31. Biomechanics Flashcards
Sigma = F/A
What is this equation for? Explain its parts
Sigma = stress (pa) F = force (N) A = area (m2)
ε = ∆L / L
ε = strain, no dimension
∆L=extension (m)
L= original length (m)
F = -K * x
Hooke’s law
F = restoring force
X = displacement
K = spring constant
Young’s modulus equation
E = σ/ε (Pa) E = (F*L0)/(A0* ∆L)
Maximum stress of collagen
60 MPa
Maximum strain of collagen
0.08
Young modulus of collagen
750MPa (stiff)
Maximum stress of elastin
0.6 MPa
Maximum strain of elastin
3
Young modulus of elastin
0.2 MPa (pretty flexible)
Distensibility equation
κ= (-∆V)/(∆p*V0)
∆V/V0 : relative expansion
P : transmural pressure
What equation is this?
σ=(r*p)/(R-r)
Laplace-Frank equation
σ: tangential stress (wall tension) r : inner radius of blood vessel R : outer radius of blood vessel R-r : wall thickness p : transmural pressure
What is the % composition of bone?
30% organic matrix (collagen) and 70% inorganic salts (hydroxyapatite)
Young’s modulus of bone
5-20GPa
Which part of the bone has higher and lower Young modulus value?
Greater in dense cortical bone
Lower in trabecular part
Young modulus of enamel
100GPa
Which equation describes the decrease of stress in a viscoelastic material?
σ= σ0*e^(-t/τ)
τ : time constant
What is transmural pressure?
Difference in pressure between 2 sides of a wall
What is tangential stress?
Direction of deforming / external force is parallel to the cross sectional area. It results in deformation of the body
What is Young’s modulus a measure of?
a measure of the ability of a material to withstand changes in length
What is collagen made up of?
AA wound together in a triple-helix (glycine, proline, hydroxyproline)
What is the protein that makes up elastin?
Tropo-elastin (contains primarily glycine, valine, and modified alanine and proline residues)
What is distensibility?
Ability to be able to stretch and expand under pressure (or change in the vessel volume under pressure)
What does the Frank-Laplace law state?
tangential stress on the blood vessel is proportional to the transmural pressure, the diameter of the lumen and the thickness of the blood vessel wall
What does energy dissipation depend on? (3)
- mass
- atomic number (Z)
- Energy of the substance
