Search

Equations are developed for predicting opening and sliding modes of crack growth along planes of geometric symmetry in viscoelastic orthotropic media with and without large prestrains. Except for the small zone of failing material at the crack tip, the body is assumed to be linearly viscoelastic with respect to the changes in stress and strain which occur during crack propagation. Results obtained previously for isotropic media are first reviewed, and then a relation is derived for predicting crack tip velocity in an orthotropic body in plane strain; included is a numerical example using constitutive properties of a fiber-reinforced plastic. Extension to fracture of prestrained media and crack growth between certain types of dissimilar media is then made. Finally, it is argued that these crack velocity relations can be employed in plane stress problems and in many three-dimensional cases, and, with a small change, can be used to predict the time of fracture initiation. (Author)

This article is devoted to the formulation of a mechanical constitutive theory accounting for deformation-induced material degradation, such as that resulting from the growth of small flaws. As in a previous investigation by the authors, the degrading material is modeled here as an effectively materially-uniform, simple body in the sense of Noll, 'damage' being interpreted as a permanent alteration in the stress-functional of this effective continuum. The authors' previous theory, which did not account for continued damage at constant strain, is shown here to provide a measure of damage incurred during a given strain history relative to the equilibrium configuration defined by the current value of strain. It is then shown that this 'relative damage functional' can be used to generate an absolute measure of damage if it is accepted that no damage can accrue in the absence of stress. In view of the physical assumptions introduced here, the present formulation appears to encompass fatigue and spallation phenomena as well as the slow deformation of most composite materials.

Microscopic theories on crack growth and macroscopic theories on cumulative damage are compared. Discussions are based on a set of laws introduced by Schapery on particulate reinforced composites and propellents. (AE-PL)

In the investigation, the elements of a mechanical constitutive theory for materials subjected to accumulated local damage, such as that resulting from the growth of small flaws, are laid down within the framework of Noll's theory of simple materials. A macroscopic definition of deformation--induced damage in a material with memory undergoing a motion having finite deformation gradients having first been given, the question of quantifying the damage done by a particular strain history is addressed. It is found that there are constitutive functionals for which the damage cannot be meaningfully measured without a knowledge of the subsequent deformation. The remainder of the paper is devoted to a consideration of a class of damageable materials (termed simple) for which the accrued damage can be measured solely in terms of the history of strain. A suitably modified fading memory postulate on the stress-functionals of such materials is introduced and its consequences explored. The significance of these theoretical notions is illustrated through a number of examples pertinent to the behavior of composite materials. (Author)