Stress concentration

About: Stress concentration is a research topic. Over the lifetime, 23250 publications have been published within this topic receiving 422911 citations.

A simplified laboratory approach for the prediction of short crack behavior in engineering structures

Abstract: — Conventionally determined fatigue threshold information (ASTM E647) can lead to non-conservative estimates of fatigue lifetimes when these data are utilized in damage tolerant design assessments. The non-conservative nature of such data can be attributed primarily to the development of excessively large amounts of crack closure at low R-ratios, particularly at near threshold stress intensity factor levels. These high closure levels attenuate the effective stress intensity condition prevailing at the crack tip and confound attempts to predict the behavior of short cracks that exhibit limited crack closure. A modified test procedure, involving constant maximum stress intensity factor (Kcmax) test conditions, is described which identifies fatigue crack propagation (FCP) threshold behavior in the absence of detectable amounts of crack closure. These data have been generated with conventional long crack specimens for several aluminum, iron, and nickel-based alloys and which are shown to closely simulate the FCP response of short cracks in these engineering materials. As such, the modified threshold test procedure, incorporating constant Kmax loading conditions, represents a valuable tool in the prediction of the cyclic lifetime of engineering components. The stress-cyclic lifetime (S-N) curve for aluminum butt-welded beams was computed based on Kcmax data and found to be in excellent agreement with actual test results.

Near-threshold fatigue crack propagation: a perspective on the role of crack closure

Abstract: In recent years, mechanistic and continuum studies on fatigue crack propagation, particularly at near-threshold levels, have highlighted a dominant role of crack closure in influencing growth rate behavior In this paper we review and model the various sources of closure induced by cyclic plasticity, corrosion deposits, irregular fracture morphologies, viscous fluids and metallurgical phase transformations It is shown that many of the commonly observed effects of mechanical factors, such as load ratio, microstructural factors, such as strength and grain size, and certain environmental conditions can be traced to the extrinsic influence of closure in modifying the effective driving force for crack extension The implications of such closure mechanisms are discussed in the light of constant and variable amplitude fatigue behavior, the existence of a threshold stress intensity for no fatigue crack growth and the validity of such threshold concepts for the case of short fatigue cracks 106 references, 21 figures

Fatigue of steel reinforcement bars in concrete: a review

Abstract: — During the last few years there has been an intensification of interest in the fatigue performance of steel reinforcement bars in concrete structures. Although fatigue has not proved to be a problem to date, loading cycles are becoming increasingly severe so that the margin of reserve strength is progressively being reduced. In this paper the main parameters associated with fatigue of reinforcement are reviewed with particular attention given to conditions related to highway bridges. Fatigue testing can be either axial in air or by bending of reinforced concrete beams. The latter is experimentally less convenient but simulates more closely the service environment. Endurances can be influenced by type of steel, geometry and size of the bars, nature of the loading cycle, welding and presence of corrosion. The relative behaviour of butt welded joints is considered and it is shown that the reduction in fatigue strength commonly attributed to flaws and to the stress concentrations associated with welds does not always occur for bending fatigue of reinforced concrete beams.