Load and Deformation Flashcards
how does collagen act under tensile loads?
they straighten/lengthen
how does collagen act with relaxation?
they return to original length
do collagen fibers exhibit elastic or viscoelastic behavior? why?
viscoelastic because of the mostly water ground substance
What types of loading does collagen exhibit?
high tensile strength, high stiffness, poor resistance to compression
What is elastin made of?
fibrous elastin protein and microfibrils
What qualities do elastin fibers carry?
high extensibility, low stiffness
what kind of deformation do elastin fibers display?
elastic until rupture
What are tendons composed of?
elastic elastin fibers and viscoelastic collagen fibers
what do tendons do in the body?
help execute joint motion by transmitting tensile forces from muscles to bones
What part of tendons act under low strains?
elastic fibers are predominantly used as they are easier to stretch
What part of tendons act under high strains?
collagen fibers take over because elastic fiber crimp is straightened (become stiffer, more viscoelastic)
How do tendons compare to bones?
stiffer, higher tensile strength, support large loads with small deformations
What are ligaments composed of?
elastic elastin fibers and viscoelastic collagen fibers
what do ligaments do in the body?
they help stabilize joints by transmitting forces from bone to bone
What is a main difference between ligaments and tendons?
Ligaments have an increased proportion of elastin compared with the tendon
what load qualities do ligaments display?
greater extensibility/elasticity
lower strength
lower stiffness
true or false: ligaments only run in parallel to the load?
false:
while they do mostly run in parallel and provide tensile strength, some fibers are oblique and run in other directions
What does bone do in the body?
provide mechanical support as the central structure of each body segment
what factors affect bone mechanics?
-age
-geometry (influence of moment arms)
-mode of loading (compression, tension, shear, bending, torsion)
-frequency of loading
-pathology
What mechanical properties affect cortical/compact bone?
-direction of load
(stronger in compression than tension. stronger, stiffer, and more ductile in longitudinal loading than transverse)
-rate of loading
(stronger and stiffer with fast vs slow loading)
- designed to resist torsion, bending, longitudinal compression
what are the mechanical properties of trabecular/spongey bone?
- difference from cortical due to physical makeup
- compared to cortical bone it is
1) 25-35% less dense
2) 5-10% as stiff
3) 5x as ductile
4) brittle in tension
What effects does age have on bone density?
- increased mineral content (change in quality of bone)
- decreased stress and strain required to reach yield point
- increased sitffness
-less ductility
how does decreased density change bone properties?
- quantity of bone changes
- decreased toughness
- decreased stiffness
- deforms easier
- fractures at lower loads -> compression fractures
What is Wolff’s Law?
- mechanical loads increase bone remodeling
- increase load = increased density
-decreased load = decreased density - strength increases in the direction of loading
What does cartilage do in the body?
facilitate relative movement of articulating bones
- increases contact area
- reduces wear due to decreased friction
- is viscoelastic
what is cartilage composed of?
-75% water, 25% solid
- collagen (strong in tension)
-ground substance (strong in compression)
- tensile/compressive strengths depend on the relative amount of each
