On the Development of a Release Mechanism for a Split Hopkinson Tension and Compression Bar

Abstract

Split Hopkinson bars are used for the dynamic mechanical characterisation of materials under high strain rates. Many of these test benches are designed in such a way that they can either be used for compressive or tensile loading. The goal of the present work is to develop a release mechanism for an elastically pre-stressed Split Hopkinson bar that can be universally used for tensile or compressive loading. The paper describes the design and dimensioning of the release mechanism, including the brittle failing wear parts from ultra-high strength steel. Additionally, a numerical study on the effect of the time-to-full-release on the pulse-shape and pulse-rising time was conducted. The results of the analytical dimensioning approaches for the release mechanism, including the wear parts, were validated against experimental tests. It can be demonstrated that the designed release concept leads to sufficiently short and reproducible pulse rising times of roughly 0.11 ms to 0.21 ms, depending on the pre-loading level for both the tension and compression wave. According to literature, the usual pulse rising times can range from 0.01 ms to 0.35 ms, which leads to the conclusion that a good average pulse rising time was achieved with the present release system.

Effect of Material Anisotropy on the Mechanical Response of Automotive Steel under High Strain Rates

“…A high-speed servohydraulic testing machine and modified Hopkinson bar system can be employed to record the mechanical behavior of materials over a wide range of strain rates [3,4]. Furthermore, researchers have designed different Hopkinson-like rods or employed resistance strain gauges to reduce the influence of stress fluctuation at high strain rates, and these attempts can reduce the fluctuation amplitude to a certain degree [5][6][7][8][9]; standard testing method has been established to obtain valid stress-strain data in the dynamic test with the consideration of stress equilibrium to avoid system ringing [10].…”