Dissipation and resilience of elastomeric segmented copolymers under extreme strain rates

The high strain rate behavior of elastomeric segmented copolymers has received significant attention in recent years in connection with the design of polymeric composites for a myriad of engineering and military applications. The presence of thermodynamically immiscible phases of hard and soft domains in these copolymeric materials enables multiple energy storage and dissipation pathways which offer new avenues towards highly resilient yet dissipative protective systems. In this research, the extreme strain rate behavior of an exemplar polyurea is addressed in Taylor impact tests to quantify ultrafast deformation processes at strain rates over 105/s which are incurred in ballistic and blast loading events. Numerical simulations of the high rate, inhomogeneous deformation incurred during Taylor impact tests are conducted using a recently proposed large deformation constitutive model implemented within nonlinear finite element simulations. The simulations show the predictive capability of the viscoelastic-viscoplastic constitutive model under extreme strain rate events and reveal the details of the evolution of the deformation and stress waves during impact loading. Additionally, the highly dissipative yet resilient features of polyurea under inhomogeneous deformation at extreme strain rates are elucidated in terms of energy dissipation and shape recovery by taking representative sets of constitutive models for rubbery and glassy polymers and their combinations. The remarkable ability of the polyurea to dissipate energy in a manner similar to a glassy thermoplastic yet exhibits the resilience of a rubbery material is shown in both the experiments and the models. This work reveals that the model of the two-phase structures of segmented copolymers is providing both dissipation and energy storage pathways under extreme deformation.