Simulation of dynamic fracture in aluminum structures
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The present thesis treats the simulation of crack initiation and growth by the use of cohesive zone models under dynamic loading conditions . The first chapter reviews the aspects of fracture mechanics that are related to the subject. The rest of the thesis consists of two self-contained articles and one conference paper. Finite element models containing rate dependent cohesive elements have been introduced in the papers. The rate dependency of cohesive elements is obtained through calculations on single elements obeying rate dependent Gurson type equations. The papers represent three main aspects: model establishment, validation, and application. In the first article, the aim is to establish a model which has the ability to account for crack growth simulations under dynamic loading conditions. A rate-dependent Gurson type model has been used to define rate and triaxiality dependency of cohesive elements. The rate- and triaxiality-dependent cohesive elements are used in a finite element model to simulate crack propagation in a middle-cracked tension M(T) specimen made of aluminum alloy. The calculations show the importance of strain rate and stress triaxiality on the rate of the crack growth and the change of the load. The second paper examines the validation of the rate sensitive cohesive elements and the proposed procedure by comparing the results of the simulations and experiments on aluminum round bars under dynamic loading conditions. Smooth and notched round bars are tested and simulated and the load-diameter reduction curves are compared. The third paper applies the model to a bi-material (laser welded) compact tension C(T) specimen under dynamic loading conditions. The specimen made of aluminum alloy contains an initial crack on the interface of fusion zone and base metal. The crack growth is simulated by rate dependent cohesive elements which are oriented in different directions so that mixed mode crack propagation is feasible. The articles show the importance of considering rate dependency in the calculation of both the energy dissipated by plastic deformation and the energy of separation. They also show that the approach used is convenient for the simulation of dynamic ductile crack initiation and growth. The procedure considered can also be used for other areas of fracture simulation where the energy of separation is a function of variables that exist at the crack tip area.
Has partsAnvari, M; Scheider, I; Thaulow, C. Simulation of dynamic ductile crack growth using strain-rate and triaxiality-dependent cohesive elements. Engineering Fracture Mechanics. 73(15): 2210-2228, 2006.
Anvari, M; Liu, Jun; Thaulow, C. Dynamic ductile fracture in aluminum round bars: experiments and simulations. International Journal of Fracture. 143(4): 317-332, 2007.
Anvari, M; Thaulow, C. Crack extension in aluminum weldment using ratedependent cohesive elements. Approaches to Fracture - Proceedings of the 9th European Mechanics of Materials Conference, 2006.