Rate-dependent self-healing behavior of an ethylene-co-methacrylic acid ionomer under high-energy impact conditions

In this work, the mechanical and the self-healing behaviors of an ethylene-co-methacrylic acid ionomer were investigated in different testing conditions. The self-healing capability was explored by ballistic impact tests at low-velocity, midvelocity, and hypervelocity bullet speed; different experimental conditions such as sample thickness and bullet diameter were examined; in all impact tests, spherical projectiles were used. These experiments, in particular those at low and midspeed, allowed to define a critical ratio between sample thickness and bullet diameter below which full repair was not observed. After ballistic damage, the healing efficiency was evaluated by applying a pressure gradient through tested samples. Subsequently, morphology analysis of the affected areas was made observing all tested samples by scanning electron microscope. This analysis revealed different characteristic features of the damaged zones affected at different projectile speed. Stress–strain curves in uniaxial tension performed at different temperatures and strain rates revealed yield strength and postyield behavior significantly affected by these two parameters. A rise of temperature during high strain rate tests in the viscoplastic deformation region was also detected. This behavior has a strong influence on the self-repair-ing mechanism exhibited by the studied material during high-energy impact tests.