Research On Fatigue Crack Growth Behavior Of Arc Sprayed 3Cr13 Coatings Based On Acoustic Emission

Remanufacturing engineering has become one of the most promising technology,for it provides a solution to the current serious shortage of resources and environmental pollution,and it is supported by the Chinese government.Crankshaft is one of the key parts of the engine,it becomes an important remanufacturing object.The two major problems of crankshaft remanufacturing include: the evaluation of remanufacturability of crankshaft and the prediction of the life of remanufacturing crankshaft.According to the research shows: the bending fatigue failure is the main failure mode of crankshaft.So it is important to use a method of non-destructive technology to predicted the fatigue crack length of crankshaft and analysis the failure mode of crankshaft remanufacturing,it have great significance to solve the above two problems and promote the development of crankshaft remanufacturing industry.In this paper,the method of acoustic emission(AE)technology and machine vision were combined to monitoring the process of the four-point bending fatigue failure,and acquire the characteristics of AE signals at different failure stages,while the SEM was used to analysis the reason of above characteristics.And the fatigue crack length of 42 CrMo was predicted during the process.The process of fatigue failure of remanufacturing standard specimen was monitored,and the crack expansion characteristics,different failure characteristics and the AE signal characteristics was obtained during the process.The research results,as follow:(1)The pre-cracked 42 CrMo specimens and no-crack 42 CrMo substrate specimens simulate the crankshaft blank and full crankshaft,respectively.The difference of failure process mainly focused on the stage of fatigue crack initiation,which a sample with pre-cracked for multi-source fatigue crack initiation and no-crack specimen is single source crack initiation;(2)Absolute energy of different specimen were obtained,and it has good characterization to the difference,and the characteristics of AE parameter and waveform characteristics were obtained during different fatigue stage through monitoring the fatigue failure stage of the pre-cracked and no-crack specimens.It achieves the dynamic monitoring of the fatigue failure process of crankshaft;(3)The model of crack length prediction that AE cumulative counts combined with Paris formula can predict the fatigue crack length,precisely.While the error is less than 3mm;(4)The AE signals of average signal level(ASL)and RMS had good effect to characterize the failure modes of different coating thickness,which is of great significance to the remanufacturing engineering.(5)The fatigue failure modes of the samples were different with different coating thickness.The failure forms of coating thickness of 100 um and 200 um is that the crack initiate from the center of coating and substrate,propagation and led to the failure of material.The failure mode of the coating thickness 300 um and 400 um is that the crack initiate from the tip of coating and gradually propagate into the substrate,and the crack connection led to delamination,resulting the materials failure;...