Strength improvement in unidirectional arrayed chopped strands with interlaminar toughening

The purpose of this study is to improve the strength of unidirectionally arrayed chopped strands (UACS), a sheet-like molding material made of regularly and unidirectionally arrayed discontinuous fiber strands impregnated with unsaturated thermoset resin. In a previous paper, we found that the final failure of UACS laminates is mainly controlled by the onset of unstable delamination growth. This paper presents interlaminar toughening of UACS laminates as a means of suppressing delamination. Specifically, we applied the following three approaches to toughening: (1) toughening the matrix resin itself, (2) inserting a toughened interlaminar layer, and (3) localizing the toughened layer only around the ends of the chopped strands. As a result, we demonstrate a tensile strength improvement of up to about 20%.