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Title: Combined finite/discrete element analysis of impact loading of composite shells
Author: Mohammadi Touchaei, S.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1998
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In this study, a three dimensional combined finite/discrete element algorithm is developed to simulate delamination and material fracture in laminated composites subjected to impact loadings. The application of the finite/discrete element strategy to modelling of dynamic loading of composites is innovative, and provides a significant advance in comparison to presently available capabilities of numerical modelling of this complex physical problem. The traditional approach to the simulation of stress distributions in arbitrary shaped components is by finite element techniques. However, this method is rooted in the concepts of continuum mechanics and is not suited to general fracture propagation problems. In contrast, the discrete element method is specifically designed to solve problems that exhibit strong discontinuities in material and geometric behaviour. In this method of modelling of composites, the possible fractured region is modelled using a discrete element mesh, and the remainder of the structure is modelled by a standard finite element mesh. Each group of similar plies is modelled by one discrete element. Each discrete element is discretized by a finite element mesh and might have material or geometric nonlinearities. The interlaminar behaviour of discrete elements is governed by bonding laws which include contact and friction interactions for the post delamination phase. A softening Hoffman criterion is adopted as the material model to determine the initiation and propagation of the material cracks. A penalty based contact interaction algorithm is used to impose the impenetrability constraint of all potential contacts. Potential contacts are first detected by an alternating digital tree approach for global search, and then confirmed by an accurate local search. A special local remeshing technique is developed for modelling of an individual crack and modifying the neighbouring mesh to satisfy the necessary compatibility conditions. This approach requires a triangular mesh for 2D and a pentahedral mesh for 3D discrete element modelling. This remeshing scheme, in addition to geometrical modelling of a crack, provides a locally finer mesh that prevents excess distortion of failed elements and improves the numerical approximation. As assumed strain hourglass stabilization procedure is developed for the pentahedral element to avoid the hourglass instability of underintegrated (one Gauss point) elements.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available