Research On The Detection Method Of The Metal Structural Stress Based On Eddy Current Thermography

Steel structure is widely used in machinery,bridges,construction and other fields for it’s excellent physical properties in terms of strength,texture,plasticity and toughness.Stress state is the vital indexes for evaluation of steel structure safety status,the detection of stress is a powerful tool to maintain regular performance of steel structure,and it’s of great significance to preventing the occurrence of safety accidents.In order to promote the development of the nondestructive testing technology in steel structure field,this paper puts forward a kind of stress testing method based on the technology of pulsed eddy current thermography.Through theoretical analysis,simulation,algorithm research and experimental verification,get the internal relationship information between the stress of the steel structure and the heating temperature,then work out the stress detection method of steel structure under pulsed eddy current excitation.It will be of great importance in promoting the development of nondestructive stress testing technology.The main contents of this research are four parts as follows:1)Briefly introduce the basic principle of infrared pulse eddy current detection,and then use the mechanical and electromagnetic theory,and the factors are analyzed.By studying the effect of stress on the material physical properties and material physical property change on the influence of the eddy current induction heating,the theoretical model of stress field,electromagnetic field and temperature field is established.Finally it introduces the design theory of eddy current probe excitation excitation device,and proposes a design model of induction heating on the U core.Through the parameter design,the excitation probe can realize the function of uniform heating.2)Establish the finite element simulation model to study the influence of heating temperature distribution on the size parameters of the strip magnetic and coil and determine the size of the excitation probe and excitation parameters.Design a complete incentive probe model,and the heating effect is evaluated.Study the thermal coupling simulation method,and construct the power thermal coupling simulation model.Then make an evaluation of the probe.The simulation calculation results are analyzed,and pulsed eddy current is established motivation 0.2s measured stress measured area and the average temperature rising.And the influence of the thickness of the steel plate on the heating effect are discussed.3)According to the character that temperature of steel plate change over time in the process of electromagnetic induction heating,this paper proposes a stress testing method based on time-temperature changing rule.Through studying the rule,construct the stress detection equation of stress time and temperature rise.According to the equation,get the stress value in the area to be tested when freely choose some time and its corresponding area being measured temperature data.The system error caused by non-stress factor,required to solve repeatedly,can be decreased.4)Build test platform and design the corresponding experiment scheme with Q235.Analyze the thermal image data to verify the relevant conclusions of the theory and the simulation and then structure the stress detection algorithm equation.Verify the accuracy of the algorithm by means of the experimental data.Through the above research,it has been proved that the pulsed eddy current thermography method has a good effect on the stress testing of the steel structure.The research has promoted the application of infrared thermal imaging method in the field of stress detection of steel structure and has a good prospect.