Impact Testing of Polymer‐filled Auxetics Using Split Hopkinson Pressure Bar

Abstract

In this paper, impact testing of auxetic structures filled with strain rate sensitive material is presented. Two dimensional missing rib, 2D re-entrant honeycomb, and 3D re-entrant honeycomb lattices are investigated. Structures are divided into three groups according to type of filling: no filling, low expansion polyurethane foam, and ordnance gelatine. Samples from each group are tested under quasistatic loading and dynamic compression using Split Hopkinson Pressure Bar. Digital image correlation is used for assessment of in-plane displacement and strain fields. Ratios between quasistatic and dynamic results for plateau stresses and specific energy absorption in the plateau are calculated. It is found out that not only the manufactured structures, but also the wrought material exhibit strain rate dependent properties. Evaluation of influence of filling on mechanical properties shows that polyurethane increases specific absorbed energy by a factor of 1.05-1.4, whereas the effect of gelatine leads to increase of only 5-10%. Analysis of the Poisson's function reveals influence of filling on achievable (negative) values of Poisson's ratio, when compared to unfilled specimens. The results for the Poisson's function yielded apparently different values as the assessed minima of quasi-static Poisson's ratio in small deformations are constrained by a factor of 15.

Split Hopkinson pressure bar: design parameters and prediction of the experiment output

“…The striker was accelerated using compressed air gas-gun with maximum operating pressure 16 bar. Other details about the used setup and its instrumentation can be found in (Fíla et al, 2017). Experimental setup is shown in Fig.…”

“…An additively manufactured 2D re-entrant auxetic lattice (Fíla et al, 2017) (structure with negative Poisson's ratio) is presented here as an example of the model functionality for linear-elastic aluminium bars at two different impact velocities. It was experimentally proven that, in case of the aluminium bars, it is not necessary to take friction and pressure losses into account as the effects can be considered negligible in the used velocity range.…”

High Strain-Rate Compressive Testing of Filling Materials for Inter-Penetrating Phase Composites

“…For the high strain-rate tests, an in-house SHPB, developed at CTU in Prague [8] was used. The apparatus is based on Kosky setup, which was adapted for testing of materials with low mechanical impedance.…”

Preprocessing of Hopkinson Bar Experiment Data: Filter Analysis

“…By using these types of materials, it is possible to significantly improve efficiency and safety of constructions or vehicles. However, proper description of their complex structural and mechanical properties might be very challenging due to their complicated structures, especially in case of high strain-rate loading [2]. Therefore, it is essential to not only perform precise high velocity material tests but also develop advanced methods that would enable reliable evaluation of such experimental data.…”