Research On Eddy Current/Magnetic Memory Testing And Life Prediction For Retired Engine Crankshaft

The remanufacturing is the most effective way to achieve material cycle utilization,energy conservation and reduce adverse effects to environment.The quality control of remanufactured blanks is a vital process to ensuring the reliability of remanufactured products.The quality control within the remanufacturing process includes three aspects: failure analysis,nondestructive testing and life assessment.Therefore,based on failure analysis of determine the macroscopic failure mode and defect evolution law of components under their service conditions,using advanced nondestructive testing technology to develop the efficient and accurate life assessment method for remanufacturing is an important subject worth to be further studied.This dissertation focused on the research of large diesel engine crankshaft.Based on an independently developed nondestructive testing platform for this type of crankshaft,the fatigue failure and defects modes under the service conditions of crankshaft were analyzed,the eddy current testing method and the magnetic memory testing method were respectively adopted to detect the surface crack and stress concentration,fatigue damage of crankshaft.Then the life prediction methods facing remanufacturing based on fatigue defects nondestructive testing were explored and developed for residual life prediction of retired crankshaft.The main research contents include:(1)Based on engine theory,rigid multi-body dynamics and rigid-flexible coupling system analysis method,a rigid-flexible coupled dynamics model of the crankshaft system was established and simulated in dynamic simulation software ADAMS.The working loads of crankshaft were obtained to provide the load data for fatigue analysis of crankshaft.The static finite element models of the crankshaft under 12 working conditions were established in finite element analysis software ABAQUS.The stress distribution and deformation of crankshaft were obtained from simulation to provide the basis for process desing of detection.(2)Based on the basic principle of materials science,electromagnetics and eddy current testing,the finite element model of eddy current testing was created and simulated in multi-physics coupling simulation software COMSOL Multiphysics.The influence law of testing parameters such as excitation frequency and lift distance on the testing signal was subsequently studied.The model of eddy current testing for the sample with surface crack was created and simulated.The relationship between crack parameters such as crack depth and eddy current testing signals was also explored by modeling and simulating,which provides a basics for identifying fatigue cracks with eddy current testing.Eddy current testing and signal analysis of a type of retired crankshaft were carried out by using the independently developed nondestructive testing platform for the crankshaft and a method for identifying the surface cracks of crankshaft was proposed and verified.(3)Based on the basic principle of materials science,fracture mechanics,electromagnetics and metal magnetic memory testing,the magnetic memory testing of standared specimens in process of fatigue experiment was carried out to investigate the variation law of magnetic memory signal during the fatigue experiment process.Then the magnetic memory characteristic signals were extracted and the relationships between magnetic memory characteristic signals and stress distribution,crack initiation and crack propagation were further studied.The correlated laws of magnetic memory signal gradient and crack state were discussed to provide a foundation and basics for identifying stress concentration regions and representing damage states.Magnetic memory testing and signal analysis of this type of retired crankshaft were carried out on the testing platform and a method for identifying the stress concentration regions of crankshaft was proposed and verified,which also indicated the consistency with eddy current testing and reliability of magnetic memory testing.(4)According to all the research above,the crankshaft fatigue analysis model was created in fatigue analysis software nCode DesignLife and the fatigue life of crankshaft was calculated to provide a reference for the residual life assessment.Based on eddy current testing results,a crack propagation life prediction method related to crack size was proposed and verified by experiment of specimens.Based on magnetic memory testing results,a residual life prediction method,using the relationship between damage model represented by magnetic memory characteristic signal and normalized life was proposed and verified by experiment of specimens.The proposed life predication methods based on eddy current testing and magnetic memory testing results can be used to provieding the basics and guidances for the remanufacturing of retired crankshafts.Combined the nondestructive testing with life assessment,the relevance between macro-microscopic fatigue defects,electromagnetic nondestructive testing representation and residual life of large crankshafts were studied in this dissertation.A testing platform for eddy current testing and magnetic memory testing of crankshaft was established.The defects nondestructive testing method of retired engine crankshaft and residual life prediction method were also developed.The research results have great significance on science guidances and high value on engineering application for improving the theory,technology and method of nondestructive testing and life assessment in remanufacturing engineering of mechanical equipment.