Short beam strength of curaua, sisal, glass and hybrid composites

In this study, the short beam strength characteristics of randomly oriented composites were comprehensively investigated. The following parameters were varied: fiber used (curaua or sisal), fiber washing or surface chemical treatment with sodium hydroxide/sodium borohydride, fiber length (from 5 to 60 mm), hybridization with glass fiber and the preprocessing of the polyester resin. The overall fiber volume fraction was kept constant (30 vol.%). In all configurations, the composites containing curaua fiber obtained higher short beam strength than those with sisal. An increase in fiber length yielded higher short beam strength. The optical and electronic micrographs showed mostly horizontal cracks, typical of shear failure. In addition, it was carried out a study of the ASTM D2344 standard regarding the span-to-thickness ratio recommended for testing, the measured strength decreased for higher span-to-thickness ratio for specimens with higher length and width, and the failure mode changed to bending around span-to-thickness >12.