Experimentation and finite element analysis of repairs on composite laminates and sandwich beam structures

Abstract

Composites like other engineering materials suffer damage due to mishandling, manufacturing defects and under design. Once they are damaged, an available option may be to restore them to working condition. This work investigated the characteristics of repairs done on wind turbine grade fiber reinforced composite laminates and sandwich beams. Two layups ([0] 2 and [45/-45/0/-45/45]) were investigated with varied forms of repair (infusion bonded, adhesive bonded, infusion with overply) conducted on them. Repaired laminate specimens and repaired sandwich beams were subjected to static tensile loads and four-point flexure respectively. Three-dimensional finite element models augmented with cohesive traction separation relationship were used to analyze bond behavior and compare with experimental observation. Strain data was collected using the process of digital image correlation. Results showed that repairs certainly reduced the stress concentration around regions of damage up to certain strain levels. Similarity in debond behavior was also observed between laminates and sandwich beams of similar ply orientation. Differences were noted in the debond behavior of the two different layups ([0] 2 and [45/-45/0/-45/45]) that were repaired and tested. The observations provided conclusions that could help improve the repair effectiveness of composites.