The development of a floating element photoelastic force balance

Abstract

We present a floating element force balance design that uses an optical measurement of the force using photoelastic stress analysis. The force-sensing element consists of pins embedded in photoelastic polyurethane pads, which generate internal stress when the floating element is loaded and observed via a transmission polariscope.
A series of known loads and their corresponding fringe patterns allow a calibration matrix to be derived using a polynomial model solved by least squares regression.
Finite Element Analysis (FEA) simulation is carried out to validate the proposed method. The balance then measured a lift curve of the NACA0015 wing at low speed.
A comparison of the photoelastic balance and a commercial, 6-axis strain-gauge load cell showed typical differences of less than 6%. This optical approach enables accurate measurements with inexpensive and simple components inside the sensor. It can also be tailored for different load cases and scaled to fit complex setups across various magnitudes. Further, this thesis explores the limits of the method's dynamic measurement capabilities by finding its frequency response and measuring the dynamic forces of a decaying pendulum. This work demonstrates that a photoelastic balance is a simple, inexpensive, sensitive force transducer.

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Identifiers

ORCID for Bradley McLaughlin: orcid.org/0009-0004-4724-0623

ORCID for Bharath Ganapathisubramani: orcid.org/0000-0001-9817-0486

ORCID for John Lawson: orcid.org/0000-0003-3260-3538

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