Study On Obtaining Mechanical Property Parameters Of Inhomogeneous Materials Of Welded Joints By Continuous Indentation Technology

The plastic hardening of nuclear power welded structures during processing would induce changes of the mechanical properties in local areas.The accurate mechanical properties of materials are of great significance for evaluating the structural integrity of welded structure.The induced inhomogeneous material mechanical properties in the local region of welded structure usually cause difficulty to obtain the precise mechanical properties in regions by traditional tensile test.The complex mechanical state in local area of welded joints has difficulty to simulated in the laboratory.In this thesis,the plastic hardening of nuclear power welding structure in manufacturing process is simplified as different degrees of prestretching deformation of materials,an approach to obtain material mechanical properties in local region of structure is proposed,which can effectively analyze and obtain indentation plastic characterization parameters of materials with different elongations.On this basis,the approach is applied to the detection of mechanical properties of the local micron-area of inhomogeneous materials in nuclear power dissimilar metal welded joints.The main research contents are as follows:(1)Aiming at the indentation deformation of materials during the indentation test and the"pile-up/sink-in" phenomenon around indentation area,and based on the detailed analysis of the correlation between the the indentation information in load-depth curves and real mechanical response of materials,the plastic mechanical parameters of materials are characterized by linear hardening constitutive relationship.(2)In the micron scale indentation test system,the continuous ball indentation tests were carried out on 304 austenitic stainless steel with different elongations.The macron morphology of indentation area is compared and analyzed.Combining with the load-depth curve to identify the indentation response parameters of material with different elongations,and effectively characterized the mechanical changes in the plastic deformation stage,and compare with the results of traditional tensile test for verification.(3)By using ABAQUS for finite element inversion analysis,a three-dimensional model of continuous ball indentation is established.By analyzing the changes of indentation response of tested materials under different elongations,the changes of accumulation in indentation area and the mechanical properties of materials under the influence of plastic hardening are studied.Combining with the linear hardening constitutive relationship to characterize the mechanical parameter changes of materials under different elongations.(4)Taking the dissimilar metal welded joints of the safety end of primary circuit of nuclear power pressure vessel as the research object,through the continuous ball indentation tests on the welding fusion line,the variation law of mechanical parameters of inhomogeneous materials at different positions from the welding fusion line is obtained.