Numerical Simulations of Void Linkage in Model Materials using a Nonlocal Ductile Damage Approximation

Experiments on the growth and linkage of 10 μm diameter holes laser drilled in high precision patterns into Al-plates were modelled with finite elements. The simulations used geometries identical to those of the experiments and incorporated ductile damage by element removal under the control of a ductile damage indicator based on the micromechanical studies of Rice and Tracey. A regularization of the problem was achieved through an integral-type nonlocal model based on the smoothing of the rate of a damage indicator D over a characteristic length L. The simulation does not predict the experimentally observed damage acceleration either in the case where no damage is included or when only a local damage model is used. However, the full three-dimensional simulations based on the nonlocal damage methodology do predict both the failure path and the failure strain at void linkage for almost all configurations studied. For the cases considered the critical parameter controlling the local deformations at void linkage was found to be the ratio between hole diameter and hole spacing

Balloon inflation revisited

In the present work, an inexpensive setup of an experiment of balloon inflation is described in order to measure its pressure and diameter. As already children know from blowing into such a (toy) balloon, the initially necessary high pressure level decreases with increasing balloon diameter. The original intention of this project has thus been to quantify this effect, which from a theoretical point of view is known as material instability. With a corresponding instrumentation of the test setup, it is additionally possible to realise and analyse further results for different load scenarios such as loading and unloading cycles, which are able to (re)produce by the presented system quite as easy

Damage and strain localisation during crack propagation in thin-walled shells

Based on the GURSON damage model a simulation of ductile crack growth in thin-walled shell structures is presented. The proposed Finite Element model for shells is based on a 5-parameter theory taking bending effect into acount. The problem of mesh dependence in strain softening materials is treated by a non-local regularisation of the damage evolution equation. As an example a cylindrical tube under internal pressure is considered. Results for the equivalent stress, the equivalent strain and the damage parameter are shown