Relationship between interfacial shear strength and impact strength of injection molded short glass fiber-reinforced thermoplastics

Short glass fiber-reinforced thermoplastics (SGFRTPs) are being used to reduce carbon dioxide emissions from transportation equipment, especially domestic vehicles, because of their properties and because they are lighter than metal or ceramic materials. Interfacial shear strength (IFSS) strongly affects mechanical properties of SGFRTPs, such as the impact strength. In recent years, investigations of IFSS and impact strength have been very active. Positive correlation between these properties is often reported, but no clearly defined quantitative relation has been found. This study used the short beam method and the notched Charpy impact test to elucidate IFSS and the impact strength of injection-molded SGFRTPs with varying fiber contents: IFSS decreases concomitantly with increasing fiber content; the notched Charpy impact strength increases concomitantly with increasing fiber content. Fiber pull-out occurred along the entire fracture surface. Findings confirmed that fiber pull-out occurred with both crack initiation and propagation, indicating that energy absorption in the impact test was entirely attributable to the frictional energy necessary for fiber extraction. Based on this conclusion, a mechanical model was developed to explain the notched Charpy impact strength of SGFRTP injection molded products in terms of their IFSS, pull-out fiber length, and fiber orientation angle. The impact strength calculated using the predicted results shows good agreement with the experimentally obtained results.