CTOD Fracture Toughness Tests And Numerical Simulation For Bridge Steel

With the rapid development of railway and highway in the recently 100 years, the construction of steel bridge will become large-span, large segment, novel style structural. In large span bridge design, because of their link force received increase, we have to use the thick plate if we choose traditional steel or use the high strength. At the same time, their work environment become worse and worse, the application of larger engineering project appear with using the high strength steel and thick plate in large amount engineering. The incident of common steel structure and welded connection which are made by the high strength steel and thick plate appear brittle fracture become more frequently. Therefore the problem come to us:the fracture toughness evaluation and control for steel structural need to research which is also very important to the problem of material strength stiffness, stability. As we known, the fracture toughness weakness of the heat affected zone and welded connection is the main reason of failure of welded structure, the thick of steel plate, the weak fracture toughness is. Therefore, the accurate evaluation fracture toughness of thick steel plate is extremely important to the anti-fracture of large span steel bridge. In this research, this paper use numerical simulation method and CTOD experimentation for bridge steel Q420qE and Q370qE to evaluation their fracture toughness, and the following efforts have been made and the conclusions are presented:(1) This research measured the mechanical behavior of bridge structural steel which was needed for the design of Dongguan east river bridge were undertook. The environmental and physical condition is determinate by the temperature region where the Dongguan east river in. This paper choosed two important bridge structural steel Q420qE and Q370qE of different thick plate and the welded seam material to do the research on their mechanical properties. This investigation can get various mechanical parameter from tests, for example:yield strength, ultimate strength, section shrinkage rate and percentage elongation and'so on.(2) At the same time, the CTOD specimens fatigue crack were made for each group specimens. in the test, firstly,these specimens were under larger fatigue load; at last,residual fatigue crack were made by smaller fatigue load. In this method, a lot of time was saved, the radious of crack which is equal to zero was made, and the crack tip was not in passivation. At the same time, the relationship of the load, crack extend growth, load cycle and frequency were record.(3) The bridge structure steel Q420qE and Q370qE of different thickness in different temperature were under fracture behavior test, the P-V curve were obtain from the specimens which contain crack, the change rule which are influence by the test temperature and the thickness of specimens were obtain from the change crack open displacement. The value of CTOD was under investigation from its accuracy and practicability, furthemore, the CTOD value of different bridge steel specimen which is affected by the change of temperature greatly is analyzed, and the crack open displacement value is close related to temperature and thick is presented. we can come to the conclusion that:except for Q370qE HAZ specimens, the fracture toughness CTOD value of bridge steel Q420qE and Q370qE specimens are greatly influenced by the test temperature, at the same time, when the base steel specimens, heated affect zone specimens and welded seam specimens are under the environment when the temperature is down quickly, the fracture toughness of welded seam specimens are the most sensitive, and all of CTOD value of the specimens is closed to the thickness of specimens.(4)Based on the linear-elastic fracture mechanics, considering the stress strange of the crack tip, the 3D 20 point special element was made for crack tip when use the FEM to compute the KI. using fatigue software to anlysis the crack growth of CTOD specimens, found the relationship of the load,crack extend growth, load cycle, the result were show that using fatigue to compute the bridge steel fatigue crack growth was right.(5) The investigation show that using finite element software ANSYS and LS-DYNA to solve the calculation of the fracture toughness of metal bridge material is correct and feasible which is basing on contrast of CTOD value and the fracture toughness test CTOD value. And the value computed by LS-DYNA is better than by ANSYS. The basic theory and numerical simulation method which is used in the fracture toughness test of metal material have been in research and summary, the mesh size, time control and precision control has been studied. From the investigation, it can come to the conclusion that the selection of mesh size are determine which are used in the three dimensional numerical simulation about the fracture toughness test of metal bridge material, from this investigation, the optimization problem between the mesh size, loading speed, using time,and precision control in the fracture toughness calculation of metal material by using universal large commercial finite element software LS-DYNA is under solution.(6) Based on the CTOD various criterion and thesis in the world, considering the security level and work temperature, the permit value of CTOD of bridge steel thick plate was under discussion. The major engineering project steel and welded seam of east river fracture toughness property was evaluation. At the same time, the permit value of CTOD is also can use in other project fracture toughness evaluation.