Experimental Stress Analysis

8

Strain Gauges

8.1 INTRODUCTION

A gauge used to measure strain is termed as a strain gauge. This gauge can be mechanical, optical, or electrical. An ordinary scale can be used to measure the strains. But the least count of an ordinary scale is 0.5 mm, if the gauge length of specimen is 100 mm, then least count of strain measurement is (0.5/100) = 0.005 = 5000 microstrain. But for accurate determination of strains at a point the least count of strain measuring instrument should be ±1 μ strain. A mechanical extensometer known as Huggenberger extensometer, with magnification of change in length of the order of 1200. The least count on measurement scale is 0.5 mm. Then least count of change in length on gauge length is 0.5/1200 = 4.166 × 10^{–4 ...}