Effect of Impact Energy in ESSO Test (Part 2: Proposal of Validity Criteria of Impact Condition in ESSO Test by FEM Crack Propagation Analysis
Based on the fundamental knowledge revealed in Part 1 of the present work, crack propagation analysis is carried out in Part 2 of the present work to the establish validity criteria for impact conditions. In cases where there is excessive impact energy in a brittle fracture test in the evaluation of crack arrest toughness, the impact energy gives conservative test results. In this research, numerical simulation was systematically conducted in order to clarify the effects of impact energy. Dynamic elastic finite element method Finite Element Method (FEM) analysis, which was validated by actual dynamic strain data in Part 1, was employed. The FEM analysis revealed that the impact effect reached its maximum immediately after impact and gradually decreased thereafter. However, the increase of the dynamic stress intensity factor Kd, with respect to the impact, remains significant in cases where applied stress is low and impact energy is high. The judgment of whether the impact had an effect on the results was made by calculating the ratio of the values of Kd both for cases where impact was considered and where it was not. The threshold condition from which the evaluated value should be corrected was set to 1.5. The specified range could be determined without considering the effect of impact by using the dimensionless ratio of the quantity impact energy Ei /(Es + Et).
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