Tensile Progressive Damage And Fracture Behavior Research On Q345 Steel With Crack

The problem of crack propagation has been a difficult and focused problem in fracture mechanics.It is a hot topic to explore the cause of crack propagation and the way of expansion.In this paper,the crack propagation and fracture mechanism of cracked Q345 steel specimen are studied by experiment and simulation.The main contents and conclusions are as follows:1?The uniaxial tensile tests on flat plate specimens and round bar specimens with different cross-sectional dimensions of Q345 steel shows that different cross-sectional dimensions have a certain influence on mechanical properties of material.The yield stress,fracture strain and elongation increase with the increase of cross-sectional dimensions,and the elastic modulus will remain unchanged.2?The uniaxial tensile tests on notched plate specimens and fatigue crack specimens whose crack was preformed by pre fatigue method,shows that no matter the fatigue crack specimens or the notched plate specimens,as long as the location and length of the cracks are the same,the propagation path,deformation and fracture morphology of the specimen are similar.3?By comparing the load-displacement curves of the notched specimens and the prefabricated crack specimens,it is found that the length of the longitudinal spacing has a great influence on the fracture displacement of the specimen when the crack length is the same and the longitudinal spacing is different,The larger the longitudinal spacing,the greater the fracture displacement of the specimens is,but the longitudinal spacing has little effect on the yield and ultimate bearing capacity of the specimens.4?The nominal tensile strain obtained by the conventional tensile test method can not truly reflect the fracture strain under the complex stress state of the ductile material.The fracture behavior of Q345 steel was determined by pre-fatigue method on Q345 steel three-point bending test piece,and the J integral value was calculated.The tensile behavior of notched flat specimens is simulated by finite element method,with different fracture strain.The J integral value is calculated by three different channel curves.The fracture strain of Q345 steel was determined by comparison with the J integral test value,which laid an important foundation for the finite element simulation.5?The tensile behavior of the cracked Q345 steel specimens was numerically simulated on the ABAQUS finite element analysis platform,and the influence of different plasticity and fracture parameters on the simulation results was compared.The simulation results show that the load-displacement curve of the model is different when the plastic parameters are different,and the curve is higher than the experimental curve.6?Considering the nonuniformity and multi-axial stress states of the stress field at the crack front,this paper proposes a method to modify the material parameters which is suitable for simulating the tensile properties of specimens with crack.The proposed method is used to adjust the material parameters of the model and the proposed tensile strain is adopted.The simulation tensile load-displacement curve is consistent with the test.