Rate-Dependent Fracture Behavior of Aerospace Epoxies: PR-520 and 3502

To understand the response of polymeric materials used in fiber-reinforced composite structures, it is necessary to examine their brittle failure mechanisms under various loading scenarios. As such, this study presents the quasi-static and dynamic fracture response of aerospace resins 3502 and PR-520. Quasi-static fracture investigations were performed on precracked samples using single edge notch tension (SENT) configuration in a standard load frame. Dynamic fracture investigations were conducted using a unique long bar device where a projectile impacts the sample to generate wave-driven Mode-I (opening) fracture. Digital image correlation (DIC) is used in conjunction with ultrahigh-speed imaging to extract the stress intensity factor (SIF) at crack initiation using the stationary crack solution. Both material systems exhibited rate-dependent fracture behavior. For 3502, the average quasi-static fracture toughness was 0.60 MPa root m, 56% lower than the average dynamic fracture toughness of 1.07 MPa root m. However the PR-520 samples exhibited the opposite behavior, demonstrating greater quasi-static fracture toughness averaging 1.60 MPa root m with dynamic values of 0.71 MPa root m. The difference in behavior between the resins may be attributed to polymer chain crosslinking, where the lower degree of crosslinking in PR-520 enables increased elastic deformation and resistance to fracture under quasi-static loading, and the higher degree of crosslinking in 3502 gives rise to an increased resistance to fracture under dynamic loading. (C) 2021 American Society of Civil Engineers.

Automated summary

This study investigates the response of aerospace resins 3502 and PR-520 in quasi-static and dynamic fracture. The results reveal that the two materials exhibit different fracture behaviors, which can be attributed to the degree of polymer chain crosslinking.