Nondestructive Testing Of Track Plate Damage Based On Thermal Imaging

CRTSⅡtype ballastless track slab is one of the main types of high-speed railway track structure in our country.With the continuous increase of line operation time,under the combined effect of train load and complex external environment,the cracks on the surface of ballastless track slab without pre-cracks become prominent,which undoubtedly brings huge hidden dangers to the long-term service performance of ballastless track structure and the safety of high-speed train operation.Therefore,it is of great theoretical value and practical significance to realize efficient and accurate detection of cracks in the short skylight of high-speed railway maintenance.Based on this,this paper proposes a non-contact infrared thermal imaging method for disease detection.Through field investigation,the characteristics and distribution of cracks on the surface of track plate were determined.Based on the basic principle of infrared thermal imaging and the heat conduction theorem,the formula for calculating the temperature difference on the surface of the track plate and the controlling factors affecting the thermal imaging detection effect are deduced.By establishing the finite element model,the effect of crack detection under different working conditions is compared and calculated,the detection method is optimized,and the detection accuracy is improved.The spatial characteristics and time-varying law of the temperature field in the cracked and non-cracked areas of the surface were compared and analyzed by the small scale model experiment of the track plate and the field experiment of infrared thermal imaging.The main research conclusions of this paper are as follows:(1)According to the field investigation and statistics,the occurrence frequency of cracks in the pre-crack area and non-pre-crack area on the rail plate surface is basically the same,but the average size of cracks in the bridge segment is larger than that in the subgrade segment.The width fluctuation range of cracks in the bridge segment is 0.02mm-0.36mm,and the length fluctuation range is 2.89cm-18.8cm.The width fluctuation range of cracks in the subgrade section is 0.01mm-0.82mm,and the length fluctuation range is 2.56cm-15.33cm.(2)The theoretical calculation results show that the track plate structure can be regarded as an infinite plane structure satisfying one-dimensional heat conduction,and the crack disease will cause the surface temperature field of the track plate to change and produce a certain temperature gradient.According to the surface temperature difference calculation formula,the main control factors affecting the thermal imaging detection effect of the crack are the crack length,crack width and ambient temperature.(3)According to the finite element calculation results,without auxiliary conditions, the environmental temperature has the greatest influence on the thermal imaging crack detection effect,and the higher the environmental temperature is,the larger the crack size is,and the better the detection effect can be achieved.Under the condition of 10℃,the maximum temperature difference between the fracture area and the non-fracture area was0.115℃,and the detection effect was poor.At 26℃,the minimum surface temperature difference of 0.2mm crack was 0.11℃.The artificial thermal excitation method can effectively improve the range and accuracy of thermal imaging detection of cracks on the surface of the track plate.According to the calculation results of the worst working condition,the maximum temperature difference on the surface of the track plate under different excitation conditions is 0.239℃.Under the condition of radiation intensity of thermal excitation of 1500 w/m~2,it is more appropriate to control the detection rate below 5 km/h.(4)Through the model experiment and the field experiment,it can be seen that the infrared thermal imaging technology can effectively detect and identify the surface cracks of the model.The average temperature of the fracture area is always higher than that of the non-fracture area.Affected by the size factor,the fracture area presents a discontinuous and highlighted state in the thermal image.At the same time,compared with the non-fracture region,the fracture region has a faster temperature change rate and a larger temperature change range.The isotherm extraction method was used to analyze the characteristics of the crack regions in the thermal image,and it was found that the isotherm distribution in the crack regions was more dense,and the identification accuracy of the crack area information and width information by infrared thermal imaging technology was up to 97.49%and 100%.Through the analysis of field examples,it can be seen that the model experiment results have good accuracy and reliability,and the minimum error of both is only 2.44%.According to the thermal image temperature extraction,the maximum detection accuracy of the area information and width information of the penetrating cracks of the actual track plate can reach 96.46%and 100%respectively by using thermal imaging technology.