The phenomenological evolution laws of damage can be defined either based on residual life or residual strength. The failure of a specimen can be defined immediately after or before fracture. The former is called in this paper by "failure defined by approach I" and the latter "failure defined by approach II." Usually at failure there is a discontinuity of loading 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 phenomenological evolution law of damage given by dD/dN = g(D)f(Φ) were studied. Thin-walled graphite/epoxy tubes consisting of four of [±45]s laminates were used for the experimental study of sequence effects and the effects of mean stress on fatigue life. It was found that the sequence effects in two step uniaxial fatigue for [±45]s graphite/epoxy tubular specimen showed that a high-low block loading sequence was less damaging than a low-high one.

Keywords: Cumulative damage, Graphite/epoxy composite, Residual life, Residual strength, Fatigue damage, Phenom- enological laws