EMPIRICAL DAMAGE EVALUATION OF GRAPHITE-EPOXY LAMINATE BOLT JOINT IN FATIGUE

The bearing and fatigue strength of a bolt joint in a (+/-45/O2/+/-45/ O2/+/-45/O2/90)s graphite/epoxy laminate is analyzed. A damage paramet er is defined in terms of the change in the elongation of the bolt hol e after a predetermined number of cyclic loading. Experimental data ar e obtained for specimens tested under a dry and wet environment at roo m and elevated temperature. Damage accumulation is reflected by data o n bolt hole elongation. Physical damage of the laminate is examined an d showed that fiber bundle fracture started at the interior of the lam inate and progressed to the exterior with increasing load. Damage arou nd the bolt hole was noticeable by the congregation of microcracks in the matrix and hence it depended on the fiber orientation. Enhancement of interfacial debonding was also observed when specimens are fatigue d in an elevated moisture/temperature environment.