June 23, 2013
June 23, 2013
June 26, 2013
23.193.1 - 23.193.7
Analytical Studies on S-N Curves for some Steels Somnath Chattopadhyay Georgia Southern University ABSTRACTExperimental data are often employed to obtain stress amplitude versus number of cycles tofailure characteristics of materials (S-N curve). This activity as a laboratory component of ajunior level materials science course explores the possible stages involved in a fatigue failureprocess. The students study the two important stages involved in fatigue failure: (a) the cracknucleation stage where a microstructurally small crack grows from a zero length to a tthresholdcrack size that depends on the applied stress level and the threshold fracture toughness (a conceptthat the students learn in the course); and (b) microstructurally long crack growth from thethreshold crack size to a characteristic size. This characteristic size is dependent on theendurance or the fatigue limit of the material as well as the threshold fracture toughness. .The students start with a given stress range and calculate the crack nucleation life (in cycles) andthe crack propagation life (in cycles) and combine them to find the number of cycles to failure.The input material properties needed for the exercise are the endurance limit and the thresholdfracture toughness.
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