Boundry Condition Testing.

OUTLINE

  •     Strain gage theory overview
  •     Select strain gage locations
  •     Perform controlled static testing
  •     Execute operational testing
  •     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

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Strain can be found directly by voltage measurements

Temperature influences strain gage resistance


SELECT STRAIN GAGE LOCATIONS TO GENERATE HIGH FIDELITY DATA

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

DEVELOP LINEAR RELATIONSHIPS WITH STATIC TESTING

  • Install strain gages onto structure
  •     Account for environmental effects
  •         Apparent strain due to temperature
  •         EMF causing current and voltage shifts
  •     Apply boundary conditions through static testing
  •     Generate Strain Versus Load Plots

 

 

VERIFY OPERATIONAL BOUNDARY CONDITIONS THROUGH TESTING

Operational Test Data
  • Replicate static test setup on operational structure
  •     Install data acquisition system (DAQ) on structure
  •     Route wires and instrumentation such that structural behavior is unaffected
  •     Account for environmental effects such as EMF and temperature
  •     Perform operational testing
  •     Examine data and look for ‘events’ of interest

 


APPLY TEST DATA TO CORRELATE MODEL

  •     Apply measured loads from operational testing
  •         Correlate measured strain gage response to FEM response
  •         Adjust material properties, boundary conditions, and theoretical connections as required
  •     Set goals for correlation
  •         Reality != Theory
  •         Correlation goals depend on structure
  •     Retest if necessary
  •         More gages
  •         At least one gage for each load

SUMMARY

  •     Select strain gage locations
  •     Perform controlled static testing
  •     Execute operational testing
  •     Apply test data to correlate model