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Considerations concerning fatigue life of metal matrix composites
Fatigue Abstracts mechanical response and structural stability through cycling of a 316L stainless steel has been investigated. Low-cycle tests, including hold periods at maximum tensile strain, were also conducted at 600 and 625°C. Use of the acquired data has been made to construct cyclic stress-strain and stress-relaxation curves of the material. Also its basic fatigue/fatigue equation has been obtained. Graphs, photomicrographs, diffraction patterns, 23 ref. Behavior of nickel-base superalloy single crystals under thermal-mechanical fatigue. Fleury, E. and Remy, L. Metall. Trans. A (Jan. 1994) 25A(1), 99-109 The thermal-mechanical fatigue behaviour of AM1 nickel-base superalloy single crystals is studied using a cycle from 600 to ll00°C. It is found to be strongly dependent on crystallographic orientation, which leads to different shapes of the stress-strain hysteresis loops. The cyclic stress-strain response is influenced by variation in Young's modulus, flow stress, and cyclic hardening with temperature for every crystallographic orientation. The thermal-mechanical fatigue life is mainly spent in crack growth. Two main crack-initiation mechanisms occur, depending on the mechanical strain range. Oxidation-induced cracking is the dominant damage mechanism in the lifetime of interest for turbine blades. Graphs, photomicrographs, 29 ref. Evaluation of strength of welded joints by maximum stress constant fatigue lest. Ohta, A., Maeda, Y. and Suzuki, N. J. Soc. Mater. Sci. Jpn (Oct. 1993) 42(481) 1167-1171 The basic fatigue strength of welded joints of steels (JIS SM50B, SPV50, SB42, and HT80), which corresponds to that of real large-scale welded structures containing high-tensile residual stresses of yield-strength magnitude, was investigated by the maximum stress constant test. The plate thickness effect was revealed to be an imaginary phenomenon occurring from the small residual stresses induced by a variation in maximum stress with the applied stress. Miner's law was applicable for the basic fatigue strength. The basic fatigue strength increased with a decrease in yield strength. Graphs, 14 ref. Selective surface ageing in the high-strength beta titanium alloy beta-C. Gregory, J.K., Wagner, L. and Muller, C. Proc. Conf. Surface Engineering, Bremen, Germany, 1993, pp. 435-440 Cold-working the surface by shot peening or rolling of beta titanium alloys can provide the stored energy necessary to accelerate the ageing kinetics in near-surface regions. Upon subsequent annealing at slightly elevated temperatures, only the surface age-hardens, leaving the bulk essentially in the as-solution heat-treated condition. The surface hardness after this process can reach values of 800 HV, comparable to values attained after nitriding treatments applied for improved wear resistance. A distinct advantage of SSA over those conventional nitriding processes is that the notched fatigue limit improves dramatically, rather than deteriorating. As fasteners are often produced by surface rolling techniques, SSA offers an elegant and unique method for combining improved fatigue behaviour with high case-hardenesses at significant depths. Graphs, photomicrographs, 9 ref. Hierarchical simulation of hot composite structures. Chamis, C.C., Murthy, P.L.N. and Singhal, S.N. NASA Technical Memorandum TM-106200 (1993) 16 pp Computational procedures are described to simulate the thermal and mechanical behaviour of high-temperature metal-matrix composites (HT-MMC) in the following three broad areas: behaviour of HT-MMCs from micromechanics to laminate via Metal Matrix Composite Analyzer (METCAN); tailoring of HT-MMC behaviour for optimum specific performance via Metal Matrix Laminate Tailoring (MMLT); and HT-MMC structural response for hot structural components via High Temperature Composite Analyzer (HITCAN). Representative results from each area are presented to illustrate the effectiveness of computational simulation procedures. The sample case results show that METCAN can be used to simulate material behaviour such as strength, stress-strain response and cyclic life in HT-MMCs; MMLT can be used to tailor the fabrication process for optimum performance such as that for in-service load-carrying capacity of HT-MMCs; and HITCAN can be used to evaluate static fracture and fatigue life of hot-pressurized metal-matrix composite rings. Examples are given with SiC/Ti-15-3 or Ti-64 and graphite/copper. Graphs, 11 ref. Considerations concerning fatigue life of metal matrix composites. Radhakrishnan, V.M. and Bartolotta, P.A. NASA Report N93-27009/8/XAB (1993) 11 pp Since metal-matrix composites (MMC) are composed from two very distinct materials, each having its own physical and mechanical properties, it is feasible that the fatigue resistance depends on the strength of the weaker constituent. Based on this assumption, isothermal fatigue lives of several MMCs were analysed utilizing a fatigue life diagram approach. For each MMC, the fatigue life diagram was quantified using the mechanical properties of its constituents. The fatigue life regions controlled by fibre fracture and matrix were also quantitatively defined. Micromechanical analysis for thermoviscoplastic behavior of unidirectional fibrous composites. Robertson, D.D. and Mall, S. Compos. Sci. Technol. (1994) 50(4), 483-496 A three-dimensional micromechanics formulation for fibre-reinforced composites containing viscoplastic matrix materials is presented. The micromechanics model is based on the relaxation of the coupling effect between the
normal and shear stresses. Three variations of Bodner's theory of viscoplasticity are used to predict the thermoviscoplastic behaviour of unidirectional metalmatrix composites: first, the original isotropic-hardening model of Bodner and Partom; second, Ramasway's extension of the theory through the inclusion of a back stress; and, third, Stouffer and Bodner's extension of the theory through a special form of directional hardening. Comparisons with numerical solutions and experimental data of other researches are made to demonstrate the accuracy of the model. Micromechanical analyses of metalmatrix composites under both in-phase and out-of-phase thermomechanical fatigue-loading conditions are also presented for comparison with experiments and previous models. Boron-6061-T0 aluminium, graphite-2024-T4 AI, silicon carbide-Ti-B21S titanium composites are discussed. Graphs, 22 ref.
The role of interface and reinforcement properties on the fracture and fatigue resistance of ductile-phuse toughened 3,-TiAI composites. Rao, K. T. V., Ritchie, R.O. and Odette, G.R. Proc. Conf. Structural lntermetallics, Champion, PA, USA, 26-30 Sept. 1993, pp. 829-835 The coupled effects of the properties and interfacial characteristics of ductileparticle reinforcements, specifically niobium and TiNb, on the fracture and fatigue-frack growth behaviour of ~/-TiAI intermetallic composites were examined at ambient temperature. Compared with monolithic -#TiAI, appreciable increases in toughness, independent of reinforcement orientation, were seen for both composites reinforced with 20 vol.% Nb or TiNb. While the magnitude of the toughening is significantly larger for TiNb reinforcements under monotonic loads, Nb reinforcements offer greater improvements in fatigue-crack growth resistance under cyclic loading does to extensive debonding at the weaker Nb/'y-TiAl interface. Unlike behaviour under monotonic loading, fatigue-crack growth behaviour in both composites is strongly dependent upon the reinforcement orientation; marginal improvements in fatigue resistance over 3,-TiAI are noted only for orientations where particle faces are oriented normal to the crack plane. In other orientations, growth rates can be faster in the composites than in the unreinforced matrix alloy. Photomicrographs, graphs. 13 ref.
Properties of functionally graded NiAI/AizO3 composites. Miller, D.P., Lannutti, J.J., Soboye]o, W.O. and Noebe, R.D. Proc. Conf. Structural Intermetallics, Champion, PA, USA, 26-30 Sept. 1993, pp. 783-790 Mechanical property data were collected from functionally graded composites consisting of both NiAl and A1203. A modified sedimentation process that allows one to fabricate FGMs from a wide variety of metal and ceramic powders was used. These assemblages were then hot-pressed to full density. Those containing three, four and six layers were fabricated. Only the threelayer composites contained stress distributions that allowed the plate to survive stress buildup during cooling. Thermal cycling tests were conducted between room temperature and 1423 K. After 1120 cycles no visible damage, change in AT or weight change was observed. Bend test values at 300 K were three to four times those of both unreinforced NiAI and sapphire-fibrereinforced NiAl. At 800 and 1000 K bend tests showed that these composites undergo serrated failure. A succession of cracks propagated through the ceramic layer and were blunted in the NiAl. In none of the tests did the ceramic layer spall off the surface. Preliminary toughness data suggest that the alumina layer contains the expeted residual compressive stresses. Graphs, photomicrographs, 18 ref.
Failure mechanisms of 0° and 9 0 ° SiC/Ti-24AI-I lNb composites under various loading conditions. Brindley, P.K. and Draper, S.L. Proc. Conf. Structural lntermetallics, Champion, PA, USA, 26-30 Sept. 1993 pp. 727-737 Recent findings on failure of longitudinal SiC/Ti-24Al-11Nb (at.%) composites in tension, after thermal cycling in vacuum, and under isothermal fatigue conditions are reviewed. Current results of transverse SiC Ti-24AI-11Nb tensile properties and failure mechanisms as a function of temperature are discussed. Acoustic emission, replication, and examination of fracture surfaces were used to define failure. At 23°C, debonding occurred near the 'knee' in the stress-strain curves and continued until matrix fracture resulted in composite failure. The 'knee' in the stress-strain curves at elevated temperatures was associated with matrix yielding. Multiple interface locations were involved in the failure at all temperatures. Issues pertinent to improving the 90° composite strength are discussed. Graphs, photomicrographs, 38 ref.
Fatigue and cyclic crack growth rates of a cast particulate reinforced aluminum composite. Andersson, C.A. and Luszcz, S.J. Proc. Conf. Advanced Composites Technologies, Dearborn, MI, USA, 8-11 Nov. 1993, pp. 223-231 Fatigue and cyclic crack growth rate tests were performed on an Al-10Si-1Mg/ SiC/30p-T6p composite. The resistance to fatigue of the composite is shown to be superior to that of 360.0 alloy, which has a composition similar to thc matrix. Since the fatigue life of the composite appears to be controlled by crack growth, it was demonstrated that the results of the two types of test could be correlated with one another. This enhances the ability to design with the composite since it is relatively easy to transform between the two approaches to material fatigue. Graphs, photomicrographs, 10 ref.
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normal and shear stresses. Three variations of Bodner's theory of viscoplasticity are used to predict the thermoviscoplastic behaviour of unidirectional metalmatrix composites: first, the original isotropic-hardening model of Bodner and Partom; second, Ramasway's extension of the theory through the inclusion of a back stress; and, third, Stouffer and Bodner's extension of the theory through a special form of directional hardening. Comparisons with numerical solutions and experimental data of other researches are made to demonstrate the accuracy of the model. Micromechanical analyses of metalmatrix composites under both in-phase and out-of-phase thermomechanical fatigue-loading conditions are also presented for comparison with experiments and previous models. Boron-6061-T0 aluminium, graphite-2024-T4 AI, silicon carbide-Ti-B21S titanium composites are discussed. Graphs, 22 ref.
The role of interface and reinforcement properties on the fracture and fatigue resistance of ductile-phuse toughened 3,-TiAI composites. Rao, K. T. V., Ritchie, R.O. and Odette, G.R. Proc. Conf. Structural lntermetallics, Champion, PA, USA, 26-30 Sept. 1993, pp. 829-835 The coupled effects of the properties and interfacial characteristics of ductileparticle reinforcements, specifically niobium and TiNb, on the fracture and fatigue-frack growth behaviour of ~/-TiAI intermetallic composites were examined at ambient temperature. Compared with monolithic -#TiAI, appreciable increases in toughness, independent of reinforcement orientation, were seen for both composites reinforced with 20 vol.% Nb or TiNb. While the magnitude of the toughening is significantly larger for TiNb reinforcements under monotonic loads, Nb reinforcements offer greater improvements in fatigue-crack growth resistance under cyclic loading does to extensive debonding at the weaker Nb/'y-TiAl interface. Unlike behaviour under monotonic loading, fatigue-crack growth behaviour in both composites is strongly dependent upon the reinforcement orientation; marginal improvements in fatigue resistance over 3,-TiAI are noted only for orientations where particle faces are oriented normal to the crack plane. In other orientations, growth rates can be faster in the composites than in the unreinforced matrix alloy. Photomicrographs, graphs. 13 ref.
Properties of functionally graded NiAI/AizO3 composites. Miller, D.P., Lannutti, J.J., Soboye]o, W.O. and Noebe, R.D. Proc. Conf. Structural Intermetallics, Champion, PA, USA, 26-30 Sept. 1993, pp. 783-790 Mechanical property data were collected from functionally graded composites consisting of both NiAl and A1203. A modified sedimentation process that allows one to fabricate FGMs from a wide variety of metal and ceramic powders was used. These assemblages were then hot-pressed to full density. Those containing three, four and six layers were fabricated. Only the threelayer composites contained stress distributions that allowed the plate to survive stress buildup during cooling. Thermal cycling tests were conducted between room temperature and 1423 K. After 1120 cycles no visible damage, change in AT or weight change was observed. Bend test values at 300 K were three to four times those of both unreinforced NiAI and sapphire-fibrereinforced NiAl. At 800 and 1000 K bend tests showed that these composites undergo serrated failure. A succession of cracks propagated through the ceramic layer and were blunted in the NiAl. In none of the tests did the ceramic layer spall off the surface. Preliminary toughness data suggest that the alumina layer contains the expeted residual compressive stresses. Graphs, photomicrographs, 18 ref.
Failure mechanisms of 0° and 9 0 ° SiC/Ti-24AI-I lNb composites under various loading conditions. Brindley, P.K. and Draper, S.L. Proc. Conf. Structural lntermetallics, Champion, PA, USA, 26-30 Sept. 1993 pp. 727-737 Recent findings on failure of longitudinal SiC/Ti-24Al-11Nb (at.%) composites in tension, after thermal cycling in vacuum, and under isothermal fatigue conditions are reviewed. Current results of transverse SiC Ti-24AI-11Nb tensile properties and failure mechanisms as a function of temperature are discussed. Acoustic emission, replication, and examination of fracture surfaces were used to define failure. At 23°C, debonding occurred near the 'knee' in the stress-strain curves and continued until matrix fracture resulted in composite failure. The 'knee' in the stress-strain curves at elevated temperatures was associated with matrix yielding. Multiple interface locations were involved in the failure at all temperatures. Issues pertinent to improving the 90° composite strength are discussed. Graphs, photomicrographs, 38 ref.
Fatigue and cyclic crack growth rates of a cast particulate reinforced aluminum composite. Andersson, C.A. and Luszcz, S.J. Proc. Conf. Advanced Composites Technologies, Dearborn, MI, USA, 8-11 Nov. 1993, pp. 223-231 Fatigue and cyclic crack growth rate tests were performed on an Al-10Si-1Mg/ SiC/30p-T6p composite. The resistance to fatigue of the composite is shown to be superior to that of 360.0 alloy, which has a composition similar to thc matrix. Since the fatigue life of the composite appears to be controlled by crack growth, it was demonstrated that the results of the two types of test could be correlated with one another. This enhances the ability to design with the composite since it is relatively easy to transform between the two approaches to material fatigue. Graphs, photomicrographs, 10 ref.
Fatigue, 1994, Vol 16, November
591