摘要:

AbstractA high speed steel, processed by two powder metallurgy routes and heat treated to give a range of microstructures, was investigated in 4‐point bending at room temperature using smooth and precracked specimens. The finer microstructures were in the material from gas atomised powder which was hot isostatically‐pressed, commercial ASP60 alloy, while the coarser microstructures derived from laboratory vacuum sintering of water‐atomised powder. The resultant hardness values Hv50were in the rage 780 to 1050, prior autenite grain sizes, 5 to 25 pm and maximum carbide sizes, 6 to 32 μm.Only some of the uncracked samples exhibited macroscopic yielding, at stresses in the range 1.64 to 2.59 GPa; the finer microstructures being asSociated with the higher strengths. Macroscopic plastic deformation never exceeded 0.33%; fracture strengths were in the range 1.46 to 2.75 GPa. Fracture toughness, Klc, varied from 12 to 17 MPa√m in the Hy50range 920 to 800 for the directly sintered steel and only from 10 to 12 MPa√m in ASP60. The insensitivity of K1cto macroscopic hardness in ASP60 is asSociated with the plastic zone size of 1.5 μm which approximates to the average carbide spacing.Nucleation and growth of natural, i.e. stress‐induced, microcracks in un notched specimens was studied by surface replica microscopy. Crack nucleation took place at stresses between 0.5 and 1.5 GPa, i.e. below those for yielding and for fracture, σF, and was by debonding of inclusions (alumina and calcium‐alumino silicates) or cracking of carbides. In the coarsest microstructure monotonic stepwise subcritical crack growth was observed from stress levels of ∼1.3 GPa, i.e. ∼0.8 to 0.9σF. Similarities to the behaviour of short fatigue cracks in metallic materials and the R‐curve behaviour of c

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1995.tb00137.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe whole fatigue domain has been divided into six Werent zones, each governed by a separate fatigue regime. Some of these regimes coincide with a known classification of fatigue, and others are new regimes, where new prediction methods have been introduced. The proposed predictions are to be considered as practical curve fitting relations for special cases, but those cases can also be fairly general and useful for design purposes. The proposed fatigue diagram can be used as a basis for a quantified explanation of several known fatigue phenomena.

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1995.tb00138.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractHigh‐cycle‐fatigue/creep experiments were performed on a 9%Cr‐1%Mo temperered marten‐site ferritic steel at 873 K in air. The stress ratio R=σmin/σmaxranged from‐1 (“pure” fatigue) to 1 (“pure” creep). The maximum stress σmaxwas kept constant at 240 MPa. The lifetime depends on the stress ratioRin a non‐monotonic way.In the stress ratio interval 0.6

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1995.tb00139.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe cyclic strain energy density parameterWfor the critical or failure plane has been successfully applied in predicting the multiaxial fatigue life of an iron‐base and a nickel‐base alloy. This parameter has the advantage of being independent of loading condition, allowing a universal energy‐life curve to be determined for a variety of torsion, tension and bending stress and strain states. The critical strain energy density parameter has been verified using experimental data obtained from tubular and notched specimens of SAE‐1045 steel and Inco

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1995.tb00140.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA closed form solution technique first presented by Hsu and Fonnan for the radial expansion of a fastener hole is extended to include elastic‐plastic unloading and therefore the creation of a reverse yielded zone. In addition, the dependence of interface pressure upon interference with an elastic insert is established. Numerous parametric studies are presented to demonstrate the effect of significant model variables and selected example calculations are compared with experimental result

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1995.tb00141.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFatigue damage in two austenitic‐ferritic duplex stainless steels, with the structure of a natural composite and different levels of nitrogen content, was studied in low‐cycle fatigue. Both steels show initial cyclic hardening followed by softening and a long stabilisation period. The cyclic stress‐strain curve increases with the nitrogen content while Manson‐Coffin curves of both steels intersect at medium fatigue lives. The study of the surface relief reveals intensive slip markings both in ferrite and in austenite. Their density is influenced by the nitrogen content. Both the intensity and density of the persistent slip band (PSB) markings are higher in the ferrite. Crack initiation was found to appear predominantly in PSBs in the ferritic grains at the low strain amplitudes, and in the ferritic and austenitic grains at the highest strain amplitudes. The level of the cyclic stress‐strain response and the fatigue lives are discussed in terms of the cyclic strain localisation and of the effect of texture and nitrogen content on the strength and fatigue damage. The increased strength of the austenitic phase, due to high nitrogen alloying, results in cyclic slip localisation in the ferrite, and the decrease of fatigue life, compared with the steel with the lower nitroge

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1995.tb00142.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA high‐cycle fatigue criterion suitable for multiaxial non‐proportional stress loading is proposed in this paper. The criterion is based on some microscopic considerations related to the crystalline structure of metals. The purpose of the present paper is mainly the application of this criterion in two loading cases: (a) biaxial loads involving two normal stresses or one normal and one shear stress, and (b) triaxial load with two normal stresses and one shear stress. Stress states of these kinds are very common in piping assemblies. Application of the proposed criterion in the case of triaxial loading, where the three stress components are of the same frequency, but out‐of‐phase, leads to a simple analytical formula. This formula is the equation of a bounding surface that delimits in the space of the above three stresses the safety domain against fatigue crack initiation. A remarkable theoretical result concerns the phase difference of the shear stress, which does not appear in the derived formula. Consequently, according to our proposal the safety domain (i.e. the limiting fatigue endurance) under combined out‐of‐phase biaxial normal stress loading and torsion is independent of the phase difference of the torsion. Obviously this result holds also for the simpler case of axial load and torsion. On the contrary the phase difference between the two normal stresses has a strong detrimental effect on the fatigue endurance of a metal. As is shown these theoretical conclusions are in good agreement with fatigue limit test data found in the scientific

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1995.tb00143.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractGrowth of a long mode I crack under variable fatigue loading was experimentally investigated on mild steel specimens. A dynamic elastic‐plastic two‐dimensional finite element program, purposely developed for the simulation of cyclic crack tip deformation, was utilised to model the transient effects on crack tip advance. The model accommodated crack tip opening displacement and both crack tip and crack edge closure. Fifty one different cycle patterns were analysed to include the application of a single overload, a single underload, a single cycle having a combined overload and underload and finally loading blocks of different sequences. Correlations of experimental fatigue crack growth rates were made from knowledge of crack tip deformation behaviour, including the use of data found in the literature. Specimens of eight materials and different geometries were analysed to determine the validity of the present appro

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1995.tb00144.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAn elastic‐plastic finite element analysis with high order elements is performed to examine closure behaviour of fatigue. cracks in residua1 stress fieids and the numerical results are then compared with experimental results. The finite element analysis, performed under plane stress using 8‐node isoparametric elements, can predict fatigue crack closure behaviour through residual stress fields very well. The crack opening and closing behaviour through a compressive residual stress field is found to be complicated and influenced by the applied load magnitude and the location of the crack tip. Three different types of crack opening behaviour, namely, normal, unsymmetric partial and symmetric partial crack opening behaviour are observed through a compressive residual stress field. The partial crack opening stress intensity factor including the partial crack opening effect is recommended for the prediction of fatigue crack growth through a compressive residual stress fi

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1995.tb00145.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn order to evaluate the notch fatigue strength and notch sensitivity of aluminum‐lithium, 2090 and 8090, alloys, rotary bending fatigue tests have been carried out using circumferentially notched specimens with different stress concentration factors. The results were compared with those of traditional aluminum, 2024T4 and 7075‐T6511, alloys. It was found that 2090 and 8090 alloys showed superior notch fatigue strength in comparison to the conventional aluminum alloys. The notch sensitivities to the crack initiation limit of the aluminum‐lithium alloys were lower than those of 7075‐T6511, while they were nearly equal to those of 2024T4 for blunt notches. The notch sensitivities to the crack propagation limit were also lower in aluminum‐lithium alloys, in particular the 8090 alloy, than in the conventional aluminum alloys. It was suggested that the decreased notch sensitivities of the aluminum‐lithium alloys were attributed to both the crack propagation mode and the excellent propagation resistance related to their micr

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1995.tb00146.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY