基于数字图像的分离式霍普金森压杆实验中试件应变及两端应力的同步测量法

本文提出一种基于高速摄像和数字图像相关方法(DIC)的分离式Hopkinson压杆(SHPB)测量技术,从而实现试件应变和两端应力的同步测量。即在与试件接触的输入输出杆两端制作散斑,通过高速摄像获取SHPB实验过程中的散斑变形图像,由DIC测得各时刻试件的应变、输入输出杆端的应变(可直接换算为试件两端的应力)。由于试件和杆端的应变都是从同一张高速摄影的图像上分析得到的,因此它们是同步的。应用该方法对钢纤维混凝土试件的SHPB试验进行了测量,测量结果与传统应变片测量结果吻合,验证了该方法的可行性。该技术不仅实现了SHPB实验中试件应变和应力的同步测量,还将有助于直接检验各材料在SHPB实验中试件两端的力在实验过程中是否平衡。

On the Synchronized Measurement of Specimen's Strain and Stress at Both Ends in SHPB Tests Based on Digital Image

A measurement technique used in split Hopkinson pressure bar (SHPB) experiment is proposed in this paper based on high-speed photography and digital image correlation method (DIC), which enables the specimen's strain and stress at both ends to realize synchronized measurement. In this technique, speckle is made first on surfaces of incident and transmission bar which are contact with specimen; the speckle image deformation during impact process of SHPB experiment is recorded by high-speed photography system, then the strains at each moment and at both ends of specimen are obtained by DIC, the strains at both ends of specimen can be converted into corresponding stress directly. Since the specimen's strain and strain at both ends are obtained from the same photography image, so they are synchronous. Applying this measurement technique, an impact experiment for steel fiber concrete specimens was carried out on SHPB. Measured results agree well with that from traditional strain gauge signal, which validates the feasibility of this measurement technique. This technique not only realizes the synchronized measurement of specimen's strain and stress at both ends of specimen, but also helps to inspect the equilibrium of forces acted on both ends of specimen during SHPB experiment.