Study Of Critical Equivalent Crack Of Three-Point Bending Beam

The concrete fracture mechanics is a subject that has developed for several decades. Applying mechanical principle, the blemish material and structure were researched. During the development of the fracture mechanics, many domestic and foreign scholars have put forward some crack models and standards successively. In each model theory, unstable fracture toughness is an important parameter. Theequivalent critical crack length a_c matching with maximum load bearing by the specimen is the key to calculate the unstable fracture toughness. This paper is focused on the research of the equivalent critical crack length a_c of three-point bendingbeam.In this paper, double-K fracture criterion is introduced. And on terms of the criterion, a calculated method based on the P- â–³ curve is presented by theoretical analysis. The formulas of elastic modulus and equivalent critical crack length of three-point bending beam are also obtained. These results are contrasted with the results calculated by based on the P - CMOD curve. And it could be considered that both of two methods are equivalence by corporation.The experiment of three-point bending beam is also carried out and gets the P - CMOD curve and P - â–³ curve. Some key parameters are obtained by the two curves. Applying the two methods to calculate the equivalent critical crack length a_c separately, it is showed that the difference of a_c calculated by the two methods is very little.The concrete equivalent critical crack length a_c is affected by different factor;each factor's affection is analyzed. Synthesized all factors, the chief factors are obtained the secondary factors are ignored. Then the regression equation is fitted. This equation can be used to forecast and estimate before engineering design.