Effect of pearlite on the vibration-fracture behavior of spheroidal graphite cast irons under resonant conditions
- PDF / 2,693,825 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 69 Downloads / 282 Views
INTRODUCTION
SPHEROIDAL graphite (SG) cast irons exhibit excellent castability, damping capacity, and mechanical properties and fair machinability.[1] Owing to these advantages, SG cast irons have been used in many structural applications. Camshafts, crankshafts, and disk-brake calipers are important examples of SG iron used in vehicles.[2] As transportation application materials, the possibility of vibration fracture resulting from resonant-vibration conditions is worthy of notice. That is, when the applied vibration frequency reaches the resonant frequency of the components, failure occurs rapidly.[3–7] Therefore, it is necessary to study the resonant-vibration failure of SG cast irons to ensure reliability. Based on earlier investigations,[3,8] the resonant-vibration test resembles the reverse-bending fatigue test, and they both suffer from alternate bending stress. However, due to the differences in damping capacity, the resonant-vibration fracture resistance of pearlitic ductile iron is lower than that of ferritic ductile iron. This contradicts traditional fatigue-test results.[9,10] Hence, the fatigue resistance may not directly correlate to the resonant-vibration fracture resistance. Although ductile irons are often subject to vibrations, little data are available in existing literature on the resonantvibration fracture behavior.[3,6,7] Our previous articles[6,7] have demonstrated that graphite nodularity and nodule count influence the resonant-vibration fracture behavior of graphite cast irons. For example, lowering the graphite nodularity can enhance the damping capacity of cast irons. Meanwhile, vermicular graphite can induce a stress-concentration effect S.C. LIN, formerly Graduate Student, Department of Materials Science and Engineering, National Cheng Kung University, is Engineer, Nan Ya Plastics Corporation, Jiayih 616, Taiwan, Republic of China. T.S. LUI and L.H. CHEN, Professors, and J.M. SONG, Postdoctoral Researcher, are with the Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan, Republic of China. Contact e-mail: [email protected] Manuscript submitted May 22, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
and cause cracks to initiate and propagate easily, thus lowering the vibration fracture resistance. It has also been confirmed[6] that a higher graphite nodule count will slightly decrease the damping capacity of SG cast iron, but will obviously increase the vibration fracture resistance. In addition, considering that the volume percentage of graphite phase embedded in SG cast iron is only about 13 to 15 pct, the influence of the matrix structure on the vibration fracture behavior should not be neglected. It is well known that the yield strength and fatigue strength increase with increasing pearlite content in ductile irons with a ferritepearlite structure.[11–14] Moreover, earlier reports indicate that high-strength cast irons may exhibit a lower damping capacity.[3,15] Therefore, after understanding the role of graphite particles on resonan
Data Loading...
