摘要:

Abstract—Fifty seven short fatigue cracks in the Ni‐base superalloy AP1 have been examined, to ascertain how the paths taken by growing fatigue cracks are determined. The observations were made on the surface of a smooth specimen, and on the exposed fracture surfaces. Three dimensional reconstructions of the vulnerable microstructures in the vicinity of the cracks were produced. Initiation occurred in mode II, with the lines of intersection of the initiation sites with the specimen top surface orientated at approximately 45° to the tensile axis. These initiation sites developed in slip bands which crossed a large grain and at least one other grain via a grain boundary with a low angle of misorientation. ‘River markings’ on one of the initiation facets, indicated that the crack first opened from the top centre of the initiation grain. Subsequent to initiation, the growth paths of these cracks are related to the misorientations of the grains and the progress of the cra

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00768.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—A fretting fatigue crack growth model is proposed accounting for the effects of tribological parameters of the contacting materials and the biaxiality of contact together with bulk stresses, upon fretting fatigue crack growth rate and direction of growth in the fretting‐zone subsurface layers. Based on this model a new technique is developed to determine fatigue life and predict the fatigue limit in an aluminium alloy, AMg6N, and a titanium alloy, VT9, under fretting conditions. For the above cases, fretting fatigue crack growth behaviour predicted by the proposed model is in good agreement with the experimental resu

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00769.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Basic diagrams of the cyclic crack growth resistance of two of the most investigated titanium alloys, namely Ti‐6A1–4V and Ti‐6A1–6V‐2Sn, are presented. Diagrams are plotted for, in‐air, distilled water and 3.5% NaCl solution, which are necessary for lifetime calculations of structural elements made of these metals. The dependency of cyclic crack growth resistance on the yield strength is established. It is shown that cyclic crack growth resistance of titanium alloys in corrosive environments is determined not only by the stress‐strain state but also by the electrochemical conditions at the corrosion fatigue crack tip, which for aqueous environments can be characterized integrally by the hydrogen index of the environment and the electrode potential of the metal. Therefore, cyclic corrosion crack growth resistance testing should be performed under constant electrochemical conditions at the corrosion fatigue crack tip or these conditions should be taken into account. A new method of plotting the basic cyclic corrosion crack growth resistance diagrams of titanium alloy

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00770.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Isothermal and thermal‐mechanical strain fatigue tests were conducted in air on representative service alloys; a 1 CrMoV steel, and two batches of 316 stainless steel. Data was obtained for thermal‐mechanical in‐phase and out‐of‐phase cycles, and also for isothermal tests at the maximum, minimum, and mid‐temperature of the thermal‐mechanical cycle. Dwell periods were also incorporated in the cycle to assess their effects.A comparative evaluation has been made on the basis of the materials' cyclic stress response. In general, the results have shown that the thermal‐mechanical strain cycling tests cause a large increase in stress range over those tested under isothermal conditions at maximum temperature. In addition, mean stress and strain offsets were developed in continuous cycle thermal‐mechanical tests, whereas negligible offsets occurred in isothermal tests.It appears that the response of the materials could not always simply be explained by reference to the temper

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00771.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Thermal‐mechanical cyclic strain tests were carried out under in‐phase and out‐of‐phase conditions on a ferritic 1 CrMoV steel in the temperature range 315 to 565°C and two different batches of a 316 stainless steel in the temperature range 400 to 625°C. The results were compared with isothermal data.In general, lives for in‐phase thermal‐mechanical tests were lower than for equivalent isothermal tests. This was substantiated by metallographic examination which indicated greater intergranular damage for the in‐phase specimens. The addition of a tensile dwell to the in‐phase condition caused even greater differences.Three life prediction methods were used: the ductility exhaustion and a modified strain range partitioning approach gave reasonable estimates of life, whilst the linear life fraction method produ

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00772.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Based on the assumption that normalized Kitagawa‐Takahashi diagrams for different materials are the same, a unified model for microstructurally small fatigue crack and physically small fatigue crack growth rates was developed to describe their behaviour under different fatigue stress ranges. The stress‐sensitive blocking effect of microstructural barriers to small fatigue crack growth is satisfactorily simulated by the model. Incorporated with the materials fatigue limit and microstructural barrier spacing, this model can be easily used in the prediction of small fatigue crack lifetime. Small fatigue crack growth rates of previous experimental studies in 7075‐T6 Aluminium alloy and HT60 steel under different stress ranges are in an envelope between two boundary prediction curves corresponding to the largest and smallest stress ranges applied in the experiments. Problems concerning model accuracy and model application are also discussed in the presen

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00773.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The local stress/strain approach has been used to predict the fatigue lives of notched composite components. The method was based on a microstress analysis and the application of a multiaxial fatigue parameter incorporating the alternating strain components on the critical plane. This parameter was able to correlate the fatigue lives obtained under a variety of multiaxial loading and geometrical configurations, enabling a generalized fatigue life curve to be determined on the basis of limited experimental data.The ability of the multiaxial fatigue parameter to relate the fatigue behaviour of composites was illustrated by predicting the locations of crack initiation sites in a unidirectional silicon carbide fibre reinforced titanium plate containing a circular hole tested under constant amplitude cyclic loading. The same approach was also successfully employed to predict the fatigue lives of graphite reinforced epoxy composite tubes with circular holes tested under several combinations of cyclic tension and torsio

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00774.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Mode I fatigue crack growth has been studied in notched specimens of 7017‐T651 aluminium alloy subjected to fully compressive cyclic loads. The specimens were first subjected to a deliberate compressive preload which causes plastic deformation at the notch tip. On unloading, this region developed a residual tensile stress field and on subsequent compressive cyclic loading in laboratory air, a fatigue crack was nucleated at the notch and grew at a diminishing rate until it stopped. The final crack length increased with an increase in the value of the initial compressive preload and with an increase in the negative value of the applied cyclic mean load. To gain a better understanding of crack growth in residual stress fields, the magnitude and extent of residual stress induced from compressive preloads have been analysed. This was achieved when extending the notch by cutting while recording the change in the back face strain. From residual strain models it was found that the fatigue crack growth was confined to a region of tensile cyclic stress within the residual stress field. The effective stress intensity range was investigated at selected mean loads and amplitudes, for correlating purposes, using both the compliance technique and by invoking the crack growth rate behaviour of the alloy. Finally, a brief discussion of the fracture morphology of cracks subjected to cyclic compression is presen

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00775.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—There is a critical stress rateKcfor each of the three ZrO2ceramics tested. Fracture is controlled by the materials polycrystal fracture toughness,Kcp, if the stress rate is less thanKc. Otherwise, fracture is controlled by the single crystal fracture toughness,Kcs. The crack growth parameters determined by dynamic fatigue experiments can only represent macrocrack growth behaviour although the fracture of specimens in experiments originates from small surface flaw

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00776.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—In this study, both sinusoidal wave loading and rectangular pulse (impact) loading are applied to a sample of rail steel in order to compare the growth rates for a surface fatigue crack. The results show that the rectangular pulse (impact) loading gives a crack growth rate on average 5 times that of the sinusoidal wave loading but can be almost 100 times in some instances. There are distinct differences between the fractograph patterns under the two modes of loading. The fractograph under sinusoidal wave loading clearly exhibits the pearlite structure of the material but under impact loading this microstructure is not revealed; only a quasicleavage pattern is observed. Analysis of the experimental fatigue crack growth data indicated that the surface fatigue crack growth rate behaviour could be described by the Paris‐type relations

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00777.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY