Concrete Penetration Theory And Concrete Thermodynamic Constitutive Model

Concrete as a kind of building material has been widely used in civil and military engineering.It is of great significance to study the response and failure of concrete structures subjected to explosive/impact loading.This thesis presents a theoretical model on the penetration of semi-infinite concrete targets struck normally by long rods at different velocities on the basis of the previous work.A thermodynamics-based constitutive model for concrete is constructed,and incoporated into LS-DYNA software.Numerical simulations are conducted to investigate the penetration and perforation of concrete targets subjected to impact by ogival-nosed projectiles.This thesis mainly includes the following parts:1.To construct a theoretical model for the penetration of semi-infinite concrete targets struck by long rods.On the basis of the unified theory for the penetration of semi-infinite metal targets by long rods suggested by Wen et al.,a theoretical model on the penetration of semi-infinite concrete targets by long rods is proposed.Concrete penetration can be generally categorized into two scenarios by the relative magnitude of projectile dynamic strength Yp and static resistance of concrete targets a0.(1)Yp<a0:The projectile cannot penetrates the concrete target when impact velocity V0 is less than the defeated velocity VID or in an erosive mode when VO higher than the defeated velocity VID(2)Yp>a0:the critical conditions for the transition among these three modes of penetration(namely penetration by a rigid penetrator,penetration by a deformable penetrator and penetration by and erosive penetrator)are determined by means of two critical velocities,namely,the rigid velocity VR and the hydrodyanmic velocity VH the rigid body velocity(VR)has been defined as the impact velocity at which the resultant target resistance force is equal to the dynamic strength of the penetrator times the cross-sectional area of the shank and the hydrodyanmic velocity as an impact velocity at which a stable mushrooming head is formed on the basis of physical consideration and second penetration by eroded rod debris is also examined.It transpires that the present model correlates well with available experimental observations for concrete penetration in terms of penetration mode,penetration depth,residual mass and deceleration-time history.2.To establish a thermodynamic constitutive model for concrete.(1)Basic laws of thermodynamics,internal variable theory and Zigler orthogonal principle are briefly introduced and the procedure of constructing thermodynamic constitutive model is given.Non-associative flow rule is determined directly by the dissipative functions and no additional defined functions(i.e.plastic potential function)are required.Examples of the generation of classical constitutive models(Mises and D-P elasto-plastic model)based on this general approach of establishing constitutive model within the framework of thermodynamics are given.(2)The free energy function and energy dissipation function for concrete materials are constructed,and a thermodynamic constitutive model for concrete is established,which considers strain hardening and softening,pressure dependence,path dependence,dilatancy and strain rate effect.The parameters in the thermodynamic constitutive model for concrete are determined and the model is validated using a single element approach.It is shown that the stress-strain curves predicted by the present themodynamic constitutive model agree well with available experimental data for concrete under uniaxial compression/tension and triaxial compression loading conditions.3.To conduct numerical simulations on the penetration and perforation of concrete targets.(1)The numerical simulations are conducted to study the penetration of 23MPa and 39MPa concrete targets struck by rigid ogival-nosed projectiles.It is shown that the numerical predicted penetration depths,residual velocity and deceleration-time curves,are in good agreement with the experimental data.It is also shown that DOP increases with increasing impact velocity;thus deceleration is only depend upon penetration velocity for given projectile-target combination.(2)Numerical simulations are performed to investigate the perforation of 48MPa concrete targets struck normally by an ogival-nosed projectile.It is demostrated that the residual velocities predicted by the present model are in good agreement with the experimental data.It is also demostrated that the numerical predicted diameters of the impact and scabbing craters are also in good agreement with the test results for the perforation of the concrete targets struck by the rigid ogival-nosed projectile at 749m/s.as that the diameter of the impact crater inceases with increasing impact velocity whilst that of scrabbing crater decreases with increasing impact velocity.