Strain rate dependent mechanical properties of a high‐strength poly(methyl methacrylate)

Abstract

Strain rate dependency is an important issue for the mechanical response of materials in impact events. Dynamic mechanical properties of a high-strength poly(methyl methacrylate) (PMMA) were studied by using split Hopkinson pressure bar technology. The maximum stress is enhanced with the increase of strain rate, and then keeps a constant with the further increase of strain rate, which is accompanied with a linear increase of fracture energy density. The critical data of strain rate and maximum stress were determined. Eyring's equation was applied for analyzing the influence factors, which relate to the hardening induced by strain rate and softening caused by adiabatic temperature rise. Inherent physical mechanisms were clarified and the strategies for designing advanced impact-resistant polymers were proposed.

Studying a Flexible Polyurethane Elastomer with Improved Impact-Resistant Performance

“…Eyring’s equation can be used to illustrate the strength of polymer materials related to the applied strain rate and inherent material parameters [54,55], which is expressed as seen below:σyT=ΔUvT+Rvln[2trueε˙e0], where σy is the yield stress; T is the ambient temperature; ΔU is the activation energy of plastic deformation/flow, i.e., the height of the potential energy barrier of two adjacent equilibrium positions for element units to jump; v is the activation volume of element motion unit; ε˙ is the strain rate; e0 is the pre-exponential factor; and R is the gas constant. Under dynamic loading at a given strain rate, yield stress is correlated with the material parameters of ΔU and v.…”

“…Along the loading direction, numerous deformation bands are formed and elongated, which construct a uniform parallel pattern (see Figure 7b). These deformation bands are expected to be induced by lateral tensile stress upon an applied dynamic compressive loading [16,55], which carry the considerable strain. By measurement, they have an average width of about 70 µm.…”