TWI Industrial Member Report Summary 592/1997
C S Wiesner and R M Andrews
Application of micromechanical failure models using numerical computer analyses allows one to predict the fracture behaviour of specimens and structures throughout the brittle-to-ductile transition.
Fracture mechanics assessment procedures have been developed for evaluating the integrity of flawed components. For precise analyses, complex finite element calculations are required to determine the applied conditions in the cracked structure. If numerical computations have established the stress/strain conditions in the structure, an alternative approach is application of micromechanical failure models, which are based on the micromechanisms of the fracture event. These models assume that fracture takes place in a given region of material when a critical stress or strain state is reached in the vicinity of the flaw under consideration. Since the fracture event is described locally, mechanical factors affecting fracture (such as constraint) are included in predictions of the model.
Correct application of micromechanical failure models will allow precise predictions of structural fracture behaviour to be made, with associated potential for reduced conservatism compared to conventional fracture mechanics analysis. The disadvantage of these models is that they require considerable computational effort and rely on thorough numerical analyses of the structure studied. In addition, their application to heterogeneous microstructures, such as welds, has not yet been fully developed.
- To review existing micromechanical failure models for cleavage and ductile fracture.