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Micromechanics of fracture under static and fatigue loading. Optical interferometry of crack tip craze zones

: Könczöl, L.; Döll, W.

Kausch, H.-H.:
Advances in Polymer Science 91/92. Crazing in Polymers Vol.2
Berlin/West: Springer, 1989 (Advances in Polymer Science 91/92)
ISBN: 3-540-51306-X
Book Article
Fraunhofer IWM ()
Brechungsindex; Bruch; crack; crack growth; craze; creep module; Dehnverhältnis; Ermüdungsrißausbreitung; extension ratio; fatigue crack propagation; finite element analysis; fractography; fracture; fracture mechanic; interference optic; Kriechmodul; micromechanism; refractive index; Riß; Rißausbreitung; strain; stress; stress distribution; stress intensity factor; thermoplastic

Brittle failure of many thermoplastics is associated with craze formation and governed by craze breakdown. Optical interferometry is a powerful tool for the investigation of this type of plastic deformation in transparent polymers, especially for the measurement of sizes of single crack tip crazes. The results of interferometric measurements are used in connection with fracture mechanic models and mathematical or numerical methods for calculations of stresses in the microregion at the crack tip and thus giving qualitative and quantitative descriptions of deformation and fracture processes. This is applied to different loading conditions and in the article the following is discussed in detail: craze growth in front of stationary cracks, crazing behavior during continuous crack growth under quasi-static load as well as during normal and retarded fatigue crack propagation. Also micro-mechanical and molecular models are derived from the experimental results, describing the different modes of crack growth behavior in connection with the crazing process. Thus this article contributes to the understanding of the basic processes involved in the fracture of thermoplastics.