Polypropylene matrix composites reinforced with pre‐stressed glass fibers

Abstract Thermoplastic matrix composites have recently emerged as promising engineering materials because of their desirable properties such as high service temperatures, high impact resistance, and processing advantages. However, residual stresses in composites introduced during fabrication are cited as one of the most significant problems in the processing of composites. In some instances these stresses have been shown to significantly degrade the strength of the material, resulting in matrix cracking, debonding, reduced fracture toughness, and delamination. In this work, studies have been carried out on glass fiber reinforced polypropylene composites formed by compression molding process from co‐mingled fabrics. The fibers were pre‐stressed during the process to produce high performance composite products with low residual microstresses, which are harmful to the properties of the composite. Mechanical tests showed that pre‐stress can increase the tensile, flexural and interlaminar shear properties of the composites, and there exists an optimum pre‐stress level to gain best properties for each external loading condition.