A New Computational Constitutive Model For Concrete Subjected To Dynamic Loadings

Concrete as a construction material has been widely used in both defense and civil engineering. An understandings of the response and failure of concrete targets subjected to projectile impact or explosive loadings is of great significance for the design of weapons as well as protective structures. This thesis presents a new computational constitutive model for concrete subjected to dynamic loadings and corresponding numerical simulations are performed to study the impact or explosive response and failure of reinforced concrete slabs. This thesis mainly consists of the following parts:A new computational constitutive model for concrete subjected to dynamic loadings is developed based on the analysis of some existing material models and newly obtained experimental data. The constitutive model can capture the basic features of the mechanical response of concrete materials including pressure hardening behavior, strain rate effect, strain-softening behavior, path dependent behavior, porosity and failure in both low and high confining pressures. The principal strain softening model is implemented to capture the tensile behavior of concrete. Semi-empirical equations are suggested for the dynamic strength enhancement of concrete-like materials on the basis of the assumptions that inertial effects in tension can be ignored and compressive and tensile strength increase increments are equal at equal strain rates. The new model is implemented in the commercial hydroscope LS-DYNA and numerical tests are carried out using the single element simulation approach. The use of a single element can eliminate undesired structural effects.Numerical simulations are performed to study the penetration and perforation of reinforced concrete targets struck normally by rigid ogival-nosed projectiles. It is found that the numerical results are in good agreement with the test data for the perforation of48MPa.140MPa and38MPa concrete slabs, as well as for the penetration of39MPa concrete slabs in terms of residual velocities, penetration depths and the deceleration-time histories. It is also found that different cracking patterns are observed and that the numerical predictions of the diameters of the impact crater spalling and scabbing are in good agreement with the experimental data for ogival-nosed projectile perforating finite thickness concrete targets at velocity749m/s.Numerical simulations are conducted to investigate the response of reinforced concrete targets struck normally by flat-nosed projectiles. The cracking patterns observed in the simulations are compared with the experimental observations and good agreement is obtained. Parametric study using different impact velocities, different projectile diameters and concrete targets with different thicknesses and sizes are also carried out and some useful results obtained.Numerical simulations are implemented to examine the behavior of reinforced concrete slabs subjected to explosive loadings. Comparisons of the cracking patterns obtained from the numerical studies with the experimental results show that the present model predictions are in good agreement with the experimental observations. Parametric studies are also conducted to further our understanding of the failure mechanisms of reinforced concrete slabs subjected to explosive loadings.A spherical cavity expansion model for concrete is first proposed by using an elastic-brittle-plastic material law with Hoek-Brown strength criterion. The constitutive model can capture the basic features of the mechanical response of concrete materials including the effects of pressure hardening and strain-softening and all the parameters used in the model can be determined from material tests. The forcing function obtained from the spherical cavity expansion analysis is then employed to construct a penetration model for concrete targets struck by ogival-nosed projectiles. It transpires that the present model predictions are in good agreement with experimental observations in terms of penetration depth and ballistic limits/residual velocities in the case of perforation.