BRAE-ENGR 213.lecture 4

BRAE-ENGR 213.lecture 4 - Bioengineering at the tissue...

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Bioengineering at the tissue  level Specialized organization of cells
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Quote of the Day Only two things are infinite, the universe  and human stupidity, and I'm not sure  about the former.  Albert Einstein
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Learning Objectives Define  the term biomaterial Explain  biocompatibility Discuss  applications and requirements  of materials for medical applications
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Bioengineers and Materials Bioengineers use materials to make  things! Cardiovascular/thoracic devices Orthopedic devices Dentistry devices and materials Environmental remediation Characterization of biologic tissue
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Engineering Materials Classes A material class is a  set of materials with  similar  microstructural  organization, and/or  performance i.e.  electronic  configuration,  bonding, structure,  function, etc. Material Classes Metals Ceramics Polymers Semiconductors Composites Biomaterials
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Engineering Materials Classes Material classes may include elements  of other material classes.  For example A certain metal may be a biomaterial However, not all biomaterials are metals And not all metals are biomaterials
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Material Properties A material property is an intrinsic  characteristic that can be used to  describe a material behavior Quality Material Property Symbol Stiffness Elastic Modulus E Strength Tensile Yield S y Fracture Resistance Fracture Toughness K Wear Resistance Hardness R (example) Conductance Resistivity ρ
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Stress Tensile stress , σ : Shear stress , τ : Area, A F t F t σ= F t A o original area before loading Area, A F t F t F s F F F s τ = F s A o Stress has units: N/m 2 or lb/in 2
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Strain Tensile strain: Lateral strain: Shear strain: ε = δ L o ε L = - δ L w o γ = tan θ Strain is always dimensionless. θ /2 π /2 π /2 - θ θ /2 δ /2 δ /2 δ L /2 δ L /2 L o w o
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Simple Tensile Mechanical  Properties Obtained by a tensile test
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Typical tensile specimen • Other types of tests:    --compression:   brittle        materials (e.g., concrete)    --torsion:   cylindrical tubes,       shafts. gauge length (portion of sample with reduced cross section) = Typical tensile test machine load cell extensometer specimen moving cross head Adapted from Fig. 6.2, Callister 6e. Stress-Strain Testing
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F F simple tension test σ Linear- elastic 1 E ε Units: E: [GPa] or [psi] Modulus of Elasticity, E Slope of the linear  portion of the stress- strain graph Hooke's Law  σ = E ε
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Poisson's ratio,  ν    metals:     ν  ~ 0.33    ceramics:  ν  ~0.25    polymers:  ν  ~0.40 ε ν =- L ε ε L ε 1 - ν F F simple tension test Units: ν   : dimensionless
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M M τ 1 G γ τ = G γ    G = E 2(1 + ν ) simple torsion test Elastic Shear modulus, G Slope of the linear  portion Pressure- volume change  curve Special relations for  isotropic materials
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This note was uploaded on 08/13/2010 for the course ENGR ENGR 213 taught by Professor Griffin during the Spring '10 term at Cal Poly.

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BRAE-ENGR 213.lecture 4 - Bioengineering at the tissue...

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