About inclusion shape effect on the endurance limit of ductile matrix materials

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The theory describing fatigue mechanism in elastoplastic material containing pores or inclusions of different shape and size has been developed. The paper is a continuation of the analysis presented in J. Mat. Sc. 31 (1996) 2475 where the effect of only circular inclusion shape was investigated. An attempt at quantitative determination of the effect of endurance limit reduction by plastic zones size formed near the inclusions, and their cracking has been done. The geometrical configuration, consisting of round inclusion, horizontal, vertical and angular elliptical inclusions, from which a nucleating crack emerged, as well as sharp cracks was considered, and the stress intensity factors of such configurations were analysed. Based on threshold value of ΔK below which crack propagation ceases, the critical value of loading stress was determined for different shapes and sizes of pores using an equivalent ellipse concept. Theoretical results were compared with results from experiments, showing quite good agreement. For plastic zones size determination finite elements technique and photo-stress experimental method were applied. Surprisingly it was found that circular shape of the pores is the most dangerous which explains why so many earlier investigations using circular pore shape model are, so well supported by the experiment.

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