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Mechanical Testing

Mechanical Testing. Here’s what we’re going to learn about!. Forces Newton’s 2nd Stress Strain Young’s Modulus. s. e. Force. A force is a push or a pull A Force is represented in diagrams by an arrow SI unit of force is Newton (N) N = . 5 N. 10 N. kg m. 20 N. s 2.

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Mechanical Testing

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  1. Mechanical Testing

  2. Here’s what we’re going to learn about! • Forces • Newton’s 2nd • Stress • Strain • Young’s Modulus s e

  3. Force • A force is a push or a pull • A Force is represented in diagrams by an arrow • SI unit of force is Newton (N) • N = 5 N 10 N kg m 20 N s2

  4. Newton’s 2nd Law of Motion Force = (mass)(acceleration) F = ma Units F: N = kg m/s2 m: kg a: acceleration (due to gravity) Symbol: a or g Value: 9.81 m/s2

  5. Newton’s 2nd Law of Motion Force = (mass)(acceleration) F = ma Newton 2 can describe weight: Weight = (mass)(acceleration) W = mg a = g = 9.81m/s2 Only on Earth!

  6. Example: Use Newton 2 to calculate your mass Formulas F = ma 1 lb = 4.45 N This is a conversion factor W= mg 150 lb 4.45 N = 668 N Convert your weight in lb to SI unit of Newtons 1 lb m= W/g Rearrange the equation to solve for mass m= 668 N / 9.81 m/s2 Plug and chug m= 68 kg

  7. Example: Use Newton 2 to calculate your weight on Mars! Hey Hi Formulas F = ma m = 68 kg W= mg 1 lb = 4.45 N W= mg W= (68 kg)(3.71 m/s2) W= 252 N 252N 1 lb = 57 lb a = g = 3.71 m/s2 On Mars 4.45 N

  8. Question: We just saw that my mass on Earth is 68 kg. What is my mass on Mars? Answer: 68 kg-my mass will not change. My weight changes because acceleration changes on mars

  9. Stress Force Stress = Area F s = A

  10. Stress Force 12 N Stress = Area 1 m Example F s = A 3 m

  11. Stress Force 12 N Stress = Area 1 m Example F s = A 3 m F = 12 N

  12. Stress Force 12 N Stress = Area 1 m Example F s = A 3 m F = 12 N A= (1m)(3m) = 3m2 We want the area that is perpendicular to the force

  13. Stress Force 12 N Stress = Area 1 m Example F F s = s = A A 3 m F = 12 N A= (1m)(3m) = 3m2 12 N = = 4 N/m2 3m2 = 4 Pascals = 4 Pa

  14. You try one! 3.14 N F = Diameter = 2 m F F s = s = A A A= =

  15. Strain Li Lf - Li Strain = Li initial Lf - Li e = Li

  16. Strain Li Lf - Li Strain = Force Li initial Lf - Li Lf e = Li final

  17. Strain Li Lf - Li Lf - Li Strain = Force Li initial Lf - Li Lf e = Li final

  18. Example 1 mm 10 N initial Li = Lf - Li 5 mm e = Li Lf = 10 N final e =

  19. Now put it together What if we make a plot of stress vs. strain? s Young’s Modulus e

  20. Stress vs. Strain The slope of the stress-strain curve is a material property of stiffness We call this parameter Young’s Modulus s Young’s Modulus e

  21. Stress vs. Strain The higher the slope, the stiffer the material Material 2 Material 3 s Material 1 e Material 3 is the stiffest

  22. Isoprene monomer H H CH3 C C CH2 C H

  23. Lab activity! H CH3 H H H H CH3 H C C C C C C C C H H H S S H H H C C C C C C C C H H H H CH3 H H CH3

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