| The problem of uniaxial impact on concrete is addressed. The viscoplastic material model is used for concrete. Program DYNPAK was amplified to take into account impact (via a developed contact element) and tension cutoff. All analyses utilized axisymmetric isoparametric finite elements, and the central difference scheme was employed for time integration.;First, the problem of an elastic rod striking a wall is analyzed. The elastic results from the program are in agreement with the simple wave theory. The effects of contact element stiffness, the addition of a steel bar to concrete, and Poisson's ratio are examined. It was discovered that Poisson's ratio has a considerable effect on the solution, and only when it is set to zero is there a very good match between the analytical results and the theoretical solution.;Second, the problem of a steel sphere striking a concrete rod is addressed. It was seen that, after proper calibration of the viscoplastic model, there is good agreement between the analytical results and the experimental data.;The third group of analyses involved a reinforced concrete specimen sandwiched between the two bars of a "Split Hopkinson Bar" apparatus. A parametric study was conducted to determine the effect of the different parameters on the solution including tension cutoff, the rubber layer at the anvil of the bar, boundary conditions, finite element mesh size, and the modulus of elasticity of a 5 mm concrete layer surrounding the steel bar. It was determined that, after proper calibration of the viscoplastic material model, the analytical results can match the measured data. It was also concluded that the steel bar should be allowed to slip with respect to concrete in the analytical model in order to better model the behavior of reinforced concrete. It was suggested that a slip layer should be investigated for reinforced concrete. |
