Piezoelectric Washer for Accurate Application of Bolt Preload

Piezoelectric Washer for Accurate Application of Bolt Preload

Docket: UAH-P-15022


Currently, there is no low-cost method to accurately apply preload to a structural bolt. Although many preload methods exist, none are both accurate and inexpensive. For example, torque control is the most common and low-cost method for applying bolt preload, but it is notoriously inaccurate. More sophisticated methods for applying preload, like ultrasonic measurement, are much more accurate but also expensive.

Researchers at UAH have developed an inexpensive washer that allows accurate application of bolt preload. The washer incorporates piezoelectric materials into its body, which when compressed generate a voltage proportional to the bolt preload. During installation the induced voltage is easily measured on the perimeter of the washer. It also has the high rigidity and strength needed for bolted connections. Since this technology is only slightly larger than a standard washer, it remains lightweight and appropriate for aerospace and other applications.

This technology is both accurate and cost effective, a combination not provided by existing preload methods.


  • Bolted connections
  • Aerospace industry
  • Automotive industry
  • Power industry


  • Inexpensive
  • Accurate
  • Lightweight


  • State of Development: Prototype
  • Licensing Status: Available for licensing
  • Patent Status: Proprietary