Investigation On Ductile Fracture Model Of Ultra-High Toughness Cementitious Composites

Ultra-high toughness cementitious composites (UHTCC) is a new type of engineering material which is composed of Portland cement, fiber, water, fine aggregate, and active mineral admixtures such as silica fume, coal ash and so on. This type of composites possesses strain hardening and multiple cracking under tensile and bending load with strain capacity more than 3% and maximum crack width below 0.1mm. This material exhibits ductile fracture, which is more safe and durable for structures in contract with quasi-brittle fracture of concrete and fiber reinforced concrete.The elastic plastic fracture mechanics can analyze UHTCC because this material has excellent ductility. The main evaluation indexes are the crack opening displacement, fracture toughness, J integral, JR curve, etc. The research is supported by the national natural science fund project (51308046).Theoretical and mechanical investigation on the ductile fracture model of UHTCC is carried out in this project. Firstly, based on the ductile fracture mechanism and the constitutive relation model, a fracture model of UHTCC with two parameters is developed, with initial-cracking fracture toughness and failure fracture toughness as its parameters. Energy field superposition theory is employed to explain the calculation relationship of the two parameters. Secondly, in order to calculate these two parameters, the fracture energy is achieved through J-integral method, while the equivalent critical quantity of crack propagation is obtained by the specimen’s deformation. Then, a calculation formula of these two parameters of fracture toughness is derived. Meanwhile, the size effect of the model parameters is studied, as well as the influence of fiber volume fraction. Thirdly, the crack propagation resistance curve (JR curve) and the simplified R model of this material are constructed according to the experimental results of type I fracture. The relation between the simplified R model and the ductile fracture model is illustrated. In addition, a comparative study on the performance of the two models on evaluating the ductile fracture toughness is taken.In a word, The research objective of this project is to develop the fracture model of UHTCC, and to calculate the model parameters, for the purpose of developing a theoretical basis for engineering application and safety assessment of this material.