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EM 304 Lecture 2

EM 304 Lecture 2. Forces vs. stresses Average normal stress Examples: Problem 1.33 Problem 1.37 Problem 1.63. 200 lb. 200 lb. 0.1 ft 2. 1.0 ft 2. Forces vs. stresses. External forces and moments quantify the action of an object applied on another object.

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EM 304 Lecture 2

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  1. EM 304 Lecture 2 Forces vs. stresses Average normal stress Examples: Problem 1.33 Problem 1.37 Problem 1.63

  2. 200 lb 200 lb 0.1 ft2 1.0 ft2 Forces vs. stresses • External forces and moments quantify the action of an object applied on another object. • Internal forces and moments quantify the action of a part of the object applied on the other part. • Stresses represent the amount of force applied to a unit surface area. • Stresses capture information on: • intensity of force • surface area of material that bears the force Same load Different surface areas Different strengths

  3. Internal loads are applied on a cross-section

  4. Consider an element Normal stresses sx, sy, sz Shear stresses txy, txz, tyz

  5. Normal stress Average normal stress P P

  6. P P Average normal stress s > 0  tension (tensile stress) • < 0  compression (compressive stress) Units: N/m21 Pa = 1 N/m2 1 MPa = 1 N/mm2 lb/in2 = psi 1000 lb/in2 = 1 kip/in2 = 1 ksi

  7. Problem 1.33 • Problem 1.37 • Problem 1.63

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