The amount of force on an object
Load
Load divided by the cross sectional area
Stress
Ex: stepping on a foot in flat shoes vs high heels
A change in length in response to a a load
Deformation
The amount of deformation - change in length divided by the original length
Strain
Shear strain is the angle of deformation expressed in _____
Radians
The ability of a substance or material to return to its original form following the removal of a deforming load With no loss of energy.
Elasticity
The property of a material to permanently deform if loaded beyond its elastic range - original form is lost and material energy is lost.
Plasticity
A measure of resistance offered to external loads by a material as it deforms.
Stiffness = the amount of stress (load)/the amount of strain (deformation)
A stiffer material needs _____ stress to
deform
MORE
A measure of compliance offered to external loads by a material as it deforms.
Flexibility = the amount of strain (deformation)/the amount of stress (load)
A flexible material needs _______ stress to
deform
LESS
The quality whereby a material exhibits little plastic deformation before FAILURE.
Brittleness
FAILURE < 5% total elongation of
material
The quality whereby a material exhibits large plastic deformation before FAILURE.
Ductility
FAILURE > 5% total elongation of
material
The property of a material that links how it will deform to how the load is applied.
Viscoelasticity
A viscoelastic material will deform differently depending on what (4) properties of loading?
- rate of loading
- speed
- quantity
- duration
How does the term stiffness differ when used in biomechanical terms vs. rheumatologic terms?
Biomechanical stiffness can be good (bones are stiff and spinal stiffness = stability)
Rheumatologic stiffness is a symptom that suggests inflammation
Material can respond in a variety of characteristic ways
- creep
- relaxation
- hysteresis
- fatigue
- damping
- thixotropy
A deformation of a viscoelastic material
with time, when the load remains constant.
Creep
Ex: Disc loss of height during the day. (Creep is
much faster with a degenerated disc.)
Ex: shortening of muscles (hip flexors) with prolonged sitting
Tissue adapting to newl unethical such that a decrease of load over time is required to maintain a fixed deformation.
Relaxation
Ex: Force needed to hold down the branch of a
tree decreases over time
Loss of energy during a loading cycle, despite returning to its original form.
Hysteresis
The process of plastic deformation or failure of a material from repeated loading.
Fatigue
Ex: Bending a paper clip repeatedly until failure.
Resistance to speed, i.e. the faster the loading, the greater the load
necessary to deform an object a given amount.
Damping
Ex: Disc compression: Slow loading causes fluid to come out,
squishes or deflates. Fast loading - fluid can’t come out, good shock
absorber
The reduction in the viscosity of a fluid
following movements
Thixotropy
Ex: ketchup, synovial fluid, muscles
The turnover of collagen is accelerated when?
- in young/growing
- in injured tissue
- in immobilized tissue
