2018, 39(3): 249-265.
doi: 10.21656/1000-0887.380324
Abstract:
A revised elastic stress wave theory was proposed. The existent theory of elastic stress waves has some deficiencies in aspects of rotational deformation as well as its corresponding internal force, and wave equations, etc. It was revealed that there exist both volumetric waves and deviatoric waves in elastic solids, the volumetric wave travels independently but the deviatoric wave is influenced by the volumetric wave, and them 2 form a weakly coupled wave system. An impacted plate should be treated as a 3D strain system other than a 1D one. In plate impact tests, the 2 wave variables remained 2ndorder tensors but the independent variable was simplified as a volumetric strain plus a principal deviatoric strain, consequently the wave equations were simplified as 2 weakly coupled wave equations. The interface effects of stress waves involved generation of stress waves on the impact surface and reflection of stress waves on the free surface. Relationships between the boundary conditions and the wave variables on the impact surface and the free surface were established. In the numerical tests, the volumetric and deviatoric waves were simultaneously generated on the impact surface, but the volumetric wave and a part of the deviatoric wave constituted a composite pulse propagating at a faster speed, and the rest of the deviatoric wave made a deviatoric pulse traveling at a slower speed. Both the 2 incident pulses on the free surface were reflected respectively to produce a composite pulse and a deviatoric pulse again, which meant 4 reflected pulses were generated. The dual pulse structure of stress waves may explain very well the recompressive phenomenon of the free surface velocity curves of plate specimens under plate impact. Recompressive signals measured on 10 alumina plate specimens of different thicknesses verify the theoretical prediction of the deviatoric pulse.
