4: Crazing & Shear Banding
Often, when an amorphous brittle polymer is loaded in tension, a phenomenon known as crazing can occur. Crazing involves the formation of small crack-shaped regions that are drawn down but remain constrained by the surrounding material.
The drawn material ends up as ligaments that link the crazed surfaces. Eventually the crazes form cracks that lead to fracture. The crazes contain air giving them a white streaked appearance.
Click here to see a graphical representation of crazing.
Shear banding is produced in polymers when they are exposed to compressive stresses.
Small stress relieving cracks nucleate within the polymer parallel to the direction of maximum shear stress at an angle of 45°.
As the number of shear bands accumulates the overall strain of the material increases.
Click here to see a graphical representation of shear banding.