Study On The Mechanical Properties Of Weld Connection After High Temperature

As the most ideal way to connect steel at this stage,welded connections are widely used in steel buildings,ships,pressure vessels,cranes and other structures.For the entire welded structure the weld seam and heat affected zone are the more vulnerable parts,The mechanical properties of the base material and the welded material of the steel structure are affected after suffering from the action of fire,Therefore,in the design,identification and life analysis of steel structures,attention should be paid to the adverse effects of fire action on the force performance of the weld.To gradually improve the mechanical properties of steel structures after high temperature weld connection research,to enrich the theoretical basis of fire safety design of steel structures.In this paper,the static loading test after high temperature for the base material is Q235 B and the welding material is E4303 docking test and the corner test are respectively,Also consider the effect of different temperatures and stress patterns on the mechanical properties of the weld.The test data such as force-displacement curve,ultimate strength and damage morphology of the specimen were finally obtained through the test,and the model of weld stress calculation under high temperature post-composite stress field was analyzed.The nonlinear finite element analysis of the corner joint and butt joint specimens with a shear to compression ratio of 0.4 was performed in combination with ABAQUS finite element software,The proposed formula for setting the strength of fillet and butt welds after high temperature is fitted,and its feasibility is verified with cases,and the calculation model is found to be applicable to the design of fire resistance of steel structure welds.The following conclusions are drawn from a combination of experiments and numerical simulations in this paper:(1)By conducting post-high temperature tensile tests on four groups of butt specimens,it can be observed that the surface color of the specimens has changed,The surface of the specimen underwent a grayish-bright-dark blue-gray-dark black color change,and the degree of carbonization layer and spalling on the surface gradually increased with the temperature.And the tensile strength of the specimen is affected by the temperature trend of first increase and then decrease,when the temperature exceeds600℃,the specimen displacement increases with increasing temperature,the mechanical parameters of the specimen after the high temperature obtained through the tensile test can be used in the finite element analysis.(2)After high temperature,30 docking specimens and 30 angular connection specimens were used in the static loading test,at different temperatures when the damage are very sudden,without any sign,and all are damaged at the weld seam.With the increase in temperature,the weld shear strength is increasing and then decreasing trend,the analysis can be seen that 400℃ on the weld strength increase the most,but the ductility of the weld has decreased.When the temperature exceeds 600°C,the weld shear strength decreases by a maximum of about 13% compared to that at room temperature.The strength and ductility of the specimens were increased due to the addition of shear ratio and increased with increasing shear ratio.(3)ABAQUS was applied to conduct finite element analysis of the post-high temperature static load test on the butt joint specimens and angle joint specimens with shear to compression ratio of 0.4,and the load-displacement curves obtained by analytical simulation and test were compared and analyzed.The agreement between the two results was found to be high,indicating that the intrinsic relationship between the base material and the weld material and the contact mode used in the established analytical model are feasible,proving that the results obtained from the analytical model can be used for the mechanical characterization of steel welds after fire.(4)By assuming that the weld damage surface occurs at the section of the maximum fracture stress,the analytical derivation of the corner joint specimen to obtain the maximum fracture stress of the section and its angle (?).The shear strength and strength relations of corner jointed and butt jointed specimens after high temperature were proposed for shear strength ratio Q and shear compression ratio strength relations (?) and K,and the shear strength relations of specimens at different temperatures and shear compression ratios were obtained.The post-temperature strength relationship fitting formula is brought into the design formula for steel welds at room temperature.This results in the proposed post-temperature mechanics equation for welds at different temperatures and different shear-to-pressure ratios.