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Frontiers of Mechanical Engineering

ISSN 2095-0233

ISSN 2095-0241(Online)

CN 11-5984/TH

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2018 Impact Factor: 0.989

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Front. Mech. Eng.    2016, Vol. 11 Issue (3) : 233-241    https://doi.org/10.1007/s11465-016-0400-3
RESEARCH ARTICLE
Fatigue features study on the crankshaft material of 42CrMo steel using acoustic emission
Yue SHI1,Lihong DONG2,*(),Haidou WANG2,*(),Guolu LI1,*(),Shenshui LIU1
1. School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130, China
2. National Key Laboratory for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072, China
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Abstract

Crankshaft is regarded as an important component of engines, and it is an important application of remanufacturing because of its high added value. However, the fatigue failure research of remanufactured crankshaft is still in its primary stage. Thus, monitoring and investigating the fatigue failure of the remanufacturing crankshaft is crucial. In this paper, acoustic emission (AE) technology and machine vision are used to monitor the four-point bending fatigue of 42CrMo, which is the material of crankshaft. The specimens are divided into two categories, namely, pre-existing crack and non-pre-existing crack, which simulate the crankshaft and crankshaft blank, respectively. The analysis methods of parameter-based AE techniques, wavelet transform (WT) and SEM analysis are combined to identify the stage of fatigue failure. The stage of fatigue failure is the basis of using AE technology in the field of remanufacturing crankshafts. The experiment results show that the fatigue crack propagation style is a transgranular fracture and the fracture is a brittle fracture. The difference mainly depends on the form of crack initiation. Various AE signals are detected by parameter analysis method. Wavelet threshold denoising and WT are combined to extract the spectral features of AE signals at different fatigue failure stages.
Keywords acoustic emission      fatigue failure      remanufacturing crankshaft      wavelet analysis     
Corresponding Author(s): Lihong DONG,Haidou WANG,Guolu LI   
Online First Date: 23 August 2016    Issue Date: 31 August 2016
 Cite this article:   
Yue SHI,Lihong DONG,Haidou WANG, et al. Fatigue features study on the crankshaft material of 42CrMo steel using acoustic emission[J]. Front. Mech. Eng., 2016, 11(3): 233-241.
 URL:  
https://academic.hep.com.cn/fme/EN/10.1007/s11465-016-0400-3
https://academic.hep.com.cn/fme/EN/Y2016/V11/I3/233
Element Mass fraction/% Element Mass fraction/%
C 0.380 to 0.450 Cr 0.900 to 1.200
Si 0.170 to 0.370 Ni ≤0.030
Mn 0.500 to 0.800 Cu ≤0.030
S ≤0.035 Mo 0.150 to 0.250
Tab.1  Chemical composition of 42CrMo
Property Numerical value
Yield strength 930 MPa
Tensile strength 1080 MPa
Elongation percentage 12%
Percentage reduction of area 45%
Tab.2  Mechanical property of 42CrMo
Fig.1  Processing size of specimen. (a) Specimen non-crack; (b) specimen with crack
Fig.2  Position of the sensor during the test. (a) Sketch map; (b) test
Fig.3  Image of machine vision sensors
Fig.4  Picture of fatigue fracture
Fig.5  SEM micrograph for the zone of A
Fig.6  SEM micrographs showing the fatigue fracture: (a) Source zone, (b) crack growth zone
Fig.7  SEM micrographs of the B zone: (a) The integral appearance of fracture; (b) SEM micrograph showing fracture
Fig.8  SEM of the crack material’s fatigue failure fracture
Fig.9  SEM amplifying morphology of the zones A and B: A is the zone of pre-crack, B is the zone of crack initiation
Fig.10  Zone of crack initiation induced by different way: (a) By the brittleness; (b) by the inclusions; (c) by the stress concentration
Fig.11  SEM of the (a) crack growth zone and (b) fracture zone
Fig.12  Acoustic emission signals at different applied stresses: (a) 550 MPa; (b) 600 MPa; (c) 650 MPa; (d) the specimen of pre-existing crack at 550 MPa
Specimen Stress intensity/MPa The numberof cycles The number of hits The numberof waveform Average AE hits
Non-pre-exiting crack 650 135900 709188 709156 5
600 294300 852427 852733 3
550 436650 921666 922451 2
Pre-existing crack 550 8040 112425 112425 14
Tab.3  Experiment results at different applied stresses
Fig.13  Absolute energy of non-pre-crack specimen
Fig.14  Absolute energy of pre-crack specimen
Fatigue failure stage Waveform signal Signal types
Crack initiation Continuous
Crack propagation Mixed
Crack propagation Burst
Fracture Burst
Tab.4  Feature of AE signals at different stages
Fatigue failure stage Spectral feature Spectral content/kHz Highest frequency/kHz
Crack initiation 63 to 114 Low frequency: 96
Crack propagation 71 to 295 Low frequency: 89High frequency: 278
Crack propagation 83 to 308 Low frequency: 108High frequency: 286
Fracture 69 to 327 High frequency: 252
Tab.5  Feature of frequency at different fatigue failure stages
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