Crack arrest capability of shock resistant PMMA under impact loading
Résumé
Analysis and understanding of failure mechanisms under high strain rate loading in engineering materials is a key point for the design of structures submitted to accidental overloads. We are here interested in the crack arrest capability under impact loading of polymers used as structural and/or protection materials. In the philosophy of the crack arrest capability considered in the present work, an engineering structure is supposed to be initially weakened by a crack and the question to answer is how this pre-cracked structure behaves when dynamically reloaded. The Kalthoff and Winkler (KW) impact test, consisting in impacting the edge of a double notched plate, was accordingly retained to that purpose A comparative study of the dynamic crack arrest capability of several grades of shock-resistant PMMA under high strain rate loading is presented evidencing the brittle feature of the material failure. High speed camera was used to record the chronology of the failure mechanisms. It is notably shown that the higher the impact velocity (in the range 50-100 m/s) the larger the number of fragments. Moreover, depending on the impact velocity, changes in the crack path and thus in the mechanisms controlling the PMMA dynamic fracture can be seen.