Mechanical Engineering Seminar: Dr. John Hutchinson
Energy States and Wrinkle Patterns of Buckled Films on Compliant Substrates
Thin stiff films on compliant elastic substrates subject to equi-biaxial compressive stress states have been observed to buckle into some fascinating periodic mode patterns including checkerboard, hexagonal and herringbone. Illustrations of these modes observed in our collaboration with an experimental group at UMass Amherst will be shown. The modes are characterized and ranked by the extent to which they reduce the elastic energy of the film-substrate system relative to that of the unbuckled state over a wide range of overstress. A new mode is identified and analyzed having node lines coincident with an equilateral triangular pattern. Two methods are employed to ascertain the energy in the buckled state: an analytical method which supplies an upper-bound and a full numerical analysis. The upper-bound is shown to be reasonably accurate to surprisingly large levels of overstress. Except at small states of overstress, the herringbone mode has the lowest energy, followed by the checkerboard, with the hexagonal and triangular patterns lowering the energy the least. Transitions between modes are discussed. Experimental observations of various periodic modes are discussed with reference to the energy landscape and with respect to the role that a slight initial curvature of the film may play in selecting specific patterns. This work is a collaboration with Shengqiang Cai and Zhigang Suo at Harvard and Derek Breid and Al Crosby at UMass Amherst.
Dr. John W. Hutchinson is the Abbott and James Lawrence Professor of Engineering at the School of Engineering and Applied Sciences at Harvard University. He received his B.S. in Engineering Mechanics from Lehigh University in 1960. He received his Ph.D. in Mechanical Engineering from Harvard University 1963. Dr. Hutchinson and his students and collaborators work on problems in solid mechanics concerned with engineering materials and structures. Buckling and structural stability, elasticity, plasticity, fracture and micro-mechanics are all relevant in their research. Dr. Hutchinson is the winner of numerous awards, including the Nadai Award (1991, ASME), Thurston Award (2000, ASME), and the Timoshenko Medal (2002, ASME).
For more information about Professor Hutchinson, please visit http://www.deas.harvard.edu/hutchinson/
Hosted by Professor Bharat Bhushan