
Boundary Condition Testing
OUTLINE
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Strain gage theory overview
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Select strain gage locations
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Perform controlled static testing
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Execute operational testing
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Apply test data to correlate model

ELECTRONIC RESISTANCE STRAIN GAGE THEORY
Electrical resistance of a wire is a function of geometry
Longitudinal strain is a function of change in resistance
Strain can be found directly by voltage measurements
Temperature influences strain gage resistance





SELECT STRAIN GAGE LOCATIONS TO GENERATE HIGH FIDELITY DATA
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Install at least one strain gage for each boundary condition
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Additional strain gages provide redundancy
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Redundancy protects against gage failure
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Select locations with large amplitude response
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Wish to maximize signal to noise ratio
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Find locations with low strain gradients
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High strain gradient locations are difficult to correlate
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Implement appropriate strain gage setup

DEVELOP LINEAR RELATIONSHIPS WITH STATIC TESTING

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Install strain gages onto structure
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Account for environmental effects
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Apparent strain due to temperature
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EMF causing current and voltage shifts
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Apply boundary conditions through static testing
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Generate Strain Versus Load Plots
VERIFY OPERATIONAL BOUNDARY CONDITIONS THROUGH TESTING
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Replicate static test setup on operational structure
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Install data acquisition system (DAQ) on structure
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Route wires and instrumentation such that structural behavior is unaffected
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Account for environmental effects such as EMF and temperature
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Perform operational testing
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Examine data and look for ‘events’ of interest
Operational Test Data

APPLY TEST DATA TO CORRELATE MODEL

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Apply measured loads from operational testing
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Correlate measured strain gage response to FEM response
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Adjust material properties, boundary conditions, and theoretical connections as required
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Set goals for correlation
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Reality != Theory
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Correlation goals depend on structure
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Retest if necessary
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More gages
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At least one gage for each load
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SUMMARY
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Select strain gage locations
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Perform controlled static testing
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Execute operational testing
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Apply test data to correlate model