Yin Lecture - BME 140 Fall 2010 Biomechanics Basics of...

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BME 140 – Fall 2010 Basics of Biomechanics Frank Yin October 4, 2010 Biomechanics Why do we care ? Biomechanics Definition Mechanics applied to biology Goals To understand and quantify the mechanical properties of biological tissues Rationale 4 Helps understand normal function Every cell is exposed to mechanical forces Many tissues and organs perform mechanical tasks 4 Predict changes due to alterations 4 Propose methods of intervening To understand how biological tissues respond to applied forces Use this understanding to treat health and disease Impact of Biomechanics Rehabilitation Kinesiology, sports medicine Physiology Prosthetics 4 Joints 4 Heart valves 4 Vessels Wound healing, tissue remodeling Cell function Protein structure and function Classes of Mechanics Problems Static vs. dynamic Fluid vs. solid Rigid vs deformable Rigid vs. deformable Time (history) - dependent Statics Deals with forces acting on bodies in equilibrium - that is, objects not moving or deforming Simple physics is sufficient
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Statics Equilibrium 4 In any direction, sum of forces must equal zero 4 Sum of moments must equal zero Free-body diagram is key concept 4 Displays all the external forces and reaction forces Sum forces in y-direction: -W b + 2*R = 0 R = 0.5 W b Sum forces in y-direction (given that weight of leg = .08 W b ): -F L – 0.08W b + 0.5 W b = 0 F L = 0.42 W b Free Body Diagram Free Body Diagram Moment (torque): • Force times the perpendicular distance (from reference point) through which force acts • At equilibrium, sum of moments about any point must = 0 • Can define any direction (CW or CCW) as positive (be consistent) thus, F p = 3W + M o = 0 = -W(7.5) + F p (2.5) Dynamics Deals with time-varying forces acting on bodies in motion Forces 4 4 Velocity 4 Acceleration Dynamics Principles of physics still apply 4 Conservation of mass Conservation of momentum 4 4 Conservation of energy Free-body diagram is still important 4 Displays all pertinent forces, velocities, masses, etc. 4 Usually only need consider center of mass, i.e. rigid bodies Rigid vs Deformable Bodies Rigid: Force produces displacement Df b l F d df t i Deformable: Force produces deformation 4 Continuum approximation 4 Stress 4 Strain 4 Stress-strain relationship
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Continuum Considerations Depends on length scale of measurement Individual vs. collective view Lower bound of size Set acceptable bounds of error Provides an “averaged” view 4 A tensor quantity Scalar vs. vector vs. tensor Has magnitude, direction and associated plane of action Stress 4 Force divided by the area on which it acts
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This note was uploaded on 02/14/2012 for the course NUBITRY 3304 taught by Professor Various during the Spring '01 term at Albertus Magnus.

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Yin Lecture - BME 140 Fall 2010 Biomechanics Basics of...

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