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Contactless Stress/Strain Measurements
Contactless technology for stress and strain measurements is developed. The technology detects changes of electric properties of the tested material with deformations. In one implementation detection is directed on measurement of the material resistivity and in another implementation variation of dielectric properties with deformation is detected. Any material can be used as the sensing media for contactless detection of the deformations. A system electrodes can detect all components of the deformations in the single measurement which includes principal directions and magnitude of the deformations, orientation of fibers in fiber reinforced materials and so on. 
- Low Profile Strain Measurement System for Parachute Suspension Lines
Non-contact technology for the load detection in individual parachute suspension and control lines is  developed. Our solution does not affect performance of the parachute in any way and can withstand any dynamic overloads. A sensing element is 2 to 25 micron thick polyimide film with deposited electrodes. A film having 10 to 20mm in length is wrapped around the cord and has electronic conditioning element for interfacing sensor and DAQ unit.  Two implementations of the sensor rosette are proposed: one implementation detects uniaxial load and another detects both uniaxial load and the yarn twisting under the load. Sensing approach is based on detection of strain induced anisotropy in dielectric properties of the sensed material. A differential sensor rosette provides self-temperature and electromagnetic noise compensation in wide range of environmental conditions
Sensor setup configuration

(a) A sensor rosette is in a close proximity to the cord line without mechanical constraints, (b) a layer of soft and elastic material such as silicone rubber is added between the parachute cord and the sensor.




Smart lines

The sensing element can be located on (a) top of the outer sheath and (b) under the sheath. If it is necessary a micro-sensor can be manufactured to fit on individual yarn (c). Thin, flexible wires needed to communicate with DAQ unit can be run on or under the surface of outer sheath.
Comparison with electro-textile technology

FeatureElectro textileDielectrostriction
Sensing mechanism

Piezoresistivity–change resistivity with deformation

Dielectrostriction–change dielectric constant with deformation
Detected parameterAverage axial component of the load All components of the load: Axial deformations and twist of the yarn  
Detection electronicsResistive bridge; AD converters Capacitor bridge; AD converter 
Energy consumptionResistive bridge dissipates energy Capacitor bridge dissipates no energy 
Sensing materialMaterial modified to become conductive  Any material including original parts  
Sensing area Whole length of the modified material Only area in the close proximity 
CostCost of material modification; cost of changing manufacturing sequence, time and efforts for certifying final product.No additional costs, besides than sensing elements 
HysteresisStrong hysteresis for cycling load due to changing structure of the sensed material Hysteresis only due to changing mechanical properties of the material  
Temperature compensationLook up tables for temperature correction  Self-compensation by sensing rosette
Thermal and electro-magnetic noiseJohnson–Nyquist noise limits sensitivity, long lines pickup electromagnetic noise, local discharge noise There is no limits due to Johnson–Nyquist noise; compensated for thermals & electromagnetic noise 
Tolerance to overloadsOverloads can destroy the sensor or dramatically change its sensitivity No effect as long as the cord material retains its properties  
- Non-Contact Torque Sensor for Unmodified Composite Shafts and Non-Ferrous Metal Shafts
A sensor capability for non-contact detection of stresses in rotating shafts is developed. A stationary sensor rosette is located near the shaft surface and records all in-plane stress components which then are linked to the torque, bending stress and deflection of the shaft.
Sensor setup configuration

The sensor rosette is positioned in a close proximity to the rotating shaft. Two configurations of the rosettes are considered: (1) electrodes are along and perpendicular to the shaft displacement as in the figure, and (2) electrodes form ±45 degrees with the shaft. Three to six pairs of the sensor rosettes will be located around the shaft. 





Stress detection

A typical shaft load involves tensile (bending) stress, σ, and shearing (torsion) stress, τ. Two sensor pairs are required. Readings from one pair are ΔR(0) and ΔR(π⁄2) which produce value of the bending stress, σ. Readings from another pair are  ΔR(+π⁄4) and ΔR(-π⁄4) which produce value of the shearing stress, τ.



Comparison with electro-textile technology

 Typical Technical


Feasibility demonstration based on Current Implementation  Further development toward Refined Objectives
The sensor solution must not modify the shaft in any way. Paint is considered as a modification; however, if the technology meets the other requirements in the topic, we encourage submission.

Operates in close proximity without touching the surface. Works with non-modified shafts. 

Resolution/stability can be enhanced by coating shaft with a protective paint. Examples of paint are epoxy with any fillers, silicone, Teflon, metal oxides. 

All components of the sensor solution must be stationary.

All components for detection stresses are stationary. 

Shaft may vibrate and/or experience bending displacements during the operation. A self-centered mechanism for sensing rosettes may be required which involves displacements of the fixtures. 

The sensor should measure torque up to a minimum of 2kHz with recorded data rates exceeding a minimum of 5kHz.

The detection frequency is currently between 10 kHz to 100 kHz which is also the data recording rate.  

Operational frequency will be adjusted to optimize sensitivity for a particular composition of the shaft. 

The solution must enable diagnostics as well as life management based on the solution’s torque measurements

 Sensor unit has onboard electronics for conditioning output signal which is further recorded by the desktop computer-based DAQ system.

Chip-size DAQ solutions are available. Portable self-contained data storage will be implemented on the final stages of the development.  

At least 5 hours of data recording capability.

We estimate data flow as 3(spots on the shaft) * 3(data channels) * 24bit*5kHz (reading rate) 

 =135kB/sec which corresponds 2.5GB portable storage for 5 hours of operation.

The sensor solution must have a large enough gap between the sensor and the rotating shaft to prevent any contact with the shaft during the severe flight maneuvers that generate large shaft deflections.

 Sensor solution was tested for gaps up to 300 microns. Estimation shows that an elastic deflection of the shaft would not exceed 30 microns for the sensor length (or the shaft segment) less 25 mm.

In Phase II dynamic positioning system will be developed to keep all assembly within safe limits. 

If the sensor can measure the shaft speed, deflections, and bending stresses, this should be noted in the proposal.

The sensing solution provides all stress component in the shaft. This information is converted in the shaft speed, torque and bending. 

Data storage and conversion in the desired format will be implemented in portable form. 

The torque measurement system should accommodate a shaft that is no more than 10 inches long and between 2 and 5 inches in diameter, operating at a nominal speed of 18,000 RPM with torque values of +/-5000 in-lb

All deformations should remain in the elastic region. Proposed solution needs only 50 mm of the shaft length and the data can be obtained for elastic and plastic ranges of deformations which exceeds the topic requirements.  

 High speed rotation may produce shaft vibrations which will interfere with the sensor reading. From three to six sensor rosettes will be utilized to provide readings circular to the shaft. Averaging procedure will be implemented.

-The torque measurement accuracy error must be no more than 2% of full scale value.

-The system should maintain this accuracy over varying operating temperatures, -25 degrees C to 80 degrees C;

-The system must operate within this accuracy for pressure altitudes from sea level to 40,000 feet.

We demonstrated 10-4 sensor resolution which corresponds to 0.01%. However, 2% resolution is a realistic requirement for high rate DAQ. Temperature compensation is approached by temperature compensated bridges, compensation and calibration of the temperature effects. External pressure does not affect the performance.    

Temperature compensation will be developed. Calibration tables will be generated for each particular shaft material. 

Area around the shaft is: Approx. 2” above shaft (min distance), a little more than 6” to the left/right of the shaft and a little less than 6” below the shaft.

 Sensing element itself is a thin polyimide film with conductive electrodes on it. Current implementations have thickness from 30 microns to 300 microns.

 Sensing fixtures and positioning mechanism would require some space but much less than 2”. Portable DAQ may be located as convenient.

A realistic weight should be less than 10 lbs but preferably less than 5 lbs.

 Weight of the sensing element is negligible. All weight contribution would come from the fixtures and DAQ systems available on the market.

 Weight of fixtures and portable DAQ system will be estimated based on the selected design. It should stay within 2 lbs. Fixtures inside the aircraft would add some weight.