A fully implicit plasticity model for the characterization of ceramics in ballistic protection

The Johnson-Holmquist-2 ceramic model is used for quasi-static indentation simulation. A modification is proposed to an associated plasticity formulation. This allows for a fully implicit solution scheme, where dilatation is used instead of the traditional explicit bulking formulation. Dilatation is shown to have an important influence on ring-crack formation during indentation. A mesh refinement study is performed to show the current tensile failure behaviour leads to mesh-dependent results.Applied Mechanic

Simulation of dynamic behavior of quasi-brittle materials with new rate dependent damage model

Stress-based nonlocal model, Damage, Rate dependency, Dynamic crack-branching Abstract. In concrete often complex fracture and fragmentation patterns develop when subjected to high straining loads. The proper simulation of the dynamic cracking process in concrete is crucial for good predictions of the residual bearing capacity of structures in the risk of being exposed to extraordinary events like explosions, high velocity impacts or earthquakes. As it is well known, concrete is a highly rate dependent material. Experimental and numerical studies indicate that the evolution of damage is governed by complex phenomena taking place simultaneously at different material scales, i.e. micro, meso and macro-scales. Therefore, the constitutive law, and its rate dependency, must be adjusted to the level of representation. For a proper phenomenological (macroscopic) representation of the reality, the constitutive law has to explicitly describe all phenomena taking place at the lower material scales. Macro-scale inertia effects are implicitly simulated by the equation of motion. In the current paper, dynamic crack propagation and branching is studied with a new rate-dependent stress-based nonlocal damage model. The definition of rate in the constitutive law is changed to account for the inherent meso-scale structural inertia effects. This is accomplished by a new concept of effective rate which governs the dynamic delayed response of the material to variations of the deformation (strain) rate, usually described as micro-inertia effects. The proposed model realistically simulates dynamic crack propagation and crack branching phenomena in concrete.Applied Mechanic

Modeling fatigue-driving delamination using a thick level set interface model

This paper presents a new discontinuous damage model for simulating fatigue-driven delamination in composites. Fatigue models commonly describe crack growth using the Paris law which provides the link between the energy released due to delamination and the crack growth rate. A core issue in implementing the Paris law is to accurately compute the energy release rate. In common cohesive fatigue models the energy release rate is extracted locally from the cohesive law where improving the accuracy of computed energy release rate needs extra treatments. The new fatigue model proposed in this paper provides an accurate non-local method for extracting the energy release rate based on the thick level set approach. This model also profits from the kinematic capabilities of interface elements for modeling discontinuities along the interface. The model is validated by comparing the model predictions under dierent fracture modes with theoretical and experimental data which shows good agreement in all cases.Applied Mechanic

Thick-level-set modeling of the dynamic double cantilever beam test

In this paper, the thick-level-set method is used to model stable and unstable (stick/slip) crack propagation in the dynamic double cantilever beam (DCB) test for unidirectional composite laminates. The thick-level-set method uses a predefined damage profile to describe the fracture process zone and allowsfor accurate evaluation of the global energy release rate. A phenomenological model is introduced to calculate the crack speed as a function of the energy release rate. The potential capability of the proposed approach is demonstrated by simulating a series of dynamic DCB tests under variable test rates.Applied MechanicsMaterials- Mechanics- Management & Desig

Experimental and Numerical Research Programme for the Design and Optimization of Various Aspects of Concrete Behaviour

Mechanics, Materials and StructuresCivil Engineering and Geoscience