present in the resin, and contrasted with other high temperature thermosetting polymers which yield thermally unstable aliphatic cross-links.
CERAMIC FIBRES Effect of friction in ceramic coating/fiber composites Lu, M.-C. and Hsueh, C.-H. Journal of Composite Materials Vol 24 No 6 (1990) pp 572-593 Using a single notional single fibre with a finite length of uniform coating on its central region, the effect of frictional interaction at a weakly bonded or unbonded coating/fibre interface was analysed. The effects of the coefficient of friction at the interface and the thermomechanical mismatch of the system on the stress transfer from the fibre to the coating were reported. A method to predict the residual thermal stress and to evaluate the coefficient of friction was suggested, with the possibility of extending the model to evaluating general residual stresses being addressed.
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A comparative study of the impact behaviour of ceramic matrix composites Macke, T., Quenisset, J.M., Neuilly, D., Rocher, J.P. and Naslain, R. Composites Science and Technology Vol 37 Nos 1-3 (1990) pp 267-278 In this paper the authors describe the use of instrumented Charpy impact testing to evaluate the dynamic toughness of ceramicmatrix composites (CMC). The authors assume the CMC to be damageable elastic materials and, utilizing a procedure based on a dynamic analysis of the notched bending specimen responses, various fracture parameters are studied. Dynamic toughness K~d, derived from fracture initiation and dynamic crack growth resistance curves, is used to characterize the dynamic toughness of various 2D and 3D ceramic-matrix composites. Significant differences in R-curves are correlated with the fibrous structure and the component nature of the composites. The usefulness of impact testing at moderate speeds is established. Creep and microstructure of electrical discharge machinable Si~4 composites Crampton, J. and Duclos, R. Acta Metallurgica et Materialia Vol 38 No 5 (1990) pp 805--810 Silicon nitride sintered with the aid of YzO 3 and AI203containing from 0 to 40 vol % of TiN particles of size 1 and 2.5 ILm were considered. Their compression creep behaviour was studied between 1260 and 1340"C at stresses ranging from 100 to 300 MPa. Viscous creep was found to be the dominant creep mechanism up to 1340°C and 200 MPa. Increasing the volume fraction of the TiN particles decreased the creep strength, as did decreasing their size. Cavities and microcracks were observed along particle/matrix
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interfaces showing that a cavitational mechanism develops from the presence of the particles. Effects of ZrO 2 and Y2Oa dissolved in zyttrite on the densiflcation and the od[3 phase transition of Si~N]4 in SI~4--ZrO 2 composites Kim, J.R. and Kim, C.H. Journal of Materials Science Vo125 No 1B (1990) pp 493-498 The effects of ZrO 2 and Y203 dissolved in zyttrite on the densification and the od[3 transition of Si3N4 were studied using pure, 3, 6 and 8 tool % Y203-doped zirconia powder. Pure zirconia powder was found to be ineffective in obtaining full density during hot pressing. Densification was promoted by Y203 diffused from the added zyttrite. Near full density was obtained in Si3N4 with 5 vol %, 6 and 8 mol % Y203-doped ZrO2 composites. The role of the reaction products, Y2Si207 and Y2Si3N403 phases during densification is considered. The impact behaviour of high performance,, ceramic matrix fibre composites Phillips, D.C., Park, N. and Lee, R.J. Corn-. posites Science and Technology Vol 37 Nos; 1-3 (1990) pp 249-265 In this paper the authors describe a study of! the impact behaviour of (0,90)z~ carbon fibre: composites with borosilicate glass and lithium t aluminosilicate (LAS) glass ceramic matrices. These materials were tested using an instru-. mented falling weight impactor on specimens; subjected to a superimposed tensile stress. The amount of damage caused was found to, be a function of applied stress and impact: energy, and led to the development of a n impact fracture map allowing the comparison of different materials and test conditions to, be made, The borosilicate glass composite, was studied over a temperature range of! 450--600"C, which encompasses the matrix softening temperature at 580°C. It is reported that impact damage was worse at elevated temperatures, even below the softening: point. Ballistic impact tests at impact velocities of between 70 and 140 m s-1 were found t o produce more localized damage than the falling weight experiments. Nucleation and growth of cracks in SiC/AIzOs composites Jakus, K. and Nair, S.N. Composites Science and Technology Vol 37 Nos 1-3 (1990) pp 279-297 The authors report on creep crack nucleation and growth studies on two grades of SiC whisker-reinforced alumina at temperatures of 1100, 1200 and 13000C in an oxidizing environment. It was found that cracking on the tensile surface initiated at a temperaturedependent threshold creep strain and, following this initiation, cracks continued to nucleate throughout the creep process. Increasing temperature delayed initiation to larger creep strains. The purity of the composite, however, did not substantially alter the initiation strain level but affected the
number of surface cracks present at a given strain. The rate of growth of creep cracks was less at any given stress intensity level than that of pre-existing cracks. With respect to crack nucleation and growth, whisker reinforcement made the composite behave in a more brittle fashion than a fine grain high purity alumina but in a less brittle manner than a large grain vitreous bonded alumina. Oxidation of an AI203 - vAION ceramic composite Goeuriot, P., Goeuriot-Launay, D. and Therenot, F. Journal of Materials Science Vol 25 No 1B (1990) pp654-660 Composites consisting of a dispersed Valuminium oxynitride (v-A1ON) in an A120 3 matrix were prepared by reaction sintering at 1800°C. Oxidation kinetics of the composites were followed by thermogravimetric analysis (TGA) in pure oxygen. After oxidation, X-ray analysis and ceramographies were performed. A v-alumina layer was found to form during oxidation, producing surface compressive stresses. Mechanical properties and wear resistance of the composites were thus improved. Toughness assessment of ceramic matrix composites Bouquet, M., Birbis, J.M. and Quenisset, J.M. Composites Science and Technology Vol 37 Nos 1-3 (1990) pp 223-248 The tensile testing of unnotched specimens o f various ceramic-matrix composites i s described. The authors observed that the composites show damag_eable quasi-elastic behaviours. These results are compared with those obtained for notched specimens tested using loading/unloading cycles, which show significant non-linearities. The discrepancy between the two tests is attributed by the authors to the presence of debris which invalidates the methods based on loading/ unloading cycles. The authors further claim that the approximation which considers tested CMC as a damageable elastic material leads to very small errors in the determination of crack growth resistance curves.
GENERAL Analysis of unbalanced multi-layered elliptical plates under varying pressure Mansfield, E.H. International Journal of Mechanical Sciences Vol 32 No 5 (1990) pp 417--422 An analysis was produced for unbalanced clamped elliptical multilayered plates under conditions of linearly varying pressure and where coupling was exhibited between moments and planar strains. Buckling analysis of FRP faced cylindrical sandwich panel under combined loading Rao, K.M. and Meyer-Piening, H.R. Composite Structures Vo114 No I (1990) pp 15-34 Fibre-reinforced plastic (FRP) faced sandwich panels are used in the aerospace industry as wing coverings or fuselage elements. This paper develops an analysis for the buckling of FRP generally orthotropic cylindrical sandwich panels which were subjected to combined loading conditions of axial compression, bending and shear. The analysis utilized the Rayleigh-Ritz method. Results obtained from the analysis were discussed.
A composite laminate box-section beam design for obtaining optimal elastodynamic responses of a flexible robot manipulator Sung, C.K. and Shyl, S.S. International Journal of Mechanical Sciences Vol 32 No 5 (1990) pp 391--404 The performance of robot arms was found to be limited by the inertia, stiffness, strength and damping characteristics of the beam sections from which it was constructed. A methodology was developed to optimize the above properties using composite materials to give beam sections with tailor-made properties. Design objectives and constraints were specified and were applied to the problem of a two-link robot linkage. This was shown to have superior properties to traditional linkages. Crack tip reinforcement by bridging elements: modelling the fracture of the matrix material Smith, E. Journal of Materials Science Vo125 No 3 (1990) pp 1632-1635 The assumption that the matrix material ahead of a crack tip behaves in accordance with the laws of linear elasticity (the crack extending when the stress intensity factor attains a critical value Kic) was examined. The assumption was tested for a semi-infinite crack in a remotely loaded infinite solid. Results show that the assumption can lead to misleading conclusions regarding determination of the 'applied' value of K required for crack tip propagation, and the size of the restraining zone when propagation occurs. Design of antisymmetric hybrid laminates for maximum buckling load: I. Optimal fibre orientation Adali, S. and Duffy, K.J. Composites Structures Vo114 No I (1990) pp 49-60 The optimal fibre orientations were determined for hybrid laminate panels designed to maximize buckling load subject to a mass constraint. The laminate panel was constructed from low stiffness material in the core and high stiffness material in the outer layers. Results were presented for simply supported plates under biaxial loading. Costs were discussed and comparisons were made with non-hybrid laminates. Dielectric studies of PZT-polymer composites Nayak, B., Mansingh, A. and Machive, M.K. Journal of Materials Science Vol 25 No 1B (1990) pp 749-752 Composite discs of lead zirconate titanate (PZT)/nylon 66 composites were prepared from formic acid solutions of nylon containing added PZT powder. Dielectric measurements were performed using a capacitance bridge. Dielectric constant was found to increase with increasing PZT content up to 50 vol % PZT, but decreased at higher powder volume fractions due to porosity. The dielectric constant was also found to increase rapidly at higher temperatures and lower frequencies due to intergrain polarization. Evaluation of testing techniques for the losipescu shear test for advanced composite materials Lee, S. and Munro, M. Journal of Composite Materials Vo124 No 4 (1990) pp 419-440 Experimental techniques for applying the Iosipescu shear test method to advanced composite materials are described. The degree of damage introduced in the machin-
ing of the notch and the effect on test behaviour was investigated. The occurrence of a pure shear strain field in the test section was evaluated using both tension and compression strain gauges. Measures adopted to eliminate in-plane or out-of-plane bending or twisting of the specimens were reported. Results analysed for 90° samples showed that the determination of the in-plane shear modulus by the tangent method had a lower scatter than that by initial modulus or secant methods. Examination of the processes of deformation and fracture in a silica-filled epoxy resin Cantwell, W.J., Smith, J.W., Kausch, H.H. and Kaiser, T. Journal of Materials Science Vo125 No 1B (1990) pp633--648 Fractographic studies of a silica-filled epoxy resin were undertaken in order to determine the processes of damage initiation, development and fracture within a particulate-filled polymer. Within the volume of the material, a number of different types of inelastic deformation and fracture mechanisms were observed. At low temperature and high loading rate, failure was associated with debonding only. At high temperatures and low loading rates, debonding and yielding were found to occur throughout the volume of the test specimen. Fracture surfaces were characterized by scanning electron microscopy and optical microscopy. An experimental study of scaling rules for impact damage in fiber composites Qian, Y., Swanson, S.R., Nuismer, R.J. and BucineU, R.B. Journal of Composite Materials Vo124 No 5 (1990) pp 559-570 Plates ranging in size from 50 × 50 × 1.072 mm to 250 × 250 × 5.36 mm of AS4/3501-6 carbon/epoxy composite were geometrically scaled and impacted with projectiles of various geometries. Analytically derived scale rules were found to accurately describe the undamaged response to impact, with an analysis based on the dynamic plate equation also showing excellent agreement with experiments, It was concluded that the formation of damage is complex, showing an apparent dependence of delamination on absolute size as suggested by fracture mechanics. Large deflections of a uniformly loaded, elastically restrained composite strip Mansfield, E.H. International Journal of Mechanical Sciences Vol 32 No 4 (1990) pp 329-334 An analysis was produced for a multilayered composite strip under uniform normal loading with elastically restrained planar boundaries. The large deflection behaviour was examined for conditions of coupling between moments and planar strains. Mode ! d e l ~ i n a t i o n of a three-dimensional fabric composite Byun, J.-H., Gillespie, J.W. and Chou, T.-W. Journal of Composite Materials Vo124 No 5 (1990)pp 497-518 Double cantilever beam specimens of carbon/ epoxy (T300/3501-6) orthogonal interlocked fabric composite were considered in a finite element analysis. The Mode I strain energy release rate was evaluated to enable determination of the influence of through-thethickness fibres on crack driving force as a function of crack length. Compared on the basis of compliance and strain energy release
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rate, the finite element analysis showed a good agreement with experimental results. It was shown that the presence of z-axis fibres reduced the strain energy release rate compared with traditional 2-D laminates. Debonding of the z-axis was also modelled, showing that the Mode I strain energy release rate increased as the fibre debonded but was always significantly less than that of the 2-D laminated materials. The inputs required to the model were the z-axis fibre properties, fibre architecture, fibre volume fraction and the Mode I critical strain energy release rate for the 2-D laminate. On isotropi¢ laminate configurations Fukunaga, H. Journal of Composite Materials Vol24 No 5 (1990) pp 519-535 Laminate composites with isotropic stiffness characteristics with respect to both in-plane and out-of-plane stiffnesses were reported. A method for the determination of isotropy was reported and examples of 40-ply laminates given. Experimental results were obtained using tensile testing and a four-point bend test, revealing almost isotropic properties in a 40-ply laminate. On sandwich beams with laminate facings and honeycomb cores subjected to hydrothermal loads: Part 1--analysis Mukhopadhyay, A.K. and Sie rakowski, R.L. Journal of Composite Materials Vo124 No 4 (1990) pp 382-400 The combined effects of mechanical, thermal and hygromatic loading on a sandwich beam with a honeycomb core and laminate facing were determined using a macromechanical approach. Negligible in-plane resistance was found in the cores; however, they were relatively stiff in the transverse direction. Equations were determined in terms of the lateral deflection and the mid-plane displacement, these being general and applicable to any construction of this type. On sandwich beams with laminate facings and honeycomb cores subjected to hydrothermal loads: Part lI---application Mukhopadhyay, A.K. and Sie rakowski, R.L. Journal of Composite Materials Vo124 No 4 (1990) pp 400-418 This paper considered a specific loading state for the beam structure analysed in Part I. The beam was simply supported under uniform load. Stiffness coefficients, pertinent parameters and the distribution of stresses across the laminate facings for varying core thickness and facing orientations were graphically displayed and discussed. Postbuckling finite element analysis of composite panels Laschet, G. and Jeusette, J.P. Composite Structures Vo114 No I (1990) pp 35--48 The pre- and postbuckling behaviour of an arbitrarily laminated composite panel under destabilizing loads was analysed. The threedimensional degenerated isoparametric multilayered finite element analysis used was described along with an automatic solution procedure. The efficiency and accuracy of the model was determined for the non-linear response of two structural examples. Wood flour as a low cost reinforcing filler for polyethylene: studies on mechanical properties Raj, R.G., Kokta, B.V. and Daneault, C.
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Journal of Materials Science Vol 25 No 3 (1990) pp 1851-1855 Composites of high density polyethylene (rIDPE) filled with wood flour were prepared and moulded into tensile test specimens. Composites having wood flour coated with aikoxy-silane coupling agents generally showed higher tensile strength and modulus values than uncoated specimens. However, the best improvement in composite tensile strength was obtained when the wood flour was pretreated with polymethylenepolyphenyl isocyanate. Better performance with the isocyanate coupling agent was attributed to the formation of bonds between the cellulose hydroxy groups and isocyanate.
METAL MA TRICES Fracture of boron particles in 2219 aluminium as a known acoustic emission source Heiple, C.R., Carpenter, S.H. and Christiansen, S.S. Acta Metallurgica et Materialia Vol38 No4 (1990) pp611-618 Aluminium 2219 reinforced with boron particles was produced using a powder metallurgy process. Acoustic emission during deformation emanated from decohesion of the boron particles from the matrix and particle fracture. Elasticity theory was used to estimate the energy associated with particle fracture. It was found that the energy in the acoustic emission signals was proportional to the fracture energy released. It was stated that the relation found between the fracture energy and acoustic emission signal energy could be used to estimate the energy released by other comparable acoustic emission sources, in samples of similar geometries, from their acoustic emission measurements. The interface microstructure in alumina (FP) fibre/magnesium alloy composites Pfeifer, M., Rigsbee, J.M. and Chawla, K.K. Journal of Materials Science Vol 25 No 3 (1990) pp 1563-1567 The reaction zone created at the interface of the metal-matrix composite system tx-AI203 (FP)/Mg (ZE41A) was characterized using electron microscopy. Composites were prepared by a vacuum infiltration technique. Morphology, interface chemistry and crystallographic features were investigated using transmission electron microscopy. The reaction zone was found, on average, to be 100 nm wide and composed of MgO. Growth of the reaction zone is thought to be controlled by a seepage mechanism involving infiltration of liquid Mg between MgO crystals. Isothermal and nonisothermal fatigue behaviour of a metal matrix composite Gabb, T.P., Gayda, J. and MacKay, R.A. Journal of Composite Materials Vo124 No 6 (1990) pp 667-686 Isothermal and non-isothermal fatigue resistance of a metal-matrix composite of Ti-15V3Cr-3A1-3Sn (Ti-15-3) matrix reinforced with 33 vol % continuous SiC fibre was investigated. A good isothermal fatigue resistance was exhibited by the composite at 300 and 550°C at low cyclic stresses, with fatigue cracks initiating from fibre/matrix interfaces and foil laminations. The isothermal composite fatigue resistance at 550°C was observed to be reduced due to stress relaxation in the
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matrix at high cyclic stresses. The composite's fatigue resistance was found to substantially degrade under non-isothermal conditions as a result of thermomechanical fatigue damage associated with the fibre/matrix interfaces.
ORGANIC FIBRES Lateral growth of microparacrystals in Kevlar 49 fibres irradiated by Co 60 Hindeleh, A.M., Heinrichsen, G. and Springer, H. Journal of Polymer Science Part B Vol28 No 3 (1990) pp 267-279 Cross-linking in the form of H-bonding in Kevlar 49 was induced by y irradiation from a Co 6° source. Wide angle X-ray diffraction techniques were used to study the phenomena. Microparacrystals (mPCs) were found to increase in size in the b direction (lateral direction), whilst the mPC size along the axis. and normal to the (002} netplanes was unaffected by irradiation. The paracrystalline disorder parameter (g) was found not to change significantly during irradiation. Liquid crystalline solutions of poly(pphenylenebenzobisthiazole) complexes in organic solvents Roberts, M.F. and Jenekhe, S.A. Polymer. Communications Vol 31 No 6 (1990) pp 215-217 The morphology, phase equilibria, rheology and liquid crystallinity of solutions of A1Cla and GaCl a complexes with poly(pphenylenebenzobisthiazole) (PBT) in organic solvents were investigated. The above properties were found to be dependent on the nature and concentration of the Lewis acid in solution. Possible implications for processing of PaT and related rigid-rod polymers to films, fibres and molecular composites are discussed. Paracrystalline, microparacrystal size and molecular weight distribution of Kevlar 49 fibres exposed to elevated temperatures Hindeleh, A.M., Hosemann, R., Hinrichsen, G. and Springer, H. Polymer Communications Vol 31 No 5 (1990) pp 205-208 The paracrystalline distortion parameter (g), the microparacrystalline (mPC) size D0o2 and the molecular weight distribution (MWD) of Kevlar 49 fibres exposed to elevated temperatures were determined by X-ray diffraction and size-exclusion chromatography. Untreated Kevlar 49 fibres were found to have a g value of 2.8%, which decreased to 2.4% at 400°C, then increased to 3.3% at 450°C, and 3.7% at 500°C. Doo2 was found to decrease gradually with increases in either the annealing temperature or the thermal ageing time. MWD remained unchanged until 300°C. The phase behaviour and gelation of a rod-like polymer in solution and implications for microcellular foam morphology Jackson, C.L. and Shaw, M.T. Polymer Vol 31 No6 (1990) pp 1070-1083 The thermally induced phase separation processes by which microcellular materials are made were studied by observing the phase separation of the rod-like macromolecule poly(~,-benzyl-L-glutamate). Microcellular materials were formed by lowering the solution temperature until phase separation and solvent freezing occurred. Solvent could
then be removed by vacuum sublimation. The morphology produced by liquid-liquid phase separation and gelation was an opencelled fibrous structure resembling a threedimensional lattice. Results are considered in terms of theories and proposed mechanisms of phase separation. Structural characteristics of aramid fibre variants Dobb, M.G. and Robson, R.M. Journal of Materials Science Vol 25 No 1B (1990) pp 459-464 A number of commercially available aramid fibres based on poly(p-pheneylene terephthalamide) were investigated in order to determine their different tensile behaviours and structural characteristics. Widely different tensile behaviour was found between the different fibres studied. Differences in breaking strength and modulus were related to structural features as determined by X-ray diffraction and electron microscopy. Results indicate that high molecular orientation, low skin content and large crystallite size favour the development of high modulus materials. However, fibre strength appears to be adversely affected by morphological defects, often resulting from the high degree of draw given to high modulus fibres.
shear and dynarmc viscosity were measured as a function of extent of reaction throughout the cure. Using the DiBenedetto model and branching theory, molecular weight, glass transition temperature and other structural parameters were predicted at various stages of the polymerization.
The crush behaviour of pultruded tubes at high strain rates Thornton, P.H. Journal of Composite Materials Vo124 No 6 (1990) pp 594-615 The crush response of pultruded glass fibrereinforced plastic tubes of polyester and vinyl resins was investigated. Crush rates from 2.1 x 10~ m s-1 to 15 m s I were used on tubes of various fibre diameters, trigger geometry and section geometry. The rate dependence of the specific energy for the polyester resin was positive whilst that for the vinyl resin was either positive or negative depending on the tube geometry. A nominal reduction of onehalf in the fibre diameter for the same glass content was found to decrease the specific energy by up to 20%. In quasi-static crush the vinyl ester resin tubes had a significantly higher specific energy than the polyester tubes; however, in dynamic crush this difference diminished. The occurrence of fibre delamination and unstable failures was noted and discussed.
RESIN MA TRICES Characterisation of creep in polymer composites by the use of frequency-time transformations Gibson, R.F., Hwang, S.J. and Sheppard, C.H. Journal of Composite Materials Vo124 No 4 (1990)pp 441-452 Time-dependent creep and relaxation properties of polymer composite materials were determined by the use of frequency-domain vibration test data. A vibration test method was used to enable the measurement of frequency-domain complex moduli over a suitable range. These were then converted into time-domain relaxation moduli or creep compliances by using an inverse Fourier transform and numerical integration. Various test functions were used to check the accuracy of the transformation, which was then used for characterization of an angle-ply graphite/ polyimide composite. The creep data generated by the frequency-time transformation showed good agreement with similar data generated by time-temperature superposition. Chemorheology reactions for epoxy-amine crosslinking Bidstrup, S.A. and Macosko, C.W. Journal of Polymer Science Part B Vo128 No 5 (1990) pp 691-709 The thermoset system consisting of the diglyeidyl ether of bisphenol A (DOEBA) and an amine curing agent, diaminodiphenyl sulphone, was chosen to study the relationship between the mechanism of bond formation, resulting structure and viscosity during the step polymerization of a thermoset. Steady
Energy release rates for cracks caused by moisture absorption in graphite/epoxy composites Tsotsis, T.K. and Weitsman, Y. Journal of Composite Materials Vol 24 No 5 (1990) pp 483-496 Energy release rates and the J-integral were calculated numerically and analytically, indicating that extremely low energies were involved in microcrack formation due to moisture absorption in graphite/epoxy composite materials. It was postulated that moisture was dramatically reducing the adhesion between the graphite and the epoxy. It was also noted that the tensile stresses at the fibre/matrix interface were substantially less than the matrix strength and therefore mechanical damage observed around the fibres was due to moisture. Epoxy resins (DGEBA): the curing and physical aging process Plazek, D.J. and Frund Jr, Z.N. Journal of Polymer Science Part B Vo128 No 4 (1990) pp 431-448 Differential scanning calorimetry (DSC) and infra-red spectrophotometry (IR) were used to monitor the degree of cure of Epon 828 epoXy/MDA samples cured at 130°C. DSC was also used to monitor the extent of 'physical ageing' which took place during the cure at 130°C. The fictive temperature (the hypothetical temperature at which the structure would be in equilibrium) was determined by DSC. IR was used to show that the greatly reduced reaction rate during the final 20% of cure was not only a consequence of vitrification, but also a result of the depletion in the number of reactive epoxide groups.
Free volume changes in epoxy adhesives during physical aging: fluorescence spectroscopy and mechanical stress relaxation Shmorhun, M., Jamieson, A.M. and Simah, R. Polymer Vo131 No 5 (1990) pp 812--817 The fluorescence probes 1,3-bis-l-pyrene propane and 1,(4-dimethylaminophenyl)-6phenyl-l,3,5-hexatriene were dispersed in fully cured epoxy (Epon 828). Free volume change during ageing was thus followed in the glassy state. During isothermal annealing the emission intensity was found to show a timedependent increase, interpreted as due to the relaxation of the matrix free volume. The ageing time dependence behaviour was found to be consistent with the application of free volume arguments to the Loufty equation for describing fluorescence intensity. Static compression failure of carbon fibre T800/924C composite plate with a single hole Soutis, C. and Fleck, N.A. Journal of Composite Materials Vo124 No 5 (1990) pp 536558 Compressive failure of carbon/epoxy composite laminates was studied experimentally and theoretically in this paper. Static tests were used to characterize the mechanics of uniaxial compressive failure in multidirectional unnotched [(+__45/02)3]s plates. It was stated that the critical damage mode causing failure was fibre microbuckling in the 0 ° plies. X-ray radiography and scanning electron microscopy were used to observe damage initiation and propogation in compressively loaded [(+45/02)3] s laminates with circular holes. Failure was initiated in the matrix with fibre microbuckling surrounded by delamination at the hole edges occurring at higher loads. The laminate was said to fail catastrophically when the damage reached a critical state. A theoretical model was submitted for predicting the static strength of the laminates, the predictions of which were compared with experimental data, an acceptable agreement wfth experimental results was found. Strength of tensile loaded graphite/epoxy laminates containing cracks, open and rdled holes Eriksson, I. and Aronsson, C.-G. Journal of Composite Materials Vol 24 No 5 (1990) pp 456-482 In this paper a damage zone criterion for predicting tensile strength of composite laminates containing holes and cracks was reported. This zone, based on fundamental physical principles, was assumed to be present in the maximum stress region of the laminate when the tensile stress reached the tensile strength of the unnotched laminate. This enabled an expression to be derived that predicted the strength of laminates with holes and cracks from two fundamental parameters. These were the unnotched tensile strength and the critical damage zone length. This expression made excellent predictions of the strength of specimens of different laminate configurations. Significantly improved accuracy compared with the point stress criterion was also reported.
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CERAMIC MA TRICES
Energy toughness parameters for a 21) carbon fibre reinforced carbon composite R'Milli, M., Rouby, D., Fantozzi, G. and Lamicq, P. Composites Science and Technology Vo137 ?Cos1-3 (1990) pp 207-221 Studies to characterize the fracture behaviour of a 2D carbon-carbon composite laminate are described. The material was produced by chemical vapour deposition at the Socitt6 Europtenne de Propulsion (SEP) in France. The authors describe several techniques for the determination of R-curves and discuss them in terms of linear elastic fracture mechanics and also in the context of a nonlinear scheme, taking into account the nonelastic behaviour. The fracture behaviour was analysed for two orientations: interlaminar cracking in compact tension, and edgewise cracking in which the notch plane and tip are perpendicular to the cloth plane. The results of this study show that for these materials the non-linear analysis is more accurate and that the measured R-curves depend neither on the notch depth nor on specimen dimensions.
Characterisation of rapidly solidified ceramic-titanium alloy powders Adams, M.L., Kampe, S.L. and Christodoulou, L. International Journal of Powder Metallurgy Vo126 No 2 (1990) pp 105-114 Induction cast (XD) titanium aluminate compositions containing particulate TiB 2 reinforcement were rapidly solidified to produce a composite powder. One alloy was atomized using a centrifugal atomization process. A second alloy was atomized via the plasma rotating electrode process (PREP). Scanning electron microscopy and X-ray diffraction techniques were used to characterize the powders prior to and after heat treatments. Results showed that atomization of TiB 2reinforced titanium aluminide produced a powder containing intrinsic TiB2 reinforcement of both a particulate and flake morphology. Heat treatment was found to coarsen the network of boride flakes to a spheroidal or particulate morphology.
Phthalonitrile as a carbon source Keller, T.M. Polymer Communications Vol 31 No6 (1990) pp 229-231 4, 4'-bis(3,4-dicyanophenoxy) biphenyl was cured with small quantities of aromatic amine to produce a thermosetting polymer resin. The polymer and its subsequent pyrolysate were found to exhibit favourable properties for the production of pore-free glassy carbon. Visually void-free pyrolysed samples were readily obtained. However, microscope examination revealed a microporous microstructure. The pyrolysis behaviour was attributed to the heterocyclic cross-links present in the resin, and contrasted with other high temperature thermosetting polymers which yield thermally unstable aliphatic cross-links.
CERAMIC FIBRES Effect of friction in ceramic coating/fiber composites Lu, M.-C. and Hsueh, C.-H. Journal of Composite Materials Vol 24 No 6 (1990) pp 572-593 Using a single notional single fibre with a finite length of uniform coating on its central region, the effect of frictional interaction at a weakly bonded or unbonded coating/fibre interface was analysed. The effects of the coefficient of friction at the interface and the thermomechanical mismatch of the system on the stress transfer from the fibre to the coating were reported. A method to predict the residual thermal stress and to evaluate the coefficient of friction was suggested, with the possibility of extending the model to evaluating general residual stresses being addressed.
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A comparative study of the impact behaviour of ceramic matrix composites Macke, T., Quenisset, J.M., Neuilly, D., Rocher, J.P. and Naslain, R. Composites Science and Technology Vol 37 Nos 1-3 (1990) pp 267-278 In this paper the authors describe the use of instrumented Charpy impact testing to evaluate the dynamic toughness of ceramicmatrix composites (CMC). The authors assume the CMC to be damageable elastic materials and, utilizing a procedure based on a dynamic analysis of the notched bending specimen responses, various fracture parameters are studied. Dynamic toughness K~d, derived from fracture initiation and dynamic crack growth resistance curves, is used to characterize the dynamic toughness of various 2D and 3D ceramic-matrix composites. Significant differences in R-curves are correlated with the fibrous structure and the component nature of the composites. The usefulness of impact testing at moderate speeds is established. Creep and microstructure of electrical discharge machinable Si~4 composites Crampton, J. and Duclos, R. Acta Metallurgica et Materialia Vol 38 No 5 (1990) pp 805--810 Silicon nitride sintered with the aid of YzO 3 and AI203containing from 0 to 40 vol % of TiN particles of size 1 and 2.5 ILm were considered. Their compression creep behaviour was studied between 1260 and 1340"C at stresses ranging from 100 to 300 MPa. Viscous creep was found to be the dominant creep mechanism up to 1340°C and 200 MPa. Increasing the volume fraction of the TiN particles decreased the creep strength, as did decreasing their size. Cavities and microcracks were observed along particle/matrix
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interfaces showing that a cavitational mechanism develops from the presence of the particles. Effects of ZrO 2 and Y2Oa dissolved in zyttrite on the densiflcation and the od[3 phase transition of Si~N]4 in SI~4--ZrO 2 composites Kim, J.R. and Kim, C.H. Journal of Materials Science Vo125 No 1B (1990) pp 493-498 The effects of ZrO 2 and Y203 dissolved in zyttrite on the densification and the od[3 transition of Si3N4 were studied using pure, 3, 6 and 8 tool % Y203-doped zirconia powder. Pure zirconia powder was found to be ineffective in obtaining full density during hot pressing. Densification was promoted by Y203 diffused from the added zyttrite. Near full density was obtained in Si3N4 with 5 vol %, 6 and 8 mol % Y203-doped ZrO2 composites. The role of the reaction products, Y2Si207 and Y2Si3N403 phases during densification is considered. The impact behaviour of high performance,, ceramic matrix fibre composites Phillips, D.C., Park, N. and Lee, R.J. Corn-. posites Science and Technology Vol 37 Nos; 1-3 (1990) pp 249-265 In this paper the authors describe a study of! the impact behaviour of (0,90)z~ carbon fibre: composites with borosilicate glass and lithium t aluminosilicate (LAS) glass ceramic matrices. These materials were tested using an instru-. mented falling weight impactor on specimens; subjected to a superimposed tensile stress. The amount of damage caused was found to, be a function of applied stress and impact: energy, and led to the development of a n impact fracture map allowing the comparison of different materials and test conditions to, be made, The borosilicate glass composite, was studied over a temperature range of! 450--600"C, which encompasses the matrix softening temperature at 580°C. It is reported that impact damage was worse at elevated temperatures, even below the softening: point. Ballistic impact tests at impact velocities of between 70 and 140 m s-1 were found t o produce more localized damage than the falling weight experiments. Nucleation and growth of cracks in SiC/AIzOs composites Jakus, K. and Nair, S.N. Composites Science and Technology Vol 37 Nos 1-3 (1990) pp 279-297 The authors report on creep crack nucleation and growth studies on two grades of SiC whisker-reinforced alumina at temperatures of 1100, 1200 and 13000C in an oxidizing environment. It was found that cracking on the tensile surface initiated at a temperaturedependent threshold creep strain and, following this initiation, cracks continued to nucleate throughout the creep process. Increasing temperature delayed initiation to larger creep strains. The purity of the composite, however, did not substantially alter the initiation strain level but affected the
number of surface cracks present at a given strain. The rate of growth of creep cracks was less at any given stress intensity level than that of pre-existing cracks. With respect to crack nucleation and growth, whisker reinforcement made the composite behave in a more brittle fashion than a fine grain high purity alumina but in a less brittle manner than a large grain vitreous bonded alumina. Oxidation of an AI203 - vAION ceramic composite Goeuriot, P., Goeuriot-Launay, D. and Therenot, F. Journal of Materials Science Vol 25 No 1B (1990) pp654-660 Composites consisting of a dispersed Valuminium oxynitride (v-A1ON) in an A120 3 matrix were prepared by reaction sintering at 1800°C. Oxidation kinetics of the composites were followed by thermogravimetric analysis (TGA) in pure oxygen. After oxidation, X-ray analysis and ceramographies were performed. A v-alumina layer was found to form during oxidation, producing surface compressive stresses. Mechanical properties and wear resistance of the composites were thus improved. Toughness assessment of ceramic matrix composites Bouquet, M., Birbis, J.M. and Quenisset, J.M. Composites Science and Technology Vol 37 Nos 1-3 (1990) pp 223-248 The tensile testing of unnotched specimens o f various ceramic-matrix composites i s described. The authors observed that the composites show damag_eable quasi-elastic behaviours. These results are compared with those obtained for notched specimens tested using loading/unloading cycles, which show significant non-linearities. The discrepancy between the two tests is attributed by the authors to the presence of debris which invalidates the methods based on loading/ unloading cycles. The authors further claim that the approximation which considers tested CMC as a damageable elastic material leads to very small errors in the determination of crack growth resistance curves.
GENERAL Analysis of unbalanced multi-layered elliptical plates under varying pressure Mansfield, E.H. International Journal of Mechanical Sciences Vol 32 No 5 (1990) pp 417--422 An analysis was produced for unbalanced clamped elliptical multilayered plates under conditions of linearly varying pressure and where coupling was exhibited between moments and planar strains. Buckling analysis of FRP faced cylindrical sandwich panel under combined loading Rao, K.M. and Meyer-Piening, H.R. Composite Structures Vo114 No I (1990) pp 15-34 Fibre-reinforced plastic (FRP) faced sandwich panels are used in the aerospace industry as wing coverings or fuselage elements. This paper develops an analysis for the buckling of FRP generally orthotropic cylindrical sandwich panels which were subjected to combined loading conditions of axial compression, bending and shear. The analysis utilized the Rayleigh-Ritz method. Results obtained from the analysis were discussed.
A composite laminate box-section beam design for obtaining optimal elastodynamic responses of a flexible robot manipulator Sung, C.K. and Shyl, S.S. International Journal of Mechanical Sciences Vol 32 No 5 (1990) pp 391--404 The performance of robot arms was found to be limited by the inertia, stiffness, strength and damping characteristics of the beam sections from which it was constructed. A methodology was developed to optimize the above properties using composite materials to give beam sections with tailor-made properties. Design objectives and constraints were specified and were applied to the problem of a two-link robot linkage. This was shown to have superior properties to traditional linkages. Crack tip reinforcement by bridging elements: modelling the fracture of the matrix material Smith, E. Journal of Materials Science Vo125 No 3 (1990) pp 1632-1635 The assumption that the matrix material ahead of a crack tip behaves in accordance with the laws of linear elasticity (the crack extending when the stress intensity factor attains a critical value Kic) was examined. The assumption was tested for a semi-infinite crack in a remotely loaded infinite solid. Results show that the assumption can lead to misleading conclusions regarding determination of the 'applied' value of K required for crack tip propagation, and the size of the restraining zone when propagation occurs. Design of antisymmetric hybrid laminates for maximum buckling load: I. Optimal fibre orientation Adali, S. and Duffy, K.J. Composites Structures Vo114 No I (1990) pp 49-60 The optimal fibre orientations were determined for hybrid laminate panels designed to maximize buckling load subject to a mass constraint. The laminate panel was constructed from low stiffness material in the core and high stiffness material in the outer layers. Results were presented for simply supported plates under biaxial loading. Costs were discussed and comparisons were made with non-hybrid laminates. Dielectric studies of PZT-polymer composites Nayak, B., Mansingh, A. and Machive, M.K. Journal of Materials Science Vol 25 No 1B (1990) pp 749-752 Composite discs of lead zirconate titanate (PZT)/nylon 66 composites were prepared from formic acid solutions of nylon containing added PZT powder. Dielectric measurements were performed using a capacitance bridge. Dielectric constant was found to increase with increasing PZT content up to 50 vol % PZT, but decreased at higher powder volume fractions due to porosity. The dielectric constant was also found to increase rapidly at higher temperatures and lower frequencies due to intergrain polarization. Evaluation of testing techniques for the losipescu shear test for advanced composite materials Lee, S. and Munro, M. Journal of Composite Materials Vo124 No 4 (1990) pp 419-440 Experimental techniques for applying the Iosipescu shear test method to advanced composite materials are described. The degree of damage introduced in the machin-
ing of the notch and the effect on test behaviour was investigated. The occurrence of a pure shear strain field in the test section was evaluated using both tension and compression strain gauges. Measures adopted to eliminate in-plane or out-of-plane bending or twisting of the specimens were reported. Results analysed for 90° samples showed that the determination of the in-plane shear modulus by the tangent method had a lower scatter than that by initial modulus or secant methods. Examination of the processes of deformation and fracture in a silica-filled epoxy resin Cantwell, W.J., Smith, J.W., Kausch, H.H. and Kaiser, T. Journal of Materials Science Vo125 No 1B (1990) pp633--648 Fractographic studies of a silica-filled epoxy resin were undertaken in order to determine the processes of damage initiation, development and fracture within a particulate-filled polymer. Within the volume of the material, a number of different types of inelastic deformation and fracture mechanisms were observed. At low temperature and high loading rate, failure was associated with debonding only. At high temperatures and low loading rates, debonding and yielding were found to occur throughout the volume of the test specimen. Fracture surfaces were characterized by scanning electron microscopy and optical microscopy. An experimental study of scaling rules for impact damage in fiber composites Qian, Y., Swanson, S.R., Nuismer, R.J. and BucineU, R.B. Journal of Composite Materials Vo124 No 5 (1990) pp 559-570 Plates ranging in size from 50 × 50 × 1.072 mm to 250 × 250 × 5.36 mm of AS4/3501-6 carbon/epoxy composite were geometrically scaled and impacted with projectiles of various geometries. Analytically derived scale rules were found to accurately describe the undamaged response to impact, with an analysis based on the dynamic plate equation also showing excellent agreement with experiments, It was concluded that the formation of damage is complex, showing an apparent dependence of delamination on absolute size as suggested by fracture mechanics. Large deflections of a uniformly loaded, elastically restrained composite strip Mansfield, E.H. International Journal of Mechanical Sciences Vol 32 No 4 (1990) pp 329-334 An analysis was produced for a multilayered composite strip under uniform normal loading with elastically restrained planar boundaries. The large deflection behaviour was examined for conditions of coupling between moments and planar strains. Mode ! d e l ~ i n a t i o n of a three-dimensional fabric composite Byun, J.-H., Gillespie, J.W. and Chou, T.-W. Journal of Composite Materials Vo124 No 5 (1990)pp 497-518 Double cantilever beam specimens of carbon/ epoxy (T300/3501-6) orthogonal interlocked fabric composite were considered in a finite element analysis. The Mode I strain energy release rate was evaluated to enable determination of the influence of through-thethickness fibres on crack driving force as a function of crack length. Compared on the basis of compliance and strain energy release
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rate, the finite element analysis showed a good agreement with experimental results. It was shown that the presence of z-axis fibres reduced the strain energy release rate compared with traditional 2-D laminates. Debonding of the z-axis was also modelled, showing that the Mode I strain energy release rate increased as the fibre debonded but was always significantly less than that of the 2-D laminated materials. The inputs required to the model were the z-axis fibre properties, fibre architecture, fibre volume fraction and the Mode I critical strain energy release rate for the 2-D laminate. On isotropi¢ laminate configurations Fukunaga, H. Journal of Composite Materials Vol24 No 5 (1990) pp 519-535 Laminate composites with isotropic stiffness characteristics with respect to both in-plane and out-of-plane stiffnesses were reported. A method for the determination of isotropy was reported and examples of 40-ply laminates given. Experimental results were obtained using tensile testing and a four-point bend test, revealing almost isotropic properties in a 40-ply laminate. On sandwich beams with laminate facings and honeycomb cores subjected to hydrothermal loads: Part 1--analysis Mukhopadhyay, A.K. and Sie rakowski, R.L. Journal of Composite Materials Vo124 No 4 (1990) pp 382-400 The combined effects of mechanical, thermal and hygromatic loading on a sandwich beam with a honeycomb core and laminate facing were determined using a macromechanical approach. Negligible in-plane resistance was found in the cores; however, they were relatively stiff in the transverse direction. Equations were determined in terms of the lateral deflection and the mid-plane displacement, these being general and applicable to any construction of this type. On sandwich beams with laminate facings and honeycomb cores subjected to hydrothermal loads: Part lI---application Mukhopadhyay, A.K. and Sie rakowski, R.L. Journal of Composite Materials Vo124 No 4 (1990) pp 400-418 This paper considered a specific loading state for the beam structure analysed in Part I. The beam was simply supported under uniform load. Stiffness coefficients, pertinent parameters and the distribution of stresses across the laminate facings for varying core thickness and facing orientations were graphically displayed and discussed. Postbuckling finite element analysis of composite panels Laschet, G. and Jeusette, J.P. Composite Structures Vo114 No I (1990) pp 35--48 The pre- and postbuckling behaviour of an arbitrarily laminated composite panel under destabilizing loads was analysed. The threedimensional degenerated isoparametric multilayered finite element analysis used was described along with an automatic solution procedure. The efficiency and accuracy of the model was determined for the non-linear response of two structural examples. Wood flour as a low cost reinforcing filler for polyethylene: studies on mechanical properties Raj, R.G., Kokta, B.V. and Daneault, C.
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Journal of Materials Science Vol 25 No 3 (1990) pp 1851-1855 Composites of high density polyethylene (rIDPE) filled with wood flour were prepared and moulded into tensile test specimens. Composites having wood flour coated with aikoxy-silane coupling agents generally showed higher tensile strength and modulus values than uncoated specimens. However, the best improvement in composite tensile strength was obtained when the wood flour was pretreated with polymethylenepolyphenyl isocyanate. Better performance with the isocyanate coupling agent was attributed to the formation of bonds between the cellulose hydroxy groups and isocyanate.
METAL MA TRICES Fracture of boron particles in 2219 aluminium as a known acoustic emission source Heiple, C.R., Carpenter, S.H. and Christiansen, S.S. Acta Metallurgica et Materialia Vol38 No4 (1990) pp611-618 Aluminium 2219 reinforced with boron particles was produced using a powder metallurgy process. Acoustic emission during deformation emanated from decohesion of the boron particles from the matrix and particle fracture. Elasticity theory was used to estimate the energy associated with particle fracture. It was found that the energy in the acoustic emission signals was proportional to the fracture energy released. It was stated that the relation found between the fracture energy and acoustic emission signal energy could be used to estimate the energy released by other comparable acoustic emission sources, in samples of similar geometries, from their acoustic emission measurements. The interface microstructure in alumina (FP) fibre/magnesium alloy composites Pfeifer, M., Rigsbee, J.M. and Chawla, K.K. Journal of Materials Science Vol 25 No 3 (1990) pp 1563-1567 The reaction zone created at the interface of the metal-matrix composite system tx-AI203 (FP)/Mg (ZE41A) was characterized using electron microscopy. Composites were prepared by a vacuum infiltration technique. Morphology, interface chemistry and crystallographic features were investigated using transmission electron microscopy. The reaction zone was found, on average, to be 100 nm wide and composed of MgO. Growth of the reaction zone is thought to be controlled by a seepage mechanism involving infiltration of liquid Mg between MgO crystals. Isothermal and nonisothermal fatigue behaviour of a metal matrix composite Gabb, T.P., Gayda, J. and MacKay, R.A. Journal of Composite Materials Vo124 No 6 (1990) pp 667-686 Isothermal and non-isothermal fatigue resistance of a metal-matrix composite of Ti-15V3Cr-3A1-3Sn (Ti-15-3) matrix reinforced with 33 vol % continuous SiC fibre was investigated. A good isothermal fatigue resistance was exhibited by the composite at 300 and 550°C at low cyclic stresses, with fatigue cracks initiating from fibre/matrix interfaces and foil laminations. The isothermal composite fatigue resistance at 550°C was observed to be reduced due to stress relaxation in the
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matrix at high cyclic stresses. The composite's fatigue resistance was found to substantially degrade under non-isothermal conditions as a result of thermomechanical fatigue damage associated with the fibre/matrix interfaces.
ORGANIC FIBRES Lateral growth of microparacrystals in Kevlar 49 fibres irradiated by Co 60 Hindeleh, A.M., Heinrichsen, G. and Springer, H. Journal of Polymer Science Part B Vol28 No 3 (1990) pp 267-279 Cross-linking in the form of H-bonding in Kevlar 49 was induced by y irradiation from a Co 6° source. Wide angle X-ray diffraction techniques were used to study the phenomena. Microparacrystals (mPCs) were found to increase in size in the b direction (lateral direction), whilst the mPC size along the axis. and normal to the (002} netplanes was unaffected by irradiation. The paracrystalline disorder parameter (g) was found not to change significantly during irradiation. Liquid crystalline solutions of poly(pphenylenebenzobisthiazole) complexes in organic solvents Roberts, M.F. and Jenekhe, S.A. Polymer. Communications Vol 31 No 6 (1990) pp 215-217 The morphology, phase equilibria, rheology and liquid crystallinity of solutions of A1Cla and GaCl a complexes with poly(pphenylenebenzobisthiazole) (PBT) in organic solvents were investigated. The above properties were found to be dependent on the nature and concentration of the Lewis acid in solution. Possible implications for processing of PaT and related rigid-rod polymers to films, fibres and molecular composites are discussed. Paracrystalline, microparacrystal size and molecular weight distribution of Kevlar 49 fibres exposed to elevated temperatures Hindeleh, A.M., Hosemann, R., Hinrichsen, G. and Springer, H. Polymer Communications Vol 31 No 5 (1990) pp 205-208 The paracrystalline distortion parameter (g), the microparacrystalline (mPC) size D0o2 and the molecular weight distribution (MWD) of Kevlar 49 fibres exposed to elevated temperatures were determined by X-ray diffraction and size-exclusion chromatography. Untreated Kevlar 49 fibres were found to have a g value of 2.8%, which decreased to 2.4% at 400°C, then increased to 3.3% at 450°C, and 3.7% at 500°C. Doo2 was found to decrease gradually with increases in either the annealing temperature or the thermal ageing time. MWD remained unchanged until 300°C. The phase behaviour and gelation of a rod-like polymer in solution and implications for microcellular foam morphology Jackson, C.L. and Shaw, M.T. Polymer Vol 31 No6 (1990) pp 1070-1083 The thermally induced phase separation processes by which microcellular materials are made were studied by observing the phase separation of the rod-like macromolecule poly(~,-benzyl-L-glutamate). Microcellular materials were formed by lowering the solution temperature until phase separation and solvent freezing occurred. Solvent could
then be removed by vacuum sublimation. The morphology produced by liquid-liquid phase separation and gelation was an opencelled fibrous structure resembling a threedimensional lattice. Results are considered in terms of theories and proposed mechanisms of phase separation. Structural characteristics of aramid fibre variants Dobb, M.G. and Robson, R.M. Journal of Materials Science Vol 25 No 1B (1990) pp 459-464 A number of commercially available aramid fibres based on poly(p-pheneylene terephthalamide) were investigated in order to determine their different tensile behaviours and structural characteristics. Widely different tensile behaviour was found between the different fibres studied. Differences in breaking strength and modulus were related to structural features as determined by X-ray diffraction and electron microscopy. Results indicate that high molecular orientation, low skin content and large crystallite size favour the development of high modulus materials. However, fibre strength appears to be adversely affected by morphological defects, often resulting from the high degree of draw given to high modulus fibres.
shear and dynarmc viscosity were measured as a function of extent of reaction throughout the cure. Using the DiBenedetto model and branching theory, molecular weight, glass transition temperature and other structural parameters were predicted at various stages of the polymerization.
The crush behaviour of pultruded tubes at high strain rates Thornton, P.H. Journal of Composite Materials Vo124 No 6 (1990) pp 594-615 The crush response of pultruded glass fibrereinforced plastic tubes of polyester and vinyl resins was investigated. Crush rates from 2.1 x 10~ m s-1 to 15 m s I were used on tubes of various fibre diameters, trigger geometry and section geometry. The rate dependence of the specific energy for the polyester resin was positive whilst that for the vinyl resin was either positive or negative depending on the tube geometry. A nominal reduction of onehalf in the fibre diameter for the same glass content was found to decrease the specific energy by up to 20%. In quasi-static crush the vinyl ester resin tubes had a significantly higher specific energy than the polyester tubes; however, in dynamic crush this difference diminished. The occurrence of fibre delamination and unstable failures was noted and discussed.
RESIN MA TRICES Characterisation of creep in polymer composites by the use of frequency-time transformations Gibson, R.F., Hwang, S.J. and Sheppard, C.H. Journal of Composite Materials Vo124 No 4 (1990)pp 441-452 Time-dependent creep and relaxation properties of polymer composite materials were determined by the use of frequency-domain vibration test data. A vibration test method was used to enable the measurement of frequency-domain complex moduli over a suitable range. These were then converted into time-domain relaxation moduli or creep compliances by using an inverse Fourier transform and numerical integration. Various test functions were used to check the accuracy of the transformation, which was then used for characterization of an angle-ply graphite/ polyimide composite. The creep data generated by the frequency-time transformation showed good agreement with similar data generated by time-temperature superposition. Chemorheology reactions for epoxy-amine crosslinking Bidstrup, S.A. and Macosko, C.W. Journal of Polymer Science Part B Vo128 No 5 (1990) pp 691-709 The thermoset system consisting of the diglyeidyl ether of bisphenol A (DOEBA) and an amine curing agent, diaminodiphenyl sulphone, was chosen to study the relationship between the mechanism of bond formation, resulting structure and viscosity during the step polymerization of a thermoset. Steady
Energy release rates for cracks caused by moisture absorption in graphite/epoxy composites Tsotsis, T.K. and Weitsman, Y. Journal of Composite Materials Vol 24 No 5 (1990) pp 483-496 Energy release rates and the J-integral were calculated numerically and analytically, indicating that extremely low energies were involved in microcrack formation due to moisture absorption in graphite/epoxy composite materials. It was postulated that moisture was dramatically reducing the adhesion between the graphite and the epoxy. It was also noted that the tensile stresses at the fibre/matrix interface were substantially less than the matrix strength and therefore mechanical damage observed around the fibres was due to moisture. Epoxy resins (DGEBA): the curing and physical aging process Plazek, D.J. and Frund Jr, Z.N. Journal of Polymer Science Part B Vo128 No 4 (1990) pp 431-448 Differential scanning calorimetry (DSC) and infra-red spectrophotometry (IR) were used to monitor the degree of cure of Epon 828 epoXy/MDA samples cured at 130°C. DSC was also used to monitor the extent of 'physical ageing' which took place during the cure at 130°C. The fictive temperature (the hypothetical temperature at which the structure would be in equilibrium) was determined by DSC. IR was used to show that the greatly reduced reaction rate during the final 20% of cure was not only a consequence of vitrification, but also a result of the depletion in the number of reactive epoxide groups.
Free volume changes in epoxy adhesives during physical aging: fluorescence spectroscopy and mechanical stress relaxation Shmorhun, M., Jamieson, A.M. and Simah, R. Polymer Vo131 No 5 (1990) pp 812--817 The fluorescence probes 1,3-bis-l-pyrene propane and 1,(4-dimethylaminophenyl)-6phenyl-l,3,5-hexatriene were dispersed in fully cured epoxy (Epon 828). Free volume change during ageing was thus followed in the glassy state. During isothermal annealing the emission intensity was found to show a timedependent increase, interpreted as due to the relaxation of the matrix free volume. The ageing time dependence behaviour was found to be consistent with the application of free volume arguments to the Loufty equation for describing fluorescence intensity. Static compression failure of carbon fibre T800/924C composite plate with a single hole Soutis, C. and Fleck, N.A. Journal of Composite Materials Vo124 No 5 (1990) pp 536558 Compressive failure of carbon/epoxy composite laminates was studied experimentally and theoretically in this paper. Static tests were used to characterize the mechanics of uniaxial compressive failure in multidirectional unnotched [(+__45/02)3]s plates. It was stated that the critical damage mode causing failure was fibre microbuckling in the 0 ° plies. X-ray radiography and scanning electron microscopy were used to observe damage initiation and propogation in compressively loaded [(+45/02)3] s laminates with circular holes. Failure was initiated in the matrix with fibre microbuckling surrounded by delamination at the hole edges occurring at higher loads. The laminate was said to fail catastrophically when the damage reached a critical state. A theoretical model was submitted for predicting the static strength of the laminates, the predictions of which were compared with experimental data, an acceptable agreement wfth experimental results was found. Strength of tensile loaded graphite/epoxy laminates containing cracks, open and rdled holes Eriksson, I. and Aronsson, C.-G. Journal of Composite Materials Vol 24 No 5 (1990) pp 456-482 In this paper a damage zone criterion for predicting tensile strength of composite laminates containing holes and cracks was reported. This zone, based on fundamental physical principles, was assumed to be present in the maximum stress region of the laminate when the tensile stress reached the tensile strength of the unnotched laminate. This enabled an expression to be derived that predicted the strength of laminates with holes and cracks from two fundamental parameters. These were the unnotched tensile strength and the critical damage zone length. This expression made excellent predictions of the strength of specimens of different laminate configurations. Significantly improved accuracy compared with the point stress criterion was also reported.
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