Biomech-Bending and Torsion-Lecture

Biomech-Bending and Torsion-Lecture - Bending 14:125:208...

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Bending 14:125:208 Introduction to Biomechanics
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Why is this important Why study bending None of us “bend” Our bones are rigid Forces from everyday movement can lead to complex loading situations
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Types of Loading and Stresses Tension Compression Shear Torsion Bending
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Beams/Stress Tension or Compression: stress=F/A stress is same throughout Bending: stress=My/I maximum=Mc/I Torsion: stress=T r /J maximum=TR/J Shear: stress= max = 3/2 V/bh So, given some complex loading situation, all of these stresses may be acting at the same time and the magnitude of stress can vary throughout the entire object! c y ydA Ib V 0 F Produces: 1) Compression (Fx) 2) Shear (Fy) 3) Bending (Fy) These stresses combine! Fy Fx
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Bending Forces Bones experience forces that lead to bending Holding things in outstretched arms Kicking objects Lifting weights
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Bending Forces What forces lead to possible bending The weight of an object and joint reaction forces
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Analysis of Forces Pure Bending
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Analysis of Forces Sign conventions
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Analysis of Forces Split into 2 parts There is tension, compression, and shear
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Analysis of Forces What do we need? It depends on what you want to look for To find forces in the y direction Placement of the forces Magnitude of the forces To find the forces in the x direction Placement of the forces Magnitude of the forces Moments of Inertia
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Analysis of Forces How do we analyze bending? Draw FBD – align beam along horizontal axis Determine tangential (axial) components of force and normal (shear) components Make a series of cuts in the beam and continue to do FBDs, finding internal forces and moments Convert these to stress, deformation, and/or strain Add axial loads (tensile and compressive) and torsion (shear) Evaluate total state of stress… Will object fail?
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Simple example- generating shear and moment diagrams P 1 P 2 a a b P 1 =P 2 =100N a=5 m b=10 m P 1 P 2 R 1 R 2 Free Body Diagram       N R N R P P R a P b a P b a R N P P R R 100 100 5 15 20 2 200 2 1 2 1 1 2 1 1 2 1 2 1
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This document was uploaded on 11/03/2011 for the course BIOCHEMIST 208 at Rutgers.

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Biomech-Bending and Torsion-Lecture - Bending 14:125:208...

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