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1.16 Mechanical failure

1.16 Mechanical failure. 1.16.1 Measuring strain 1.16.2 Measuring stress 1.16.3 Why materials exhibit elastic behaviour 1.16.4 Toughness 1.16.5 Hardness 1.16.6 Stresses on oblique planes 1.16.7 Failure theories. Applying load - mechanical. Applying Loads (hydraulic).

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1.16 Mechanical failure

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  1. 1.16 Mechanical failure • 1.16.1 Measuring strain • 1.16.2 Measuring stress • 1.16.3 Why materials exhibit elastic behaviour • 1.16.4 Toughness • 1.16.5 Hardness • 1.16.6 Stresses on oblique planes • 1.16.7 Failure theories

  2. Applying load - mechanical

  3. Applying Loads (hydraulic)

  4. Quarter bridge strain gauge circuit.

  5. LVDT Circuit

  6. Dial Gauges Digital demec gauge

  7. 1.16 Mechanical failure • 1.16.1 Measuring strain • 1.16.2 Measuring stress • 1.16.3 Why materials exhibit elastic behaviour • 1.16.4 Toughness • 1.16.5 Hardness • 1.16.6 Stresses on oblique planes • 1.16.7 Failure theories

  8. Measuring Stresshttp://www.rdpe.com/uk/hiw-sglc.htm

  9. Measuring modulus of elasticity

  10. 1.16 Mechanical failure • 1.16.1 Measuring strain • 1.16.2 Measuring stress • 1.16.3 Why materials exhibit elastic behaviour • 1.16.4 Toughness • 1.16.5 Hardness • 1.16.6 Stresses on oblique planes • 1.16.7 Failure theories

  11. Why Materials show elastic behaviour Force between nucleii Attraction Distance between nucleii Repulsion Compression Tension

  12. 1.16 Mechanical failure • 1.16.1 Measuring strain • 1.16.2 Measuring stress • 1.16.3 Why materials exhibit elastic behaviour • 1.16.4 Toughness • 1.16.5 Hardness • 1.16.6 Stresses on oblique planes • 1.16.7 Failure theories

  13. Toughness For an elastic system Stress (force) Area = average stress  final strain = Energy absorbed = work done Strain (distance) Final strain

  14. 1.16 Mechanical failure • 1.16.1 Measuring strain • 1.16.2 Measuring stress • 1.16.3 Why materials exhibit elastic behaviour • 1.16.4 Toughness • 1.16.5 Hardness • 1.16.6 Stresses on oblique planes • 1.16.7 Failure theories

  15. Shear stress and strain Area resisting shear Shear displacement (x) Shear Force Shear strain is angle  L Shear force

  16. Stress on oblique planes  = ½y sin(2θ)

  17. Movement of dislocation Grain Boundary

  18. Material subject to two perpendicular stresses  = 0.5 (x - y) sin 2θ

  19. 1.16 Mechanical failure • 1.16.1 Measuring strain • 1.16.2 Measuring stress • 1.16.3 Why materials exhibit elastic behaviour • 1.16.4 Toughness • 1.16.5 Hardness • 1.16.6 Stresses on oblique planes • 1.16.7 Failure theories

  20. The Von Mises criterion 2y2 = (1 - 2)2 + (2 - 3)2 + (3 - 1)2 Where y is the tensile strength 1, 2, 3 are the principal stresses

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