基于3D细观模型的混凝土动态压缩行为分析

Analysis on dynamic compressive behavior of concrete based on a 3D mesoscale model

通过建立混凝土的3D细观模型,在细观尺度上分析动态压缩荷载作用下混凝土材料内部裂缝的产生和发展、损伤演化和动态强度及其影响因素。首先,基于传统的“生成-投放”法生成粒径、形状和空间分布均随机的凸多面体粗骨料模型,并通过骨料沉降和粒径缩放实现粗骨料的大体积率(达50%)和可调控;使用四面体网格划分骨料和砂浆表征其真实物理形状;使用界面粘结接触表征界面过渡区(ITZ)提升计算效率。进一步通过对比不同粗骨料粒径混凝土的分离式霍普金森压杆(SHPB)试验数据与模拟结果,如杆上应变时程、试件动态应力-应变曲线和试件损伤破坏模式,验证了建立的混凝土3D细观有限元模型、参数确定方法和数值仿真方法的准确性。最后,分析了30~100 s^(-1)应变率范围内骨料粒径(4~8、10~14和22~26 mm)、体积率(20%、30%和40%)和类型(石灰岩、花岗岩和玄武岩)对混凝土动态压缩强度的影响。结果表明:粗骨料粒径增大,混凝土动态压缩强度先增大后减小;粗骨料体积率越高,混凝土动态压缩强度越大;混凝土动态压缩强度随粗骨料强度的增加而提高。

As the most widely used construction material,concrete is common in military protection and civil transportation infrastructures.During its services life,concrete may bear dynamic loads such as high-speed penetration,blast and impact of vehicle,ship,rockfall and so on.On the mesoscale,concrete is three-phase material composed of mortar,coarse aggregates and interface transition zone(ITZ).The concrete 3D mesoscale model was established to analyze the crack generation and development,damage evolution,dynamic strength and its influencing factors of concrete.Firstly,randomly distributed convex polyhedron aggregates of random shapes and sizes were modeled based on the conventional“take-and-place”method and Monte Carlo algorithm,and drop of aggregates under gravity were simulated in finite element software LS-DYNA to make aggregates more dense,improving aggregate volume fraction to 50%.After that,aggregate size was reduced by a trial value to control aggregate volume fraction conveniently.Then,aggregates and mortar were meshed with tetrahedral elements to display their actual physical shapes.Besides,ITZ was represented by interface cohesive contact which equals zero-thickness bonding elements to improve computational efficiency.Furthermore,SHPB simulations of different coarse aggregates sizes concrete were conducted and the accuracy of finite element model,parameter determination method and numerical simulation methods were proved by comparing test and simulated bar strain-time history,dynamic stress-strain curves and failure patterns of specimens.Finally,influences of the aggregate size(4−8,10−14 and 22−26 mm),volume fraction(20%,30%and 40%)and type(limestone,granite and basalt)on concrete dynamic compressive strength under the strain rate within 30−100 s^(−1) were analyzed.It shows that the dynamic compressive strength of concrete increases first and then decreases with the increase of aggregate size;the dynamic compressive strength of concrete increases with the increase of volume fraction;the dynamic compressive strength of concrete increases with the increase of aggregate strength.