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Micromechanics of a craze zone at the tip of a stationary crack

: Bevan, L.; Koenczoel, L.; Doell, W.


Journal of polymer science. B, polymer physics 24 (1986), Nr.11, S.2433-2444
ISSN: 0887-6266
ISSN: 1099-0488
ISSN: 0098-1273
Fraunhofer IWM ()

The finite element method is applied to contours (measured by interferometry) of craze zones in front of stationary crack tips in polymethylmethacrylate (PMMA) in order to compute the stress distribution. The stress along the craze zone has its maximum at the crack tip, being about twice that predicted by the Dugdale model; and it decreases at first sharply and then more gradually, being almost constant as the craze tip is approached. Stress distributions, in a growing craze at the still stationary crack tip, at various times can be combined in a normalized curve. Craze stresses relax with time as the craze continues to propagate in a stable manner. When the specimen is unloaded, the craze stress is compressive near the crack tip, but is tensile at the craze tip and for most of the craze length. Analysis of measurements made during a loading cycle establishes miniimum stress intensity levels at which no fibrils are in compression. The levels are different for increasing and decreasing loads, and it is found the craze stresses are tensile for most of the cycle. Throughout the cycle, there is an excellent correlation between the average craze stress and the theoretical stress predicted by the Dugdale model.