Impact of Crack Location, Crack Initial Length, and Crosshead Speed on Fracture Toughness of Polypropylene and Glass Fiber-Reinforced Polypropylene Pipes

Fracture toughness (KIC) is a critical parameter for evaluating the performance of materials, particularly in engineering applications where structural integrity is crucial. The objective of this study is to investigate the fracture toughness characteristics of polypropylene (PP) and glass fiber-reinforced polypropylene (GFPP) pipes. Specifically, evaluating the influence of crosshead speed, crack location, and initial crack length on the KIC of these materials under both tensile loading (Mode I fracture) and bending conditions. Tensile tests were conducted on both materials using two specimen configurations and varied notch lengths to simulate Mode I fracture conditions. Additionally, three-point bending tests were performed on single-edge notched specimens under various crosshead speeds. Fracture toughness parameters were determined using linear elastic fracture mechanics (LEFM) and J-integral principles, depending on the materials' deformability. The resulting (KIC) values indicated that GFPP achieved a maximum of 5.47 MPa √m at 500 mm/min, while PP reached 4.61 MPa √m at the same speed. In bending tests, GFPP exhibited (KIC) values of 4.82 MPa √m and 5.24 MPa √m at 50 mm/min and 500 mm/min, respectively, compared to PP's 3.89 MPa √m and 4.53 MPa √m at the same speeds. These findings highlight the influence of crosshead speed and crack location on the (KIC) of both materials, providing critical insights for the design and evaluation of piping systems in engineering applications.