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The Ohio State University

College of Engineering


Glenn S. Daehn

Professor

Ph.D. Stanford University, 1988

Tel. (614) 292-6779

Office: 347 Fontana Labs

daehn.1@osu.edu

  • National Science Foundation Young Investigator
  • Robert Lansing Hardy Gold Medal of TMS recipient-1992
  • Grossman Young Author Award of ASM-1990
  • Mars G. Fontana Professor of Metallurgical Engineering

Link to Dr. Daehn's research site

Prof. Daehn has been on the Faculty since 1988 when he completed his formal education at Northwestern University (B.S.) and Stanford University (M.S. and Ph.D.) He maintains wide interests in problems related to mechanical behavior, plasticity and mechanical processing in manufacturing. His research is in areas where fundamental principles can be applied in new ways to solve practical problems:

Hyperplasticity and High Velocity Metal Forming

Recent work in Daehn's group has shown that high velocity sheet metal forming can dramatically improve material formability (the amount of stretch available without tearing) and wrinkling can be greatly suppressed. Electromagnetic forming is a very convenient way of flexibly producing very high velocity deformation (see example at right of non-contact launch of an aluminum sheet). Presently Daehn's group is working with automotive, aluminum and aerospace companies and the National Science Foundation to develop this process.

Details are available at www.osu.edu/hyperplasticity.

 
Electromagnetic launch of an aluminum plate. 30µs between images.
Our Concept of a hybrid press

 

Rate Dependent Plastic Deformation

Daehn has long-standing interests in creep, plasticity and superplasticity. His group has carefully considered how thermal expansion mismatch in composites can accelerate plastic deformation when temperature is changed. This understanding has been applied to life assessment in high temperature composites and to thermal-cycling superplastic forming. More recently activities are centered on modeling rate dependent deformation considering how many obstacles and load shedding act together. The figure at the left comes from some of that work and shows the variation in slip activity in varied parts of a microstructure resulting from local 'hard' and 'soft' spots.

 

Powder Consolidation in Metal Matrix Composites

Motivated by the studies of thermal expansion mismatch induced superplastic deformation discussed above, we postulated that metal matrix composites may be compacted more effectively under cyclic pressure than static pressure, and found this was indeed the case. For moderate to large volume fractions of reinforcement with different compressibility than the matrix, compaction with cyclic pressure yields significantly higher compacted density, improved uniformity of density and dramatically improved strength.

Some details are available at a developing website on compaction of powder compacts using cyclic pressure.

. 5μm . static consolidation (left) cyclic (right).  

Ceramic-Based Composites

While studying as an undergraduate, Michael Breslin made the surprising discovery that if dense silica is immersed in liquid aluminum at a temperature around 1100 C the stable oxide, alumina, will form in a porous morphology and aluminum will fill the pores. This reaction takes place replicating the shape of the silica precursor. With Hamish Fraser, we have studied the kinetics, structure (right) and mechanical properties of these composites. Presently, the development of these and similar composites based on this flexible reaction scheme is being handled by a new venture, Excera Materials Group, Inc.

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