Introduction

Experimental stress analysis of structural materials sometimes requires testing to complete failure. In such cases, particularly with ductile materials, failure is often preceded by large local strains, the magnitudes of which are of interest to the test engineer.

High-elongation strain measurements place severe demands on the gage installation, and necessitate special gage and adhesive selection and surface preparation procedures. This publication outlines recommendations for gage and adhesive selection, surface preparation, gage bonding and wiring, and protective coating selection for high-elongation strain measurements.

NOTE : High elongations are usually expressed as percentages: 1% elongation is equal to 10 000 microstrain; 5% elongation is equal to 50 000 microstrain. The maximum rated elongation of any bonded strain gage is based on a single tensile measurement. Cyclic strains of high levels must be limited to a value much lower than maximum due to fatigue limitations on the strain gage foil. Consult the Vishay Measurements Group Tech Note TN-508, Fatigue Characteristics of Micro-Measurements Strain Gages , for details on strain gage performance under repetitive loading conditions.

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