PSI - Issue 7

Igor Varfolomeev et al. / Procedia Structural Integrity 7 (2017) 359–367 Igor Varfolomeev et Al./ Structural Integrity Procedia 00 (2017) 000–000

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Weibull dist ribut ion Hist ogram

Weibull dist ribut ion Hist ogram

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Relat ive f requency

Relat ive f requency

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Fig. 4. Probability density functions for the defect size (a) and distance between neighboring defects (b). Specimen FZ1.

3. Numerical analysis To develop a computational framework for predicting crack initiation from a defect group, some additional tests were first performed on small cylindrical specimens taken from defect-free material regions. Subsequently, a continuum mechanics approach was adopted for modeling deformation behavior and damage evolution in a representative material volume starting from a predefined distribution of defects. In the following, the analysis steps and results are briefly described. 3.1. Enhanced material tests The goal of these tests was to derive basic mechanical properties required for numerical analyses of specimens with defects. Besides quasi-static monotonic tensile tests, a number of specimens were tested under strain controlled low cycle fatigue (LCF) conditions, at a strain ratio of = − 1 , while stepwise increasing the strain amplitude (incremental step tests). The resulting monotonic and cyclic stress vs. strain curves are shown in Fig. 5a. In the diagrams, both the stress and strain are normalized with respect to the monotonic yield strength, 0 , and Young’s modulus, . 1.2

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LCF tests trend line

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Fig. 5. Monotonic vs. cyclic stress-strain curve (a); fatigue life curve (b).