Bruno Leblé

Assessment and Comparison of Several Analytical Models of Water Impact

This paper deals with the accuracy of several analytical models for the prediction of the hydrodynamic force and pressure distribution acting on a body entering initially calm water. The problem of water entry is important for the analysis of slamming loads undergone by boats operating in waves, as well as of the steady behaviour of high-speed planing vessels. The considered models are briefly described and the obtained results are compared to those of numerical computations and experimental observations for a number of two-dimensional and axisymmetric cases of water impact.

Modeling the Transition between Dense Metal and Damaged (Microporous) Metal Viscoplasticity

This article presents a physically motivated approach, which has been developed in order to describe the transition of behavior between dense metal plasticity and microporous metal plasticity in the context of dynamic plasticity and adiabatic conditions. Considering that void germination requires a certain amount of plastic deformation, a ‘primary’ hole nucleation criterion as well as a statistical law governing the ‘secondary’ hole formation kinetics has been proposed. In a consistent way, the hole nucleation criterion accounts for the accelerating effects of stress triaxiality and the delaying effects of temperature and strain rate. In addition, a modification of the GTN model was proposed, allowing for describing cavity growth under shear loading. The 3D constitutive equations were implemented as user material in the engineering finite element computation code Abaqus®. Numerical simulations were conducted considering a single finite element under uniaxial tensile loading and simple shear then notched cylindrical samples under remote uniaxial tensile loading. The numerical results clearly show the influence of the hole nucleation criteria on the ductile damage and failure.

Simulation of the shear-tensile mode transition on dynamic crack propagations

We propose an approach to the simulation of the shear-tensile transition in dynamic crack growth based on two points: a new crack propagation criterion which is suitable for shear, and an algorithm which is capable of handling the transition from shear mode to tensile mode and back in the same simulation. The new crack propagation criterion for brittle crack growth is based on the maximum shear stress rather than the maximum hoop stress. The shear stress direction becomes the new crack’s direction in which propagation is initiated for shear-type failure. The stress state at the crack’s tip is obtained through a local approach which can be used even in the case of extensive plasticity. Additionally, we propose to control the transition from shear mode to tensile mode during the simulation of crack propagation using an equivalent strain estimated at the crack’s tip. Depending on a threshold strain, the propagation direction is predicted using the maximum shear stress (in the shear case) or the maximum hoop stress (in the tensile case).

Temperature- and Rate-Dependent Failure in Dynamically Loaded Viscoplastic Materials

This work aims at studying experimentally and reproducing numerically the failure mechanisms of a ship structure constitutive material when submitted to airblast loading. With this aim in view, a physically motivated approach has been developed and applied in order to describe the transition of behaviour between dense metal plasticity and micro-porous metal plasticity in the context of dynamic plasticity and failure. The viscoplastic material is supposed to be initially exempt of micro-voids. Subjected to a monotonic loading involving a positive or null stress triaxiality, it behaves elastic-(visco)plastically. As soon as the conditions of plastic strain, plastic strain rate, temperature and stress triaxiality for the germination of a given volume fraction of voids are satisfied, the material behaviour becomes pressure dependent. Its damage-plastic yielding is consequently described using a micro-porous metal plasticity potential. The latter is proposed in the form of a modified version of the Gurson-Tvergaard-Needleman model allowing for describing cavity growth and further fracture under shear loading. The 3D constitutive equations are implemented as user material in the engineering finite element computation code Abaqus®. Numerical simulations are conducted and compared with experiments considering airblast loaded ship structures. The numerical results show clearly the influence of the hole nucleation criterion related constants and of the loading conditions (temperature, strain rate) on the damage and further fracture of the material.