What is the tension-applied load that a fastener must support without evidence of deformation called?

The correct term for the tension-applied load that a fastener must support without any signs of deformation is "proof load." This measurement is critical in fastener design, as it helps to ensure that the fastener can withstand the expected loads during its service life without experiencing any permanent deformation. The proof load is often set at a predetermined fraction of the fastener's yield strength, typically around 85%, allowing engineers to account for safety factors in their designs.

Yield strength refers to the maximum stress that a material can withstand while still being able to return to its original shape when the load is removed. While this is related, it does not specifically designate the load a fastener must hold under operational conditions.

Ultimate strength is the maximum load that a material can withstand before failure, which is typically beyond the acceptable operating conditions for fasteners.

Max load is a non-specific term and does not provide the clarity needed to define a fastener's performance under tension in standard engineering practice. Hence, proof load is the precise term used in this context to ensure safe operation and design integrity of the fastener.