The Effects of Cure Temperature and Time on the Stress-Whitening Behavior of Structural Adhesives. Part II. Analysis of Fractographic Data
In this second part of the paper on the effects of cure conditions on the stress-whitening behavior of structural adhesives, fractographic data are presented and discussed. For this purpose, the size and nature of crack-tip-whitening zones obtained using single edge notched tension specimens of the model adhesive Metlbond with and without carrier cloth are studied. Scanning electron photomicrographs are utilized to investigate the effects of cure temperature and time on the crack-tip stress-whitening behavior. A brief discussion on the formation of inherent voids during the cure process is also presented since they are observed to enhance the crack-tip-whitening zones. Experimental results reveal that both the extent of voids produced during the cure process and the size of the crack-tip-whitening zones on the fracture surface increase with increasing cure temperatures. The presence of carrier cloth produces a similar effect with increases in both inherent voiding and stress-whitening sizes. The creation of stress-whitening zones are linked to stable crack propagation in those areas.