Research On Fracture Parameters For Non-standard Wedge Splitting Specimen Of Concrete

With the extensive application of concrete structures, fracture mechanics of concrete has also been further developed in recent years, the research on the fracture properties of concrete has been extensively taken seriously. However, concrete is a multiphase composite material, different from the ideal brittle materials, the fracture process of concrete shows three typical stages: crack initiation, crack stable propagation and unstable propagation. Therefore, studying the crack initiation, unstable and corresponding resistance curve has been widely concerned. In allusion to these problems, the following research work had been accomplished in this paper:1. The wedge splitting (WS) test is one of the most widely used forms to perform fracture mechanics, but there is no specifically calculate expression of the stress intensity factor for wedge splitting test, no matter it is standard or non-standard. With test simulation on non-standard wedge splitting specimen, expressions were proposed for stress intensity factor at the pre-cast tip and crack mouth opening displacement on the load line for specimen with different depth and initiation crack length, and their validity has been confirmed by comparison with the data in the literature. Based on the work above, size effect on the unstable fracture toughness and crack extension were investigated, and the consistency of fracture toughness data for various specimen depth as well as initiation crack length is demonstrated. The crack extension is little sensitive to the initiation crack length though, it increases along with the depth of specimen, which can be explained by the boundary influence of the specimen.2. According to the load - strain curve measured in the experiment, obtain the initial cracking load, and calculate the initial fracture toughness using the expression of the stress intensity factor for wedge splitting test, found that using this formula to calculate the initial fracture toughness is little sensitive to size effect; Comparing the initial fracture toughness measured by experiment with the initial fracture toughness evaluated by an analytical method, found that the latter is slightly larger than the former, then analysis the reasons for this phenomenon.3. The new K_R-curve based on the cohesive force acted on the fictitious crack zone which was proposed by Xu and Reinhardt is combined with concrete nonlinear strain-softening curve, the size effect of the new K_R-curve is researched, the results show that the new K_R-curves are independent of the specimens.