Design Of T Jionts And Cross Joints Based On Principle Of The Equal Load-carrying Capacity

T joints and cross joints’load-carrying capacity is limited by its serious geometric discontinuity and material unevenness when under-matching weld joints are used. The traditional design concepts and methods cannot completely solve this problem, there are obviously deficiencies and gaps in current studies. This article establishes the strength theory of T joints and cross joints, analyzes their fracture mode, then puts forward a new design concept, equal load-carrying capacity, which aims at improving joints’load-carrying capacity to a level that equals to the base metal’s yield strength. Using fracture mode as macroscopic criterion, theoretical stress concentration factor as control parameters, the realization conditions of equal load-carrying capacity are determined. Through linear elastic analysis, the relationship between theoretical stress concentration factor and geometric parameters is established, thus the design principles of equal load-carrying capacity joints are established. Through elastic-plastic analysis, examine whether the desired design goal is reached.The strength theory of T joint and cross joint is established to study the effects of the geometry parameters on the load-carrying capacity of the joint. The average shear stress and tensile stress in the weld throat section, the max shear stress and tensile stress and there positions are expressed under the hypothesis that the materials’plasticity is good enough and there is no self balancing stress within the joint. Further research shows that when mechanical properties of materials is fixed, the failure cause and load-carrying capacity of the joint depend on the geometry parameters, thus their relationship can be given.Since fracture model can reflect the load-carrying capacity and plasticity of the joint, and, the stress-strain differences between the weld metal and the base metal, it can be used as a criterion to assess the reliability of the joints. The equal load-carrying capacity design requires that the fracture model of the joints be at least (ligament) overall yield fracture model. Using theoretical stress concentration factor as control parameters, the realizations condition of equal load-carrying capacity design are given.Calculate the theoretical stress concentration coefficient under different joints’ geometric parameters (thickness, leg size, weld toe’s angle,weld toe’s transition arc radius), establish the equation of them, then put forward the equal load-carrying capacity design principles for T joints and cross joints.A elastic-plastic finite element model of a equal load-carrying capacity designed cross joint designed is built to analyze the stress-strain distribution,to forecast the fracture model and location. Results show that the joint fractured in (ligament) overall yield fracture model, its load-carrying capacity reached a level that equals to the base metal’s yield strength.The equal load-carrying capacity designed joints have equal load-carrying capacity to the base metal, thus, in the design of welding structure, there is no need to add the base metal’s thickness because of the existence of joints.