Engineering designers have to tackle various fatigue problems in their routine work. Some problems are simple and other are complex. Most of the designers have been taught only a small part of the suitable fatigue knowledge needed to successfully deal with many of these problems except for the most trivial ones. The main reason is the vast amount and complexity of the fatigue discipline, and lack of a clear integrated approach to the main fatigue problems that may be conveniently utilized by designers. An integrated approach to fatigue, that has been introduced by one of the authors in the past, is here extended, simplified and proposed as a comprehensive fatigue design tool for engineers. The whole fatigue domain is divided into six zones that include different fatigue regimes. The propagating crack length is considered as the sole parameter to evaluate safe fatigue life, including the use of an ''equivalent crack propagation rate " , which averages the intense variations of CPR in the vicinity of grain boundaries. Contrary to the many unified relations to evaluate fatigue crack propagation that were proposed in the past, the current study is based on separation. For each fatigue zone a unique prediction relation is presented. Flow chart of comprehensive software for calculation of crack propagation in the whole fatigue domain is explained, and simulation results show good fit to published test results. The method is claimed to fit for use mainly by design engineers, but possibly by fatigue experts as well.
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International Journal of Fatigue
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Fatigue is without doubt one of the most complex branches of mechanical and material engineering. Complex perhaps not in the classical sense of mathematics or material behaviour modelling, but more in terms of the number of unknowns that influence any attempt to predict the fatigue life of a machine element or an entire mechanical structure. This complexity stems from a multitude of input sources; test data extraction, load representation, material structure, manufacturing methods to mention just a few. One attempt at reducing such complexity has classically been to introduce reduction- or influence factors which are then applied to material properties, the endurance limit, component size and other relevant fatigue quantities. The danger of such simplification is that it becomes error-prone due to relying heavily on subjective application of said factors. Another issue at hand is the availability of fatigue life data, which is not always adequately referenced and therefore limited in its applicability. With the help of modern numerical fatigue analysis software the complexity can be put in a systematic perspective, provided the algorithms offered are contemporary in nature and rely on a physically correct representation of the unique fatigue behaviour. AVL EXCITE Fatigue developed by Safe Technology Ltd. is such a software package, offering advanced multiaxial stress-based fatigue life prediction capabilities. This paper offers an in-depth look at the two most advanced multiaxial algorithms available in EXCITE Fatigue; the stress-based Brown-Miller algorithm and Findley’s method. These algorithms are different from traditional stress-based methods in that the life data used in fatigue life prediction is derived from a strain-based approach, providing a second-to-none level of accuracy and reliability. In addition, the most recent findings both in stress and strain-based fatigue research have been integrated on a material science level, making them more than able to address a near limitless fatigue task spectrum.
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Advances in Materials Science and Engineering
Metallic materials are extensively used in engineering structures and fatigue failure is one of the most common failure modes of metal structures. Fatigue phenomena occur when a material is subjected to fluctuating stresses and strains, which lead to failure due to damage accumulation. Different methods, including the Palmgren-Miner linear damage rule- (LDR-) based, multiaxial and variable amplitude loading, stochastic-based, energy-based, and continuum damage mechanics methods, forecast fatigue life. This paper reviews fatigue life prediction techniques for metallic materials. An ideal fatigue life prediction model should include the main features of those already established methods, and its implementation in simulation systems could help engineers and scientists in different applications. In conclusion, LDR-based, multiaxial and variable amplitude loading, stochastic-based, continuum damage mechanics, and energy-based methods are easy, realistic, microstructure dependent, well ti.
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