Nonlocal formulation of the evolution of damage in a one-dimensional configuration

The constitutive modelling of distributed damage evolution with strain-softening effects causes serious problems when local concepts are employed: numerical approximations obtained by finite element techniques show unlimited localization of deformation and energy dissipation decreases to unrealistic values when element meshes are refined. To overcome these problems nonlocal formulations have been introduced; a particular continuum damage example is presented which allows an analytical elaboration in the one-dimensional case. For a bar in uniaxial tension the exact solution is derived and the physical implications are examined

Experimental analysis of the evolution of thermal shock damage using transit time measurement of ultrasonic waves

Thermal shock is a principal cause of catastrophic wear of the refractory lining of high temperature installations in metal making processes. To investigate thermal shock experimentally with realistic and reproducible heat transfer conditions, chamotte and corund refractory samples of ambient temperature were subjected to surface contact with molten aluminium followed by passive cooling in ambient air. The evolution of damage was characterized by measuring the transit time of ultrasonic longitudinal waves at various sample locations after each test cycle. The mechanical validity of transit time measurement was confirmed in independent experiments. The single test cycle performed with chamotte material indicated the reproducibility and reliability of the experimental set-up and damage characterization method. Multiple test cycles performed with corund material yielded a reliable set of data, to be used for model validation purposes. Both non-uniform damage due to temperature gradients as well as uniform damage due to exposure to a uniform temperature were determined experimentally. The interaction between both damage mechanisms requires further investigation as well as the possible shielding of heat transport by damage. © 2008 Elsevier Ltd. All rights reserved

Prediction of the large strain mechanical behaviour of heterogeneous polymer systems by a multi-level approach

Shear band formation in heterogeneous tensile bars was studied using an accurate homogenization method that allows for a numerical coupling between the microscopic and macroscopic stress-strain behavior. The procedure is based on a classical homogenization theory, assuming local spatial periodicity of the microstructure, and supplies a consistent objective relation between the local macroscopic deformation and the microstructural deformation of a spatially periodic representative vol. element (RVE), representing the local microstructure. The method was used to predict the influence of the microstructure on localization phenomena in plane strain hour-glass-shaped polycarbonate specimen with different vol. fraction of non-adhering low-modulus rubbery particles. An irregular particle distribution seems to promote deformation spreading over the sample, which leads to enhancement of toughness of heterogeneous polymer systems by the addn. of easily cavitating rubbery particle