Characterisation of Mechanical Behaviour of Engineered Cementitious Composites under Static and Fatigue Loading

摘要

Engineered Cementitious Composites (ECCs) are a unique member of high performance fibre reinforced cementitious composites, featuring outstanding tensile strain-hardening capacity with superior tensile strain capacity and multiple microcracking with self-controlled tight crack width. Due to the importance of the tensile behaviour of the ECC, a hierarchical multiscale modelling method is developed for effective and efficient characterisation of the mechanical behaviour of ECCs under static and fatigue tensile loading. A generic analytical model is developed for crack bridging analysis in short fibre reinforced cementitious composites such as ECCs, which is the characteristic mechanical behaviour of ECCs at the microscale and lower mesoscale. The model predicts well the crack bridging stress-crack opening displacement relation. A representative volume element (RVE) model is proposed to model the joint response of the uncracked matrix and multiple cracks of ECCs at the upper mesoscale. The material randomness of ECCs is also considered in the RVE model. The RVE model is analysed by a hybrid cohesive zone model-extended finite element method (hybrid CZM-XFEM) method introduced in this work, which is used to simulate the multiple cracks adaptively as well as describe the crack cohesive behaviour using a simplified efficient cohesive model proposed based on the crack bridging analysis at the microscale and lower mesoscale. To characterise the mechanical behaviour of ECCs under fatigue tensile loading, degradation models of the micromechanical properties are proposed, and a cycle-dependent crack bridging relation, which accounts for both the interface degradation and fibre fatigue rupture, is developed based on the degradation models. The bridging stress degradation of ECCs under fatigue loading is modelled through a cyclic analysis based on the multiscale modelling method and the cycle-dependent crack bridging relation. A polyvinyl alcohol (PVA) fibre reinforced ECC (PVA-ECC) by using a local sand instead of the normally used fine silica sand is developed. The effect of the mix proportion, specimen dimension on the static mechanical properties of the PVA-ECC is investigated experimentally. The characteristics of the variation in the static tensile properties of the ECC is also demonstrated. The crack bridging degradation of the PVA-ECC under fatigue tensile loading is tested.