CUMULATIVE DAMAGE THEORY IN MULTIAXIAL FATIGUE OF GRAPHITE/EPOXY ((+,-45)(S)) COMPOSITES AND WEIGHT FUNCTION THEORY FOR A RECTILINEAR ANISOTROPIC BODY (COLLINEAR CRACKS, STRESS INTENSITY)

The phenomenological evolution laws of damage based on residual life and residual strength were critically examined. The failure of a specimen can be defined immediately before or after fracture. The former is called "failure defined by approach II" and the latter "failure defined by approach I." Usually at failure there is discontinuity of forcing variables and, because of this, damage at failure is discontinuous. Therefore the values of damage at failure by two different approaches are not the same.; Based on this idea the sequence effects of the phenomeno- logical evolution law of damage given by dD/dN = g(D) f((')(PHI)) were studied. A multiaxial growth law of damage was proposed based on experimental data of axial, torsional, combined axial and torsional inphase, and step loading fatigue in thin-walled Graphite/Epoxy tubes consisting of four layers of (+OR-)45 (,s) laminates.; Interlaminar normal stress effect on the fatigue behaviour of a tubular specimen was studied experimentally. It was concluded hat the interlaminar normal stress has no discernible effect on the fatigue life.; In the second part of this thesis Bueckner's weight function theory is extended to rectilinear anisotropic bodies for two-dimensional loading systems. Explicit solutions for the configuration of collinear cracks are provided. A numerical example for the edge crack in a bar of finite length is presented.