Quantifying thermoset polymers healing efficiency: A systematic review of mechanical testing

The study of fracture behavior of self-healing polymers is the key-tool that issues the efficacy of the advanced healing functionality. Damage mechanisms of autonomously healed polymers resemble the adhesive joints one. Thus, well-established fracture testing configurations of adhesive composites are acquired and adopted in order to monitor the damage initiation (cracking) that calls for healing recuperation. As soon as healing is achieved the loading tests are repeated in order to evaluate the newly built resistance to damage. The innovative analysis of crack arrest (and/or closure) fracture mechanisms due to healing requires simple and sophisticated crack opening (mode I of fracture) settings as the commonly used tapered double cantilever beam (TDCB) test. Experimental research on TDCB shaped polymers has always gone along with self-healing technology (introduced on White's protocol). Furthermore, other classical testing configurations contribute as alternatives of TDCB setting (e.g. single-edge notched beam tensile tests) measuring the fracture toughness or as complementary mechanical features evaluating systems (e.g. tensile, shear, debonding tests).A step further, the set-ups evaluating the healing evolution under quasi-static impact and dynamic load are critically reviewed. This article focuses on the evolution of testing methods applied to quantify extrinsic crack healing on thermoset. The study aims to exemplify the documented experimental settings and to provide practical tools that facilitate work hereafter.