Research On Crack Detection Of Compressor Blade Based On Pulse Eddy Current Thermal Imaging

As the key part of compressor,blade directly affects the normal operation of equipment.Under extreme and long-term working conditions,blades will appear different degree of damage,such as surface damage,mechanical damage,creep and crack,etc.These defects will affect with the normal operation of the equipment,reduce the service life of the device,and greatly reduce the safety and reliability of the equipment.In severe cases,it will cause blade fracture and cause incalculable loss.Nondestructive testing technology plays an important role in industry.Using nondestructive testing technology to monitor equipment work can not only ensure the engineering safety,but also enhance the product quality.At present,there are many methods to identify the cracks of the blade without contacting the blade.The pulsed eddy current thermography detection technology selected in this paper is a transient eddy current detection technology,which does not need to contact the test piece,has wide measurement range,high efficiency,low system cost and high sensitivity,and has certain advantages in the defect detection of complex curved components.This technology is used to detect the cracks on the blades of axial-flow compressor,and the cracks are identified by the thermal imaging method of uneven temperature distribution on the blade surface.The main research contents of this paper are as follows:(1)The excitation coil in the pulse eddy current thermography detection system is studied.The structures of rectangular coil,solenoid coil and Helmholtz coil are analyzed.then,the magnetic field generated by the three coils and their defect detection characteristics of the tested parts are studied from two aspects of theory and finite element simulation.Finally,the rectangular coil is selected as the excitation coil for subsequent research.(2)The three-dimensional model of the blade is established,and the artificial cracks are established on the model.The pulse eddy current thermography simulation of the blade surface cracks are carried out by using COMSOL Multiphysics simulation software.The influence of the excitation current and excitation frequency on the simulation results is analyzed.The influence law of the blade surface crack on the eddy current field and temperature field of the blade specimen is studied.At the location of the blade crack,the eddy current is more concentrated,and the temperature will rise,compared with the defect free area,the maximum temperature rise of crack 1 is 21%,and that of crack 2 is 29.5%.(3)The artificial cracks are processed on the blade specimen by laser processing.After the experimental platform is built based on the pulse eddy current thermography detection technology,the pulse eddy current thermography experimental research on the blade cracks are carried out,and the thermal image of the temperature distribution on the blade surface is obtained,there will be obvious color change at the crack.An improved true color image enhancement method is proposed to process the experimental thermal images.The results show that this method can realize defect enhancement and reduce the interference of blade edge temperature rise on the experimental results.