Two Pulse Shaping Techniques For SHPB Test

SHPB method is commonly applied techniques to experimentally characterize the mechanical properties of materials undergoing the dynamic loading. It needs to meet two assumptions:(1) the one-dimensional wave propagation in the rods. (2) the uniform stress in the samples. In addition, the strain rate is one of the key parameters of dynamic mechanical properties for strain-rate-sensitive materials, so the constant strain rate in the loading process is another requirement.The characteristics of rock-like materials are complex because of its features such as nonlinearity, discontinuity, heterogeneity and anisotropy, etc. In a standard SHPB experiments, the input pulse is of a square shape, featuring a short rising time, commonly, a stress peak possibly caused by wave dispersion effects, which makes it difficult meet the assumptions and requirements. Therefore, it is essential to adopt some specific measures to get a preferable incident wave in order to get the correct and effective experimental results of the rock materials. In this paper, stress pulse shaping technology is put forward. The pulse shaping technology can not only extend the incident wave rise so that the specimen can get enough time to achieve the stress uniformity, but also can eliminate the high frequency oscillation of stress wave and smooth the wave. What’s more, the pulse shaping technology makes the incident wave to be adjustable, so that it is convenient for specimens to achieve longer constant strain rate in the loading process.In this thesis, the pulse shaping technology was studied from two aspects:pulse shaper and novel striker.In the aspect of the pulse shaper, a new type of pulse shaper was introduced. The mechanism of the new pulse shaper was studied by changing the diameter and the impedance ratio in different interface. Some theory bases for the pulse shaper design are provided.In the aspect of the novel striker, according to the one-dimensional stress wave and local Hertz contact theory, a series of impact hammers with different weight, cross-sectional area and radius of curvature were designed, and the incident waves with different velocities were obtained. The stress wave rising time, peak, rising slope and the time length was picked. Based on the orthogonal test design method, parameter sensitivity analysis was carried out. A series of impact hammers with different geometric parameters were designed according to the results of orthogonal test design. With the impact hammers, impact test was carried. Finally, the assumptions of one-dimensional wave, uniform stress and the constant strain rate in the process of loading were examined with the ANSYS/LS-DYNA.