Strain Gauges CE 307-01
Nathaniel R. Gant
Date Performed: November 15, 2011 Date Submitted: November 29, 2011 Submitted To: MAJ Idewu
Virginia Military Institute Department of Civil and Environmental Engineering Help Received: None
Introduction Structures in the world battle daily against various forces that cause destruction. For example, earthquakes send vibrations through static materials that cause bolts to snap and beams to bend. And over time, these continuous forces cause catastrophic failure in which a structure will not be about to function and must be replaced. One force that engineers analyze is stress which is the force applied on the surface of any object. Stress causes materials to elongate which is called strain. The purpose of this experiment was to use material properties in order to predict the strain at 14 locations in an aluminum beam. Results 1
2
3
12 13 14
4
5
9 10 11 6
7
8
LOAD Location 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Strain (10-6) 106 238 363 558 540 117 244 374 100 005 118 059 005 062
Discussion The force applied on the beam revealed strain in relation to location of the beam. The highest strain observed was located at location 4 on the beam. Strain gage 4 was located on the top of the beam closest to where the load was applied. It makes sense that the highest strain was located here because it was where the load was applied. The lowest strain observed was located at location 10 and 13 on the beam. These two strain gages were located on the middle of the vertical portion of the beam. The reason why these
locations had the lowest strain was that the load was not acting on those locations as much as the other part of the beams. This is important to know because if a beam was used to design a structure, the weakest point of the beam should beam known. By knowing where the weak point on a beam is, engineers can create a support that will protect that weak point. When tension and torsion test were performed on aluminum, it had high strengths compared to the other metals were tested which were steel, brass, and cast iron. Based on those results, steel would have less strain than aluminum because it had higher values for the tension and torsion test. However, cast iron and brass would have more strain compared to aluminum. If temperature was taken into consideration, a cooler temperature would increase the brittleness of the beam and a warmer temperature would increase the ductility of the beam. If a bridge were loaded in the center, the highest stress would occur in the center of the bridge because that is where the load is applied. The lab reveals this true because the strain gage closest to the center had the highest strain.