Exam 1 - Biomechanics

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Terms in this set (...)

Hardness
Resistance of a material to scratching, wear or penetration
Anisotrophy
Dependent on orientation
Heterogeneity
non-uniformity
Viscoelasticity
Viscious: The geleatinous property of tissue, refers to a materials ability to dampen the imposed load

Elastic is the recoil property of tissue
Linear elastic materials
Normal stress is function of normal strain

Time independent behavior

Deforms instantaneously and restore instantaneously

Repeatable
Viscoelastic materials
Stress is a function of strain and strain rate

Time dependent behavior

Gradual deformation and recovery

History dependent
Hysteresis
Differs between loading and unloading

Area between the two lines on the curve

Go up on line during loading, go down the other line during unloading
Strain rate sensitivity
Curve shifts under different conditions of the load

Ex) increasing load rate - slope gets steeper and steeper, curve is more vertical
Creep
Constant applied stress

Time dependent strain state

Describes progressive strain on a material when exposed to a constant load over time
Stress relaxation
Constant applied strain

Time dependent stress state
Fatigue
Repeated loading below ultimate stress
Endurance limit
Stress at which infinite cycles does not damage tissue

*Above this failure(micro damage) can occur due to repeated loading
forces acting on a joint: (3)
Displace structures

Are transmitted

Deform structures
Load:
A force applied to a material
Deformation
The change in length or shape of a material due to an applied load
Relationship between Force and displacement
Stiffness
Poisson Ratio
Lateral strain/axial strain
Tension
A force tending to stretch or pull apart
Compression
A force tending to push or press together
Bending
Combination type of deformation due to loading of a structure; one part of a structure experiences a tensile effect, and another part a compressive effect
Shear
A force applied parallel to plane or surface within an object
Torsion
Force tending to twist a body
Axial load
A force applied parallel to the long axis of a bone structure
Stress
Internal reaction to the deforming action of an outside force

Force per unit area over which it acts (N/m2)
Strain
Measure of deformation - normalized

Change in length (dimensions of a body) of a material expressed relative to its original length
Ductility
Characteristic of a material that undergoes considerable plastic deformation before rupture
Brittleness
Absence of any plastic deformation prior to failure
Toughness
Energy expended in deforming a material to failure

Measured by area under both elastic and plastic portion of the stress-strain curve
Bone - Mechanical properties
Nonhomogenous
Anisotrophic
Stiff
Tough -absorb energy and plastically deform without fracturing
Cancellous bone
Made of thin plates in mesh like arrangement
Cortical bone
The shell or cortex and is very dense

Stiffer, stronger, low energy storage
Biomechanics of bone
Anisotrophic: orientation dependent

Rate dependent

Age, density and disuse
Tendons
Withstand unidirectional loads
Ligaments
Resist tensile stress in one direction and smaller stress in other directions
Purpose of Ligaments
Provide joint stability

Load transmission

Limit motion

High tensile forces
Purpose of tendons
Attach muscle to bone

Force transmission

High tensile forces
Biomechanics of ligaments
Orientation

Loading rate

Temperature