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Unformatted text preview: ME 382 Lecture 02 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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- Fall '08