High strain rate compressive behavior of epoxy LY 556: Radial constraint effect

A projectile impacting onto a target is a typical loading case. For the analysis of such cases, knowledge of high strain rate behavior of target materials is essential. Split Hopkinson pressure bar (SHPB) apparatus is generally used for evaluating the high strain rate behavior of materials. In conventional SHPB testing, the diameter of the incident and the transmitter bars is larger than the diameter of the specimen allowing for the radial expansion of the specimen due to Poissonʹs effect under compressive loading. However, in practical cases, the contact area of the projectile striking onto a structure is much smaller than the surface area of the structure. In such cases, radial expansion of the structure at the point of impact is constrained by the surrounding material. Materials may behave differently in the presence of radial constraint. The objective of the present study was to evaluate the effect of radial constraint on high strain rate properties of epoxy LY 556 using compressive SHPB apparatus. Two types of arrangements were used for providing radial constraint: (i) specimen with larger diameter than the diameter of the incident and the transmitter bars, (ii) specimen with diameter equal to the diameter of the incident and the transmitter bars with a metallic holder providing radial constraint. Epoxy LY 556 specimens were tested over a range of striker bar impact velocities. It was observed that the resistance of the specimen under compressive loading increases with radial constraint. Photographs of the fractured specimens and the schematic representation are also presented. The results of the earlier work have been found to be inline with the findings made in the present study.