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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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
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
Analysis of Forces Pure Bending

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Analysis of Forces Sign conventions
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
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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