Study On The Representation Relation Between Stress Concentration And Magnetic Memory Signal For Q235B Component

Metal magnetic memory testing technique is a kind of rapid and nondestructive detection methods to judge component of stress concentration position,the concentration degree and the type of component defect.Comparing with the traditional non-destructive testing,the metal magnetic memory testing had some advantages:it was no pollution for the workpiece and could diagnose the microdefects of building and damage.So far it has been gradually applied in many fields.In this paper,combined with the research status of metal magnetic memory testing technique and the technical difficulties in the practical testing of pressure equipment,through the experimental and numerical method,the characterization relationship between the stress concentration of Q235B component defects and the magnetic memory signal was analyzed and studied.Firstly,the Q235B plate specimen with hole defect was processed,and the influence of the detection orientation and lift-off value of the sensor probe on the magnetic memory signal was discussed.The results showed that the detection orientation only affected the numerical value of the magnetic memory signal,and the regularities of distribution of each position was the same.When the specimen was vertical and the hole was placed to the south,the result was more accurate.The theoretical analysis indicated that when the size of the hole was invariant,the smaller the lift-off value of the sensor probe was,the more obvious the magnetic memory signal was,the test results verified the correctness of the theoretical analysis.In engineering application,in the premise of no damage detection instrument,the smaller the lift-off value was,the more accurate the detection result was,the lower the value of the test equipment is not damaged.Secondly,the Q235B plate analysis model with different sizes of hole defect was established.The nonlinear numerical analysis of the plate model was carried out the ANSYS software,and the stress distribution of plate under tensile stress was obtained.The surface leakage magnetic signals of the defect specimen under static load with different damage stages were detected.The results showed that in the center round-hole defect,the tangential component H_P(x)of magnetic leakage field has maximum value,the normal component H_P(y)appeared change,and the gradient K of H_P(y)reached the maximum value;The specimens with different size round-hole defects to multi-stage loading,the results show that the magnetic memory signal could accurately reflect the degree of the stress concentration in the defects.By comparing the numerical results with the experimental data,the results indicated that there is a consistent relationship between the numerical results and the experimental data,which show that the magnetic memory testing technology can accurately judge the degree and the position of stress concentration,the last have got relational of H_P(y)and??relational for the Q235B specimen with hole defect.Finally,the influence regularities of heat treatment on magnetic memory signal is studied by the contrast test.The results indicated that,due to the welding residual stress,in the initial stage of loading,the characteristics of magnetic memory signal((?),K,S(H)and S(K))of the untreated specimen were gradually weakened.When the tensile stress fully offset residual stress,continuing to increasing the load,the characteristics of magnetic memory signal gradually increased.The magnetic memory characteristic signal((?),K,S(H)and S(K))of the heat treated specimen were gradually strengthened with the increase of the tensile load.MMMT technology not only could accurately determine the stress concentration of welded joints,but also could be used as an effective method to detect the quality of heat treatment process.