On SHPB Technique And Lagrangian Analysis Used For Studying The Impact Response Of Concrete-like Materials

The problems encountered in SHPB tests for concrete and concrete-like materials such as how to correct the transverse inertia effect of waves propagating in large diameter pressure bar and how to satisfy the stress uniformity requirement for SHPB specimens under impact loading, are systematically analyzed and discussed in this paper. The results show that the expected reliable dynamic constitutive relation is in fact difficult to be gotten by traditional SHPB technique when the test material is not only a visco-elastic but also a brittle one like concrete, so a new method combining the Hopkinson technique with the Lagrange analysis based on pathline method is proposed to determine the constitutive relationship of concrete-like materials, and thus the dynamic stress-strain relationship of concrete C30 at high strain-rates is successfully obtained.By using the Fourier transform, both the positive and inverse analyses for the wave dispersion due to transverse inertia effect in 037mm Hopkinson bar are presented in Chapter 2. This method is compared with and validated by ANSYS numerical calculations. Furthermore, a BP NN (back-propagation neural network) technique combined with ANSYS simulation is developed to correct the wave dispersion. It is found that such a new technique can also be used to resolve the positive and inverse problems, particularly for a given large diameter bar.In Chapter 3, the results of numerical analyses on stress uniformity of visco-elastic specimens reveal that the stress uniformity of visco-elastic specimens, different from that of elastic specimen in SHPB tests, is not only dependent on the rise-time Ï„_s/t_L of incident wave front and the wave impedance ratio Ri but also on the relaxation time θ₂. The stress uniformity of brittle concrete-like specimens whose fracture strain is e.g. ε_f=5‰, has been analyzed also in the chapter. It is found that the strain in non-uniformity stage is as larger as 2.0².5‰, so either the traditional three-wave method or the two-wave method is not able to provide reliable constitutive relationship again for concrete-like specimen, while the dynamic fracture strength could be credible if the fracture occurs after the stress uniformity is realized in...