摘要:

Abstract—Near threshold fatigue crack growth under mixed‐mode loading and elastic plane‐strain conditions has been studied in 316 stainless steel in laboratory air at room temperature. Particular emphasis was placed on the influence of the mode II component. Crack growth from the starter crack, although initially coplanar, branches to be perpendicular to the maximum normal stress. However the threshold for the branched crack growth is controlled not only by mode I displacement, but also by the mode II component. Upper and lower bound curves are obtained for the threshold condition and discussed in terms of crack tip reversed plastic deformation, crack surface rubbing and oxide‐induced closure. A theoretical method for predicting the lower bound curve is proposed and compared with the maximum normal stress and strain energy density criteria. The new theory shows the best agreement with experimental results, giving a safe prediction for design p

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1982.tb01220.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Starting from a knowledge of inhomogeneous dislocation structures observed in cyclically strained metals, a model for cyclic straining is developed. A distribution of volumes with different internal critical flow stresses is assumed characterized by a probability density function. A generalization which includes a thermally activated component of the flow stress is derived assuming that the saturated microscopic effective stress, μes, is equal in all volumes. The relations to obtain the probability density function from experimental data are derived. The theory yields the macroscopic internal stress, σeand the macroscopic effective stress, σe, along the hysteresis loop. Experimental observations on cyclically strained metals can be explained using this statistical th

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1982.tb01221.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Hysteresis loops of a low carbon steel measured at various temperatures and plastic strain amplitudes are analysed using the statistical theory of the hysteresis loop. It is shown that the parameters of the statistical theory characterizing the saturated hysteresis loop, i.e. the probability density function and effective saturated stress, can be obtained from experiments. The probability density function is influenced mainly by strain amplitude; the effective saturated stress mainly by temperatur

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1982.tb01222.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—A stress‐dip technique for the determination of an effective stress in cyclic straining has been improved. The critical stress drop, ΔσC, for which zero strain relaxation rate is observed can be obtained from experiments. The significance of this quantity is discussed in terms of the statistical theory of the hysteresis loop. The measurements of the effective stress at different temperatures and along the hysteresis loop are reported. The observed asymmetry of stress in cyclic straining is ascribed to asymmetry of effective s

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1982.tb01223.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Fatigue thresholds and crack growth rates were studied in the experimental alloy, Ti—5Al—4Mo, as a function of temperature, grain size and hydrogen concentration. Deformation is confined to planar slip bands along which fracture occurred at low hydrogen concentrations. Hydrogen accelerated crack growth rates at various combinations of temperature, grain size and hydrogen with a corresponding change in fracture from “cleavage’ to interface phase fracture. In addition, hydrogen was found to promote interface phase formation. It is proposed that stress‐assisted hydrogen accumulation increases the interface phase hydrogen concentration which reduces the interface phase fracture stress. This process depends on the local stress andβ‐phase hydrogen concentrations, temperature and the time under load. At 340 K, hydrogen had a relatively small effect on crack growth due to a change in slip behavior with increased hydrogen

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1982.tb01224.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Room temperature fatigue crack propagation in a sintered tungsten alloy was studied. The fatigue crack growth rates were found to be identical for the material in the sintered and forged and as sintered conditions. The propagation rates are slower when compared with other metals due to the relatively high Young's modulus of tungsten. The value of the exponentmin Paris' power law equation was found to be 12 which is higher than for most metals. This was ascribed to the activity of a cleavage mechanism through some of the tungsten grains along with the ductile decohesion fatigue mechanis

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1982.tb01225.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—It was found in a previous publication that stress fields around notches are quantitatively very similar, if the peak stress at the notch root (σpeak) and the notch root radius (ρ) are the same. As a consequence, small cracks (lengthl) should have the same stress intensity factor, if σpeakandρare similar. This implies that the geometry factorCinshould primarily depend onl/ρonly, and not on other dimensions. Available data on calculatedKvalues was analysed, which confirmed the similarity concept. An equation forCas a function ofl/ρwas obtained. It was shown thatK‐values calculated with this equation are an accurate approximation for the stress intensity factor of small cracks a

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1982.tb01226.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The use of d.c. electrical potential methods is described for the monitoring of Mode III (anti‐plane shear) fatigue cracks in circumferentially‐notched cylindrical specimens subjected to cyclic torsion. Calibration of potential change with crack depth and optimization of current input and potential measurement probe locations are achieved using simple finite element procedures, and are verified experimentally. The use of the method for Mode III crack growth studies is described in the light of crack face electrical shorting problems associated with torsional crack cl

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1982.tb01227.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The present work emphasizes the need to understand the processes involved in fatigue–creep interactions before reliable life predictions may be sensibly made. In particular, the simultaneous interaction involving a strain controlled cycle with a dwell period at maximum tensile strain is analysed and the accumulation of fatigue–creep damage computed in terms of strain range, extent of dwell and microstructure. Dominant failure modes are thus identified and the findings are used to explain the apparently different failure mechanisms previously reported for a 1Cr–Mo–V alloy steel and a Type 316 stainless steel. Due to lack of data overall mapping of regimes of dominance is not possible, but in cases where a single mechanism prevails throughout the duration of dwell accurate lifetime prediction may be

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1982.tb01228.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY