Numerical and experimental investigation and development of three dimensional mixed-mode fracture criteria

Machine parts and engineering structures encounter with cracks or fracture problems in many areas depending on material, geometry, environmental conditions, loading and boundary conditions. In some critical structures, these problems may become a huge problem. These cracks can remain in the structure until a certain size or sometimes with a sudden fracture may cause serious financial losses that led to disaster and even in some cases may cause a loss of life. The structure or machine parts must be determined whether it is safe to resume the function with existing cracks and, if safe, fracture parameters must be calculate accurately for assessment of remaining life of a damaged structure. In this study, to predict crack propagation surfaces and life of structures containing cracks under two and three-dimensional mixed-mode loading accurately and reliably, experimental analyses, experimental method and fracture criteria are developed. In this context, two and three-dimensional mixed-mode crack propagation analyses and experiments are performed with specimens and test systems that some of them are exist in the literature and the others are designed for this study. Validation studies are performed for new proposed specimen and test systems. The data obtained from all analyses and experiments are compared with existing criteria and new two and threedimensional fracture and crack propagation criteria which are predict fracture/braking load, crack propagation life/surface accurately are developed. Finally, the effect of rolling direction on fracture toughness and crack propagation behavior is investigated and especially under low loading conditions, high differences are obtained for different rolling directions up to about five times. The results show that the rolling direction has a significant effect on crack growth behavior.