Chapter 1 - Introduction

Abstract

This chapter provides an overview on fracture mechanic concepts and discusses various fundamentals like failure of solids. Failure of solids and structures can take various forms. A structure may fail without breaking the material, such as in elastic buckling. However, failure of the material in a structure leads to failure of the structure. Fracture mechanics is a subject of engineering science that deals with failure of solids caused by crack initiation and propagation. There are two basic approaches to establish fracture criteria, or crack propagation criteria: crack tip stress field (local) and energy balance (global) approaches. In the crack tip field approach, the crack tip stress and displacement states are first analyzed and parameters governing the near tip stress and displacement fields are identified. A fundamental concept of fracture mechanics is to accept the theoretical stress singularity at the crack tip but not use the stress directly to determine failure/crack extension. This is based on the fact that the tip stress is limited by the yield stress or the cohesive stress between atoms and singular stresses are the results of linear elasticity. It is also recognized that the singular stress field is a convenient representation of the actual finite stress field if the discrepancy between the two lies in a small region near the crack tip. This notion is referred to as small-scale yielding.