Numerical Study On Mesoscale Damage And Energy Evolution Of Lightweight Aggregate Concrete Under Static-dynamic Loads

Lightweight aggregate concrete(LWAC)has been widely used because of its lightweight,good thermal insulation,sound insulation and seismic performance.The structure will inevitably be subjected to cyclic load and impact load during its service life.In order to understand the damage evolution process and the law of energy absorption and dissipation of LWAC under static and SHPB impact loads,a mechanical model and a back analysis method of mesoscopic elastic parameters were proposed based on the mechanics theory of composite materials.And the elastic parameters of each mesoscopic phase were obtained based on laboratory test results.A method for mesoscopic numerical modeling was established.Besides,the damage evolution process and energy dissipation of LWAC with different aggregate replacement rates under different strain rates were analyzed through experiments and numerical simulations.The main results and conclusion are as follows:(1)The mesoscale mechanical model and elastic parameter prediction model for LWAC were established.The mechanical tests of elastic parameters of concrete with different mix proportions were carried out.By using the inversion method and prediction model of elastic properties,the elastic parameters of each mesoscopic phase were obtained.In addition,the thickness of the interface transition zone around lightweight aggregates was given.(2)Random polyhedrons of aggregates were generated without collision according to the specified gradation.Three-dimensional FEM models of alllightweight aggregate concrete and gravel lightweight concrete(GLWC)with different replacement rates of aggregates were established.(3)A damage evolution constitutive equation for concrete was established and loaded in a numerical model by self-programming.Its mesoscopic parameters were calibrated based on laboratory test results.Through uniaxial compression tests and simulation,the evolution law of mesoscopic damage of LWAC corresponding to the macroscopic deformation and failure were revealed.Through simulation and experiments of cyclic loading and unloading,it was found that with the increase of loading grade,the total absorbed energy,elastic strain energy and dissipated energy of the sample show a nonlinear growth trend.Besides,all the kinds of energy decreased with the increase of gravel replacement rate;(4)A 3D FEM model of electromagnetic driven SHPB impact system was established.And the parameters in HJC model for mesoscale phases of GLWC were determined according to laboratory test results.The relationships between target speed and initial voltage and power-off time were proposed for this self-developed equipment.A series of simulations were carried out for GLWC with different gravel replacement rates under different strain rates.Then a prediction model for the dynamic of GLWC was proposed.And it was found that the energy absorption capacity of GLWC increases with the increase of strain rate.Besides,when the gravel replacement rate is between 25-35%,the strength of GLWC can be effectively improved on the premise of ensuring its energy absorption capacity.There are 65 figures,9 tables,113 references in this thesis.