摘要:

AbstractCrack propagation rates have been measured in two aluminium alloys under cyclic and static loading, in air, and in salt solution. On the basis of these results, a model is proposed, whereby corrosion fatigue crack propagation may be interpreted in terms of fatigue and static stress corrosion characteristics. Two interacting processes are operative; one is “stress assisted dissolution”, which tends to inhibit mechanical failure by crack blunting and microbranching. The other is “environment assisted fracture” which occurs too rapidly for dissolution to occur. One or other of these processes is always observed to be dominant. This proposal is discussed in relation to other recent models for corrosion fatigue cracking. The effects of frequency, waveform and mean stress variations are also con

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1979.tb01326.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractA study was made on the effects of stress rise timeT1, maximum stress holding timeT2, stress decreasing timeT3and minimum stress holding timeT4of a cycle on fatigue crack growth for a low alloy carbon steel in 3% NaCl solution. Measurements of the effective stress intensity range ratioUand observations of crack tip response were performed to clarify the causes of waveform effects.The results were summarized as follows;T1had a strong accelerating effect due to corrosive dissolution of the fresh surfaces of the crack which were formed duringT1. The crack growth rate was enhanced asT1increased and reached a constant value (about 3 times that in air) afterT1= 10s. The crack growth rate at low ΔK, however, decreased asT1increased more thanT1= 1 s.T2,T3andT4decreased the crack growth rate. The extent of decrease not only depended on the period ofT2(orT3,T4), but also on ΔKandT1. A previously derived crack growth law which considered waveform and frequency effects, is also valid to a first approximation for the present result

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1979.tb01327.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThis paper presents a simple algorithm of hysteresis loop counting to make on‐line data processing much easier. It involves a modification of the range pair counting method and the rain flow method and yields practically the same result as these methods. In addition, the applicability of the present method to cumulative damage estimation is examined in experiments on fatigue crack growth rates under stationary random loads and low cycle fatigue lives under stationary random loads together with non‐stationary random loads such as seismically excited lo

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1979.tb01328.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractResults of an elastic–plastic finite element analysis of crack closure effects under mode I Spectrum loading are presented. Various factors that cause crack growth acceleration or retardation under low‐to‐high, high‐to‐low, and single overload cyclic loadings are

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1979.tb01329.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractFatigue crack closure in air and vacuum was studied under constant amplitude loading in tension, on compact tension specimens of the aluminium alloy 7175. The experimental techniques used were: (1) the compliance method in air, and (2) the compliance method and the potential drop technique in vacuum.From the test results in vacuum a correspondence was established between the results obtained using the two different techniques which led us to propose a closure model.AsRincreases, crack closure decreases to attain a minimum value forR>Rc. The value ofRcdepends on the specimen thickness and is greater in vacuum.Crack closure is more pronounced in vacuum than in air which can be partly associated with a larger plastic zone of greater work hardness.

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1979.tb01330.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractDisplacements in the region very near to a fatigue crack tip have been observed using a stereoimaging technique. The results of changing the minimum/maximum stress ratio, for a single overload and a single underload are given for a powder metallurgy aluminum alloy. Material motions near the crack tip are complex and depend on the loading characteristic. Compressive strain fields near the crack tip in the unloaded state were found to be highly dependent on load characteristic due to variation in reversed plasticity.

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1979.tb01331.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractA method for quantifying the effect of plane stress, plane strain, mean stress and pre‐strain on fatigue crack propagation rates in plates of different thicknesses is proposed. Experimental verification was carried out on mild steel plates of 0·2, 0·4, 0·6, 0·8, 1·0, 1·2 and 1·4 mm thick specimens. The conflicting effects of variations in stress intensity factors along the crack front and changes from plane stress to plane strain conditions along the crack front are also d

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1979.tb01332.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe influence of stress ratio and the loading frequency on fatigue crack growth rates in BS 4360–50C steel was investigated in laboratory air.Fatigue crack growth tests were performed on compact tension specimens (CTS) made in two thicknesses 12 and 24 mm. Tests were conducted at two frequencies of 0·25 and 30 Hz, applying a stress ratioRvarying from – 0·7 to 0·7. The results were analysed using the linear elastic fracture mechanics approach. They showed that the increase in both positive and negativeRcaused increased fatigue crack growth rates. Also an empirical effective stress intensity factor range, ΔKeff, was found more appropriate to correlate the fatigue crack growth data than the ΔKfactor frequently used in crack growth studies.The loading frequency had only a little influence on crack growth rates at lowR. However, at highR, growth rates were significantly higher at lower frequencies. It is suggested that this frequency influence may be associated with environmental effects, due to the embrittlement caused by hydrogen from the moist air, while the crack was fu

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1979.tb01333.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractFatigue tests were carried out on mild steel with small cracks for which linear fracture mechanics is not effective. A fatigue limit criterion, based on the cyclic plastic zone size at a crack tip being a material constant at the fatigue limit, can effectively evaluate the effects of crack length and stress ratio. Regarding flaws as cracks, the theory gives fatigue limit values close to those obtained in experiments on specimens with natural defects, such as surface roughness, micro‐shrinkage cavities, inclusions etc. The effect of water corrosion was also investigate

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1979.tb01334.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractMicrocrack growth in a ferrite grain in a two phase martensitic–ferritic steel was studied. A local deformation parameter, the unzipping crack increment, can be used to characterize crack tip deformation and crack growth rate. The microcrack growth behavior is interpreted in terms of the calculated unzipping crack incremen

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1979.tb01335.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY