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
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摘要
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。
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.
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.
引文
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[7]赵磊,李玉龙,陈煊.一种绸布的冲击拉伸性能实验[J].爆炸与冲击,2014,34(4):476-482.Zhao Lei,Li Yulong,Chen Xuan.Experimental study on dynamic tensile behavior of a kind of fiber silk[J].Explosion and Shock Waves,2014,34(4):476-482.
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[9]Sutton M A,Orteu J J,Schreier H.Image correlation for shape,motion and deformation measurements:Basic concepts,theory and applicants[M].New York:Springer,2009.
[10]Pierron F,Sutton M A,Tiwari V.Ultra high speed DIC and virtual fields method analysis of a three point bending impact test on an aluminum bar[J].Experimental Mechanics,2011,51(4):537-563.
[11]Liu J G,Saletti D,Pattofatto S,et al.Impact testing of polymeric foam using Hopkinson bars and digital image analysis[J].Polymer Testing,2014,36(6):101-109.
[2]Chen W,Song B.Split Hopkinson(Kolsky)bar:Design,testing and application[M].New York:Springer,2011.
[3]胡时胜,王礼立,宋力,等.Hopkinson压杆技术在中国的发展回顾[J].爆炸与冲击,2014,34(6):641-657.Hu Shisheng,Wang Lili,Song Li,et al.Review of the development of Hopkinson pressure bar technique in China[J].Explosion and Shock Waves,2014,34(6):614-657.
[4]Owens A T,Tippur H V.A tensile split Hopkinson bar for testing particulate polymer composites under elevated rates of loading[J].Experimental Mechanics,2009,49(6):799-811.
[5]Gerlach R,Kettenbeil C,Petrinic N.A new split Hopkinson tensile bar design[J].International Journal of Impact Engineering,2012,50(12):63-67.
[6]田宏伟,郭伟国.动态拉伸试验中试样应变测试的有效性分析[J].实验力学,2008,23(5):403-410.Tian Hongwei,Guo Weiguo.Validity analysis of sample strain measurement in dynamic tensile experiment[J].Journal of Experimental Mechanics,2008,23(5):403-410.
[7]赵磊,李玉龙,陈煊.一种绸布的冲击拉伸性能实验[J].爆炸与冲击,2014,34(4):476-482.Zhao Lei,Li Yulong,Chen Xuan.Experimental study on dynamic tensile behavior of a kind of fiber silk[J].Explosion and Shock Waves,2014,34(4):476-482.
[8]胡时胜,邓德涛,任小彬.材料冲击拉伸实验的若干问题探讨[J].实验力学,1998,13(1):9-14.Hu Shisheng,Deng Detao,Ren Xiaobin.A study on impact tensile test of materials[J].Journal of Experimental Mechanics,1998,13(1):9-14.
[9]Sutton M A,Orteu J J,Schreier H.Image correlation for shape,motion and deformation measurements:Basic concepts,theory and applicants[M].New York:Springer,2009.
[10]Pierron F,Sutton M A,Tiwari V.Ultra high speed DIC and virtual fields method analysis of a three point bending impact test on an aluminum bar[J].Experimental Mechanics,2011,51(4):537-563.
[11]Liu J G,Saletti D,Pattofatto S,et al.Impact testing of polymeric foam using Hopkinson bars and digital image analysis[J].Polymer Testing,2014,36(6):101-109.
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