chapter 9 Flashcards
mechanical responses of structures are related to
injury
when external forces imposed are resisted by internal forces it causes
deformation of the body
external applied load: stress
deformation caused: ___
strain
mechanical stress
how an applied force is distributed over the body it acts on
cross-sectional area: the force is the resultant of the
intermolecular bond forces
the cross-sectional area of the imaginary plane is the area over which ____ force is applied
internal
3 principal stresses depending on applied loading
tension, compression, shear
axial stress
external forces act perpendicular to the analysis plane
uniaxial load
external forces are colinear
tensile stress occurs at the _____ as a result of a force or load pulling the molecules apart at that plane
analysis plane
tension causes body to deform by
stretching (elongating)
bone cross-sectional area depends on
plane of analysis
larger cross-sectional area=___stress
lower
smaller cross-sectional area=___stress
higher
cross sectional area: 1cm^2
tensile force applied: 700,000N
what is the max tensile stress
7GPa
compressive stress occurs at the analysis plane as a result of ______ at that plane
a load squeezing the molecules together at that plane
compression causes body to deform by shortening or elongating
shortening
shear stress is a ____ stress
transverse
shear stress acts parallel to____as a result of non-collinear forces sliding molecules at that plane
analysis plane
sprains are in ____
strains are in ____
ligaments/tendons
muscle/cartilage
compression is
bruises of soft tissue, crushing fracture of bone
shear is
blisters on skin, joint dislocation
when external forces are not uniaxial more complex loading occurs as (3)
bending, torsion, combined loads
complexity of loading reflects ___, ___ and ___ of external forces imposed
number, direction and location
bending load
nonaxial
tension and compression produced at the analysis plane from 3 or more forces creating force couples at opposite ends of the object
bending loads cause the body to deform by
curving
torsion load
nonaxial
shear stress acts parallel to the analysis plane as a result of opposing torques applied about the long axis of the body
torsion causes body to deform by
twisting
what resists torsion
tubular and hollow cross-section of bone
combined loading
bones under complex loading from gravity, tendons ligament and other bones, contact forces
sustained loading a combination of
tension, compression, simple shear loads, bending, torsion
strain quantifies the materials ____
deformation
linear strain
change in an objects length
linear strain produced by
tensile or compressive stress
change in orientation of an objects molecules
shear strain
shear strain produced by
shear stress
liner strain deformation by
tensile or compressive stress (change in length)
linear strain reported in ____ terms, describing change in length
absolute
linear strain reported in ____ as proportional length change
relative
unit of linear strain
dimensionless; is a ratio
poissons ratio
width of an object also changes as it lengthens or shortens
poissons ratio range
.1 to .5
stress-strain relationship describes
behavior of material under load
elastic behavior
material deforms and returns to original length when unloaded
plastic behavior
material deforms but doesn’t return to original length
permanent deformation
slope of the stress-strain curve
elastic modulus
stiff material: ___ strain per unit of stress (___ E)
less, large
pliant material: ___ strain per unit of stress (___ E)
more, low
elastic limit
the yield point for a material on the o/e curve
stress above the elastic limit causes
permanent deformatin
example of plastic behavior
ankle sprain; ligaments get stretched and dont hold the bones together as closely as they once did
mechanical strength of a material
max stress a material can withstand before failure
yield strength
stress at the elastic limit
disruption of internal organization
max stress material can withhold
material starts to give away
ultimate strength
stress level where total failure occurs
breakage or complete rupture of materialfailure strength
failure strength
strain exhibited when ____ occurs
total failure
ductile material exhibits a ____ failure strain
large
brittle material
exhibits a low failure strain
deforms minimally before giving away
toughness
ability of a material to absorb energy before failure
are bones or ligaments/tendons tougher
ligaments/tendons
active element of connective tissue
muscle
passive elements of connective tissue
bone, cartilage, ligament, tendon
____ is very stiff while ___ is pliant
collagen, elastin
failure strain of collagen
8-10%
failure strain of elastin up to ___%
160
isotropic
stiffness similar in different directions
stiffness dependent on load direction
ansiotropic
bone: ___% mineral, ____% collagen, ___% water
45, 30-35, 20
strongest and stiffest material in musculoskeletal system
bone
bone strength affected by rate of
loading
cartilage: ___% water, ___%collagen
60-80, 10-30
what cartilage covers bone ends at joints
hyaline (articular) cartilage
fibrous connective tissue specialized in
joints
tendons and ligaments: ___% water, ___%collagen
70, 25
do ligaments or tendons have more elastin
ligaments
what determines muscle stiffness
active component, sarcomere
tendons and ligaments collagen fibers in bindles aligned with
functional axis
