Investigation of mixed mode-I/II fracture problems - Part 2: evaluation and development of mixed mode-I/II fracture criteria

A O Ayhan,O Demir

doi:10.3221/igf-esis.35.39

Abstract

In this study, experimental and numerical results of compact tension shear (CTS) specimen and a new specimen type under in-plane mixed mode (Mode-I/II) loading conditions are compared with existing inplane mixed mode fracture criteria to investigate and understand the nature of fracture behavior properly. The material used in numerical and experimental analyses is Al 7075-T651 aluminum machined from rolled plates in the L-T rolling direction (crack plane is perpendicular to the rolling direction). In Part 1 of the study, results from numerical and experimental analyses are given. Having computed the mixed mode stress intensity factors from the numerical analyses, fracture loads are predicted and compared with different mixed mode-I/II fracture criteria. The experimental and numerical results show that many criteria are in good agreement with each other for predominately mode I to moderate mixed mode conditions. However, existing criteria increasingly differ from the experimental measurements for highly mode-II conditions. Using the computational and experimental results obtained, improved empirical mixed mode I/II fracture criteria for fracture condition and angle are also proposed.

Highlights

A lthough many fracture mechanics problems seen in practice can adequately be analyzed by taking into account mode-I conditions, there are still many problems that are subjected to mixed mode loading, for which mode-I analysis approaches are not sufficient
The most basic type of mixed mode fracture is mode-I/II, in which both mode-I and mode-II loads act on the crack tip
One of the most common fracture criterion for in-plane mixed mode problems is maximum tangential stress (MTS), which was proposed by Erdogan and Sih [1]

Summary

Introduction

A lthough many fracture mechanics problems seen in practice can adequately be analyzed by taking into account mode-I conditions, there are still many problems that are subjected to mixed mode loading, for which mode-I analysis approaches are not sufficient. The mode mixity of the problem can be due to orientation of an initial defect existing in the structure due to imperfections or processes such as manufacturing operations Another source of mixed mode loading on the crack is due to the nature of loads that exist on the structure. One of the most common fracture criterion for in-plane mixed mode problems is maximum tangential (circumferential) stress (MTS), which was proposed by Erdogan and Sih [1] This criterion assumes that, crack propagation starts from the crack tip radially when the tangential stress reaches a maximum value and exceeds a critical value or if an equivalent stress intensity factor (Keq) reaches the fracture toughness (KIC) propagation becomes unstable and fracture occurs. In this criterion Keq and crack deflection angle are given by: Keq cos 0 2

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Conclusion