Thoughts on the present and future interrelation of theoretical and experimental mechanics

During the last five years, the long-overdue improvement in attitude of academic and other research people toward experimental mechanics has begun. This welcome change is attributed, in large measure, to their renewed interest in the behavior of real materials. Many have come to the realization that idealizations which served them so well for past problems are inadequate not only for living systems but for brittle and ductile fracture of metals, for sufficiently detailed prediction of behavior of composite materials, for incisive application of continuum mechanics on the microscale, and for thermodynamics. An attempt is made to bring out general aspects of a few of these problems of current interest and to show how careful experimentation has produced and interacted with new theoretical developments. A distinction is drawn between a true experiment and one which is no more than an analog computation. Illustrations of misleading analogs are given from both fluid and solid mechanics. Except for some remarks on possible difficulties in distinguishing constitutive relations and boundary conditions in living tissues and body fluids, however, thoughts for the future are restricted to the mechanics and the thermodynamics of solids. Emphasis is placed throughout on the fact that a good experiment and a good theory start at very much the same point and have a great deal in common.