摘要:

Abstract—Creep‐fatigue crack growth behaviour of a Type 304 stainless steel under four types of reversed loading patterns (P‐P, P‐C, C‐P and C‐C) was investigated and the results are discussed in the light of fracture mechanics and fractography. The crack growth rate for all of the four types of loading was successfully correlated in terms of the cyclic integral range λJ.It was unnecessary, for practical purpose, to divide Ay into a fatigue component, λJf, and a creep component, λJc, as has been done elsewhere. The transition of the correlating fracture mechanics parameter from fatigue to creep was not necessarily associated with the fracture morphology. This was related to the longer transition hold time in morphology in C‐C type loading compared to C‐P type loading, and was attributed to recovery of grain boundary sliding during the compression hold in th

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00638.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—In this paper the line‐spring model (LSM) developed by Rice and Levy is used to obtain an approximate solution of the stress intensity factor for a partial circumferential, externally cracked tube under axial tension and four point bending. The calculation is based on the work done by Delale and Erdogan for cylindrical shells containing a circumferential or an axial semi‐elliptical, part‐through crack. The range of utility of their analysis is enlarged to thicker wall tubes with nonelliptic and longer part‐through circumferential cracks. Values ofK1calculated by the LSM are compared with those from a finite element analysis for remote tensile loading and bending cases, which shows fairly good agreement. The calculations are also applied to a fatigue crack growth test in a tube in four point bending to correlate the da/dNv

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00639.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—This paper is concerned with various problems related to laboratory experimental verification of fatigue endurance under random loading. Based on statistical characteristics of stationary and non‐stationary operating random processes (probability density function and/or power spectral density, transition probability densities) it is shown how to design real time simulation algorithms that are further used to create inputs of computer controlled electrohydraulic loading systems. The corresponding fatigue tests (strain or stress constrolled) produce endurance curves that can be plotted in various coordinates (peak or RMS values vs fictitious number of cycles or time to failure) offering non‐identical conclusions and qualitative interpretations. Some examples of the influence of simulated random process probability density function and/or power spectral density on the resulting fatigue endurance are presented and also certain suggestions concerning prospects for random load fatigue tests are summa

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00640.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The results of fatigue tests on specimens containing parallel offset and parallel collinear configurations of multiple non‐coplanar cracks are presented. The fatigue growth of parallel collinear cracks is shown to be significantly affected by crack‐tip shielding and parallel offset cracks are shown to grow almost independently before their adjacent tips overlap. Subsequent growth in the region of overlap results in coalescence which begins when the deviating crack tips come into contact below the surfaces of the specimens. Simplified predictions of the propagation of offset non‐coplanar semi‐elliptical cracks are also presented and their implications for the prediction of fatigue lives in structures containing offset coplanar cracks are

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00641.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—It is well known that the fatigue strength of a thick‐walled cylinder is enhanced by autofrettage. However, this does not appear to have been explained from fracture mechanics. The present paper shows that two uncertainties arise when this is attempted. Firstly, the distribution of residual stress resulting from the autofrettage pressure must be estimated and secondly a realistic stress intensity factors for subsequent fatigue cracking must be defined. A number of available stress intensity solutions are modified with the author's predictions to the residual stress following an elastic‐plastic autofrettage pressure in a closed cylinder of hardening material. A comparison with experiment has enabled the various approaches to be appraised. It is shown that a modified stress intensity factor of Bowie and Freese is most consistent with the propagation fatigue life observed in autofrettaged cylinders provided their solution is adapted to account for the propagation of a semi‐elliptical crack front in the presence of residual stress. OtherK1estimates appear to lead to dangerously optimistic predictions particularly within the range of fluctuating pressure where failure occurs between 105and 106cycles. The contribution to fatigue failure from initiation cycles is expressed as a power function of the observed life for cyclic pressures in the region of the fatigu

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00642.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Fretting fatigue tests of high tensile roping steel, 1.5 mm in diameter, 1770 MPa grade, were carried out in air and seawater. S‐N curves were completed in both the environments and under cathodic protection at‐850 mV (SCE). The crack growth curves were determined at three different alternating stress levels. The coefficients of friction between the specimen and the fretting bridge, where the macro‐slip occurred, were found to be 0.63 in air and 0.38 in seawater. The prediction of the fretting fatigue lives were made according to the Tanaka—Mutoh model, where the frictional force was taken into consideration. The predicted fatigue life agreed well with the experimental results in air but in seawater the prediction defined a much higher fatigue limit compared with the experimental results which showed the absence of the fatigue limit. These results indicate that the method of removing the electrochemical component is very promising for the prevention of fretting fatigue failure in

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00643.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The fatigue crack growth behavior in a titanium aluminide (Ti3Al) alloy under thermo‐mechanical loading as well as under elevated temperature conditions was investigated. The thermal mechanical fatigue crack growth behavior appears, in a general sense, to follow the same trends observed in similar data obtained in tests on nickel‐base superalloys. However, crack growth in Ti3Al appeared to be influenced by blunting of the crack tip due to creep in addition to a cyclic‐dependent contribution together with time dependent or environmental enhanced degradation. This complex phenomenon in Ti3Al is unlike that in nickel‐base superalloys where crack growth was found to be due to a linear combination of cycle and time dependent contributions. Thus, the linear cumulative modelling technique is not applicable to the tes

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00644.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—A SAE1010 plain carbon steel and a SAE945X HSLA steel were cold rolled to various thickness reductions. Centre notched specimens were tested under stress control at a stress ratio of—1. The effect of loading direction on the fatigue strength was examined. The notched specimen fatigue strength was only slightly increased by cold rolling, since two opposing factors: the smooth specimen fatigue strength and the notch sensitivity, were increased by cold rolling. The notched specimen fatigue strength in the transverse direction was approximately the same as that in the longitudinal direction. An empirical equation and equations derived from fracture mechanics and Neuber's rule were applied to predict the fatigue notch factor for the sharp and blunt notch geometries examined. A reasonable agreement between the predictions and the experimental results was observed for the sharp notches. For the blunt notches, the predicted fatigue notch factors were conservat

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00645.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The microstructure, deformation behavior, and crack growth relationships have been examined for an Al‐5Cu‐1.3Li‐0.4Mg‐0.4Ag‐0.1Zr alloy. TEM of deformed samples revealed that the T3 temper deformed via highly localized planar slip due to the presence of small, coherent precipitates (GP zones and δ') while the T8 temper deformed homogeneously with T1as the strengthening phase. Both constantKmaxand constantR(0.1) fatigue curves were generated for the T3 and T8 tempers in both the T‐L and L‐T orientations. The T3 temper exhibited high closure levels and an apparent intrinsic threshold of 2 MPa m1/2. The T8 temper did not exhibit high closure levels, and the intrinsic threshold was determined to be 1.3 MPa m1/2. Weldalite‐T3 has a strength comparable to 2024‐T3 but has a higher resistance to fatigue crack growth, whereas Weldalite‐T8 has a much higher strength and a comparable fatigue crack growth

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00646.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The thermal‐mechanical fatigue behaviour of a cast cobalt based superalloy, MAR‐M 509 was investigated. Hollow smooth specimens were submitted to temperature cycling between 600 and 1050°C. The mechanical strain vs temperature cycle shows a diamond shape with peak strains at intermediate temperatures. The stress‐strain behaviour as well as fatigue life curves are reported. A significant part of total life is spent in crack initiation. Comparison with isothermal low cycle fatigue was made at the temperature where peak strains occurred. Isothermal low cycle fatigue life to crack initiation was shown to give a conservative estimate of thermal mechanical fatigue life provided extra strains due to differences in thermal expansion coefficients of the oxide scale and base alloy were taken into

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00647.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY