Research On Mechanical Properties Of Q355B Butt Weld After Repeated High Temperature Loading

When fires occur,they are often uncertain and complex,and sometimes they are resurgent due to insufficient extinguishing.As the basic component of steel structure and the weak link under fire,the mechanical properties of butt welds after fire are bound to be different from homogeneous metals,and the study of high temperature mechanical properties is of indispensable significance for the detection and identification of the overall post-fire performance of steel structures.The vast majority of fires have not caused fundamental damage to the steel structure,and the direct dismantling of these structures that have not been fatally damaged after the fire will cause significant losses,so the study of the mechanical properties of the weld joint after high temperature is very important for the repair after the fire and the fire resistance design of the steel structure.Therefore,this paper studies the mechanical properties of butt weld specimens under single and repeated high temperature loads.The coefficients in the theoretical equation were obtained by analyzing and fitting the test data.Thus,the mathematical model of the correction factor of mechanical properties of Q355 B butt weld after high temperature with respect to temperature T is obtained.Finally,the test results were verified by the tensile test of the simulated butt weld after high temperature.The main content of this paper includes the following aspects:1.A theoretical model for correcting mechanical properties of butt weld after high temperature was proposed.By analyzing the strength of the butt weld after high temperature cooling,a theoretical model for modifying the residual mechanical properties of the butt weld after high temperature cooling is proposed,which provides theoretical support and reference for the design and application of steel structures.2.The effects of high temperature times and cooling methods on the residual mechanical properties of welded joints were studied,and the parameters in the polynomial equation of correction factor in the theoretical model were identified.Under the action of single high temperature load,the welds began to fracture at 500°C and 600°C under natural cooling and immersion cooling,respectively.Under repeated high temperature loading,all welds break at the weld.By fitting the test data,various parameters in the polynomial equation of correction factor in the mechanical theoretical model of butt weld correction after high temperature were identified,so as to obtain the mechanical theoretical model of butt weld correction after repeated high temperature load.The results can provide a theoretical basis for the repair of steel structure after fire.3.The correctness of the theoretical model is verified by finite element simulatio-n.Through the finite element analysis of the welding and high-temperature tensile process of the model,and the comparison of the fracture morphology and stress-strain curve of the specimen between the simulation and the test results,it is found that the er-ror between the simulation and the test results is less than 10%,indicating that the tes-t process and the simulation process are feasible,and the theoretical model proposed is reliable.The results can provide reference for the analysis of mechanical properties of butt weld joints after fire.