Experimental Study And Theoretical Analysis On Brazing Residual Stress In Austenitic Stainless Steel Core Plate

Stainless steel core plate(SSCP)is a novel building structural element.It consists of two stainless steel panels and a certain number of stainless steel core tubes by brazed.Due to the significant differences in physical properties between stainless steel and copper-based filler alloys,the brazing residual stresses(BRSs)are generated during the copper brazing process.The BRS is significantly affect the load resistance of the SSCP,and the previous study in SSCP lacks a suitable BRS distribution model.Therefore,it is the necessary to investigate the BRS magnitudes and distributions in SSCP.In this study,a simplified predictive model for BRS distribution is proposed accordingly by experimental measurement and numerical calculation.Combined with the sandwich panel design method for SSCP floor,the stiffness of the SSCP has been studied in depth,and its main research work includes as follow:(1)This thesis overviews the constitutive model of stainless steel materials,the methods of measuring residual stresses,the progress of research on residual stress in stainless steel members and the current status of research on SSCP.(2)The basic principle of hole-drilling(HD)method and X-ray diffraction(XRD)method has been introduced in detail.The equations of residual stress measurement values and strain release coefficient of the HD method have been derived.The equations of the plane stress and the three-dimensional stress of the XRD method have been provided.(3)A total of 24 tensile coupons were conducted by material properties test,and the basic mechanical properties and stress-strain curves of the stainless steel materials were obtained.The grading calibration of stainless steel materials was carried out.The experimental calibration values and theoretical calculation values of the strain release coefficient were obtained by the grading calibration.The magnitudes and distributions of surface BRS in 35 specimens of SSCP were measured by HD method and XRD method.Based on the test results and the position of measurement point,the BRS distribution patterns of single-unit SSCP have been plotted.(4)The magnitudes and distribution pattern of the surface BRS for the single-unit SSCP have been studied and analyzed.A simplified predictive model for the surface BRS distribution of the single-uint SSCP is proposed accordingly.The correlation of the BRS distribution were investigated.The BRS of nine-unit panel specimens for SSCP were measured by HD method.The test results were compared with the proposed simplified distribution model to verify the applicability of the simplified distribution model in whole SSCP.The multi-directional validation of the simplified BRS distribution models for single-unit specimen was carried out,and the three-dimensional BRS distribution of the single-unit for SSCP was provided.(5)Based on the three-point bending test of SSCP,the SSCP floor finite element model(FEM)was set up.The BRS simplified distribution model was applied to the SSCP floor FEM with the initial stress field.The stiffness and load-displacement curves of the SSCP floor under different initial stress states were compared with test results to verify the applicability of the simplified distribution model.Parametric analysis of the main factors affecting the shear stiffness of the SSCP floor under different initial stress states was carried out.The formula for calculating the shear stiffness of the SSCP floor was modified.