Study On Impact Toughness And Fracture Mechanism Of Steel Bridge Thick Plate

With the rapid development of the national economy and the long-term rapid growth of steel production capacity,steel has become a common building material and has been widely used in long-span bridges,resulting in an increasing demand for thick steel.With the increase of thickness,the stress-strain state of the crack or crack-like defect in the steel bridge slab changes from plane stress to plane strain,and the constraint increases and the brittle fracture tends to increase.In addition,the northern part of China has a severe cold weather,and the minimum temperature is below-40 °C.The toughness of thick steel plates(thickness exceeding 50 mm)in the low temperature environment will be worse,and brittle fracture will be more likely to occur.Based on the above situation,in order to ensure that there is no brittle fracture accident in steel bridge thick plates at low temperature,it is of practical significance to study the impact toughness and fracture mechanism of steel bridge thick plates.The main work of this paper is as follows:(1)Through the analysis of several classical fracture mechanics theories(stress field strength factor theory,J-integral threshold theory,crack tip opening displacement),it is concluded that under certain conditions,there is a certain correlation between the impact toughness index and the fracture toughness index.When the thickness of the steel plate does not exceed a certain value,the fracture toughness of the steel can be evaluated by the Charpy V-type impact toughness test.When the value exceeds a certain value,the steel needs to be corrected by CTOD test.(2)At four temperature points of +20,0,-20,-40 °C,the impact test of structural steel Q345 B thick plate(60,90,120 mm thickness)was carried out,and the corresponding impact energy value AK was obtained.The Origin software was used to linearly analyze the experimental results,and compared with the normative values.Finally,the weighted average method was used to correct the thick plate impact energy.(3)In order to understand the distribution of stress field at the ideal crack tip,the finite element software LS-DYNA is used to consider the influence of factors such as material constitutive relation,lateral constraint condition,meshing density and initial crack defect.Metamodel.Through the model loading P-V curve,qualitatively judge the fracture toughness of Q345 B steel under different temperature environments,and determine its CTOD critical value.(4)Combined with the above research,the experimental results of the impact toughness test of Q345 B steel and the numerical analysis results of CTOD fracture toughness are compared with relevant literatures and specifications.In this paper,a simplified calculation method for the impact toughness of steel bridges and a method for determining the critical value of CTOD are proposed,which provides some reference value for engineering related tests and steel bridge related design parameters.