Essay about Strain Gauges

2438 Words Mar 26th, 2013 10 Pages
T.C.D | Measurement of Strain using Electrical Resistance Strain Gauges | 3B3 - Mechanics of Solids | | Adam McCreevey | 3/15/2013 |

This is a laboratory to learn how to make measurements using a strain gauge by using different configurations, also to determine experimentally the axial and transverse stress at the surface of the beam and compare them to theoretical calculations |

Introduction

If a length of wire is subject to a stress within its elastic limits, the resulting elongation and change of diameter alters the resistance. The resulting principle is used in the resistance strain gauge, which consists of many turns of resistance wire, wound on an insulating former, the strain gauge wire is selected for the
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The deflection of the beam was measured using LDVT and its units were expressed in mm. A setup of the rig can be seen in the figure below:

Diagram showing the set up of the rig
Method
1. Set up the rig as previously discussed 2. Take an initial measurement for the deflection from the LDVT 3. Apply the first weight of 1Kg and wait for the results on the screen to settle slightly 4. Take note of all the readings in a tabulated format 5. Repeat the process, increasing the load by 1Kg up to 8 Kg taking measurement at each interval 6. Do this twice to get an average for the acquired results

Results

These first two tables are the actual results from the experiment: Weight (Kg) | G1 | G2 | G3 | G4 | G5 | Deflection (mm) | Deflection actual (mm) | 1 | 7 | -5 | 44 | 66 | -9 | 0.218 | 0.21 | 2 | 14 | -7 | 92 | 137 | -15 | 0.428 | 0.42 | 3 | 17 | -36 | 114 | 183 | -47 | 0.642 | 0.634 | 4 | 23 | -41 | 158 | 250 | -57 | 0.856 | 0.848 | 5 | 29 | -48 | 202 | 315 | -68 | 1.068 | 1.06 | 6 | 39 | -52 | 244 | 381 | -77 | 1.266 | 1.258 | 7 | 44 | -61 | 284 | 445 | -90 | 1.481 | 1.473 | 8 | 50 | -69 | 328 | 509 | -101 | 1.695 | 1.687 |
Actual deflection is the measured deflection less 0.008, which was the initial reading on the LDVT

Weight (Kg) | G1 | G2 | G3 | G4 | G5 | Deflection (mm) | Deflection actual (mm) | 1 | 6 | -8 | 42 | 65 | -11 | 0.223 | 0.212 | 2 | 12 | -18 | 82 | 120 | -25 | 0.437 | 0.426 | 3 | 18 | -29 | 121 | 190

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