摘要:

AbstractRetardation in the fatigue crack growth rate following the application of a single peak overload in a fatigue loading sequence has been studied for a low carbon structural steel. Tests have been performed at load ratios ofR= 0.2 andR= 0.6 at a baseline stress intensity range, ΔKb, corresponding to fatigue crack growth rates in the Paris regime. Single peak overloads were applied at a crack‐length to specimen‐width ratio ofa/W= 0.5. At the load ratio ofR= 0.6 monotonic or “static” fracture modes were observed upon application of the overload, and these produced an immediate increase in growth rate. A subsequent retardation is attributed to the presence of a residual compressive stress field ahead of the crack tip. A similar retardation was observed at a load ratio of 0.2. The importance of residual stress was established by performing stress relieving experiments. In addition, removal of the surface deformation after an overload by machining “T” sidegrooves resulted in an extended transient, which could not be explained by residual machin

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00700.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractCyclic tests, with and without dwell periods, were carried out at temperatures of 750, 850 and 1000°C on a cast nickel base super alloy MAR M002. The cracking mechanism was mainly transgranular in the continuous cycle tests. The incorporation of a tensile dwell had little effect on life compared with the continuous cycle data though there was a significant amount of additional internal intergranular cracking. However, an unbalanced compressive dwell at 750 and 850°C caused a shorter life with transgranular cracking: only at 1000°C was the life not reduced. Prediction of life was attempted by means of what were thought to be three of the more promising methods, i.e. ductility exhaustion, crack propagation and hysteresis energy. However, these did not appear to be accurate, and it is clear that more appropriate base line data are requir

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00701.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIn this study, the effects of stress ratio, microstructure and fracture surface roughness on the fatigue properties of a two‐phase cast stainless steel were investigated. This behaviour was examined by means of the fracture mechanics approach and fractography. The fatigue crack growth rate decreased with decreasing stress ratio. The stress ratio markedly influenced the fatigue crack growth rate as ΔKapproached the ΔKthvalue. The roughness of the fracture surface was greater in the as‐cast material than in the heat‐treated material. Analysis of the crack growth data using ΔKeffshowed that the effect ofRratio could be explained but that the effect of microstructure on crack growth rate c

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00702.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper presents a new model to predict the high temperature, intergranular crack growth rate behavior in alloy 718 at 650°C. The model is based on the concept that the crack tip oxidation‐fatigue damage is a nonlinear process governed by the chemical‐mechanical interaction along the grain boundary fracture path at the crack tip. A concept of two‐stage oxidation mechanism was used here. This mechanism depends on the rate of formation of the chromia layer in relation to the build‐up of other oxide types at the crack tip. The saturation of the Cr2O3build‐up signifies the occurrence of the oxide passivation effect. The determination of the amount of Cr2O3depends on the amount of both oxygen diffused along the affected grain boundary and chromium transported via a mobile dislocation network. Here, both the grain boundary and effective dislocation pipe are treated as short‐circuit diffusion paths along which the diffusion process can be described using Whipple's solution. The model yields sufficient information to correlate the amount of Cr2O3with the reduction in the grain boundary ductility within the affected oxide zone. The grain boundary ductility is balanced by the effective strain at the crack tip resulting from the external loading. This balance defines the fracture criterion of the model and permits the calculation of the crack advance per cycle which is the ultimate goal

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00703.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIn previous work by the authors, a quantitative model based on a two‐stage oxidation mechanism was developed to describe the oxidation‐assisted crack growth behavior in alloy 718. This model is used here to predict the crack growth rate in this alloy at 650°C for two different loading conditions: one is a continuous cycle with a hold time duration of 300 s imposed at minimum load, the other is a continuous cycle without a hold time duration. The results obtained from applying the model to these loading profiles were then compared with those obtained experimentally. Good agreement was observed between the two data sets. Details of the model calculations are discussed, and suggestions to further extend the model capabilities are made in this p

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00704.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe fatigue crack propagation behaviour of polycarbonate and glass fibre reinforced polycarbonate was studied in hot distilled water. The effects of temperature, distilled water and glass fibre content on fatigue crack growth rate were determined. In distilled water at 333 K, the fatigue crack growth rate decreased with increasing glass fibre content. A melting was observed of the adhesive bond between the glass fibres and the matrix. It was evident that the fracture morphology closely relates to the fatigue crack growth rate which depends on the ΔKparameter rather than theKmaxparameter when the materials are tested in hot distilled water

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00705.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper presents results from an experimental programme to study size effects inJ‐Rcurves. Results are presented from unloading complianceRcurve tests on different sized single edge notch bend specimens of nickel aluminium bronze and compared with previously publishedRcurve data on a Ti3A1‐2.5V titanium and an HY 100 steel alloy. The crack growth resistance was measured in terms of the standard fracture resistanceJ, Jcorrected for crack growth and theJmodified parameter proposed by Ernst. It was observed that following a region of size independence small specimenJ‐Rcurves could fall either above or below the large specimen curve. It was found that although the limit toJcontrolled crack growth could be extended the limit is not unique but dependent on material

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00706.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe fretting fatigue behaviour of several alloy steels is reported in this paper. Fretting fatigue experiments were conducted on flat fretting junctions in axial tension at a stress ratio of 0.1. In all cases the same materials were fretted against each other. The fretting fatigue strength at a slip amplitude of 45 μ is rather insensitive to the hardness of the materials. The fretting fatigue strength at the slip amplitude of 10 μ increases with increase in hardness. As the slip amplitude increases the fretting fatigue life of 3SCrMo steel decreases, the depth of wear scars increases and the wear damage becomes more severe. The reason for similarity of fretting fatigue to the fatigue of notched specimens is that the effect of wear scars is similar to that of notche

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00707.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1991.tb00699.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY