Hygrothermal effects on quasi-isotropic carbon epoxy laminates with machined and molded edges

Polymer matrix composites, when exposed to temperature and humid environment, undergo dimensional and stress state changes due to moisture induced swelling and thermal expansion. Moisture absorption may induce mechanical and physic-chemical changes that toughen the polymeric matrix and/or deteriorate matrix–fiber interface by interface debonding or micro-cracking. In the present paper, the effect of edge finishing combined with hygrothermal conditioning on the tensile strength of quasi-isotropic laminates is experimentally investigated. The results indicate that moisture may either increase or decrease the tensile strength of quasi-isotropic laminates with machined or molded edges depending on dominant effect (matrix toughening vs interface degradation). Transverse sections of specimens were observed by scanning electronic microscopy (SEM).