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Fatigue crack propagation tests were performed on a high-strength steel with yield strength of 598 MPa under various stress ratios. A fatigue crack opening model, which contains both the effects of R and ?K, was investigated based upon the cyclic elasto-plastic finite-element analysis (FEA) and the fracture mechanics approach with the small-scale yielding concept. Assuming the existence of the residual deformation in the wake of a crack, the crack opening stress-intensity factor can be calculated as the value at which the fatigue crack opening displacement becomes zero. Using this model, how R and ?K affect U was investigated. The resultant formula for U contains two parameters, one for the plastic deformation at a crack tip, and the other for the oxide and the roughness in a fatigue crack. The effective stressintensity factor range, based on the measurements of crack opening loads, gives the same crack propagation behavior for various stress ratios. It is observed in experiments, however, that U depends on the stress ratio R and the stress-intensity factor range ?K. The model successfully explains the experimental results. The fatigue crack propagation behavior under various stress ratios is described by the formula with five parameters, which can be obtained with only one specimen. The predicted crack propagation rates and threshold stress-intensity factor range agreed with empirical results. Therefore, the formula derived from this model may be applied well to the evaluation of fatigue crack extension.
Advances in Research on the Strength and Fracture of Materials: Volume 2Bs—Fatigue contains the proceedings of the Fourth International Conference on Fracture, held at the University of Waterloo, Canada, in June 1977. The papers review the state of the art with respect to fracture in a wide range of materials such as metals and alloys. This volume is comprised of 85 chapters and opens by discussing the metallographic aspects of fatigue in pearlitic structures and the dislocation diffusion mechanism of fatigue crack formation. The reader is then introduced to localized plastic deformation and fracture in slip bands during fatigue loading of age hardening aluminum alloys; the microstructure of fatigue fracture surfaces in titanium; mechanisms of liquid metal embrittlement, stress corrosion cracking, and corrosion-fatigue; and the fatigue behavior of macroscopic slag inclusions in steam turbo-generator rotor steels. A model for fatigue crack initiation in polycrystalline solids is also described. This monograph will be a useful resource for metallurgists, materials scientists, and structural and mechanical engineers.
The purpose of this Handbook is to provide a review of the knowledge and experiences in the field of fatigue fracture mechanics. It is well-known that engineering structures can fail due to cyclic loading. For instance, a cyclically time-varying loading reduces the structure strength and can provoke a fatigue failure consisting of three stages: (a) crack initiation (b) crack propagation and (c) catastrophic failure. Since last century many scientists have tried to understand the reasons for the above-mentioned failures and how to prevent them. This Handbook contains valuable contributions from leading experts within the international scientific community and covers many of the important problems associated with the fatigue phenomena in civil, mechanical and nuclear engineering.
In the preliminary stage of designing new structural hardware that must perform a given mission in a fluctuating load environment, there are several factors the designers should consider. Trade studies for different design configurations should be performed and, based on strength and weight considerations, among others, an optimum configuration selected. The selected design must be able to withstand the environment in question without failure. Therefore, a comprehen sive structural analysis that consists of static, dynamic, fatigue, and fracture is necessary to ensure the integrity of the structure. During the past few decades, fracture mechanics has become a necessary discipline for the solution of many structural problems. These problems include the prevention of failures resulting from preexisting cracks in the parent material, welds or that develop under cyclic loading environment during the life of the structure. The importance of fatigue and fracture in nuclear, pressure vessel, aircraft, and aerospace structural hardware cannot be overemphasized where safety is of utmost concern. This book is written for the designer and strength analyst, as well as for the material and process engineer who is concerned with the integrity of the structural hardware under load-varying environments in which fatigue and frac ture must be given special attention. The book is a result of years of both acade mic and industrial experiences that the principal author and co-authors have accumulated through their work with aircraft and aerospace structures.