The Microstructure and Properties of Crazes
A brief résumé of the established characteristics of craze deformation and structure is given along with a summary of the significance of crazing in the bulk deformation and fracture of high polymers. This is followed by a more detailed consideration of recent work in two important areas of interest, viz (1) microstructure of crazes and (2) stress-strain response of crazes.
The microstructure of crazes has been studied using high-resolution transmission electron microscopy. The crazes were produced in bulk specimens, microtome thin sections, and solvent-cast thin films. The structure of crazes was similar in all specimens and consisted of highly drawn fibrils normal to the craze-matrix interface with linking, finer cross fibrils. In the thin films it was possible to obtain much larger craze strains and this resulted in a finer fibril structure. A model of the microstructure of a craze is presented.
The stress-strain characteristics of a craze have already been studied by Kambour and Kopp using a method which requires direct observation of the change in thickness of a thick craze during the application of a loading cycle. An alternative approach is described which is based on microstrain measurements of specimens containing a high density of very fine crazes. Quantitative microscopy is used to determine the craze density and average thickness. The results obtained on polystyrene are similar to Kambour and Kopp’s observations on solvent induced crazes in poly-carbonate. The results are discussed in the context of the observed craze microstructure.
KeywordsGlassy Polymer Stress Whitening Craze Growth Craze Formation Molded Polystyrene
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