Stress relaxation is a condition that results in joint deterioration and possible fault or fastener failure. Your fastener distributor can help to identify the conditions and applications where stress relaxation is commonly found, helping you to avoid this problem and the subsequent costs and inconveniences.
When Does Stress Relaxation Occur?
This condition occurs when bolts are used in high temperature applications where constant load or stress exists for a time before being relieved, such as in engines and other automotive applications.
Stress relaxation is slightly different than creep, which causes deformation of bolts and gaskets due to constant load or stress in high temperatures. Both result in deformation of the fastener, although stress relaxation tends to result in a very specific type of deformity.
While damage from creep depends on the placement of the load, stress relaxation always results in a loosening or lessening of the fastener's preload. It does not usually continue to the point of completely loosening the bolt or screw, but stress relaxation does result in a clamp force reduction that can cause further issues with the joint and all fasteners involved.
Your fastener distributor will confirm that the repair required when facing stress relaxation involves retightening or replacement of the fasteners. Not only does this require labor, but also the added expense of replacement fasteners that will, in all likelihood, be subject to the same problem.
How To Avoid Stress Relaxation
Both stress relaxation and creep are difficult to avoid completely, given the unavoidable conditions of the applications prone to this issue. When using fasteners in high temperatures with constant or near constant loads on the joint, consider designing for stress relaxation.
Install a locking nut for protection against the reduction in clamp force, and to negate the effects of deformation. Inspect the joints in these applications on a regular basis, completing the maintenance and replacement when and where necessary.
Your fastener distributor can also help to choose materials that have greater resistance to stress relaxation and creep in the operating temperatures and load. Use extreme cases where applicable, allowing you to choose the strongest material for the job where budget allows. Fastener experts can also recommend durable materials that fit into your budget while still providing some protection against this phenomenon.
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.