Tissue Loading

(cont...) Frequency of Loading

Fatigability - Measure of the weakening of tissue subject to repetitive loading (how tired a tissue gets) -do it over and over--eventually it will fail

Stiffness

Relationship between stress and strain (slope) -doesn't deform a lot -curve will be less steep -steeper slope = stiffer

Elasticity

The ability to reform after a stress has been applied -where the failure point is -deform a lot - give a lot of energy

Strength

the amount of load that a tissue can withstand -stronger: where it is on the load side of the curve -how high it is on the load axis

3 types of loading

-compression: smashing something down (shorter & fatter) -tension: pull at each end (longer & thinner) -shear: one side going in one direction and the other side going in another direction (friction btwn too surfaces)

Stress/Strain Curve

-how much load and how much deformation -amount of energy released by system represented by area underneath the curve -load enough - fail; area under curve all energy released (tear something in body, makes sounds) -Strain energy: amount of energy that is released to a system when you take the load off or it fails (area under curve) -can draw for ever tissue in body -what matters: type of movement, range of motion (determines direction)

Factors that Determine Mechanical Behavior

-structure: determine how it responds when loaded -Geometric Characteristics -->Tissues are anisotropic: property varies with direction of the load *tissue changes to direction of load; respond differently; designd to be loaded in a particular direction will fail otherwise; related to the structure *bone strongest under compression determined by direction *ligament & tendon strongest under tension -Mode of Loading: how it's loaded (load type) -Rate of Loading: ↑ Stiff when ↑Rate (load quickly; no time to deform) *get stiff, then break--how injury occurs *load slow--stretch

combinations

-torsion: twist along an axis; rotational shear -3 pt bending: push down on sides and push up in middle (compression & tension)