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Title: Progressive fracturing under dynamic loading conditions
Author: Ren, Z.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1994
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The finite element method in conjunction with the theory of viscoplasticity, and to a lesser extent plasticity, have been used for modelling of plasticity base progressive fracturing in transient dynamic problems. The difficulties associated with the computational modelling of wave propagation problems are discussed. The central difference method is utilised for step-by-step direct time integration of equations of motion, which is coupled with the lumped mass and proportional damping matrices. Special attention is devoted to a correct integration of energy states. Computer implementation takes advantage of modern computer languages and programming techniques, which results in a efficient and fully portable computer code. The strain softening phenomenon is explained in some detail. The consequences of the change of type in the governing of classical rate-independent continuum at the onset of strain softening are investigated. As a solution to that problem, the enrichment of the continuum with the higher-order derivatives in form of strain-rate dependent model (viscoplasticity) is explored and unique, stable and mesh insensitive results are observed for mode-I and mode-II failure problems. A constitutive model for quasi-brittle materials is proposed. The progressive damage is assumed to be isotropic and is modelled with the decohesion process. To account for different behaviour of heterogeneous materials under increasing hydrostatic pressure the degree of softening is rendered state-of-stress dependent. The model is based on the Mohr-Coulomb yield criterion and non-associated flow rule is utilised. The problems associated with non-smoothly intersecting yield surfaces for Mohr-Coulomb yield criterion are discussed with emphasis on correct evaluation of the viscoplastic parameters in singular regions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available