Proof Strength (psi):
The tension-applied load that a fastener must support without evidence of deformation. Proof load is often used interchangeably with yield strength.
Tensile Strength (psi):
Ultimate tensile strength (UTS), often shortened to tensile strength (TS) or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before failing or breaking. Tensile strength is the opposite of compressive strength and the values can be quite different.
Some materials will break sharply, without deforming, in what is called a brittle failure. Others, which are more ductile, including most metals, will stretch some – and for rods or bars, shrink or neck at the point of maximum stress as that area is stretched out.
Rockwell Hardness Test:
The Rockwell scale is a hardness scale based on indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload. There are different scales, denoted by a single letter, that use different loads or indenters. The result is a dimensionless number noted as HRA, where A is the scale letter.
When testing metals, indentation hardness correlates linearly with tensile strength. This important relation permits economically important nondestructive testing of bulk metal deliveries with lightweight, even portable equipment, such as hand-held Rockwell hardness testers.
According to the Research Council on Structural Connections c/o American Institute of Steel Construction (AISC), for structural applications there are generally three types of connections in which a bolt is used; snug-tightened, pre-tensioned, and slip critical connections. In accordance with the AISC, bolts used in pre-tensioned or slip-critical connections are required to be installed to within 70% of the minimum tensile strength of the bolt.