Failure Research On Internal Crack Of Q345 Steel Under Uniaxial Tensile Load

The propagation of crack is one of the main factors leading to material failure, the crack propagation would be very complicated if component contains multiple crack. Therefore, the research of material crack propagation is particularly necessary. A total of 96 rectangular plate specimen were made of typical plastic material Q345 steel., and to research of crack propagation and connection behavioral under uniaxial tensile load, the research contents and related conclusion mainly has the following several aspects:(1) Comparing with the no-crack smooth specimen, the specimen with cracks has a short yield platform of load-displacement curve, but the yield load and ultimate load are directly proportional to the decreasing of length and increasing of angle. The increase of the initial crack length and fracture energy required to reduce without linear relationship. The specimens with initial crack angle more than 30° have a relatively obvious yield platform, and the 90° specimen has the same load-displacement curve with smooth specimen, the crack of tensile direction has little impact on the specimen failure. The angle of initial crack has little impact on propagation direction on of the crack. The relative position of internal crack has little impact on failure energy and crack load. Crack load is directly proportional to the reduction of the initial crack length and angle increases, the initial crack needs to extend a little before specimen reaches ultimate load state. Axial strain and shear strain are directly proportional to the initial crack length in the field of crack tip,45°and 60° specimens’shear strain is larger than others.(2) The test results of two cracks specimens, the longer horizontal spacing, the bigger ultimate load, and the internal crack is larger than the edge crack. The failure stage of load-displacement curve of specimen with internal two cracks falling faster than two cracks specimen with one edge crack and one internal crack, and cracks become connection first or not would affect the bearing capacity of the specimen, if cracks connected, the bearing capacity relatively large. When the vertical spacing of double cracks is 20mm, cracks would to connect or not. If specimen has two internal cracks, the two cracks would not connected when vertical spacing greater than horizontal spacing. If specimen has one internal crack and one edge crack, the two cracks would not connected when vertical spacing greater than or equal to horizontal spacing. The horizontal and vertical spacing of initial crack have less effect on the crack load, but crack load of internal crack slightly bigger than edge crack. The initial crack needs to extend a little before specimen reaches ultimate load state. With the increase of crack vertical spacing, axial strain and shear strain will be increased at the same time. If one crack tip is closer to another, axial strain and shear strain would change fast. The axial strain of edge crack tip change faster than two internal cracks no matter inside or outside crack.(3) Based on different initial crack geometric model, adopted several common failure criterion and the new proposed failure criterion of finite element simulation analysis, the simulation results show that:The new proposed failure criteria can accurately simulate crack extension behavior of Q345 steel specimen, the crack extension and connection results of test and simulation were very close. The predicted values and experimental values of specimens crack load and ultimate load was close. Therefore, it can be seen that the new proposed failure criterion analysis damage behavior of ductile material such as Q345 steel has a good applicability.