Aging Effects on Craze Growth Under Stress Relaxation Conditions

Mats Delin and Gregory B. McKenna, Polymers Division, Building 224, Room
A209, NIST, Gaithersburg, MD 20899, email: delin@nist.gov.

 

Crazing is a deformation process occurring in glassy polymers which can be the precursor to failure in long term conditions. Craze initiation and propagation are known to be related to the viscoelastic properties of the bulk material. The initiation and propagation are resultingly sensitive functions of such parameters as temperature that influence these properties. Therefore, one would also expect the physical aging process, in which viscoelastic properties are observed to change due to, e.g., densification of the polymer after a quench, to also impact the craze process. Here we present an examination of the physical aging effects on the growth in length of crazes for a styrene-acrylonitrile copolymer in stress relaxation conditions. The craze length was found to vary linearly in the logarithm of the loading time. The logarithmic rate of growth was found to depend on both aging time and temperature in such a way that a rapid transition from fast to slow growth rate was observed as either aging time or temperature increases.