Strain Gauged Bolts

Matrix offers custom strain-gauged bolts for data collection in bolted joints. Strain gauges can be installed in bolts as small as M8 (5/16”) that are at least 14mm (9/16”) long. After applying the strain gauge, the bolts can be installed in the joint using normal assembly processes. Custom adapters will be provided to connect the strain gauge to your specific DAQ, allowing data collection to begin. This solution helps engineers verify preload, balance load sharing, and correlate fatigue to integrate real data into your testing and design decisions.

What this solves

Preload you can prove: Verify torque-to-tension on real assemblies (including coatings, lube, paint, and sequence) and tighten specs with Torque Tension Testing and Torque to Yield Tests built into the plan.
Joint reliability by the numbers: See per-bolt clamp load and detect opening/slip under pressure, shock, vibration, and thermal cycles; route those results back into VDI-2230 Bolted Joint Analysis.
FEA correlation that closes the loop: Feed mean/range and rainflow histograms into FEA Modeling to calibrate friction, gasket curves, and contact—then lock the validation block inside Product Validation & Testing.
Process improvement: Update company tightening standards, after-paint torque, re-torque schedule, and inspection steps with help from Fastener Specification Consulting.

When to use strain-gauged bolts

Programs with field issues (leakage, loosening, bolt fatigue) that are undergoing a root-cause investigation
When there is a need for measured stress data to verify the expected load matches the actual load in a joint
Multi-bolt patterns or asymmetric housings where the load doesn’t share evenly
Gasketed or painted joints where embedment and relaxation affect preload

How we instrument and test

Plan the measurement: Select bolt size/grade, gauge type and placement (shank interior or exterior), and number of channels. If your joint has special requirements such as water-resistant fittings, we can create a custom solution that fits your needs.
Prepare the fastener: Surface prep, machining, bonding, and continuity checks.
Calibrate: Test each fastener with a load cell to calibrate the strain gauge to a known force.
Install & load: Apply the production tightening method, then run the test load sequence to record data with the gauged bolts. Variations needed in this process can be identified by Matrix prior to installation. [Field & Lab Data Acquisition].
Analyze: Compute mean/range per event, flag bolts crossing slip/open thresholds, and compare life drivers to your model. Matrix has the expertise to assist with interpretation of results.
Utilize: Update FEA parameters for more accurate analysis and revise designs or processes to resolve issues identified by the gauged bolts. [Product Validation & Testing].

Technical options

Placement: Gauges can be installed on the interior or exterior of the bolt shank.
Data Targets: Type of data collected determines what type of gauges are installed. Matrix has experience installing uniaxial, triaxial, and full rosette gauges to measure bending, torsion, and tension. Other solutions can be developed as needed.
DAQ: Custom adapter harnesses are included to attach gauges to your specific data collection equipment. Matrix also offers data collection services using our own equipment if desired.
Reuse: Gauged fasteners can be reused for multiple tests. However, they are intended as test articles and should not be used as a permanent fastener.

Example applications

Slewing Ring: Measure bending and axial load for each bolt in the ring to verify bolt size is appropriate for the duty cycle.
Nitrile gasket: Measure axial load to verify gasket compressive load over time.
Bracket under mixed bending: identify high-risk bolts carrying secondary bending; redesign pattern to rebalance load
Critical Joints: Data collection can verify design targets match actual stresses, preventing joint failure in critical locations.

FAQs

How accurate is the tension reading?

With proper calibration and temperature compensation, tension can typically be measured within 2%.

Will gauging change the joint?

Machining the bolt removes a small amount of material for gauge installation. Small bolts are more affected than large bolts. The smallest single-axis bolt (M8) loses 1.6% of its cross-sectional area for gauge installation due to the interior hole, and the channel sizes for exterior gauges vary. The new proof strength of the bolt is accounted for in the recommended tightening torques we provide.

Can we correlate directly to fatigue?

Yes—mean and range from gauges drive your critical-plane or S-N/ε-N model in FEA; we document mapping and validation targets inside [Virtual Validation].

Can you support yield-based tightening?

Yes—pair gauged bolts with Torque to Yield Tests and angle control for consistent clamp under friction scatter.

Engineer examining digital schematics on touchscreen in modern facility.

Next steps

If you’re chasing leakage, loosening, or fatigue and need hard evidence, start by talking to an engineer so we can scope which bolts to gauge and what duty cycles to replicate. To get the most out of the data collected by gauged bolts, scheduling a training. For methodology notes, example plots, and correlation checklists, explore our technical publications.