Offset yield strength. Arbitrary approximation of elastic limit. It is the stress that corresponds to the point of intersection of a stress-strain diagram and a line parallel to the straight line portion of the diagram. Offset refers to the distance between the origin of the stress-strain diagram and the point of intersection of the parallel line and the 0 stress axis. Offset is expressed in terms of strain (often 0.2%).

Olsen cup test. Method for measuring metal ductility by determining cup height. A sheet metal blank, restrained on all edges, is deformed by pressing a specified steel ball at its center. Height (or depth) of the cup when rupture occurs is reported in thousandths of an inch.

Operating stress. Stress imposed on a part in service.

Overstressing. Application of high fluctuating loads at the beginning of a fatigue test and lower loads toward the end. It is a means for speeding up a fatigue test.