基于超高速相机的数字图像相关性全场应变分析在SHTB实验中的应用

基于超高速相机和数字图像相关性全场应变分析方法对传统的分离式Hopkinson拉杆(SHTB)实验系统进行改进，获得尼龙和铝合金材料的动态拉伸应力应变曲线，验证了数字图像相关性全场应变分析在SHTB实验中的有效性。实验结果显示:该方法测量的平均应变与应变片测量结果一致性很好, 而传统的SHTB实验原理计算的应变结果则明显偏大，需要对试件原始标距进行修正后才能获得有效的试件应变，并且在试件的材料和几何尺寸不变的条件下标距修正不依赖于应变率。基于数字图像相关性全场应变测量，讨论了应变均匀性问题:脆性的尼龙试件在标距范围内应变均匀性良好，而韧性的铝合金试件表现出比较严重的应变不均匀性，归因于颈缩变形的影响。

Full field strain measurement in split Hopkinson tension bar experiments by using ultra-high-speed camera with digital image correlation

In this work the digital image correlation (DIC) technique was used for the full field measurement of the dynamic tension strain in traditional split Hopkinson tension bar (SHTB) experiments using the commercial image correlation software and the digital ultra-high-speed camera. This system was used to study the dynamic tensile response of nylon and aluminum alloy. The dynamic tensile stress-strain curves of nylon and aluminum alloy were accurately obtained to verify the validity of the dynamic tensile strain measured by the DIC technique. The results show that the average strain thus determined agrees well with the strain measured with a strain gauge attached to the specimen, but the traditional SHTB experiment's analytic strain is larger than the strain measured from the DIC method, which can be rectified by using the effective gauge length in consideration of the effect of rounded fillets. The effective gauge length does not depend on the strain rate. Based on the full filed strain measurements of the specimen, the strain distribution within the gauge length is uniform for the brittle nylon specimen, but the strain distribution for the ductile aluminum alloy specimen is not uniform due to the effects of the necking.