Stress State, Strain History and Microstructural Effects in Ductile Fracture

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Ductile fracture is a ubiquitous mode of failure in metals and some polymers whose main function is load bearing. Predicting material failure is essential to many engineering applications, including those in transportation, energy and manufacturing. Current understanding of ductile fracture is based on a theory of microvoid growth which is unable to rationalize the type of failures observed in various manufacturing or penetration processes, or the fracture of technologically important, lightweight materials. This award supports fundamental research to provide needed knowledge for the development or robust models and simulation tools of ductile fracture in structural materials under loading conditions for which yet no satisfactory solution exists. As one potential benefit, the research outcomes will aid in the development of strong and tough lightweight materials in transportation vehicles, which will ultimately lead to less fuel consumption and reduced emissions with a positive impact on the environment. The outreach activities will create an interdisciplinary and international research environment for both undergraduate and graduate students through interactions with French and Qatari laboratories. In addition, the developed simulation software will be made available to researchers and engineers through a GNU licensing process. The PI plans to document the results in a monograph on the subject matter.One of the most challenging problems the mechanics of materials community presently faces is the prediction of failure in advanced metallic materials, particularly at low stress triaxiality where seemingly important effects of the third stress invariant have been noticed. So far, the community has responded to this challenge by developing empirical failure criteria or ad hoc extensions of existing void growth models. The Lode parameter (L) and the stress triaxiality both are considered. The present research will help answer important questions such as: (i) What is the origin of the Lode effect? (ii) How to apportion the intrinsic effects of the Lode parameter (L) among void nucleation, growth and coalescence? (iii) How to quantify the extrinsic (or apparent) effect of L on the occurrence of plastic instabilities? Answers will be provided using a micromechanical modeling approach that is true to the physics of the fracture phenomena at the governing length scales. A computational implementation of the model will be conducted and the model prediction will be tested against available and newly acquired experimental data.