At Brown University and during his 36 years at Cornell, Lance and his graduate students focussed their research on the mechanical behavior of solids, particularly the non-elastic behavior. All engineering materials behave inelastically, i.e., their response to mechanical and thermal loads always leads to some permanent change in shape. In the design of critical structural components such as high-temperature piping and blades and rotors for turbines, permanent (nonelastic) deformations can lead to failure through rupture, low-cycle fatigue, or mechanical interference. On the other hand, most manufacturing processes involving metals and polymers depend on the material's inelastic properties; permanent deformation is a desired quality. It is the job of research engineers who study the mechanics of solids to determine the fundamental laws of material behavior-constitutive relations, in the jargon of the theoretical mechanics community-and build such laws into models of material behavior, and ultimately into the codes that guide designers
