Study Of Hopkinson Bar Bundle Technique And Dynamic Bahaviour Of Large-size Concrete Specimens

Concrete is a widely used engineering construction material. Study on the dynamic behav-ior of concrete under high strian rate loading is of great importance in the circle of engineering or academic. Due to its remarkable multiphase and non-homogeneous property, the size of the concrete specimen must be large enough to representive the engineering concrete of real-size aggregate. Therefore it is necessary to design and erect a set of testing device fitting for the experimental research on such big size of concrete as it is difficult for the available SHPB facilities to meet such requirement.ates.It is found that stress wave is dispersed because of radial inertial effect during the propaga-tion in the big-size bar when study on the dynamic characteristics of reactive power concrete with the SHPB of 100mm-diameter. Such dispersion on the one hand causes waveform distortion, which makes the acquisition stress wave different from the actual one of the interface between the specimen and bars, another hand, it causes waveform oscillation,which makes the stress-strain curves of specimens kink exceptionally.Based on the idea of Hopkinson bar bundle, combining the existing large-scale rail-type drop hammer impact device, through the analysis of wave propagation and numerical simulation, Vertical Hopkinson Bars Bundle Setup(VHBBS) is established for the experimental study on the dynamic behavior of engineering concrete. Both the input and output bars bundles consist of 5×5=25 aluminum rods with a cross section of 3cm side. Thus wave pro-pagation in the bars can be described by one-dimensional wave propagation theory and, by comparing the reflected or transmitted pulse of each pair of bars, it is possible to realize the properties of initial defects and the process of damage evolution for the portion of the specimen facing the cross section of each particular pair. Besides, as the energy loading system is easily controlable and the ratio of wave impedance between the specimen and bar is 0.5, the assumption of"uniform distribution of stress/strain along the length of the specimen"could be allowable as long as the loading pulse and the thickness of the specimen are suited.The experimental study on the dynamic mechanics hehaviour of C40 concrete specimens with the VHBBS is presented detailedly in this paper. According to the experimental result, the dynamic compression strength of concrete specimen increases with the increase of starin rate, which proves that engineering material as concrete is a kind of strain rate-dependent material. Besides, it can be investigated the properties of initial defect and the process of damage evolution of the large concrete specimen through the experimental study with the VHBBS..