Mechanism-Based Modeling of Strain Rate–Dependent Transition of Macromechanical Behavior Accompanied by Temperature Rise Effects of a Toughened Polymer Composite

Recently, the unusual macromechanical behavior of a soft–hard-blend polymer composite was discovered, which is rubber-like at a low strain rate and glass-like at a high strain rate. Such strain rate–dependent mechanical behavior contributes to an outstanding impact resistant property, and consequently raises scientific interest in developing a mechanism-based modeling. In this work, a new mechanism-based modeling that involves the thermoelastoviscoplastic issues was developed. It considers the polymeric physics that accounts for the activation of the segmented molecular chains motion upon an applied stress and the strain rate dependency. The interactions of molecular chains among the hard and soft segments are captured through several relaxation spectrums. Each relaxation spectrum has a unique definition of material parameters and the activation range against the applied loading rate. In addition, the ductility originating from the large straining of soft parts that can cause a resistance to molecular chains alignment is modeled individually. Temperature rise also is addressed by a thermomechanical coupling relation which was developed by specifically targeting the related thermal parameters. The transportation of heat to the surroundings is considered on the basis of adiabatic thermodynamic flow, and the net equivalent temperature rise is calculated. The results from the modeling simulations were found to well match the experimental data. This work developed a thermomechanical model for illustrating the strain rate–dependent transition of mechanical behavior of a toughened polymer composite, which is isotropic and appliable to both small strains and large strains.

This study presents a general numerical framework for developing a mechanism-based constitutive model with thermomechanical coupling considerations. It can illustrate the rate-dependent mechanical behavior of isotropic polymer composites, and can specifically target the thermal parameters based on adiabatic thermodynamic characteristics. Herein, the modeling mechanical features include the initial linear elasticity to nonlinear transition to yielding, followed by slight softening, and then plastic flow at a plateau stress with a large strain and final densification. The rate dependency involves the strain rate from $0.0001/\mathrm{s}$ to $\mathrm{7,455}/\mathrm{s}$. In the modeling, the motion activation of the segmented molecular chains upon an applied stress and the strain rate dependency are addressed. Herein, the unique definition of material parameters for several relaxation spectrums that can capture the interactions of molecular chains among the hard and soft segments is given. Each relaxation spectrum has its own activation range of the applied loading rate. In addition, the ductility, that is, from the large straining of soft segments, is addressed that has a capability of causing the resistance to the alignment of molecular chains. This model produces a well-matched illustration of stress–strain relations of polymer composites at various strain rates. This work offers an insightful understanding of the rate-dependent mechanical behavior of polymer composites for developing the high impact–resistant polymers and guiding their applications in impact events.