A criterion for micro crack propagation based on double-column instability

摘要

Structures and components perform their intended purpose, e.g., carrying the load, retaining pressure etc, only within its failure limits. Excessive deformation or fracture can lead to failure. Fracture results under the action of applied stresses and strains from the development of damage in the form of micro-voids or cracks within the material matrix which is continuum body. The damage models for engineering materials should include the failure criteria for the micro-cracks too in order to make realistic predictions of failure. In cracked bodies, the stress triaxiality, i.e., the ratio of hydrostatic stress to equivalent stress which depends on the geometry and in-plane dimensions of the specimen/component has a strong influence on the local strain near the crack at fracture. Thus, applicability of the near crack tip failure criteria to components depends on whether these are independent of the constraints/triaxiality or not. The present continuum damage mechanics models for ductile fracture do not consider the microcracks in the damage zone. A continuum mechanics based failure theory for microcracks is proposed in this paper, drawing analogy with micro-column buckling. The failure limit based on crack propagation is arrived at phenomenologically by testing the specimens in the form of twin-columns to show the applicability of the formulated failure theory. Prediction of failure using this criterion would permit transferability of data from specimen level to the component level.