Failure mechanisms of scarf-repaired composite laminates under tensile load

An investigation based on experimental and finite element (FE) studies was carried out to understand the failure mechanisms of scarf-repaired T700SC/NY9200GA composite laminates under tensile load. Test specimens were categorized into 4 groups based on the type of scarf patch (pre-preg and pre-formed) and scarf angles (6A degrees and 10A degrees). A 3-D progressive damage accumulation model was developed to understand the damage mechanisms and predict the ultimate strength of repaired laminates. Damage characteristics of specimens were observed by optical microscope and scanning electron microscopy. Test results have shown that the laminates repaired with pre-preg scarf patch and 6A degrees scarf angle have higher failure strength. It was also found that the fracture morphology of failed laminate is different but failure mode was found to be the same. The crack initiated from highly stressed adhesive regions and then circumferentially propagated throughout the adhesive interface thus causing adhesive failure. FE results were found to be in good agreement with experimental results.