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CE Home > Warren Lecture Series
Warren
Lecture Series - Winter 2008
Materials With Extremely High Damping and Modulus
Speaker: R. S. Lakes
Department of Engineering Physics
University of Wisconsin-Madison
Date: April 11, 2008
Time: 3:30 p.m.
Location: Civil Engineering Building Room 210
High mechanical damping in materials is of interest in the context of damping of vibration in machinery, automobiles, and airplanes. The figure of merit for structural damping and damping layer applications is the product E tan delta for tension or bending, or G tan delta for torsion or shear. For most materials, even practical damping layers, E tan delta is less than 0.6 GPa, since in the polymers used, high damping is accompanied by low stiffness. High damping materials is possible based on metal alloys and metal matrix composites. The latter do not obey time temperature superposition. Mechanical damping, tan delta, of several composites was determined experimentally over a wide range of frequency and time, up to eleven decades (a factor one hundred billion) from slow quasistatic tests to 100 kHz in the ultrasonic domain, using a unique broadband viscoelastic spectroscopy (BVS) apparatus. No appeal was made to time temperature superposition. Composites were made including composites containing inclusions which undergo phase transformation were made. The latter are predicted to exhibit enhanced anelastic damping by virtue of the partially constrained negative stiffness of the inclusions in the vicinity of a ferroelastic phase transformation, and are predicted to become unstable for sufficiently high concentration of inclusions. Extreme values of damping and modulus were observed. The maximum elastic modulus exceeded that of diamond by almost a factor of ten.
Refreshments will be served in the rotunda following the seminar.
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