Experimental procedure to characterize the mode I dynamic fracture toughness of advanced epoxy resins

• We develop a dynamic three point bending test to fracture notched specimens of epoxy.
• We realize experimental asymptotic strain analysis around moving crack tips in epoxy.
• We measure fast crack propagation speeds up to 345 m/s by high speed cinematography.
• We identify the dynamic stress intensity factor of fast running cracks in epoxy.
• The dynamic fracture toughness of toughened epoxies depends on the crack velocity.

This research aimed at developing an experimental procedure to characterize the dynamic fracture toughness of a fast running crack in advanced epoxies enriched with thermoplastic particles and demonstrating quasi-brittle fracture. A strain gauge method was defined to determine the dynamic stress intensity factor KIDKID for the mode I crack opening with various crack speeds. This strain gauge measurement was associated with high speed cinematography on a three point bending test dedicated to the fracture of notched specimens made of the Hexply®M21 epoxy resin. Results demonstrate that the crack propagation speed has a large influence on the dynamic fracture toughness of advanced epoxy resins.