Numerical Simulation And Experimental Research On Dynamic Fracture Of Three-Point Bending Specimen

Dynamic fracture mechanics takes the effect of inertia into account and is widely applied in engineering structure and validity analysis of equipment. In virtue of inertia effect, dynamic fracture is more complicated than quasi-static fracture, and the interrelated theory hasn't been fully founded. Three-point bending specimen is simple crack structure and frequently applied in testing material dynamic initiation toughness. In this dissertation, the issues of dynamic fracture numerical simulation and experiment research on three-point bending specimen are discussed.Firstly, the basic theory of dynamic fracture mechanics is introduced, including the fracture criterion of crack in common experiment, numerical simulation methods of dynamic fracture, loading technology in dynamic fracture experiment and determination of crack initiation time, etc.Three-point bending specimen loaded by impact loading is analyzed by ABAQUS and MSC/DYTRAN respectively. Displacement of the nodes around crack tip, which is perpendicular to surface of crack, is computed. Then the displacement method and Least-Square Method theory are used to gain the dynamic stress intensity factors. The result indicate that K(t) is varying along thickness direction of specimen. In the middle of the specimen, K(t) is larger than that in the other area. But the most difference is no more than five percent.Based on the result of FEM, dynamic stress intensity factor of three-point bending specimen is computed by approximate formulas. When specimen is loaded by regular impact loading, for example linear and sine loading, the results are consistent with that by FEM. But when specimen is loaded by experimental testing loading, the results are different from each other.Coarse and fine meshing model of three-point bending specimen is analyzed. The result indicates that dynamic stress intensity factors obtained by different node-group nearby crack tip are not in linear relation with r(displacement to crack tip). K(t) becomes less when node-group is closer to crack tip.The experiment of three-point bending specimen impacted by Hopkinson pressure bar is conducted. The dynamic stress intensity factor is computed by strain information around crack tip. And compared with the result by FEM. When strain gauge is affixed in reasonable position, the K(t) is consistent with that by FEM. When strain gauge is affixed in different position, the result indicates that the ascertaining crack tip position and affixing strain gaugein accurate position are important in dynamic fracture testing.Numerical simulation and experiment research on three-point bending specimen in this dissertation provide basis for the computation of dynamic stress intensity factor and dynamic fracture research.