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SmartBolts®

DTI SmartBolts®

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Stress Indicators, Inc.
6307 Wiscasset Road
Bethesda, MD 20816
Tel: (240) 631-7246
Fax: (301) 320-3303
inquiries@smartbolts.com

 
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 patented DTI optical microindicators into a dramatic and reproducible color change.

 
    The DTI MicroIndicator
The DTI MicroIndicator is an incredibly simple device that performs a rather sophisticated function. The microindicator is actually 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 and 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.
  DTI MicroIndicator example  
    Indicator Sensitivity
Indicator Sensitivity may be precisely controlled by adjusting the composition of the indicator fluid and the mechanical arrangement of the different grades. Apart from sensitivity considerations, the operating concept is similar for all grades: when the tensile load is applied to the fastener, the relative deflection is mechanically coupled to the microindicator and the reflected brightness or color of the indicator will exhibit a dramatic and sensitive change as a direct function of bolt tension.

 
       
     
Typical Performance Specifications

Bolt Properties Units DTI HR
Minimum Tensile Strength psi 150,000 150,000
Proof Stress psi 120,000 120,000
Proof Load psi 17,000 17,000
Indicator Properties Units DTI HR
Indicating Tension (90% proof)
lbf 15,300 15,300
Indication at Zero Tolerance   Red-Orange Yellow
Indication at 50% Tension   Maroon Yellow
Indication at Design Tension   Black Green
Indication at 110% Design Tension   Black Blue-Black
Indicator Sensitivity (Tension for 63% Brightness Change) lbf 2000 350
Standard Deviation of Tension Distribution lbf 1500 750
Coefficient of Variation % 10 5
Temperature Sensitivity %/C <0.1 <0.05
Temperature Range C -20 to 75 -20 to 75