Hygrothermal aging effects on the mechanical behavior of scarf-repaired composite laminates

Adhesively bonded techniques have been widely used to joint or repair composite components in aircraft structures, which are inevitably subjected to various environmental conditions in service. Aiming to investigate the effect of hygrothermal aging on scarf-repaired composite structures, bulk adhesive specimens and scarf-repaired composite laminates of three different laminate thicknesses were tested before and after hygrothermal aging in this paper. Experimental results indicate that the strength reduction of scarf-repaired composite laminates after aging is less evident than that of bulk adhesive. For scarf-repaired composite laminates, a linear relation is found between the strength reduction and their moisture contents. Visual inspection and microscopic observation were performed to investigate the damage mechanism. In addition, a finite-element model based on continuum damage model and a degraded bilinear traction–separation cohesive zone model considering hygrothermal aging degradation was established. The predicted strength and failure modes achieve good agreement with experimental results.