Engr244.Lab5.SenouciAnas

docx

School

Concordia University *

*We aren’t endorsed by this school

Course

244

Subject

Mechanical Engineering

Date

Jan 9, 2024

Type

docx

Pages

14

Uploaded by mannybenka

Report
DEFLECTION OF BEAMS ENGR 244 Mechanics of materials Section H-X By Senouci Anas ID: 40132281 Professor: Dr. Michelle Nokken Group members: Senouci Anas and Rafayal Islam Concordia University March 30 th 2020 1
Objective: Applying loads on simply supported beams and cantilever beams made of brass, steel and aluminum in order to measure their deflections and finally calculate the modulus of elasticity of each material. Introduction: Applying a load on a beam will cause a deflection. The amplitude of the deflection depends on multiple factors. The location where the load is applied and the moment it creates is a factor. The supports of the beam are another factor. The cross-section and the moment of inertia also affect the deflection. The material and its modulus of elasticity plays also a role. In our experiment, we are testing aluminum, steel and brass. Based on knowledge form previous experiments and the elastic modulus of each material, I can assume that aluminum will deflect the most followed closely by brass and finally steel, which will deflect considerably less. Beams are the basic structural component of any building. Since under heavy loads beams bend, it is very important to know how much they will deflect for the safety and integrity of the structure. The bending and torsion tests are also good to calculate the modulus of elasticity. Equipment: Load machine Deflection gauges Vernier caliper Beams of aluminum, brass and steel of rectangular cross section 2
Procedure: 1. Simply supported beam: -Measure the cross-sections. -Install the beam on the supports of the load machine and make sure that the load will act on the center of the beam. -Place the deflection gauges at the center of the beam and at the one quarter of the length. -Apply the load with increments of 200N until you reach 1000N. -For each increment, note the vertical deflection at each gauge. -Repeat the previous steps for the 2 other beams. 2. Cantilever beam: -Measure the cross-sections. -Place the load hanger at the free end of the beam, under the display meter. -Place the loads on the hanger with increments of 100g until 500g. -For each increment, note the deflection at the free end L and at L/2 Simply-supported beams Table 1: Width W, height H and moment of inertia I for each material W (mm) H (mm) I (mm 4 ) Brass 19.10 12.72 3275 steel 19.04 12.68 3235 aluminum 19.19 12.75 3315 3
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
Table 2: Experimental deflections Deflection in y (m) Brass Steel Aluminum Load (N) x=L/2 x=L/4 x= L/2 x= L/4 x= L/2 x= L/4 200 -0.00129 -0.00094 -0.00056 -0.00042 -0.00176 -0.00124 400 -0.00286 -0.00204 -0.00119 -0.00085 -0.00356 -0.00248 600 -0.00450 -0.00319 -0.00182 -0.00130 -0.00535 -0.00373 800 -0.00615 -0.00433 -0.00246 -0.00175 -0.00712 -0.00496 1000 -0.00778 -0.00547 -0.00310 -0.00220 -0.00888 -0.00620 Derivation of the elastic curve equation: Curvature of neutral axis: ? : radius of curvature I: moment of inertia E: modulus of elasticity Mx: bending moment = load*distance x 1 ρ = Mx EI Deflection curve: 1 ρ = d 2 y d x 2 ( 1 + ( dy dx ) 2 ) 3 2 It can be approximated to 1 ρ = d 2 y d x 2 4
Substituting the first equation, we have Mx EI = d 2 y d x 2 Mx = d 2 y d x 2 EI Deflection is represented by y, so in order to isolate for y we have to integrate twice. EIy = 0 x dx 0 x Mx dx + C 1 x + C 2 After doing the integral and finding the values for C1 and C2 with the initial conditions, we have the following equation for the deflection: EIy = Px 3 12 + PL x 2 4 3 P L 2 x 16 + P L 3 48 L: length of the beam x: distance between the center of the beam and the point of application of the load P Theoretical deflection for brass at mid-span, sample calculation: y = P x 3 12 + PL x 2 4 3 P L 2 x 16 + P L 3 48 EI E for brass = 105 GPa I cross section = (1/12)WH 3 = 3275mm 4 = 3275*10 -12 m 4 5
L = 0.455m x = 0.2275m P = 400N y = 400 ¿ 0.2275 3 12 + 400 0.455 0.2275 2 4 3 400 0.455 2 0.2275 16 + 400 0.455 3 48 1.05 10 11 3331 10 12 y =− 0.002244 m Table 3: Theoretical values of deflection for brass, steel and aluminum. Deflection in y (m) Brass Steel Aluminum Load (N) x=L/2 x=L/4 x=L/2 x=L/4 x=L/2 x=L/4 200 -0.001122 -0.000631 -0.000607 -0.000341 -0.001648 -0.000927 400 -0.002244 -0.001262 -0.001213 -0.000682 -0.003296 -0.001854 600 -0.003367 -0.001894 -0.001820 -0.001024 -0.004944 -0.002781 800 -0.004489 -0.002525 -0.002426 -0.001365 -0.006593 -0.003708 1000 -0.005611 -0.003156 -0.003033 -0.001706 -0.008241 -0.004635 Estimating E for each material using the experimental deflections: Sample calculation for Brass: P = 400N y = -0.00327m L = 0.2275m x = 0.11375m E = Px 3 12 + PL x 2 4 3 P L 2 x 16 + P L 3 48 yI 6
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
E = 400 ¿ 0.2275 3 12 + 400 0.455 0.2275 2 4 3 400 0.455 2 0.2275 16 + 400 0.455 3 48 0.00327 3275 10 12 E = 72.06 GPa Table 4: Estimated E for each material at x=L/2 x = 0.2275m, L = 0.455m Brass Steel Aluminum Load (N) Deflection (m) E (Pa) Deflection (m) E (Pa) Deflection (m) E (Pa) 200 -0.00129 71846309947 -0.00056 1.78527E+11 -0.00176 6.4387E+1 0 400 -0.00286 72066023434 -0.00119 1.75863E+11 -0.00356 6.4387E+1 0 600 -0.00450 72287084855 -0.00182 1.76742E+11 -0.00535 6.4153E+1 0 800 -0.00615 72176384878 -0.00246 1.76521E+11 -0.00712 6.4830E+1 0 1000 -0.00778 71934034380 -0.00310 1.76919E+11 -0.00888 6.4599E+1 0 Average E 72061967499 Average E 1.76914E+11 Average E 6.4471E+1 0 Table 5: Estimated E vs. Theoretical E for each material E estimated (GPa) E theoretical (GPa) Brass 72 105 Steel 177 200 Aluminum 64.5 70 Figure I 7
Except for Brass, the estimated values are within around 10% error compared to the theoretical ones. The discrepancies with the values for Brass can also be seen in the following deflection graphs. Theoretical vs. experimental deflection at mid-span as a function of the load for each material: Figure II Figure III Figure 1V 8 0 200 400 600 800 1000 1200 0 0.5 1 1.5 2 2.5 3 3.5 Steel Experimental Linear (Experimental) Theoretical Linear (Theoretical) Load (N) Defection (mm) 0 200 400 600 800 1000 1200 0 1 2 3 4 5 6 7 8 9 Brass Experimental Linear (Experimental) Theoretical Linear (Theoretical) Load (N) Deflection (mm) 0 200 400 600 800 1000 1200 0 1 2 3 4 5 6 7 8 9 10 Aluminum Experimental Linear (Experimental) Theoretical Linear (Theoretical) Load (N) Defection (mm) 0 200 400 600 800 1000 1200 0 1 2 3 4 5 6 7 8 9 10 Experimental Defection of Brass vs. Steel vs. Aluminum Brass Linear (Brass) Steel Linear (Steel) Aluminum Linear (Aluminum) Load (N) Defection (mm)
Cantilever beams Table 6: Width b, height h and moment of inertia I for each material W (mm) H (mm) I (mm 4 ) Brass 19.05 3.14 49.15 steel 19.01 3.51 68.50 aluminum 19.21 3.48 67.47 Table 7: Experimental deflections Deflection in y (mm) Brass Steel Aluminum Load (N) x=L/2 x=L x=L/2 x=L x=L/2 x=L 0.98 0.37 1.13 0.27 0.69 0.47 1.42 1.96 0.78 2.37 0.45 1.22 0.89 2.70 2.94 1.16 3.51 0.64 1.79 1.32 4.00 3.92 1.53 4.61 0.83 2.37 1.75 5.34 4.90 1.87 5.68 1.03 2.96 2.18 6.63 Theoretical deflection for Brass at mid-span, sample calculation: E for brass = 105 GPa I cross section = (1/12)WH 3 = 49.15mm 4 = 49.15*10 -12 m 4 L = 0.250m x = 0.125m P = 1.96N y = P ( x 3 3 L x 2 ) 6 EI y = 1.96 ( 0.125 3 3 0.250 0.125 2 ) 6 1.05 10 11 49.15 10 12 9
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
y = 0.000618 m Table 8: Theoretical values of deflection for brass, steel and aluminum. Deflection in y (m) Brass Steel Aluminum Load (N) x=0.125m x=0.25m 0.125 0.25 0.125 0.25 0.98 0.000309093 0.000989096 0.000116427 0.000372567 0.000337727 0.001080727 1.96 0.000618185 0.001978192 0.000232854 0.000232854 0.000675455 0.002161454 2.94 0.000927278 0.002967289 0.000349281 0.000349281 0.001013182 0.003242182 3.92 0.00123637 0.003956385 0.000465709 0.000465709 0.001350909 0.004322909 4.90 0.001545463 0.004945481 0.000582136 0.000582136 0.001688636 0.005403636 Estimating E for each material using the experimental deflections: Sample calculation for Brass: P = 1.96N y = 0.00078m L = 0.250m x = 0.125m E = P ( x 3 3 Lx 2 ) 6 yI E = 1.96 ( 0.125 3 3 0.250 0.125 2 ) 6 0.00078 49.15 10 12 E = 83 GPa Table 9: Estimated E for each material at x=0.125m x = L/2 Brass Steel Aluminum Load (N) Deflection E (Pa) Deflection E (Pa) Deflection E (Pa) 10
(m) (m) (m) 0.98 0.37 8.3217E+10 0.27 1.0584E+11 0.47 4.9252E+10 1.96 0.78 8.3217E+10 0.45 1.1088E+11 0.89 5.1393E+10 2.94 1.16 8.6932E+10 0.64 1.1267E+11 1.32 5.2149E+10 3.92 1.53 8.5407E+10 0.83 1.1359E+11 1.75 5.1115E+10 4.90 1.87 8.8192E+10 1.03 1.1304E+11 2.18 5.1618E+10 Average E 8.5393E+10 Average E 1.1120E+11 Average E 5.1105E+10 Table 10: Estimated E vs. Theoretical E for each material E estimated (GPa) E theoretical (GPa) Brass 85 105 Steel 111 200 Aluminum 51 70 Theoretical vs. experimental deflection at mid-span as a function of the load for each material: 0 1 2 3 4 5 6 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Brass Experimental Linear (Experimental) Theoretical Linear (Theoretical) Load (N) Defection (mm) Figure V 11
0 1 2 3 4 5 6 0 0.2 0.4 0.6 0.8 1 1.2 Steel Experimental Linear (Experimental) Theoretical Linear (Theoretical) Load (N) Defection (mm) Figure VI 0 1 2 3 4 5 6 0 0.5 1 1.5 2 2.5 Aluminum Experimental Linear (Experimental) Theoretical Linear (Theoretical) Load (N) Defection (mm) Figure VII 12
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
Discussion: The theoretical deflections, for the most part fall in range with the experimental values. We can note that in all the experiments the theoretical values are always lower than the experimental ones. There are only two bigger discrepancies, for brass in the simply supported beams and for steel in the cantilever beams. 30% error for brass and almost 100% error for steel. Since the error for steel is so big compared to the others, it is possible that something occurred during the experiment that could have affected the readings. Maybe because the sample wasn’t placed well or the fatigue due to other tests could be some explanations. In general, if we compare figures 1,2 and 3 to figures 5,6 and 7 we can observe that the theoretical and experimental values are much closer in the simply-supported beams than in the cantilever beams. The application of the load in the cantilever experiment wasn’t as precise due to the fact that the load was hanging from the beam and it was moving around a bit. It must be noted that for the simply supported tests, we used ticker specimens with greater moments of inertia and we also applied a much larger load on them, and we obtained results that were more accurate. Maybe for beam deflection experiments it’s better to use bigger loads and ticker samples for the best results. When we compare Table 5 to Table 10, we can again see that theoretical values of E are closer to the experimental ones in simply supported than in cantilever. The difference in the values of E is probably caused by material fatigue. After multiple tests, the modulus of elasticity of the specimens decreased and it shows in our experiment. Each experimental E is lower than the theoretical one. Conclusion: With the experimental data we were able to plot the graph of deflection vs. load for each material (Figure 4) and it allows us to confirm our original assumption that aluminum will bend the most, followed by brass and steel. This again goes in accordance with the results and conclusion of the previous labs. Knowing how beams of different materials bend under certain loads will guide us, engineers, in making the best decision when it comes to structural safety. 13
14