Compression Fracture and Size Effect in High-Strength Concretes

混凝土的断裂力学有了很大的进展，但仅限于拉伸断裂，本质上是一种单轴断裂现象。压缩断裂是一种三轴断裂现象，其断裂力学基本上是不可用的。目前的建议，包括理论和实验研究，试图填补这一空白。理论程序包括：(1)基于能量的轴向劈裂裂纹带（含微裂纹材料内屈曲）扩展数学模型；(2)尺寸效应和形状效应的渐近分析，得出简单的“渐近匹配”公式；(3)确定压缩断裂特征的尺寸效应法；(4)对现有的压缩损伤微平面模型进行推广，考虑时间或加载速率的影响；(5)应用于高强混凝土柱或墙在火灾作用下的爆炸破坏分析。实验程序旨在验证和校准理论，包括：(1)压缩-拉伸加载双悬臂断裂试件的尺寸效应试验；(2)小缺口和大缺口圆柱形试样压缩断裂尺寸效应试验；(3)速率或时间影响的试验。＊＊＊

9713944 Bazant The fracture mechanics of concrete has progressed greatly, but only for tensile fracture, which is essentially a uniaxial phenomenon. The fracture mechanics of compression fracture, which is a triaxial phenomenon, is essentially unavailable. The present proposal, involving both theoretical and experimental studies, attempts to fill this gap. The theoretical program involves: (1) energy-based mathematical model for the propagation of a band of axial splitting crack (with internal buckling of microcracked material); (2) asymptotic analysis of size effect and shape effect, leading to simple `asymptotic-matching' formulas; (3) formulation of size-effect method for deternining compression fracture characteristics; (4) generalization of the existing microplane model for damage in compression, with consideration of the effect of time or loading rate; and (5) application to the analysis of explosive failure of high-strength concrete columns or walls subjected to fire. The experimental program, designed to verify and calibrate the theory, involves: (1) size-effect tests of double- cantilever fracture specimens with compression-tension loading; (2) size effect tests of compression fracture of cylindrical specimens with small or large notches; and (3) tests of the influence of rate or time. ***