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
|
Definition
| when a force is applied parallel to surface of an object |
|
|
Term
|
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
|
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
|
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
|
|
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
|
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
|
|
Term
| cortical bone is often referred to as |
|
Definition
|
|
Term
| internal to the cortical bone is what |
|
Definition
| cancellous bone; has trabeculae of spongy bone |
|
|
