Issue 35

O. Demir et alii, Frattura ed Integrità Strutturale, 35 (2016) 340-349; DOI: 10.3221/IGF-ESIS.35.39 340 Focussed on Crack Paths Investigation of mixed mode-I/II fracture problems - Part 2: evaluation and development of mixed mode-I/II fracture criteria O. Demir Department of Mechanical Engineering, Sakarya University, 54187, Sakarya, Turkey Department of Mechanical and Manufacturing Engineering, Bilecik Şeyh Edebali University, 11230, Bilecik, Turkey oguzhan.demir@ogr.sakarya.edu.tr A. O. Ayhan Department of Mechanical Engineering, Sakarya University, 54187, Sakarya, Turkey ayhan@sakarya.edu.tr A BSTRACT . 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 in- plane 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. K EYWORDS . Fracture; Mixed Mode; Mode-I/II; Compact Tension Shear; Fracture Criteria. I NTRODUCTION 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. For such situations, analyses of the cracked structure under mixed mode loads and related criteria for fracture conditions are needed. The most basic type of mixed mode fracture is mode-I/II, in which both mode-I (opening) and mode-II (shearing) loads act on the crack tip. A