Experimental investigation of the effect of natural microfibers on the mode I fracture toughness of plain-woven laminated composites

In the present study, the effect of natural microfibers (cork particles) on the mode I fracture toughness of plain-woven laminated composites has been investigated. For this purpose, double cantilever beam (DCB) specimens manufactured using hand lay-up method with stacking sequence of [0]28. To investigate the effect of cork particles on fracture toughness, samples with two different weight percentages (1% by weight and 3% by weight) were manufactured and the experimental results were compared with one obtained from sample with pure epoxy resin. Experimental results show that as the amount of cork particles increases, the onset of crack growth requires more energy. The amount of improvement in initiation fracture toughness for the DCB sample with 1% and 3% cork weigh has been increased by 67.15% and 71.96%, respectively which is due to the role of the cork in the resin rich area near the crack tip that arrested the delamination growth. Unlike the initiation fracture toughness, the propagation value is reduced by adding cork particles to the resin.   During delamination growth, due to the agglomeration of micro fiber at delamination interface and role of stress concentration of these particles, hence, micro-cork fibers have not been able to increase the propagation fracture toughness and in some cases have slightly reduced the propagation fracture toughness of the delamination. Also, in order to investigate the mechanisms of damage, the fracture surfaces of the samples were scanned using scanning electron microscopy.