Benefits of Force Sensing Fasteners

March 15, 2022

Strainsert force sensing fasteners, bolts and studs utilize a patented internal gaging method to indicate bolt tension due to preload with strain gage accuracy. Fasteners provide a means for accurate, independent inspection of an assembled bolt for preload, thereby enhancing the structural integrity and reliability of both the bolt and the assembly.

Main Features:

  • Measurement of preload induced in fasteners
  • Uniform fastener tightening in a bolt pattern
  • Use of fasteners as load link transducers
  • Accurate tightening within 1% of load typically
  • Overload detection in bolted machinery
  • Quarter; and full bridge configurations

Strainsert Fasteners Offer:

Bolts with Full Load Carrying Capacity – Bolts with Strainsert internal gage installations have the full load carrying capacity of the original ungaged bolt. Cross-sectional area of the threaded portion of a full shank bolt is always smaller than the cross sectional area of the shank. The difference in areas permits a hole to be drilled in the shank for the gage installation without weakening the bolt. (1/4” diameter and smaller bolts may have reduced load carrying capacities).

Guaranteed Accuracy – Giving precise calibration and accuracy guarantees for Strainsert Bolts and Studs is not a simple matter. Most gage installations are in fasteners supplied by the customers or purchased from the fastener manufacturers. Therefore, Strainsert does not control the supplied fasteners material, design or quality.

For this reason, Strainsert Bolts and Studs to have a combined error due to repetition, nonlinearity and hysteresis of, typically, less than 1% of maximum load. Actually, the combined error is usually less than 1/2%.

Loading of Gage Installations – Prior to shipment, all gage installations are calibrated as part of the quality control procedure. Unless otherwise specified, bolts and studs are normally loaded to approximately 70% of yield.

Internal Gage Installations – Gages installed in Strainsert Bolts and Studs are foil type, electric resistance strain gages. They are bonded and sealed in a small hole along the longitudinal neutral axis of the bolt. After installation the gages are practically immune to physical and environmental damage and the gages in a full-bridge internal installation are located very close to each other in a relative uniform temperature environment.

Gage Configuration Compensates For Bending And Torque
Quarter-bridge installations consist of two gages in series mounted 180 degrees apart on the circumference of the hole with the grid in an axial direction. This arrangement provides the best indication of bolt load and also helps minimize bending and torque influences. To eliminate lead-wire temperature effects, a three-wire lead system is used. Trim resistors or other compensations are not furnished with quarter-bridge gage installations.

Full-bridge internal gage installations are made in the same size hole as for quarter-bridge. They are wired as shown with axial active gages and circumferential complementary gages. Trims and compensations are offered only if there is room for the necessary components.

Please contact us for any of your fastener, bolt or stud force sensor needs.