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Computational modelling of cracks in viscoplastic media
A newly developed numerical model is used to simulate propagating cracks in a strain softening viscoplastic medium. The model allows the simulation of displacement discontinuities independently of a finite element mesh. This is possible using the partition of unity concept, in which fracture is treated as a coupled problem, with separate variational equations corresponding to the continuous and discontinuous parts of the displacement field. The equations are coupled through the dependence of the stress field on the strain state. Numerical examples show that allowing displacement discontinuities in a viscoplastic Von Mises material can lead to a failure mode that differs from a continuum-only model
Evolving discontinuities and cohesive fracture
Multi-scale methods provide a new paradigm in many branches of sciences, including applied mechanics. However, at lower scales continuum mechanics can become less applicable, and more phenomena enter which involve discon- tinuities. The two main approaches to the modelling of discontinuities are briefly reviewed, followed by an in-depth discussion of cohesive models for fracture. In this discussion emphasis is put on a novel approach to incorporate triaxi- ality into cohesive-zone models, which enables for instance the modelling of crazing in polymers, or of splitting cracks in shear-critical concrete beams. This is followed by a discussion on the representation of cohesive crack models in a continuum format, where phase-field models seem promising
A generalisation of J2-flow theory for polar continua
A pressure-dependent J2-flow theory is proposed for use within the framework of the Cosserat continuum. To this end the definition of the second invariant of the deviatoric stresses is generalised to include couple-stresses, and the strain-hardening hypothesis of plasticity is extended to take account of micro-curvatures. The temporal integration of the resulting set of differential equations is achieved using an implicit Euler backward scheme. This return-mapping algorithm results in an exact satisfaction of the yield condition at the end of the loading step. Moreover, the integration scheme is amenable to exact linearisation, so that a quadratic rate of convergence is obtained when Newton's method is used. An important characteristic of the model is the incorporation of an internal length scale. In finite element simulations of localisation, this property warrants convergence of the load-deflection curve to a physically realistic solution upon mesh refinement and to a finite width of the localisation zone. This is demonstrated for an infinitely long shear layer and for a biaxial specimen composed of a strain-softening Drucker-Prager material
Cranial Nerve Palsy Should Not Be Included within a Primary Composite Endpoint in Carotid Surgery Trials
A new era in cardio-renal risk management:overview of landmark papers published in NDT in 2021
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