Alan T. Zehnder

Professor and Chair

Professional Biography

Dr. Zehnder received his doctorate in mechanical engineering with a minor in materials science from the California Institute of Technology. He stayed on as a postdoctoral research fellow for one year, and joined the Cornell faculty in 1988. In 1993 he was the faculty member in residence in Hamburg, Germany, for the Cornell Engineering Abroad program. He was a visiting Professor at Caltech in the 1996-97 academic year. In summer of 1998 he served as a Senior Faculty Fellow at the Naval Surface Warfare Center in Carderock, Maryland. In 2004 he was a Guest Professor at the Vienna University of Technology. He was awarded the 1988 Rudolf Kingslake Medal and Prize for his paper on optical methods in dynamic-fracture experimentation, which appeared in Optical Engineering. Zehnder is a member of the American Society of Mechanical Engineers and the Society for Experimental Mechanics.

Research Interests

My current research focuses on the fracture of nanoscale systems, nonlinear dynamics of nanomechanical oscillators and  damage tolerance of polymer matrix composite materials.
Nanoscale systems, although still large enough to obey the laws of continuum mechanics, show surprising effects due to their small size. For example, the nanomechanical oscillators can interact with light through heating and optical interference to become self oscillating. These self, or limit cycle, oscillations can be entrained to a small amplitude pilot signal suggesting that arrays of nanomechanical limit cycle oscillators should be able to synchronize, but under what conditions and with what phase relations? We have shown that nanoscale beams fabricated from single crystal silicon can have strengths close to the theoretical strength of the material. Although this strength degrades after extended exposure to air, we found that by coating the beams with self-assembled monolayer high strengths are maintained.
In the area of composite materials we study the failure and damage tolerance of high temperature properties of polyimide matrix composites (PiMC’s). Problems addressed include shear strength, moisture diffusion, nonlinear viscoelastic and viscoplastic constitutive behavior and blistering of the neat resin and laminate under very high heating rates. Future work will include considerations of impact damage and strength after impact.
Past work includes dynamic fracture, development of a patented, million frame per second infrared imaging system, fracture in plates and shells, high speed metal cutting, metal-ceramic interface fracture (nickel-alumina and copper-silica), fault propagation folding modeling and the use web-based tools in undergraduate engineering education.