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Fatigue life prediction of fibre reinforced titanium matrix composites
Fatigue abstracts Crack initiation, crack growth and fracture bebaviour of large diameter pipes with circumferential defects under internal pressure and superimposed alternating bending load. Stoppler, W., Sturm, D., Hippelein, K. and de Boer, A. Nacl. Engng Design (1996) 160 (1-2-I), 137-152 Pipes made of steel 20 MnMoNi 5 5 and MnMoNiV special melt having an external diameter of 800 mm, wall thickness of 47 ram, and length of up to 5500 mm were provided with circumferential defects of defined length and depth. They were loaded by internal pressure and a superimposed alternating bending moment. During the tests deformation and crack growth were determined in the wall thickness and circumferential direction. Pipes with an outer diameter of 226 mm and a wall thickness of 20 nun were used to investigate the leak-before-break behaviour in the dynamic sphere. These pipes were also made of steel 20 MnMoNi 5 5 and a MnMoNiV special melt and were loaded with internal pressure and an alternating bending moment. The excitation took place at the resonance frequency of the pipes. The pipes also contained circumferential defects of defined length and depth. Graphs, 7 ref.
Cyclic stress--strain response and dislocation substructure evolution of a ferrite--austenite stainless steel. Llanes, L., Mateo, A., Itargoyen, L., Anglada, M. Acta Materialia (1996), 44, 1143-1153 The hardening-softening response, the cyclic stress-strain behaviour and the evolution of dislocation structures of an AISI 320 ferrite-austenite stainless steel have been studied. Fatigue testing has been conducted under fully reversed total strain control and constant total strain rate. Detailed transmission electron microscopy studies have been carried out in order to determine the individual substructure evolution, as a function of increasing imposed strain amplitude, in each constitutive phase. In general, the cyclic response of the studied material may be described in terms of three different regimes within the plastic strain amplitude (%0 range investigated, i.e. from 2 × l0 S to 6 x 10-3; at %t < 10-4 the dominant cyclic deformation mechanisms are those correlated to planar glide of dislocations within the austenite which is the phase which carries a large part of the macroscopic strain in this first regime. On the other hand, at *p~ > 6 x 10-4 the dominant substructure evolution is observed inside the ferritic matrix. In this case, strain localization is enhanced, within the ferritic grains, through the development of veins into the wall structure. Such evolution induces a pronounced decrease of the cyclic strain hardening rate in the cyclic stress-strain curve. At %~ in between these values, the cyclic behaviour is characterized by a relatively high strain hardening rate and may be classified as a mixed ferritic/austenitic like behaviour. In this intermediate regime substructural changes are observed in both phases and the dislocation activity in each of them seems to be strongly influenced by their particular cyclic strain hardening behaviours. Finally, the results are analyzed and compared with data from the literature in terms of volume fraction and chemical composition of the constitutive phases. Graphs, photomicrographs, 31 ref.
Fatigue life prediction of fibre reinforced titanium matrix composites. Mal, A.K., Wang, P.C., Jeng, S.M. and Yang, J.-M. Acta Mater. (Mar. 1996) 44, 1097-1108 A micromechanical model was developed to predict the fatigue life of SiC fibre reinforced Ti matrix composites. The propagation of matrix cracks was modelled by calculating the stress concentration factor at the matrix crack tip in a fibre bridged center matrix crack. The residual stiffness was then predicted by using the partial crack shear lag model, and the post fatigue tensile strength was predicted by using the load carrying capacity of fibres proposed previously for brittle matrix composites. Finally, the catastrophic failure and fatigue life of the composite was determined by Monte Carlo simulation. An integrated computer simulation code was developed to simulate the evolution of fatigue damage, degradation of mechanical properties, and to predict fatigue life. The predicted matrix crack propagation rates, residual stiffness, residual tensile strength, and fatigue life were also correlated with experimental results. Graphs, photomicrographs, 30 ref.
Study of fractal characteristics of fatigued fracture surfaces at elevated temperature in Zircaloy-4 by secondary electron line scanning. Xiao, L, Gu, H.C. and Kuang, Z.B. Xiyou Jinshu Cailiao yu Gongcheng (Rare Metal Mater. Engng) (1995) 24 (2), 22-26 Fractal characteristics of fracture surfaces in Zircaloy-4 specimens fatigue at RT, 400 and 600°C have been investigated by means of secondary electron line scanning. It is believed that the range of validity of fractals for Zircaioy4 is associated with prominent fractographic features, i.e. with the grain size. The linear relationship of fractal dimension and fatigue lifetime is established. An explanation is given why the fractal dimension increases as the test temperature increasing for Zircaloy-4 at the same cyclic plastic strain amplitude. Graphs, photomicrographs, 10 ref.
Reliability of composite steel bridge beams designed following AASHTO's LlZD and LRFD specifications. Tabsh, S.W. Structural Safety (1996) 17, 225-237 Composite steel beam bridges designed following ASSHTO's load factor design (LFD) method and the newly developed load and resistance factor design method (LRFD) are proportioned for different loading conditions. They need to satisfy these conditions at maximum design load, an overloading condition, and fatigue load. The ultimate strength of compact composite steel beams is based on the fully plastic stress distribution. The capacity of non-compact beams is based on the yield or partially-plastic moment, depending on whether the beam violates all or few of the compactness or ductility requirements. In
353
this paper, the reliability for the ultimate flexural capacity limit state of composite steel beams is investigated. The structural reliability is measured in terms of the reliability index. The statistical data on strength are generated starting from statistics on material properties and using the Monte Carlo simulation method. Statistical data on load components are compiled from the available literature. The scope of the study covers a wide range of rolled beams, span lengths, beam spacings, and two yield strengths. The deterministic study showed that the design of composite steel beams is usually not governed by the maximum design load combination, but rather by the overloading condition. The results of the reliability study indicate non-uniformity in the safety of steel bridges that are designed by the AASHTO LFD code. This is also true for AASHTO's LRFD code since it is not calibrated for the over loading condition. The value of the reliability index is a function of the compactness classification, method of design, beam spacing, span length, and section size. Graphs, 15 ref.
The investigation for the temperature dependence of fatigue crack-tip deformation for 1Cr-Mo-V steel. Jeong, C.Y., Lee, S.C. and Nam, S.W. J. Korean Inst. Metals Mater. (1995) 33, 1170-1175 For the theoretical discussion of the crack advance phenomena, many models have been suggested. However, most of them could not suggest the exact processes of the crack-tip region in the low cycle fatigue conditions, but only rough approximations in terms of LEFM for the damage of crack-tip region. Recently, Oh and Nam suggested a new model of crack advance and life prediction based on the damage formation in fatigue process zone, where the concentrated degradation of the material occurred with crack advance. In the previous studies a parameter of ots which is the term of correcting plastic zone size was suggested to be constant by many researchers in a fixed temperature. But the experimental results for 1Cr-Mo-V steel showed that oq is a function of temperature, and the microhardness test proved that the smaller the value of af in high temperature, the smaller the size of cyclic plastic zone (r0. Graphs, 16 ref.
Fatigue crack propagation in AI-Li 8090 alloy at room (300K) and cryogenic (77K) temperatures. Park, K.J. and Lee, C.S. Scripta Mater. (1996) 34, 215-220 The fatigue crack propagation behaviour of 8090 AI-Li alloy and the effect of microstructure on the cryogenic fatigue properties of this alloy were studied at room (298 K) and cryogenic (77 K) temperatures. Two different thermomechanical treatments were used to produce test specimens with two different microstructures that are referred to a ( 3 " - 3") and a'. It was found that the fatigue resistance of both the T' and (s'+ 3") microstructures was significantly enhanced at 77 K as compared to room temperature. The 3" microstructure represented higher fatigue resistance than the (S'+ 3") microstructure, especially in the low A K region at both 298 K and 77 K. In the 3" microstructure, the crack closure levels at 77 K were slightly lower than those at 298 K. Closure levels were significantly increased at 77 K in the (S'+ 3") microstructure. As a result, the crack closure levels for the two microstructures at 77 K were almost equal to each other. It was concluded that the excellent fatigue resistance of the 3" microstructure is attributable to the superior intrinsic nature of the 3" microstructure. Photomicrographs, graphs, 9 ref.
Cyclic deformation behaviour of a co-axial symmetrical copper bicrystal. Hu, Y.M., Wang, Z.G. and Li, G.Y. Scripta Mater. (15 Jan. 1996) 34, 331-336 The cyclic stress-strain curve (CSSC) of a copper single crystal oriented for single slip is well documented. It is characterized with a plateau of the saturation stress over a wide shear plastic strain range which extends from just below 10-4 almost to 10z. Most workers find the plateau saturation stress at room temperature to be in the range 27-30 MPa. Chert and Laird have reported that the plateau saturation stress is independent of orientations inside the stereographic triangle. The cyclic stress-strain curves of Cu single crystals oriented for double slip were recently reported. In contrast to the case of single slip, it was found that the saturation stress and the strain range of the CSSC plateau depended on the side of the stereographic triangle where the orientation was located. It is believed that the involvement of the secondary slip and the dislocation interaction are responsible for the feature of the CSSC plateau. During the last two decades, cyclic deformation of Cu polycrystals was also studied intensively and there have been prolonged arguments on if the CSSC of polycrystalline Cu contains a plateau. Bicrystals are widely used to demonstrate the grain boundary (GB) effects on plastic deformation behaviour of metals and alloys. In a series of reports to be followed we will investigate the effect of the slip continuity across GB, the strain incompatability at GB and the interaction of dislocation with GB on the cyclic deformation behaviour by using different types of Cu bicrystals. The cyclic deformation behaviour of a co-axial symmetriai bicrystal of which the component crystals are single-slip oriented was investigated. Graphs, photomicrographs, 17 ref. Dynamic strain aging influence on the cyclic behaviour of Zircaloy-4. Armas, A.F., Alvarez-Armas, L and Moseato, G. Scripta Mater. (1996) 34, 281-286 Dynamic strain aging is a very important factor in the plastic deformation of zirconium and Zr alloys and its aspects in uniaxial tensile tests have been the subject of several studies. Evidence of yield points in the stress-strain curve, appearance of plateaus or peaks in the flow stress-temperature diagram, discontinuous plastic flow, abnormal strain rate sensitivity have been reported. These anomalous mechanical behaviours were observed in these metals within the temperature range 473-823 K. Little attention, however, has been paid to the
Cyclic stress--strain response and dislocation substructure evolution of a ferrite--austenite stainless steel. Llanes, L., Mateo, A., Itargoyen, L., Anglada, M. Acta Materialia (1996), 44, 1143-1153 The hardening-softening response, the cyclic stress-strain behaviour and the evolution of dislocation structures of an AISI 320 ferrite-austenite stainless steel have been studied. Fatigue testing has been conducted under fully reversed total strain control and constant total strain rate. Detailed transmission electron microscopy studies have been carried out in order to determine the individual substructure evolution, as a function of increasing imposed strain amplitude, in each constitutive phase. In general, the cyclic response of the studied material may be described in terms of three different regimes within the plastic strain amplitude (%0 range investigated, i.e. from 2 × l0 S to 6 x 10-3; at %t < 10-4 the dominant cyclic deformation mechanisms are those correlated to planar glide of dislocations within the austenite which is the phase which carries a large part of the macroscopic strain in this first regime. On the other hand, at *p~ > 6 x 10-4 the dominant substructure evolution is observed inside the ferritic matrix. In this case, strain localization is enhanced, within the ferritic grains, through the development of veins into the wall structure. Such evolution induces a pronounced decrease of the cyclic strain hardening rate in the cyclic stress-strain curve. At %~ in between these values, the cyclic behaviour is characterized by a relatively high strain hardening rate and may be classified as a mixed ferritic/austenitic like behaviour. In this intermediate regime substructural changes are observed in both phases and the dislocation activity in each of them seems to be strongly influenced by their particular cyclic strain hardening behaviours. Finally, the results are analyzed and compared with data from the literature in terms of volume fraction and chemical composition of the constitutive phases. Graphs, photomicrographs, 31 ref.
Fatigue life prediction of fibre reinforced titanium matrix composites. Mal, A.K., Wang, P.C., Jeng, S.M. and Yang, J.-M. Acta Mater. (Mar. 1996) 44, 1097-1108 A micromechanical model was developed to predict the fatigue life of SiC fibre reinforced Ti matrix composites. The propagation of matrix cracks was modelled by calculating the stress concentration factor at the matrix crack tip in a fibre bridged center matrix crack. The residual stiffness was then predicted by using the partial crack shear lag model, and the post fatigue tensile strength was predicted by using the load carrying capacity of fibres proposed previously for brittle matrix composites. Finally, the catastrophic failure and fatigue life of the composite was determined by Monte Carlo simulation. An integrated computer simulation code was developed to simulate the evolution of fatigue damage, degradation of mechanical properties, and to predict fatigue life. The predicted matrix crack propagation rates, residual stiffness, residual tensile strength, and fatigue life were also correlated with experimental results. Graphs, photomicrographs, 30 ref.
Study of fractal characteristics of fatigued fracture surfaces at elevated temperature in Zircaloy-4 by secondary electron line scanning. Xiao, L, Gu, H.C. and Kuang, Z.B. Xiyou Jinshu Cailiao yu Gongcheng (Rare Metal Mater. Engng) (1995) 24 (2), 22-26 Fractal characteristics of fracture surfaces in Zircaloy-4 specimens fatigue at RT, 400 and 600°C have been investigated by means of secondary electron line scanning. It is believed that the range of validity of fractals for Zircaioy4 is associated with prominent fractographic features, i.e. with the grain size. The linear relationship of fractal dimension and fatigue lifetime is established. An explanation is given why the fractal dimension increases as the test temperature increasing for Zircaloy-4 at the same cyclic plastic strain amplitude. Graphs, photomicrographs, 10 ref.
Reliability of composite steel bridge beams designed following AASHTO's LlZD and LRFD specifications. Tabsh, S.W. Structural Safety (1996) 17, 225-237 Composite steel beam bridges designed following ASSHTO's load factor design (LFD) method and the newly developed load and resistance factor design method (LRFD) are proportioned for different loading conditions. They need to satisfy these conditions at maximum design load, an overloading condition, and fatigue load. The ultimate strength of compact composite steel beams is based on the fully plastic stress distribution. The capacity of non-compact beams is based on the yield or partially-plastic moment, depending on whether the beam violates all or few of the compactness or ductility requirements. In
353
this paper, the reliability for the ultimate flexural capacity limit state of composite steel beams is investigated. The structural reliability is measured in terms of the reliability index. The statistical data on strength are generated starting from statistics on material properties and using the Monte Carlo simulation method. Statistical data on load components are compiled from the available literature. The scope of the study covers a wide range of rolled beams, span lengths, beam spacings, and two yield strengths. The deterministic study showed that the design of composite steel beams is usually not governed by the maximum design load combination, but rather by the overloading condition. The results of the reliability study indicate non-uniformity in the safety of steel bridges that are designed by the AASHTO LFD code. This is also true for AASHTO's LRFD code since it is not calibrated for the over loading condition. The value of the reliability index is a function of the compactness classification, method of design, beam spacing, span length, and section size. Graphs, 15 ref.
The investigation for the temperature dependence of fatigue crack-tip deformation for 1Cr-Mo-V steel. Jeong, C.Y., Lee, S.C. and Nam, S.W. J. Korean Inst. Metals Mater. (1995) 33, 1170-1175 For the theoretical discussion of the crack advance phenomena, many models have been suggested. However, most of them could not suggest the exact processes of the crack-tip region in the low cycle fatigue conditions, but only rough approximations in terms of LEFM for the damage of crack-tip region. Recently, Oh and Nam suggested a new model of crack advance and life prediction based on the damage formation in fatigue process zone, where the concentrated degradation of the material occurred with crack advance. In the previous studies a parameter of ots which is the term of correcting plastic zone size was suggested to be constant by many researchers in a fixed temperature. But the experimental results for 1Cr-Mo-V steel showed that oq is a function of temperature, and the microhardness test proved that the smaller the value of af in high temperature, the smaller the size of cyclic plastic zone (r0. Graphs, 16 ref.
Fatigue crack propagation in AI-Li 8090 alloy at room (300K) and cryogenic (77K) temperatures. Park, K.J. and Lee, C.S. Scripta Mater. (1996) 34, 215-220 The fatigue crack propagation behaviour of 8090 AI-Li alloy and the effect of microstructure on the cryogenic fatigue properties of this alloy were studied at room (298 K) and cryogenic (77 K) temperatures. Two different thermomechanical treatments were used to produce test specimens with two different microstructures that are referred to a ( 3 " - 3") and a'. It was found that the fatigue resistance of both the T' and (s'+ 3") microstructures was significantly enhanced at 77 K as compared to room temperature. The 3" microstructure represented higher fatigue resistance than the (S'+ 3") microstructure, especially in the low A K region at both 298 K and 77 K. In the 3" microstructure, the crack closure levels at 77 K were slightly lower than those at 298 K. Closure levels were significantly increased at 77 K in the (S'+ 3") microstructure. As a result, the crack closure levels for the two microstructures at 77 K were almost equal to each other. It was concluded that the excellent fatigue resistance of the 3" microstructure is attributable to the superior intrinsic nature of the 3" microstructure. Photomicrographs, graphs, 9 ref.
Cyclic deformation behaviour of a co-axial symmetrical copper bicrystal. Hu, Y.M., Wang, Z.G. and Li, G.Y. Scripta Mater. (15 Jan. 1996) 34, 331-336 The cyclic stress-strain curve (CSSC) of a copper single crystal oriented for single slip is well documented. It is characterized with a plateau of the saturation stress over a wide shear plastic strain range which extends from just below 10-4 almost to 10z. Most workers find the plateau saturation stress at room temperature to be in the range 27-30 MPa. Chert and Laird have reported that the plateau saturation stress is independent of orientations inside the stereographic triangle. The cyclic stress-strain curves of Cu single crystals oriented for double slip were recently reported. In contrast to the case of single slip, it was found that the saturation stress and the strain range of the CSSC plateau depended on the side of the stereographic triangle where the orientation was located. It is believed that the involvement of the secondary slip and the dislocation interaction are responsible for the feature of the CSSC plateau. During the last two decades, cyclic deformation of Cu polycrystals was also studied intensively and there have been prolonged arguments on if the CSSC of polycrystalline Cu contains a plateau. Bicrystals are widely used to demonstrate the grain boundary (GB) effects on plastic deformation behaviour of metals and alloys. In a series of reports to be followed we will investigate the effect of the slip continuity across GB, the strain incompatability at GB and the interaction of dislocation with GB on the cyclic deformation behaviour by using different types of Cu bicrystals. The cyclic deformation behaviour of a co-axial symmetriai bicrystal of which the component crystals are single-slip oriented was investigated. Graphs, photomicrographs, 17 ref. Dynamic strain aging influence on the cyclic behaviour of Zircaloy-4. Armas, A.F., Alvarez-Armas, L and Moseato, G. Scripta Mater. (1996) 34, 281-286 Dynamic strain aging is a very important factor in the plastic deformation of zirconium and Zr alloys and its aspects in uniaxial tensile tests have been the subject of several studies. Evidence of yield points in the stress-strain curve, appearance of plateaus or peaks in the flow stress-temperature diagram, discontinuous plastic flow, abnormal strain rate sensitivity have been reported. These anomalous mechanical behaviours were observed in these metals within the temperature range 473-823 K. Little attention, however, has been paid to the