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This chapter examines the understanding of dynamic fracture processes based primarily on experimental results, with purely analytical treatments taking on a decidedly secondary character. The specific field of dynamic fracture mechanics is typically characterized in terms of far-field loading and crack-tip local response characteristics that invoke motions strongly influenced by material inertia and high rates of deformation of the material in the crack tip vicinity. These latter conditions generate a constitutive response that is significantly different from its quasi-static counterpart. Constitutive behavior that is independent of deformation magnitude and rate is the classical basis for all elastodynamic analyses. Sufficient information has surfaced during the last two decades which explains the significant differences between elastodynamic analyses and laboratory experiments: on the one hand, these discrepancies are the result of the idealization of the fracture process in the analyses, and, on the other, of the truly complicated details accompanying fracture in the small region around the crack tip when a crack propagates rapidly.

The Image Moire method is employed to determine the Poisson’ ratio for PMMA at different temperatures. Simultaneous recording of the tensile stress yields the Young's modulus in relaxation and the corresponding Poisson effect. The constant temperature ranges from room temperature to 125° C. Master curves for relaxation Young's modulus and Poisson's Ratio are obtained. The Relaxation bulk modulus is calculated from the experimental data.

The task of characterizing the mechanical properties of fibers from intervertebral discs has led to a simple non-contact method for measuring lateral contraction in such specimens. Experiments to evaluate the method are described. Utilizing the results of these tests, resolution levels and practical limitations for the method are discussed.

Following a brief general review of developments in dynamic fracture, four problem areas in this discipline are examined: Crack initiation under stress wave loading, crack propagation, branching, and arrest. These topics are discussed from the viewpoint of understanding the physical fracture process at the tip of dynamically loaded cracks. Time scales, other than those governed by the elastic wave speeds, are important in connection with dynamic fracture. These time scale differences are connected with the establishing of the process zone which consists of an ensemble of micro cracks. Direct evidence of these micro cracks is reviewed as well as the importance of strain rate history effects in dynamic fracture.