Learn How Visual Tension Indicators Work

Technical Information for Direct Tension Indicating (DTI) SmartBolts®

Operation

Operation of Stress Indicator’s DTI SmartBolts® is based upon the response of an optical microindicator element to the deflection of one internal portion of a fastener relative to another as the fastener elongates under tensile loading. This miniscule relative movement is transformed by optical microindicators into a dramatic and reproducible color change.

The MicroIndicator

The MicroIndicator is an incredibly simple device that performs a sophisticated function. The microindicator is a miniaturized optical absorptance cell or variable-density filter that reproducibly changes its spectral transmittance as the cell thickness is varied. A brightly colored indicating area is placed at the rear wall of the cell.  A fraction of a drop of an optically dense fluid, which strongly absorbs the spectral color of the indicator area, is contained in a hermetically sealed envelope between the indicator area and the clear window. Ambient light passing through the window is selectively absorbed by the filter cell, and is selectively reflected by the indicator area to pass once again through the cell and window to the observer.

HexHead Capscrew DTI SmartBolts Characteristics*

*Contact us at Stress Indicators for other externally wrenched bolt designs or for possible stud designs