损伤跨尺度演化导致的混凝土强度尺寸效应

Size effect on concrete strength caused by trans-scale damage evolution

基于直接从混凝土破坏机理出发建立的混凝土材料微裂纹模型,对不同尺寸的混凝土三点弯梁试样进行了多尺度建模,对损伤演化导致的试样破坏进行了数值仿真分析,探讨了混凝土尺寸效应的发生机理.研究结果表明:混凝土材料微裂纹模型能成功模拟混凝土中微裂纹分布式生长、聚合、宏观裂纹形成与扩展、试样破坏的全过程;随着混凝土梁试样尺寸的增大,试样中的微裂纹数目及其分布的随机性也随之增加;这些裂纹在微细观尺度上的无序效应在损伤跨尺度演化过程中被放大,导致混凝土试样的宏观力学行为随之变化,即强度减小,断裂能增大,宏观性能的离散度减小;损伤跨尺度的非线性串级发展是导致混凝土强度尺寸效应的根源;相较于Bazant尺寸效应,模拟结果更符合Carpinteri多重分形尺寸效应律.

Based on the micro-crack model established directly from the failure mechanism of con-crete material,the concrete three-point bending beam specimens with different length scales were multi-scale modeled.The damage evolution leading to samples＇ failure was numerically simulated and the mechanism of the size effect of concrete was discussed.The results show that the micro-crack model can successfully simulate the whole process of rupture,including the growth and aggre-gation of distributed micro-cracks,formation and propagation of macro-crack,and broken of the sample.The number of micro-cracks as well as their distribution randomness in the sample increase with the increase of the size of the concrete beam.The disorder effect of these cracks in the micro-scale view is amplified during the cross-scale damage evolution,inducing the change of macro-me-chanical behaviors of the concrete specimen,i.e.the increase of the fracture energy and the decrease of the strength and the discreteness of macroscopic properties.The concrete size effect results from the trans-scale nonlinear damage progress.Compared with the Bazant size effect theory,the simula-tion results are more consistent with the Carpinteri＇s size effect theory.