水泥砂浆断裂韧度的尺寸效应研究

Size effect study of fracture toughness for cement mortar

用两种不同配合比的水泥砂浆分别制作了三组几何相似的矩形截面直裂缝三点弯曲梁。在MTS815材料试验机上进行试验,记录了试件的荷载-加载点位移(P-δ)和荷载-裂缝端口张开位移(P-ωCMOD)的全过程曲线。利用最大荷载和初始裂缝长度求得的线弹性断裂韧度存在明显的尺寸效应。为此,基于虚拟裂缝模型,认为裂缝端口张开位移是荷载、自重和黏聚力共同作用的结果,求解该位移公式得到断裂过程区长度值,用断裂过程区长度修正初始裂缝长度后,再代入三点弯曲梁应力强度因子公式,进而得到尺寸效应程度较弱的等效断裂韧度值。

Three groups of geometrically similar three-point bending beams with rectangular cross section and straight-through crack were prepared for cement mortar of two compositions.Using MTS815 material test machine,load vs.LPD （load point displacement） curves and load vs. CMOD （crack mouth opening displacement） curves of entire loading process were recorded for the specimens.There is a distinct size effect for fracture toughness calculated with linear elastic fracture mechanics using maximum load and initial crack length.Therefore,based on fictitious crack model, the CMOD can be expressed in an equation containing the load, the deadweight and the cohesive force.Solving the CMOD equation, the length of the fracture process zone can be obtained.Modify the initial crack length with fi-acture process zone length,then take it into the formula of the stress intensity factors of three-point bending beams, the equivalent fracture toughness with less size effect is derived.