Refinement Research And Application Of Incident Wave Shaping In SHPB Experiment

The SHPB experiment is the most important and reliable experimental method for studying the mechanical properties of materials at high strain rates,and also it is an important part of the explosion and impact dynamics experimental technology.In the range of high strain rate,it has been widely used to study the dynamic mechanical properties of metal materials,brittle materials,soft materials,foam materials and so on.In order to obtain effective and accurate experimental data,the stress balance of the specimen and the constant strain rate of the specimen in the SHPB experiment must be guaranteed,so it is necessary to modify the SHPB experimental device to obtain an appropriate incident waveform,and use the pulse shaper technology to adjust the incident waveform is convenient and can be operated easily.So it is widely used in the SHPB experiment.This paper firstly analyzes the core technology in the SHPB experiment based on the wave dynamics theory.We clarify the one-dimensional stress wave propagation theory and the collision model of two elastic bars.And we introduce three types of the SHPB experimental device used in this paper and the function of each part.Also we analyze the principle of SHPB experimental technology theoretically,and deduce the relationship between the stress,strain,strain rate of the specimen and the incident wave,reflected wave and transmitted wave signal.In the light of the incident wave shaping technology based on the pulse shaper,in order to analyze the influence of the shaper on the incident waveform,this article first uses the dimensional analysis theory to study the factors affecting the incident waveform,and demonstrates that the incident wave shaping technology experiment satisfies the strict similarity law.The conclusion is verified by the experiment and simulation.Then the red copper material was selected as the research object.The influence of the diameter and thickness of the shaper,the impact bar speed and length on shaping the incident wave were experimentally studied on the 37 mm SHPB experimental equipment.And also the simulation was performed.We analyzed the influence of each factor on the two important inflection points T1 and T2 of the incident waveform,and obtained the dimensionless expressions of the inflection points T1 and T2.The research results show that the shaper can extend the rising edge time of the incident waveform,and filter out the high-frequency oscillation waves in the experiment at the same time;The increase in the diameter of the shaper increases the generalized strength of the shaper,and results in an increase in the height of the first inflection point T1;The increase in the thickness of the shaper results in a decrease in the strain rate of the shaper under impact compression and an increase in the compression time,so the first inflection point T1 gradually decreases,and the second inflection point T2 gradually moves to the right;With the increase in the speed of the impact bar,the height of the inflection point T1 will increase and the position of the second inflection point T2 will be shifted to the left;In the end,the length of the impact bar only affects the duration of the incident wave,and will not affect the shape of the incident wave.Finally,we analyze the two common reflection waveforms of metal materials and brittle materials in the SHPB experiment.Based on the above research conclusions,the specific adjustment methods of the two reflected waves are given to achieve an approximate platform wave to satisfy the stress balance and constant strain in the SHPB experiment.We select concrete material as the specimen.Through the design of the size of the shaper,the correctness of the influence of the shaper size on the incident waveform is verified.And the stress-strain curve of the concrete is obtained.The design of the shaper in the SHPB experiment of brittle materials in this paper is significant for others.