Stable Crack Propagation in a Viscoelastic Strip

Citation

Mueller, Hans-Karl Christian Alfred (1968) Stable Crack Propagation in a Viscoelastic Strip. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/MGSD-R362. https://resolver.caltech.edu/CaltechETD:etd-11152005-142505

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. A crack of length 2a which propagates with small, constant speed through a viscoelastic strip of width 2b is considered. The strip is strained by displacing its shearfree edges. Linear theory is applied. The stress on the line of crack advancement and the shape of the crack surface are calculated for a state of plane stress. The stress intensity factor which is independent of material properties is given as a function of a/b. It exhibits a maximum at [...]. For a/b > 1.5 the stress intensity factor becomes essentially independent of crack length. The crack surface deflection is obtained in the form of a superposition integral and is a function of material properties and crack speed. The energy which is released when the crack extends a small distancee is calculated. This crack energy depends on the crack speed and involves the creep function of the material. A characteristic length enters in the course of its derivation. This length does not appear in the case of an elastic material and is considered as an additional material property necessary to describe viscoelastic crack propagation. The energy conservation equation is established by considering a small control volume surrounding the crack tip. A relationship emerges from this equation which implicitly gives a stable crack speed as a function of applied strain, temperature, and material properties. The creep function is the controlling factor in this equation. The relevant material properties are discussed and presented for a Polyurethane rubber (Solithane 113 - 50/50). The lower bound of the surface energy is determined from fracture tests on the swollen material. The results of the material characterization are used to calculate the crack speed as a function of applied strain and temperature. Good agreement is found to exist between theory and experiment.

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