A Long Split Hopkinson Pressure Bar (LSHPB) for Intermediate-rate Characterization of Soft Materials

Abstract

In this study, we developed a long split Hopkinson pressure bar (LSHPB) for mechanically characterizing soft materials at intermediate strain rates. Using a proper pulse shaper, a loading pulse over 3 ms was produced for compression experiments on a PMDI foam material at the strain rates in the order of 10/s. The pulse shaping technique minimized the dispersion effects of stress wave when propagating through such a long bar system. Consistency of stress-strain curves obtained from the LSHPB and an MTS in the same strain rate range shows that a gap currently existing in intermediate strain-rate range is closed by the introduction of the LSHPB.

High Strain Rate Mechanics of Polymers: A Review

“…In addition, it is necessary to overcome the effects of the inertia of the apparatus, so that high speed deformations can be applied after a very short period of acceleration. Hydraulic machines are often used; however, systems based on dropping weights [39][40][41][42][43][44][45][46][47][48], fly wheel systems [49,50], expanding ring [51], cam plastometer [52], very long Hopkinson bars [53], or the 'wedge bar' [54] have also been applied successfully. Accurate experiments in this strain rate regime are key because molecular mobility transitions often become activated between 1 and 1000 s -1 .…”

“…These include pulse shaping [62], low impedance Hopkinson bar materials to increase the transmitted force [76,77,81,82,148] or use of more sensitive force gauges to directly measure the force at the specimen bar interface [62][63][64]. Longer Hopkinson bars may be used to increase the duration of the experiment [53], as can direct impact systems [149], in addition, if stress gauges are combined with optical measurements of specimen deformation, the experiment duration is no longer limited by wave overlapping in the bars and longer durations can be achieved [150]. The challenges associated True Strain Fig.…”

The Rate Dependent Tensile Response of Polycarbonate and Poly-methylmethacrylate

“…Some of these techniques include flyer plate impact, Taylor impact, drop tower methods, and pressure shear experiments, but perhaps the most widely used would be the Kolsky bar or split Hopkinson pressure bar (SHPB). Since its original development by Kolsky [13] the method has seen much refinement; most developments for low impedance materials involve polymeric bars [14,15] and associated dispersion corrections [16], wave separation [17,18], pulse shaping [19,20], long bar lengths [21], high sensitivity semiconductor strain gages, hollow transmission bars [22], or embedded quartz load cells [23]. Each evolution poses advantages and shortcomings and none have proven to be ideal for all materials or loading conditions.…”

Pulse Shaper and Dynamic Compressive Property Investigation on Ice Using a Large-Sized Modified Split Hopkinson Pressure Bar

“…Frantz et al (1984) was the first to design a thin disk on the head of the incident bar to increase rising time and eliminate the dispersion of incident wave. An extensive set of materials have been tested by researchers (Hsiao and Daniel, 1998;Togami et al 1996;Vecchio and Jiang, 2007) and found copper is ideal for the SHPB tests (Rome et al 1998;Song et al 2008). Meanwhile, the effect of wave shaping by changing the dimensions of the pulse shaper has also been discussed (Song et al 2007;Sedighi et al 2010).…”

“…There are several types of materials that have been tested for making a pulse shaper for SHPB testing, such as rubber (Hsiao and Daniel, 1998), plexiglass (Togami et al 1996), fabric (Vecchio and Jiang, 2007) and copper (Song et al 2007(Song et al , 2008. In this research, copper has been selected for the pulse shaper due to its strain rate independent material properties.…”