Amount of compressive stress at the onset of failure. The definition of failure tends to vary with material type.
As with tensile tests, the terms ultimate and yield can be used. However, ductile materials do not break during compressive testing, and therefore have no ultimate compressive strength. And materials that are brittle enough to fracture under compressive testing generally lack a distinct plastic zone, and therefore have no compressive yield strength. The fact that any given material can normally only have a value for either ultimate or yield compressive strength, and not both, has made it typical to cite a compressive strength value without specifying the type.
The term crushing strength is also used, mainly in the context of ceramic materials. In the context of refractories, the term cold crushing strength is used for compressive strength measured at room temperature, to highlight the fact that the value does not reflect performance at high temperatures.
Compressive strength is almost always cited for ceramic materials, where it is substantially higher than compressive strength. For metals, data sheets often omit compressive strength. As a rule of thumb, the compressive strength of metals is approximately equal to the tensile strength. For polymeric materials, no consistent relationship between tensile and compressive strength exists.
ASTM testing standards include C39 for concrete, C133 for refractories, C165 for thermal insulations, C773 for fired whitewares, C1194 for architectural cast stone, C1424 for advanced ceramics, D575 for rubber, D695 for rigid plastics, D1621 for rigid plastic foams, D3501 for wooden panels, E9 for metals, and F1574 for gaskets at elevated temperatures.
ISO standards include 604 for plastics, 844 for rigid plastic foams, 9895 for paper and board, 10059 for refractories, 14126 for fiber-reinforced plastic composites, and 14317 for sintered metals. Additional standards exist for highly specific materials tested under highly specific circumstances.