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

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

• 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