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Biomechanics
Exam 3 part ii
31
Physiology
Undergraduate 4
12/07/2011

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Term
name 5 types of loading on human bones
Definition
compression
tension
shear
torsion
bending
Term
what are effects of compression on our bones?
Definition
key to development and growth, can cause chrondomalacia, allows us to be weight bearing
Term
what are the effects of tension?
Definition
-can get an avulsion fracture which is failure at site of tendon attachment
-the bone strengthens in direction of tensile forces
(also responsible for apohyses, bony outgrowths)
Term
when does shear occur?
Definition
when a force is applied parallel to surface of an object
Term
when does torsion occur?
Definition
when the bone twists, like wringing a towel
think humerus, thin-walled tube better
Term
what is the polar moment for inertia?
Definition
J = (pie * r^4) / 2
and T(torque) = (F*r)/ J
Term
bending
Definition
compression and tension. 3 point bending
Term
in a femoral neck, what forces normally act superiorly, and inferiorly to the cortex?
and explain a ski boot
Definition
superiorly: tensile force
inferiorly: compressive force
ski boot: 3 pt bending, causes extreme tensile strength, bone is stronger with compressive forces than tensile loads
Term
load and injury can occur when?
Definition
high load, one time (acute)
low load, frequently (chronic)
Term
Biomechanics of bioligical materials: how do we do it?
Definition
instron testing: apply load to tendon and device assesses changes
Term
what is anisotropic?
Definition
bone is anisotropic b/c it responds differently when load is applied in different directions
Term
whats is bone made up of? (%)
Definition
30% collagen (withstands tensile forces), 70% organic and inorganic minerals (withstands compressive forces), inorganic is massive because allows bone to withstand compression, no other part of body can do this
Term
what direction is bone stronger in?
Definition
longitudinal because this is the way it is mostly loaded
Term
what does it mean if something is viscoelastic?
Definition
it's mechanical properties are affected by the rate at which load is applied
the materials show stress-strain charactereistics that are not strictly linear, have nonlinear (or viscous properties) and linear elastic properties
Term
what is strength of a bone and how do we measure it? what is max strength?
Definition
it is the energy stored in the bone, is the area under the stress-strain curve
max strength is the failure point or load sustained before failure
Term
if you increase loading rate onto a bone, what increases of the quality of the bone?
Definition
increase in strength and stiffness
Term
how are stress and strain related?
Definition
stress is the cause, strain is the effect
Term
what is a definition for stress and a formula?
Definition
stress is the external force applied to any cross-section, F/A
Term
what is strain? what are the units?
Definition
it is the result of stress, a deformation of an object's shape,
=(y)*(change in L/ initial L)
it is dimensionless
Term
why does the bone completely shatter at higher military bullet rates?
Definition
because the loading rate is way higher, therefore the ENERGY STORAGE is higher
Term
Bone is elastic. explain the differences in the stress-strain curves for ductile material, brittle material, and bone:
Definition
ductile: indicated by long plastic region
and deforms considerably before fracture
bone: deforms slightly before failure
brittle: fails at end of elastic region
responds linearly and breaks before any deformation
Term
what does the slope of the stress-strain curve signify?
Definition
the modulus of elasticity, higher slope, stiffer object
Term
when is the most strength expressed on the stress-strain curve?
Definition
when stress is at a max
Term
what does the cortical bone represent on the stress-strain curve?
Definition
that it is very strong and very stiff
Term
what is cartilage similiar to?
Definition
it is like a sponge, low levels of stress can maintain a lot of strain
Term
what is stiffness?
Definition
the modulus of elasticity, determined by the slope of the load deformation curve in the elastic response range. it represents the material's resistance to load as the structure deforms.
aka k = stress/ strain
Term
what are two types of stress?
Definition
tension (pulling stress) and compression (pushing stress)
Term
when the slop of the curve decreases, the structure is said to reach what? and is now in what region?
Definition
yield point, and is now in the plastic region
Term
what is the region before the yield point called?
Definition
plastic region
Term
cortical bone is often referred to as
Definition
compact bone
Term
internal to the cortical bone is what
Definition
cancellous bone; has trabeculae of spongy bone
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