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Biomechanics (Commonly used variables (Strain (no unit (only…
Biomechanics
Commonly used variables
Stress
measure of F
O= F/A
Understand
Strain curve & structure
Strain
Responsible for stress
frictional and increase in length
no unit
only number/percentage
E = change of L/L
young's modulus
yield strength
ultimate Strength
failure fracture strength
Soft tissue
P(3) increase in strain (less than ultimate tensile Strength)
strayning
P(2) stain increase
Collagen fibers become straigthening
P(1) deforming tensile deformation
small tensile deformation
viscous elastic (heterogeneous structure)
Elastic deformation
return to original size and shape
ultimate tensil stress
Maximum stress
Without breaking
Many obey Hookes law
Yield Stress
Youngs modulus
Measures stiffness
stress begins to deform plastically
irreversible
Proportional limit
Cell mechanical properties
Rp = radius or micropipette
Rc = radius of the cell
Fluid Viscosity
Strain rate (s.r) (dvx/dy)
shear stress(s.s) (txy)
Material (vxos)
Fluids: piston & cylinder
Both?
can combine both
models (elastic)
springs
Energy storage with deformation
energy added when stressed
Strainenergy storesd
energy storage with deformation
Stores more energy than brittle material
Bone
10% water
60% material
30% rich matrix
Bone structure
anisotrophy
Tested different directions
metals which display isotrophy
Compact
spongy
Collagens assemble together
fibrils - fibers
calcium & phosphate = hydropapile crystal = mechanical strength
Mechanical aspect of lungs
elastic enroll lungs (collapse)
E.r chest (expansion)
intrafluid provides mechanical couplin between chest & wall
Intrapleural pressure
pressure pleural cavity
prd = palu - pip/end
Properies
exposed to forces
Human body
force & movement analysis
Neutrons law
1st no force = velocity no change
2nd F=MA
3rd Action = equal opposite reaction
Surface Tension
Young Modulus
Attention to units
Mega
giga
Surface T
Elastic tendency after fluid service
liquid air
greater attraction to molecules
Micropropeties
Microfilaments cytoskeleton
intermediate filaments
wall T & pressure
change of p = (2t)/r sphere
