Research On Anti-penetration Performance Of Concrete Target At Mesoscale

At present,the research on the anti-penetration performance of concrete target is mainly based on homogeneous method,so it can neither reflect the influence of components on the anti-penetration performance of concrete,nor characterize the distribution of cracks in concrete.In this paper,the anti-penetration performance of concrete target is studied from mesoscale(mainly including coarse aggregate,mortar and crack)by experiment,numerical simulation and theory,including the equivalent mechanical properties of concrete with different components under confining pressure,the influence of concrete components on nose erosion,projectile bending,ballistic deflection,penetration depth and target cratering,and the distribution and propagation of cracks in target.A foundation is laid for the mix proportion design of anti-penetration concrete and damage assessment of concrete structure by research results.The main contents of this paper are as follows:A two-phase meso-mechanical model of the confining pressure mechanical properties of concrete is established,including the equivalent equation of state model and the equivalent confining pressure strength model.The confining pressure experiments of concrete(containing coarse aggregate)and the corresponding coarse aggregate and mortar are carried out.The results show that the equivalent mechanical properties of concrete calculated by meso-mechanical model are consistent with the experimental results.And then,the equivalent mechanical properties of concrete with different coarse aggregate volume fractions and different coarse aggregate types are obtained by model calculation.Through macroscale and mesoscale numerical simulations of deep penetration of a projectile into concrete target,the influence of coarse aggregate on projectile motion and the distribution and propagation of cracks in target are studied.When projectile diameter is larger than maximum coarse aggregate grain size,the motion law of the projectile obtained by macroscale and mesoscale numerical simulation is consistent.The constitutive parameters of concrete with different components calculated by meso-mechanical model are used in the macroscale penetration numerical simulation,and the corresponding penetration depth of concrete with different compositions is obtained,and then verified by mesoscale numerical simulation.The internal crack distribution and internal tangential crack propagation direction of mortar target and concrete(containing coarse aggregate)target are obtained by macroscale numerical simulation.A penetration depth model of a rigid projectile considering the volume fraction of coarse aggregate is established.For gap-containing concrete,a gap volume fraction factor is taken into consideration.For the conditions where the projectile diameter is smaller than the maximum coarse aggregate grain size,size effect factors,including mean and standard deviation,are taken into consideration,which take into account the coarse aggregate volume fraction and the projectile diameter/maximum coarse aggregate grain size.Experimental studies on the effects of coarse aggregate on the target crater,projectile damage and projectile movement are carried out.The basic variables include coarse aggregate volume fraction,coarse aggregate type(quartzite,granite and limestone)and projectile diameter/maximum coarse aggregate grain size.The results show that the increase of the coarse aggregate volume fraction is beneficial to reduce the penetration depth,but the increase of the gap volume fraction has opposite effect.The coarse aggregate type has a significant influence on the target resistance.The relative static resistance stress of quartz coarse aggregate concrete,granite coarse aggregate concrete,limestone coarse aggregate concrete and mortar is 1.71:1.73:1.45:1.When the diameter of the projectile is significantly smaller than the maximum coarse aggregate grain size,the static resistance stress and its standard deviation of target increase significantly.Through experiments of wire saw cutting of targets,X-ray computed tomography(X-CT)of core samples in target and mechanical properties of damaged concrete,the distribution and propagation of cracks in mortar targets and concrete targets(containing coarse aggregate)are studied,and a crack propagation model is further established.The experimental results show that the crack distribution in target is divided into a plastic damage zone and a brittle damage zone.The initial growth process of the three-dimensional cracks is obtained,that is,the cracks direction in mortar target gradually develop from the radial direction to tangential direction,and the target containing coarse aggregate directly form cracks in tangential direction.The propagation progress of cracks is obtained,that is,the tangential cracks propagate asymmetrically,and the number of radial cracks in target is reduced due to being blocked by tangential cracks;the tangential cracks bend in mortar target,and are relatively straight in the target containing coarse aggregate.A crack propagation model is established,and the tangential crack formula and the crack propagation velocity are obtained.