# Lecture_1 - MECH 320-Mechanics of Materials 1 Prepared by Nasser-Eddin Mohamad Ph.D Lecture Outlines What is stress Deriving the traction vector

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MECH 320-Mechanics of Materials Prepared by: Nasser-Eddin Mohamad, Ph.D 1

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2 Lecture Outlines •W h a t i s stress Deriving the traction vector Force components on a body
3 Stress

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4 Stress Analogies ) ( Hands Many Object Heavy Stress Low Work Light =
5 As demonstrated by the piano movers, stress may be thought of as a load divided over some number of things supporting that load. As engineers you will need a more rigorous definition of stress. Consider the amorphous body loaded by a set of external forces. If we remove the top half of the body and focus on the material along at the cut, we will see a distribution of forces across the cut. These forces must equilibrate the external loads F 3 and F 4. Stress concept

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6 Resultant Forces and moments Equilibrium is satisfied if the sum of the forces and the sum of the moments for the "half-slice" are zero. If these sums were not zero then the body would be accelerating off the screen and/or spinning around.
7 Example Problem I The force plate depicted in the figure has four sensors, one at each corner, that read the vertical forces F1, F2, F3, and F4. If the plate is square with side of length l and forces F1 - F4 are known, write two expressions that will give the x and y locations of the resultant force R.

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8
Example Problem II Figure 1 shows a Russell’s traction rig used to apply an axial, tensile force to a fractured femur for immobilization. (a)

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## This note was uploaded on 02/07/2011 for the course MECH 320 taught by Professor D.a during the Spring '09 term at American University of Beirut.

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Lecture_1 - MECH 320-Mechanics of Materials 1 Prepared by Nasser-Eddin Mohamad Ph.D Lecture Outlines What is stress Deriving the traction vector

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