tissue loading - biomechanics

define isotropic materials

same mechanical behavior no matter the direction to which forces are applied

define anisotropic materials

different mechanical behavior depending on size and direction of applied forces

anisotropic materials are ____ (solid and semisolid components)

heterogeneous

musculoskeletal connective tissues are ______ (anisotropic or isotropic)

anisotropic

define load

force applied to a structure

when a force acts on an object, it _____

deforms

simple loads (stresses) to which connective tissues can be subjected result in _____/_____

deformation, strain

tensile stress results in

elongation

compression stress results in

shortening

shear is

force directed parallel to surface

torsional is a ___ force

twisting

bending is ___ and ___

compression, tension

toe region of load deformation curve

crimp straightens (take up slack)

in elastic region of load deformation curve, stretching of ____ fibers takes place

collagen

yield point of load deformation curve

further force application causes deformation that cannot be reversed

ultimate failure point of load deformation curve

rupture (ligament) or fracture (bone)

in elastic region of load deformation curve, increase in load is proportional to increase in ____

deformation

in load deformation curve, a steeper slope means

stiffer/less compliant material

in load deformation curve, a less steep slope means

material more compliant

a load deformation curve represents the ____ properties of something

structural

load deformation curve accounts for _____

size

what does force values on the load deformation curve depend on

structural properties (size of structure)

for structures of the same length:

a structure that has more CSA can withstand ____ force, meaning it is ____

a structure that has less CSA is more _____

more, stiffer

compliant

for structures of same CSA:

a longer structure will deform ____, is more ____

a shorter structure will deform ____, is ____

more, compliant

less, stiffer

stress equation

force/area

stress is a ____ property (independent of size of sample)

material

material property

independent of size of sample

strain is a ___ property

material

strain definition

normalized change in dimension

strain is usually expressed as a ___

percent

stress strain curve represents the ____ properties of a ____

material, tissue

stress strain curve is not influenced by ___ or ____

structure or size

bone would be on ___ curve

femur would be on ___ curve

stress strain, load deformation

what does the slope of stress strain curve represent

young's modulus (rigidity or stiffness)

area under the stress strain curve is

toughness, how much energy a material can take before it breaks

in the plastic region, ____failure occurs

failure of ____ fibers begin (what grades of ligament sprain)

micro, failure of collagen fibers begins (grade I and II ligament sprain)

toe region - ___ force applied produces deformation

minimal

elastic region aka ___ region

linear

ultimate failure point of stress strain curve is ____failure, what grade ligament sprain

macro, grade III

ligaments have ____-____ stiffness, explain this

non linear, laxity at low loads and high stiffness at high loads

ligaments have ___ aligned collagen fascicles

highly

what makes ligament curve non linear

crimp

grade I ligament sprain

pain, no laxity

grade II ligament sprain

some torn fibers, minimal laxity

grade III ligament sprain

completely torn, lots of laxity

ligament sprain/injury is always from

excessive tension

dislocated joints always include

ligament sprain/injury

all connective tissues are _____ materials

viscoelastic

viscoelastic materials have behavior dependent on ___, ___ and ____ of loading

time, rate, history

elastic

ability to return to original shape/length when deforming load is removed

elastic deformation is ____ to applied load and force

proportional

elastic ability depends on ___ and ___ content and organization

collagen, elastin

define viscoelastic

material resistance to fluid flow

high viscosity has high

resistance to deformation

higher viscosity with loads applied more ____

quickly

viscosity tissue response to force is ___ and ___ dependent

rate, time

creep

constant stress, strain changes

stress relaxation

constant strain, stress decreases

creep hamstring example

flex at hips to touch toes

hamstrings stress relaxation example

flexed at fixed distance (such as coffee table)