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DUCTILE FRACTURE: Theory, Model Identification and Industrial Applications
=Tomasz Wierzbicki, Ph.D.= === DUCTILE FRACTURE: Theory, Model Identification and Industrial Applications=== The talk will consist of five parts:(i)Historical note,(ii) Development of the Modified Mohr-Coulomb Fracture criterion,(iii) Multi-axial fracture tests and calibration,(iv) FE implementation and (v) Applications to the automotive, steel, aluminium and offshore industry. (i) The development of the concept of ductile fracture is briefly reviwed from the point of view of author's personal experience in working with the industry. (ii) Ductile fracture is first formulated under proportional loading for isotropic materials. The concept of the 3-D fracture locus is systematically developed and illustrated on examples of axisymmetric, plain stress and plain strain states. An extension to non-proportional loading involves a concept of a linear or nonlinear damage accumulation rule. The importance of the stress triaxiality and the Lode angle parameters in correctly defining the constraints is emphasized. (iii) All plasticity and fracture parameters are identified through carefully performed bi-axial tests using a unique dual actuator loading frame. The error in the experimental determination of the fracture strain is critically assessed. Examples of a calibration procedure are given for several high strength steels and aluminium alloys. (iv) The element delition technique in Abaqus is used to visualize crack paths. Fracture propagation is assumed to consists of a continuing process of crack initiations with the evolving amount of constraint. For a proper formulation of the post-failure behavior of elements, the concept of the material softening is introduced. Such a formulation reduces the mesh size effect and accounts for the mechanics of the process zone near the crack tip. (v) A driving force of most of the work on ductile fracture has been several industrial consortia organized by the author at MIT. Applications to real world fracture problems will be presented along with a comparison between the tests and simulations.
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