Fatigue limit

About: Fatigue limit is a research topic. Over the lifetime, 20489 publications have been published within this topic receiving 305744 citations. The topic is also known as: endurance limit & fatigue strength.

A general criterion for high cycle multiaxial fatigue failure

Abstract: A new simple general criterion of failure for high cycle multiaxial fatigue, τ a /t A,B +σ n,max /2σ T =1, is presented. The failure criterion is based on a critical plane approach where fatigue strength is a function of the shear stress amplitude and the maximum normal stress on the critical plane of maximum shear stress amplitude. The criterion takes account of whether case A cracks, growing along the surface, or case B cracks, growing into the surface, occur. It requires knowledge of the material properties, tensile strength, σ T , and reversed shear fatigue strength for case A, t A , or case B, t B , cracking whichever is relevant, t A is the reversed torsion fatigue strenght and t B is found from a case B cracking test case. The criterion is applicable in the region, 0.5t≤τ a ≤t, and 0≤σ n,max ≤σ T

Casting defects and the fatigue behaviour of an aluminium casting alloy

Abstract: — The fatigue properties of un-notched polished specimens of an aluminium casting alloy have been measured for various heat-treatment conditions and at various mean stresses. The relation between fatigue life and alternating stress is insensitive to heat-treatment and, apparently, to mean stress. It was observed that failure initiated at interdendritic shrinkage defects: evidence of classical crack initiation from persistent slip bands was also seen but such cracks, being less severe than the casting defects, never caused failure. A fracture mechanics analysis for the growth of fatigue cracks from the pores is described. It shows that the fatigue life can be quantitatively predicted from a knowledge of the size of casting defects: in particular it explains the lack of effect of heat-treatment and the apparent absence of a mean stress effect is shown to be caused by the variation in size of maximum defect present among the specimens tested. It is shown that reducing the size of shrinkage defects will increase the life, but only up to the stage at which initiation from persistent slip bands becomes operative.

Fatigue strength of steel and aluminium welded joints based on generalised stress intensity factors and local strain energy values

Abstract: Weld bead geometry cannot, by its nature, be precisely defined. Parameters such as bead shape and toe radius vary from joint to joint even in well-controlled manufacturing operations. In the present paper the weld toe region is modelled as a sharp, zero radius, V-shaped notch and the intensity of asymptotic stress distributions obeying Williams’ solution are quantified by means of the Notch Stress Intensity Factors (NSIFs). When the constancy of the angle included between weld flanks and main plates is assured and the angle is large enough to make mode II contribution non-singular, mode I NSIF can be directly used to summarise the fatigue strength of welded joints having very different geometry. By using a large amount of experimental data taken from the literature and related to a V-notch angle of 135°, two NSIF-based bands are reported for steel and aluminium welded joints under a nominal load ratio about equal to zero. A third band is reported for steel welded joints with failures originated from the weld roots, where the lack of penetration zone is treated as a crack-like notch and units for NSIFs are the same as conventional SIF used in LEFM. Afterwards, in order to overcome the problem related to the variability of the V-notch opening angle, the synthesis is made by simply using a scalar quantity, i.e. the mean value of the strain energy averaged in the structural volume surrounding the notch tips. This energy is given in closed form on the basis of the relevant NSIFs for modes I and II and the radius RC of the averaging zone is carefully identified with reference to conventional arc welding processes. RC for welded joints made of steel and aluminium considered here is 0.28 mm and 0.12 mm, respectively. Different values of RC might characterise welded joints obtained from high-power processes, in particular from automated laser beam welding. The local-energy based criterion is applied to steel welded joints under prevailing mode I (with failures both at the weld root and toe) and to aluminium welded joints under mode I and mixed load modes (with mode II contribution prevailing on that ascribable to mode I). Surprising, the mean value of ΔW related to the two groups of welded materials was found practically coincident at 2 million cycles. More than 750 fatigue data have been considered in the analyses reported herein.