PSI - Issue 20

N.A. Makhutov et al. / Procedia Structural Integrity 20 (2019) 63–74 N. A. Makhutov and V. V. Zatsarinnyy / Structural Integrity Procedia 00 (2019) 000–000

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This difference between experimental and calculation values can be explained by the fact that during the disruption of a specimen the additional local stress concentration arises at its neck leading to the increase of breaking force. Besides, the variation coefficient for the “direct” distribution is 25% larger than for the experimental one, which also contributes to the safety factor, while the “inverse” one is 15% lower (this calculated cace is not conservative). On this basis, the formula (1) is applicable for engineering designs, when it is necessary to compose a conservative design which contributes to the safety factor.

Fig. 2. Comparison of experimental and calculated functions oa the rupture strength S k .

The performed comparison of ψ k direct and ψ k inverse calculation distribution curves testifies that the employment of ψ k inverse characteristic values in the field of small P probabilities leads to a considerable non-conservatism of strength calculations. 3. Effect of temperature factors According to the experiments, the resistance to elastic-plastic deformations and destruction increases with the decrease of temperature at an exponential rate as shown by Makhutov (1981, 2008, 2015). If direct experimental characteristics of mechanical properties obtained at negative temperatures are absent, the calculation methods can be applied to determine these characteristics obtained by Makhutov (2008), Makhutov and Permyakov (2005):