Tensile strength and yield strength are two of the mechanical properties of externally threaded Building Fasteners such as Hex Cap Screws, Heavy Hex Bolts or Heavy Hex Screws. These factors help determine how strong the fastener will be and what situations and projects they can best be used for.
The maximum load that can be supported by a fastener before it fractures or breaks is tensile strength. Tensile strength is expressed in pounds per square inch (psi) to describe the stress that a fastener can handle. This is calculated by multiplying the stress area of the thread (in square inches) by psi. Guidelines can be found for these calculations in the ASME (American Society of Mechanical Engineers).
Externally threaded products with less than 100,000 lbs. of tensile strength are usually tested in full size, whereas stronger fasteners use reduced size pieces that have been cut from the actual fastener and are machine tested. Fasteners can also be wedge tested, which means that a hardened washer with a beveled surface will be placed beneath the test fastener; a wedging action provides extreme bending stress with a concentration on the part where the head and shank meet. This is most common with hex flange screws, studs, hex socket screws, and hex bolts and screws. This test shows that the fastener has structural integrity at the head-to-shank position, which is critical.
A specific amount of deformation is experienced by a fastener when a tension-applied load is set to test yield strength. It forces the fastener to be stressed beyond the elastic limit and enter the plastic zone. It is easy to use machine testing for yield strengths because of the uniform cross sectional area that exists throughout the stressed length. This kind of testing is not always an accurate reflection of the full sized product though. When the specimen is machined from the parent product, the beneficial effects of the cold working can be lost. Because of the different strain rates in the threaded section, the unthreaded shank, and the thread runout, it can be very difficult to conduct an accurate yield strength test.
Started my career in the fastener world in 1969 at, Parker Kalon Corp. a NJ based screw manufacturer located in Clifton, NJ working in inventory control, scheduling secondary production and concluding there in purchasing. In 1971 I accepted a sales position at Star Stainless Screw Co., Totowa, NJ working in inside sales and later as an outside salesman, having a successful career at Star I had the desire with a friend to start our own fastener distribution company in 1980 named: Divspec, Kenilworth, NJ. This was a successful adventure but ended in 1985 with me starting Melfast in August 1985 and have stayed competitive and successful to date. Melfast serves the OEM market with approximately 400 accounts nationally.