Superplasticity by internal frictional heat under biased cyclic loading
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A new damping method was developed not only as a testing tool to investigate in situ deformation under stress, but also as a processing method to superplastically deform ceramics. The specific damping capacity (SDC) at low frequencies (<0.2 Hz) decreased with increasing frequencies, which matched previous internal friction results. However, at higher frequencies (0.2–5 Hz) SDC increased with frequencies, which was explained by a new internal frictional heat mechanism. Three different ceramics: a non-superplastic one and two superplastic ones with different activation energies, showed the same behavior at the high frequency damping tests (1–5 Hz). From these results, it was deduced that a cyclic load at high frequencies, superimposed on a static one, has a great potential to enhance superplasticity by specifically heating up grain boundaries from internal frictional heat.
KeywordsFriction Coefficient Internal Friction High Strain Rate Frictional Heat Superplastic Deformation
We thank Mr. D.M. Hulbert and J.D. Kuntz for experimental assistance and Drs. R.G. Duan and G.D. Zhan and Mr. N.A. Mara for helpful discussion. This research is supported by US Office of Naval Research under the grant number N00014-03-1-0148.
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