Research For Mechanical Properties Of Brittle Fracture Of Structural Steel Thick Plate And Its Weld

With construction industry developing rapidly in domestic, structural steel thick plate is used more and more widely. Thickness increase leads to the deterioration of stress and strain state, center segregation and weldability, which causes the toughness performance to get worse. Meanwhile, the construction expansion in the cold region makes more structural steels work at low temperature, which results in brittle fracture of structural steel thick plate more serious. This paper makes FEA analysis on brittle fracture tendency of steel thick plate, does an experimental study on the mechanical and toughness properties of steel thick plate and its butt weld at low temperature, and then puts forward selection methods of structural steel thick plate against brittle fracture. The main conclusions are as following:(1) This paper makes FEA and theoretical analysis on elastic and plastic stress field of the crack tip of 60mm-150mm Q345 thick plate in tension, obtains the distribution law of stress field of the crack tip, and especially studies on the brittle fracture tendency deeply.(2) This paper does experimental study on mechanical properties, impact toughness and fracture toughness of 60mm-150mm Q345 thick plate at low temperature, obtains the relevant variation of mechanical and toughness index with low-temperature effect, thickness effect and location difference along the thickness direction, and then researches into the ductile-brittle transition temperature of toughness index.(3) This paper does experimental study on impact toughness and fracture toughness of butt weld of 150mm Q345 thick plate at low temperature, obtains the relevant variation of A_kv and CTOD of weld area and heat-affect zone with low-temperature effect and location difference along the thickness direction, and then researches into the ductile-brittle transition temperature. (4) this paper, basing on impact toughness index (A_kv), supplement the current selection methods against brittle fracture of steel structures from three aspects: low temperature level, affect of thickness and ductile-brittle transition temperature; the paper also puts forward an evaluation method of fracture security level of steel thick plate basing on fracture toughness index (CTOD), and after quantitative processing, finally gets an improved selection method against brittle fracture of steel thick plate.