Compressive evaluation of homogeneous and graded epoxy–glass particulate composites

• We studied stress propagation in particulate composites.
• Low particulate volume fraction causes deterioration in impact performance.
• Higher particulate volume fraction enhances impact attenuation.
• Impact on stiff side of FGM offers superior attenuation than impact on soft side.

The propagation of stress waves in epoxy–glass particulate composites and graded materials was studied experimentally. Materials tested in this study consisted of an epoxy matrix with various concentrations of spherical glass particles having a mean diameter of 42 μm. Plate impact experiments were performed using a gas gun. Embedded within the specimens were manganin stress gauges used to record propagating compressive longitudinal stress waves through the material. High strain rate experiments using a Split Hopkinson Pressure Bar (SHPB) apparatus were also performed to evaluate the dynamic strength of the specimens, while quasi-static compression tests were undertaken to characterize their quasi-static behavior. Ultrasonic wave speed measurements were carried-out in order to obtain additional material properties and characterize the gradation in functionally graded materials (FGM). It was found that low volume fractions of particles are detrimental to the performance of the material under impact loading, while concentrations in the range of about 30 to 45% by volume exhibit characteristics of higher degrees of scattering. This suggests that materials in this latter range would be more effective in the thwarting of destructive shock waves than the homogeneous matrix material. Impact testing of FGM specimens suggests that impact loading on the stiff (high volume fraction) face results in much higher levels of scattering. Therefore, such materials would be effective for use in light weight armor or as shielding materials due to their effective attenuation of mechanical impulses.