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首页> 外文期刊>The Journal of Strain Analysis for Engineering Design >Characterization of low-impedance materials at elevated strain rates
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Characterization of low-impedance materials at elevated strain rates

机译：在高应变速率下表征低阻抗材料

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Experimental characterization of materials at elevated strain rates of the order of 10~3 s~(-1) is typically performed by Hopkinson-bar-type facilities. The specific nature of Hopkinson bar tests is that a specimen is loaded by waves. As both the input and output bars are often made from high-impedance metallic materials, the ratio between transmitted and reflected wave components is very poor in the case of low-impedance specimen materials such as rubbers and foams. That poor wave transmission brings with it a limited quality of the signal-to-noise ratio. Changing the bar materials (e.g. to polycarbonate) is of little help because of the related viscous effects. A further deficiency of the wave-driven Hopkinson bar test for many rubber and foam applications is the comparably small amount of compression that is achievable. Maximum compressions of 95 per cent and above, often expected for damping and energy absorption applications, are out of the range of most Hopkinson bar set-ups. In order to overcome these deficiencies, first a split Hopkinson pressure bar (SHPB) facility was equipped with polyvinyli-denefluoride (PVDF) thin-film sensors. Second, a direct-impact set-up for low-impedance materials was developed and calibrated at the Ernst Mach Institute (EMI). With the PVDF gauges, the range of application both for the SHPB and for the new set-up was enhanced. This is demonstrated with an SHPB-based investigation of stress homogeneity in polyurethane (PU) specimens. The direct-impact facility made it possible to derive the stress-strain relations for PU-rubber up to strain rates in the range of several 10~3 s~(-1). Maximum compressions of more than 95 per cent were achieved. The paper describes the limitations of a classic SHPB set-up applied to low-impedance materials. The problem of stress homogeneity is addressed, and a set-up for a new direct-impact facility is presented. As an example application, a Confor-Blue foam, typically used for automotive crash-test dummies, is characterized at strain rates between 160 and 1115 s~(-1).
机译：通常通过Hopkinson-bar型设备对材料进行10〜3 s〜（-1）量级的应变速率实验表征。霍普金森棒检验的特殊性质是，试样是通过波浪加载的。由于输入和输出条通常都是由高阻抗金属材料制成的，因此在低阻抗样品材料（例如橡胶和泡沫）的情况下，透射波分量和反射波分量之间的比率非常差。较差的波传输带来了有限的信噪比质量。由于相关的粘性效应，改变条状材料（例如，变成聚碳酸酯）几乎没有帮助。对于许多橡胶和泡沫塑料应用，波动驱动的霍普金森棒试验的另一个缺陷是可实现的压缩量相对较小。通常在阻尼和能量吸收应用中期望的最大压缩率达到95％以上，这超出了大多数Hopkinson杆的设置范围。为了克服这些不足，首先在Hopkinson压力棒（SHPB）分离设备上安装了聚偏二氟乙烯（PVDF）薄膜传感器。其次，在恩斯特·马赫研究所（EMI）开发并校准了用于低阻抗材料的直接碰撞装置。有了PVDF压力表，SHPB和新装置的应用范围都得到了扩大。基于SHPB的聚氨酯（PU）试样应力均质性研究证明了这一点。直接冲击装置使得可以推导出PU橡胶的应力-应变关系，直至高达10〜3 s〜（-1）的应变速率。最大压缩率达到95％以上。本文介绍了适用于低阻抗材料的经典SHPB设置的局限性。解决了应力均匀性的问题，并提出了一种新的直接冲击设备的设置。作为示例应用，通常用于汽车碰撞测试假人的Confor-Blue泡沫的特征是应变速率在160到1115 s〜（-1）之间。

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