Prior to curing a composite workpiece assembly, an expandable element can be inserted into a cavity of the workpiece assembly. The expandable element is configured to expand when a predetermined change is produced in an attribute of the element. The attribute can be a temperature of the element. The element is expanded by producing the predetermined change, and the workpiece assembly is cured while the expanded element is in the cavity, so that the expanded element applies positive pressure to inner surfaces of the cavity during curing. The expanded element can be removed from the cavity after curing. The expanded element can comprise a plurality of expandable pellets.

Prior to curing a composite workpiece assembly, an expandable element can be inserted into a cavity of the workpiece assembly. The expandable element is configured to expand when a predetermined change is produced in an attribute of the element. The attribute can be a temperature of the element. The element is expanded by producing the predetermined change, and the workpiece assembly is cured while the expanded element is in the cavity, so that the expanded element applies positive pressure to inner surfaces of the cavity during curing. The expanded element can be removed from the cavity after curing. The expanded element can comprise a plurality of expandable pellets.