摘要:

Abstract—Different aspects of fatigue design problems are indicated and uncertainties are listed. Scatter as observed in many laboratory studies is analyzed. It is argued that scatter of crack initiation and crack growth are different issues. Various sources of scatter are discussed and illustrative examples are presented. Comments are given on statistical distribution functions, scatter under Variable‐Amplitude loading, and scatter in service. The discussion touches upon the experience and meaning of scatter of laboratory test series related to practical probl

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00239.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—A series of crack growth experiments has been preformed on the near alpha titanium alloy, Ti‐1100, to determine the mechanism of the creep‐fatigue interaction. Based on pure creep crack growth results, the increase in the creep‐fatigue crack growth rate is not amenable to separate contributions of creep crack growth and fatigue crack growth.A mechanism has been proposed to account for the increase in creep‐fatigue crack growth rate that is based on the planar slip of titanium alloys which results in the formation of dislocation pileups at the prior beta grain boundaries and leads to intergranular fracture. This mechanism has been validated through crack growth experiments preformed on a Ti‐1100 that has been microstructurally modified through the precipitation of internal slip barriers. These show that the intergranular fracture and increase in crack growth rate

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00240.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The notched strengths of four woven laminates (two orthotropic, one quasi‐isotropic and one square symmetrical) under monotonic uniaxial loading, predicted with the point and average stress criteria, the two parameter criterion, the progressive degradation model, and the initial and improved point and minimal strength models, have been respectively compared with the experimental data. The damage mechanisms for the laminates were tentatively studied. The results show that, for minimal experimental information, the notched strengths predicted by the improved minimal strength models are the most precise and the progressive degradation model can numerically illustrate the damage mechanisms in detail. The damage mechanisms of the woven laminates were found to be very different from those of non‐woven lami

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00241.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The small‐crack effect, where small fatigue cracks grow faster and at lower stress‐intensity factors than large cracks, has been found to be significant for many materials and loading conditions. In this paper, plasticity effects and crack‐closure modelling of small fatigue cracks are reviewed. A crack‐closure model with a cyclic‐plastic‐zone‐corrected effective stress‐intensity factor range (related to the cyclicJ‐integral) and microstructural data on crack‐initiation sites were used to calculate small‐crack growth rates and fatigue lives for unnotched and notched specimens made of two aluminum alloys. The crack‐closure transient from the plastic wake was shown to be the dominant cause of the small‐crack effect and plasticity effects on the cyclic‐plastic‐zone‐corrected stress‐intensity factor range were negligible except at extremely high stress levels. Small‐crack growth rates and fatigue lives under both constant‐amplitude and spectrum load

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00242.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The static and dynamic fracture toughness of an Al‐Li 8090 alloy plate was evaluated as a function of notch orientation. Static fracture toughness is marginally lower than the dynamic fracture toughness in all the three notch orientations that were studied. The fracture mechanism remains unchanged and the degree of in‐plane anisotropy is significant, but more or less similar under static and dynamic condi

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00243.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The dislocation substructures of ferrite in plain carbon, ferrite plus martensite, dual‐phase steels in different stages of fatigue crack propagation were examined by transmission electron microscopy. The experimental results show that the dislocations are in random arrays in the ferrite before cyclic loading. At stages of low ΔK(near threshold) values, parallel clusters of dislocations and prolonged dislocation lines can be observed. At stages of intermediate ΔKvalues, the dislocations are rearranged into networks and loops while at stages of high ΔK(prior to failure) values, they are changed into dislocation cells or patches. It was also found that the volume fraction and carbon content of martensite have significant effects on the dislocation substructures of ferrite after cyclic defor

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00244.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Previous work has shown that the inclusion of the strain energy released by crack blunting leads to an energy minimum for fatigue crack growth that can be used to predict stage II fatigue crack growth. The present work assumes a polynomial relation between crack blunting and crack extension to derive an expression for the rate of fatigue crack growth that is dependent upon only the applied ΔK,E, σys,Kc, and the exponentpin the relation between crack blunting and crack extension. This expression is thought to be generally valid since it accurately predicts fatigue crack growth rates for a wide variety of titanium, nickel, aluminium and steel alloys. A unique characteristic of the model is its ability (for long crack, slow crack growth) to account for the different slope for different materials in the Paris Law region of the da/dNvs. δKcurve. The model specifically shows that this slope,m, is dependent solely upon the exponent,p, in the relation between crack blunting and crack exten

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00245.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—An engineering fracture parameter (CTOA) is studied under non‐J‐controlled growth. Based on the asymptotic solution of the crack tip field and the concept of theJ̃1integral, an analytical relation linking the crack tip opening angle (CTOA) and theJ̃1integral is established. A numerical investigation of the process of crack growth is carried out by the finite element method. The whole field solution, fracture parameters and indeterminate parameters are determined by FE analysis. An experimental investigation on a ductile structural steel has also been conducted and the crack resistance curve (CTOA)Ris obtained. The numerical and experimental results validate the theoretical analysis and show that they are consistent. It can be concluded that CTOA is always constant during steady crack prop

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00246.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Thermo‐mechanical fatigue stress‐strain data on ferritic/austenitic steels and superalloys from a variety of sources are analysed with regard to hysteresis loop stress asymmetry. This arises from a decoupling of the thermal and mechanical strain signals in the test technique so that many tension‐compression load combinations are possible. Data from simplified isothermal and bithermal tests are also examined. Taking a typical example of an “out‐of‐phase” thermo‐mechanical loop on a 1/2 CrMoV steel cycled between 200 and 550°C, isothermal stress‐strain data were generated at 50°C intervals on material from the same cast and, used in conjunction with the elastic characteristics of the apparatus, an attempt was made to re‐create this loop. The methods employed were (i) a graphical construction between appropriate isothermal yield contours (ii) a tangent modulus calculation (iii) a secant modulus calculation. Method (i) appeared to give the closest agreem

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00247.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The plastic deformation of thin‐walled cylinders has been experimentally examined for the loading conditions of ±1% axial strain with hoop stresses of approximately 0, 1/4, 1/2 and 3/4 of the initial uniaxial yield stress.Two materials similar to those used in the pipework of PWR nuclear plant in the U.K. have been tested, namely 304S11 stainless steel and En6 low‐carbon steel. The results of the tests were to be compared with the allowable stresses and deformations specified in the ASME Boiler and Pressure Vessel Code, Section III. The code specifies that a prescribed combination of primary stresses must not exceed 1.5Sm, whereSmis a stress value defined for each material.The results indicate that the limit of 1.5Smis excessively low for both materials and that in particular, the stainless steel could tolerate 5Sm. Although the En6 steel is more prone to ratchetting than the stainless steel, the results suggest that it too could tolerate a higher primary stress than the code allows. Both materials are shown to satisfy the proposed ASME ratchet strain limit of 5% hoop strain after 10 cycles of ±1% axial strain range, for any value of internal p

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00248.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY