A theoretical and experimental technique to measure fracture properties in viscoelastic solids

Prediction of crack growth in engineering structures is necessary for better analysis and design. However, this prediction becomes quite complex for certain materials in which the fracture behavior is both rate and path dependent. Asphaltic materials used in pavements have that intrinsic complexity in their behavior. A lot of research effort has been devoted to better understanding viscoelastic behavior and fracture in such materials. This dissertation presents a further refinement of an experimental test setup, which is significantly different from standard testing protocols, to measure viscoelastic and fracture properties of nonlinear viscoelastic solids, such as asphaltic materials. The results presented herein are primarily for experiments with asphalt, but the test procedure can be used for other viscoelastic materials as well. Even though the test is designed as a fracture test, experiments on the investigated materials have uncovered very complex phenomena prior to fracture. Viscoelasticity and micromechanics are used to explain some of the physical phenomena observed in the tests. The material behavior prior to fracture includes both viscoelastic behavior and a necking effect, which is further discussed in the appendix of the present study. The dissertation outlines a theoretical model for the prediction of tractions ahead of the crack tip. The major contribution herein lies in the development of the experimental procedure for evaluating the material parameters necessary for deploying the model in the prediction of ductile crack growth. Finally, predictions of crack growth in a double cantilever beam specimens and asphalt concrete samples are presented in order to demonstrate the power of this approach for predicting crack growth in viscoelastic media