Comparison of strain gauge, clip-on extensometer and Video Gauge outputs in the tensile testing of steel samples

The Problem

To generate confidence in any new measurement technique it is necessary to carry out trials unambiguously comparing the new technique with established and accepted standards.

The Solution

A standard steel dog-bone test specimen was taken and a strain gauge was attached to the back face of the sample, Video Gauge targets to the front and a clip-on extensometer was attached across the sample. The strain gauge and extensometer measured longitudinal strain, the Video Gauge both longitudinal and Poisson strains.

All three devices returned the correct value for the specimen modulus with similar levels of noise on the data.

Advantages of the Video Gauge

The specimen preparation and set-up time for the Video Gauge was far lower than for the strain gauge and an additional strain gauge would have had to be used to extract Poisson�s ratio as well as longitudinal strain. The extensometer required no specimen preparation and low set-up time, but only gave longitudinal strain and was removed prior to failure to avoid any possibility of damage to it. In addition the use of four targets for the Video Gauge gave data for both edges of the specimen allowing specimen alignment to be checked. Additional targets could give information on strain uniformity in the specimen.