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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 • 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
Dial Gauges Digital demec gauge
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
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
Why Materials show elastic behaviour Force between nucleii Attraction Distance between nucleii Repulsion Compression Tension
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
Toughness For an elastic system Stress (force) Area = average stress final strain = Energy absorbed = work done Strain (distance) Final strain
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
Shear stress and strain Area resisting shear Shear displacement (x) Shear Force Shear strain is angle L Shear force
Stress on oblique planes = ½y sin(2θ)
Movement of dislocation Grain Boundary
Material subject to two perpendicular stresses = 0.5 (x - y) sin 2θ
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
The Von Mises criterion 2y2 = (1 - 2)2 + (2 - 3)2 + (3 - 1)2 Where y is the tensile strength 1, 2, 3 are the principal stresses