摘要:

Abstract—Plastic zone size and shape and the distribution of strain within the plastic zone are determined for the high‐strength aluminium alloys 2024‐T4, 6061 T6, and 7075‐T6 using the technique of selected area electron channeling. Plastic zone size is found to correlate with the work done in creating a unit of new crack surface and the yield stress, rather than with the stress intensity factor and yield stress. Plastic strain distribution is found to be a logarithmic function of distance from the crack tip, in agreement with the mathematical analysis for a moving crack in plane

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01379.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—This paper deals with the effect of accumulated (oriented) plastic deformation (cyclic creep) on the life of metals under conditions of cyclic loading typically in the range of low‐cycle fatigue. Specific features of cyclic creep of aluminium, titanium alloys and structural steels were investigated for the lives ranging from 05 to 2 × 105cycles to rupture as well as specific features of transition from quasistatic to fatigue fracture associated with the variation in the mode of deformation of metals. It is shown that under conditions of repeated stress‐controlled loading in a wide range of low temperatures, the cyclic creep processes are the predominant ones determining life of metals over a wide range of cycles, and when calculating life under these conditions it is necessary to take into account the rate of these processes irrespective of the type of fracture: quasistatic or fatigue. An equation was obtained for calculating life under low‐cycle loading conditions which takes into account the interrelationship between the life, the accumulated plastic strain, steady‐state cyclic creep rate and the resistance of the material to cy

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01380.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—–The da/dNvsΔKrelation for Torbar Steel is obtained by testingspecimens cut from 32 mm bar. This relation is compared with available data for Unisteel 410 and with medium strength steels. Also, the pattern of fatigue cracking in Torbar is studied by inspecting bars retrieved from reinforced concrete beams which were subjected to repeated loading. It has been observed that fatigue crack locations in the bars coincided with the locations of concrete cracks traversing the bars. Tension tests on the fatigue cracked bars show that the cracks considerably reduce the ductility of the

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01381.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—Stress gradients at the root of a notch are significant for the notch effect and the size effect of fatigue properties. Usually the gradient of the stress distribution in the minimum section is considered. In the present paper the variation of the tensile stress along the edge of the notch is considered. Calculations are made for a variety of notches. The results indicate a remarkable conformity of stress distributions at the notch root if the same peak stress and notch root radius (ρ) apply. ConsequentlyK1and ρare highly characteristic for the stress distribution around the notch. Along the edge of the notch the stress decreases at a much slower rate than in the minimum section going away from the material surface. For the stress along the edge of the notch a stress gradient coefficient is defined. The variation of this coefficient is fairly small for several notches andK1, values. A 5% lower stress as compared to the peak stress at the notch root is obtained at about 0.02 ρbelow the material surface and at a distance of about 0.18 ρalong the material su

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01382.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—Optical and scanning electron microscopy have revealed the existence of grain boundary cavities in a series of specimens which had been cyclically deformed in the strain range ±0.25% with hold times ranging from 0 to 1000 min. The way in which these defects increase in size and number has been measured and found to correlate with the creep strain accumulated during the hold periods.A further observation is that a critical amount of deformation is required before either fatigue or creep type damage is nucleated. These observations lead to an alternative method to the currently accepted linear damage summation rule for estimating a lower bound of the creep‐fatigue endur

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01383.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—Impact fatigue tests were carried out using a rotating‐disk type impact fatigue testing machine. The influence of prior austenite grain size, ductile‐brittle transition temperature and test temperature on impact fatigue crack growth rate was investigated by means of fracture mechanics and fractography in quenched and tempered Cr‐Mo alloy steel in which the prior austenite grain size was varied from 8–3 to 25‐4 μm. The results in impact fatigue tests were compared to those under non‐impact conditions. The crack growth rates associated with striation formation were insensitive to the change in prior austenite grain size, ductile‐brittle transition temperature and test temperature regardless of impact and non‐impact fatigue. When the material was in the brittle condition, impact fatigue gave rise to a transition from striation formation to intergranular and cleavage cracking. Such a transition will result in the acceleration of crack growth rate. The Paris Law exponent values in impact fatigue were reasonably expressed by the ratio of test temperature to ductile‐brittle tr

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01384.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—–The rate of propagation of macrofatigue cracks down to near threshold was measured in air in three tempered martensitic steels; HY80, HY130 and 4140 (650°C temper). The value of ΔKthwas determined by the load‐shedding technique in center notched panel specimens. Of the three steels, 4140 tempered at 650°C had the lowest ΔKth, 3–5 MN/m3/2, while HY80 had the highest, 4.2 MN/m3/2. The 4140 (650°C temper) is intermediate in strength between HY80 and HY130. The results are discussed in terms of a recent theory of one of the authors.The fatigue crack propagation rates in the mid‐ΔKrangein HY80 and HY130 in argon were also studied by measuring, with foil strain gages, the cyclic plastic work to propagate a fatigue crack by a unit area,U.HY80 has a lower crack propagation rate and correspondingly higherU.This was attributed in part to the higher yield strength of HY130 but the dislocation structure and carbide composition and morphology also play roles. Microstructural changes due to cyclic plastic deformation inside the plastic zone in HY80 and HY130 were observed by TEM of thin foils. SEM studies of the fracture surfaces at ΔK= 20 MN/m3/2indicate a more ductile fracture mode for HY80 than for HY130. The fatigue crack propagation rate of HY130 is substantially higher in laboratory air (47% relative humidity) than in dry argon. This is not t

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01385.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY