摘要:

Abstract—Fracture toughness tests were performed in the ductile‐brittle transition temperature range using 110 specimens of the three‐point bend and CT types. Probabilistic characteristics of fracture toughness and cleavage crack initiation sites were analysed in detail, together with the fibrous crack shape, from which the plane strain region in the specimen was deduced. The criterion for obtaining plane strain at the mid plane of the specimen was established as:B≤ 0.004{Kc(J)/σy}2+ 0.01. The thickness effect of cleavage fracture toughness for the specimen satisfying this equation is mainly caused by the statistical distribution of the weakest points ahead of the crack front (the Weibull volume

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01255.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—A series of experiments have been conducted on cruciform specimens to investigate fatigue crack growth from circular notches under high levels of biaxial stress. Two stress levels (Δσ1= 380 and 560 MPa) and five stress biaxialities (λ=+1.0, +0.5, 0, −0.5 and −1.0; where λ=σ2/σ1were adopted in the fatigue tests in type 316 stainless steel having a monotonic yield strength of 243 MPa. The results reveal that fatigue crack growth rates are markedly influenced by both the stress amplitude and the stress biaxiality. A modified model has been developed to describe fatigue crack growth under high levels of bia

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01256.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Long‐crack (LEFM) fatigue threshold, Δ,K0values are predicted which include the commonly observed effects of stress ratio,R, and yield strength, σy. It is assumed that the yield strength effect on threshold is indirectly related to grain size and so is not an independent variable. Two intrinsic thresholds of a material are invoked to explain the observations of higher ΔK0values and a higherR‐ratio sensitivity of ΔK0in low strength materials compared to high strength materials. The paper shows that ΔK0is almost independent of both yield strength and stress ratio at high values of the stress ratio. Quantitative relations are developed to estimate curves of (i) ΔK0versusRand (ii) ΔK0versus σy. These curves show good agreement with experimental data for steels and aluminium alloys. A method is presented that may be used as an alternative procedure for obtaining quick and conservative estimates of ΔK0for desig

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01257.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—A simple approach to predict the fatigue crack initiation (FCI) life of notches at low temperatures is developed. The stress cycle to initiate a 0.25 mm crack at a notch tip is presented as a function of an equivalent stress amplitude. The results of the study indicate that the FCI life of an aluminium alloy increases with decrease in temperature and the effect of temperature on the FCI resistance can be predict in the form of an FCI coefficientCand the FCI threshold. The coefficientCis the parameter controlling FCI resistance in the low cycle fatigue region and it can be calculated from the elasticity modulus and the strain hardening exponent. The threshold is the parameter governing FCI resistance in the high cycle fatigue region and its value depends mainly upon the endurance limit. The temperature‐ dependence of the endurance limit can be predicted by a thermal activation model. By means of this approach, the fatigue crack initiation life at low temperatures can be predicted from the material tensile properties without any additional low temperature fatigue tests and without any empirical modification so long as the endurance limit of the metal at room temperature is predetermined. The results suggest that this approach is applicable to other aluminium all

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01258.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Torsion fatigue tests were conducted at room temperature on plain specimens of a 1.99% NiCrMo steel subjected to various combinations of mean and alternating shear stress. The growth behaviour of both microstructurally short cracks (MSC) and physically short cracks (PSC) has been studied. Mean shear stress was found to play a fundamental role in promoting both MSC and PSC cracks. The empirical Brown‐Hobson model, relating the alternating shear stress (or strain) to the short crack growth rate, is modified to incorporate the influence of mean shear stress in both the MSC and PSC growth regimes. The investigtion of the two crack growth equations leads to a satisfactory prediction of the fatigue endurance curves determined for a variety of mean and alternating shear stress lev

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01259.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The results of investigations into fatigue crack behaviour of laser‐hardened, medium‐carbon steel specimens under reversed bending (R= ‐1) are presented. Characteristic features of crack behaviour, such as crack source location, temporary crack arrest at the border between laser tracks and the matrix material, and discontinuous crack growth in the laser tracks are discussed. In order to explain the sites of primary crack sources, results of residual stress measurements are included as well as analytical descriptions of these stress distributions as a function of sample depth. A mechanism of cracking has been established on the basis of fractographic analyses of fracture s

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01260.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The WPS effect has been shown to be beneficial in increasing the lower shelf fracture toughness of A533B weld metal for both the load‐unload‐cool‐fracture (LUCF) and the load‐cool‐fracture (LCF) cycles. The LCF cycle gives a greater apparent increase in fracture toughness than the LUCF cycle but only a small increment of load in the lower shelf region is needed to propagate failure compared with a much increased fracture load which is required in the LUCF case. Models predicting the increase in apparent fracture toughness by superposition of the stress and strain distributions from each step in the prestress cycle are shown to be non‐conservative for failures occurring in the lower shelf brittle regime. There is evidence for the operation of a “microcrack blunting” mechanism, but the extent to which it contributes to the WPS effect is small. Stress‐relief heat‐treatments after prestressing remove nearly all the beneficial effects of WPS. Residual stresses clearly play an important role in the WPS phenomenon, and the models successfully predict experimentally observed trends. Prestressing “deactivates” failure initiation from the larger inclusions in the weld metal. This however does not affect the intrinsic fracture toughness of the material. Fracture in this weld metal, where initiation sites (inclusions) abound, appears to be a co‐operative process, and fracture is controlled by inclusions of the mean (and hence most plentiful) diameter rathe

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01261.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—In order to calculate the stress concentration caused by shot‐peening dents, three simplified models, namely a one‐pit model, a seven‐pit model and a pit‐loop model, are proposed in this paper. By using a finite element program for automatic dynamic incremental non‐linear analysis, the stress concentration coefficients based on these models are calculated for different pit parameters and different stress fields. When considering the stress concentration and residual stress field produced by shot peening, a modified Goodman formula is proposed and used for forecasting the fatigue strength of peened specimens having the fatigue sources at the surface. The forecasted results were verified by peening followed by fatigue tests on

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01262.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The possibility of using specially prepared single crystals as indicators of fatigue damage is outlined. Results are described of an analysis of deformation patterns developed in the single‐crystal indicator surface, under fatigue and static loading. It is shown that the density and direction of deformation bands correlate with the number of loading cyc

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01263.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1992.tb01254.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY