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Unformatted text preview: ME 382 Lecture 02 10/ix/10 1 T HREE I MPORTANT TERMS FOR MECHANICAL DESIGN • Stiffness: Ability of an object to resist deformation A stiff object can support large loads with little deformation A compliant object has large deformations under low loads • Strength: Ability of an object to resist failure A strong object can support large loads without failing A weak object fails under low loads • Toughness: Ability of an object to dissipate energy A tough object can absorb a large amount of energy before fracture A brittle object fails with little dissipation of energy • Stiffness: ≡ applied load / resultant deformation (N.m-1 ) • Compliance: ≡ resultant deformation / applied load (m.N-1 ) • Strength: ≡ applied force to cause failure (N) • The term “toughness” is used differently in different contexts Energy absorbed has units of (N.m) = (J) • “Strength” and stiffness” depend on material , geometry , and dimensions of object • Need to separate material properties from geometrical properties • Elastic modulus - stiffness of a material (Nm-2 = Pa) Typically resistance to changing bond length between atoms or molecules...
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- Winter '08
- Deformation, Tensile strength, 0.1%, work-hardening, εn