Mechanical Response of Materials with Physical Defects. Part I. Modeling of Material Damage for Center Cracked Panel

摘要

This is the first part of an investigation dealing with the global load-displacement behavior of a stationary center cracked panel in which material damage is accumulated for each increment of loading. The finite element procedure was used where the local stiffness in regions ahead of the crack undergo changes in accordance with a predetermined failure criterion. The resulting non-linear behavior of the load-displacment curves are obtained by two different damage models. Growth of the crack will be considered in the second part of this work. The proposed damage concept models the development of microcracks and/or voids ahead of a macrocrack by altering the local stiffness. As the material elements are damaged, the linearly elastic behavior changes to pseudo-linearly elastic behavior, under the assumption that any energy dissipated due to microcrack generation is no longer recoverable upon unloaidng. No other dissipative mechanism is assumed. A Single Damge Level model was based on a 'damaged/undamaged' evaluation of each finite element in the panel specimen. The damage threshold was based on the elastic strain energy density at the yield stress level of an uniaxial tenisle test specimen. The effect of damage on the bulk material properties in the damage zone were taken to be a reduced secant elastic modulus consistent with the uniaxial tenisle test specimen and with the effective elastic properties of the microcracked portion of the medium. A Multiple Damage Level model incorporated twenty-four discrete values of the secant elastic modulus of a specified uniaxial tensile specimen true stress-true strain curve. The strain energy density level at yield stress was taken to be the damage threshold level.