General Tissue Mechanics Flashcards
(33 cards)
Injury occurs when
an imposed load esceeds the tolerance (load carrying ability) of a tissue
What can change tissue and its tolerance?
Training effects
Drug effects
Equipment design effect
Structural properties
Load-deformation relationships of like tissues
Apply force on a structure and will experience some deformation
Material properties
Stress-strain relationships of different tissues
Normalizing so that we can compare muscle to tendon or bone (different tissue comparisons)
Stress
A force tries to rearrange the molecule in an object –> the internal resistance to an external load
Units = pascal
Push them closer (compressive)
Pull them apart (tensile)
Slide one across the other (shear stress)
Strain
Change in shape or deformation - absolute and relative
comp, tensile, shear
Measured as a proportional change in dimension so no units - is a ratio
Relationship with stress and strain
Stress is what is done to an object and strain is how the object responds
THey are proportional to one another
Stress Strain ratio
Stiffness or compliance of the material
Biologic material - linear?
no - due to viscoeleastic properties
Extensibility and Elasticity
THe ability of a material to resume its original size and shape upon removal of applied loads
No known material is elastic at all stresses
Determination of elastic limit establishes elastic range of limit of elasticity
Bending - long bones
Compressive stress - inner portion
Tensile stress - outer portion
Max stresses near the edges
Less near the neutral axis
Three point bending
Failure at the middle
Four point bending
Failure at the weakest point btw two inside forces
Bending summary
Id a moment is applied to an object –
it will produce bending
The amount of bending depends on the magnitude of the bending moment and on the shape and properties of the object being bent
When an object bends…
one side becomes concave (compress) and the other becomes convex (tensile)
Btw the two sides is an unstressed neutral axis
Torsion
Twisting action applied to a structure
Larger radius of the shaft - greater resistance
Stiffer the material - the harder to deform
Brittleness
absence of any plastic deformation prior to failure
Resilience
Measure of energy absorbed by a material and returned when load is removed; material that quickly return to their original shape are called resilient
Toughness
Property of a material enabling it to endure high impact shock loads; ability to absorb energy during plastic deformation; measure of the capacity of a material to sustain permanent deformation
Unique properties of biologic materials
Anisotropic = not uniform throughout the material Viscoelastic = time dependent, loading rate dependent Organic = self repair, adaptation to changes in mechanical demand
Viscoelasticity
Provided by the fluid component in biological tissue
Resistance to flow
Affects stress/strain
Inc strain rate produces inc stiff of the material
Pure elastic material - viscoelasticity
Not viscoelastic
All energy is returned and no energy is lost
Viscoelastic tissues
Loss energy due to heat, energy is not returened immediately
Hysteresis
area reperesneting the energy that was lost
