Multi-dimensional SHPB Experimental Device And Its Application

The mechanical properties of engineering materials under impact or blast loading are essentially different from those under static loading,which is mainly caused by that the inertial effect and strain rate effect cannot be ignored,thus showing different deformation processes,different failure forms and other chemical or physical responses.The existing constitutive models of engineering materials are based on the data and strength theory of one-dimensional impact loading experiments.Can the strength model,strain rate effect,deformation processes and failure forms of materials under multi-axial impact loading be consistent with the theory under uniaxial loading? Therefore,in order to study the dynamic properties of materials under multi-axial impact loading,it's urgent to develop high-speed impact experimental devices for two-dimensional or three-dimensional synchronous loading.In this paper,the development and application research of multi-dimensional impact experimental device are carried out,specifically as follows:(1)Based on the mechanical design of physical mechanism,a single striker bar is used to impact simultaneously three incident bars whose physical dimensions are same,and combined with the design of steering head,the generation of three-dimensional stress waves and their synchronous loading to the tested specimen are solved.Then a three-dimensional split Hopkinson pressure bar(SHPB-3D)device is developed to realize the experimental study of complex three-dimensional dynamic mechanical properties of engineering materials under impact loading.(2)A wedge-shaped dual-wave bar is designed,which can make that a single incident stress wave can be decomposed into two symmetrical transmitted stress waves,and their synchronization of propagation can be satisfied.Adopting multi-layer ultra-thin gaskets between the wedge-shaped section and the pressure bar,and applying lubricant evenly between the gaskets and the pressure bars can eliminate the shear stress wave,and solve the problem of propagation coupling between the longitudinal stress wave and the shear stress wave.Incombination with the wedge-shaped dual-wave bar and the transmission bar,several sets of strain gauges are pasted symmetrically on the horizontal surface of the transmission bar,and the wave speeds of the longitudinal stress wave and the shear stress wave can be measured simultaneously by measuring the propagation of stress wave though a single strain gauge.(3)The propagation theory of stress wave between wedge-shaped interface is deduced,and the correctness of the propagation theory is verified by experiments considering whether there is lubricant or not at the pressure bar interface;Based on one-dimensional stress wave propagation theory,the stress wave theory under multidimensional impact loading is deduced,which provides theoretical support for data processing of multidimensional impact loading test.(4)Combining with the design of wedge-shaped dual-wave bar and according to the arrangement and combination of pressure bars,a SHPB-2D experimental device with threewave decomposition and a SHPB-2D experimental device with two-wave decomposition are developed,which can realize the generation of two incident stress waves and their synchronous loading to the cube specimen;According to the experimental research,the feasibility of these two sets of SHPB-2D experimental devices is analyzed,and the technical problem of the SHPB-2D experimental device with three wave decomposition is discussed.(5)The experimental study on dynamic mechanical properties of beech wood under one-dimensional impact loading is carried out,the influence of strain rate and fiber direction on the dynamic mechanical properties of beech wood are analyzed,and the failure mechanism of beech wood along different fiber directions is analyzed by means of microscopic scanning electron microscope and macroscopic failure morphology.The experimental study on dynamic mechanical properties of beech wood under one-dimensional impact loading coupled with lateral confining pressure,and two-dimensional impact loading are carried out,the dynamic stress-strain relationships of beech wood along different fiber directions at different strain rates are analyzed,and the influence of three different loading conditions on the dynamic mechanical properties of materials is compared and analyzed.