Biomechanics Exam One Flashcards
Stress (σ)
Force applied to an area
Measured in N/m^2 or pascals
σ = F/A
Strain (ε)
Deformation caused by applied stress
Tension
the act or action of stretching
Compression
the state of being compressed
Shear
unaligned forces acting on one part of a body in a specific direction, and another part of the body in the opposite direction.
Torsion
the twisting of an object due to an applied torque.
Bending
to turn or force from straight or even to curved or angular.
Stress/Strain Curve
Slope is Young’s Modulus/Stiffness
Elastic region which can go back to how the object was once stress is removed
After elastic region is yield point before plastic region
Plastic region is permanent deformation
After the plastic region the specimen fails
a type of test where a load is continuously applied to a test specimen until it fractures
Young’s modulus
Stiffness for material
Y=σ/ε=F/A=L/ ∆L
Residual Strain
Difference between original length and length resulting from stress into the plastic region
Stiffness
Resistance to deformation
Strength
Resistance to failure
expressed as force required to produce:
a permanent deformation: yield strength
a fracture: fracture strength
Metal vs glass
Metal: ductile-large plastic region
Glass: brittle-fracture and yield at the same time
Elastic material
Linear between stress and strain
Mechanical energy is fully recovered (provided it stays in elastic region)
Viscoelastic
Same definitions for elastic materials apply
Exhibits non-linear stress strain characteristics
Ex. Bone. Has these characteristics because of the liquid in bone
Hysteris
Loss of energy into the material and time dependent delay
Stress relaxation
Time dependent decrease in load or force or stress required to maintain a constant deformation
The deformation is temporary until the stress is removed
Creep
Time dependent increase in deformation while under constant load/force/stress
Bone tissue
connective tissue
short bones
square, triangular shape
Flat bones
flat
scapula, skull
irregular bones
irregular in shape
Long bones
has one dimension longer than another dimension
facet
small, smooth area
foramen
a hole in a bone
For blood vessels/nerves to attach to it
Condyle
rounded process
Articulates with other bone to form a joint
Fossa
A large smooth area
Process
Bony promiscue
Does not have clearly distinct role
Tuberosity
Like a process but has a very specific process
Regions of long bone
Diaphysis
Metaphysis
diaphysis
shaft of long bone
ends are epiphysis
metaphysis
two areas in-between diaphysis and the epiphysis
Compact bone
hallow center
is arranged in units called osteons
osteons
are aligned by lines of stress
not cells! Units!
periosteum
outside layer of bone
dense irregular CT
what is the compact bone made out of
osteons
Is the periosteum
endosteum
inner most layer of bone
central canal
space in center of osteons
space for blood vessels and nerves
what is the primary stress for bones?
Compressive stress
concentric lamellae
rings around central canal
Lucnae (lucuna is one)
one type of bone cell resides
Canaliculi
connects lucnae to allow communication between cells
Histology of bone
20% water
30% collagen fibers
50% mineral salts –> calcium phosphate
spongy bone or cancellous bone or trabecular bone tissue
consists of red and yellow bone marrow
osteocytes get nutrients directly from circulating blood
osteocytes
bone cell
retired
maintain and no other role
before retirement they are osteoblasts
osteoblasts
produce collagen fibers
osteogenic
mitotically active
help make more cells
osteoclast
break down bone
could be for nutrition
ex. If there is low Ca2+ in the blood, the body will break down bone tissue in order for the heart to function
How does bone ocify?
Bone oficies from middle to ends
replaces cartilage to bone
Wolff’s law
shape of bone reflects its function
Bone is laid down where needed and reabsorbed where not needed
Regular exercise provides stimulation to maintain bone throughout the body
Which bone is more adaptive, trabecular or cortical?
Trabecular because it is less stiff than cortical bone
Cortical bone is more stiff than trabecular
Cortical does well under compression dur to gravity
Viscoelastic load vs deformation graph
A fast, higher load is going to cause more deformation and when it fails will have a bad fracture
A slow, lower load is going to make a stress fracture and it will be tiny in comparison with the fast, higher load
What forces are involved with bending?
compression, tension, shear
Compression forces
necessary force for proper development
Stiffness of bone resists compression
excessive compression force can lead to compression fractures
Tensile loading rate
Main source is muscle contraction
Avulsion fracture
occurs when a ligament or other soft tissue attachment to bone overcomes the stress capacity of the bony attachment and tears off a portion of the bone.
Osgood-Schlatter’s
pulling of the patellar tendon away from its insertion point on the tibial tuberosity
When tendon is pulled it can cause mini fractures around the tibial tuberosity
an overuse condition or injury of the knee that causes a painful bump and swelling on the shinbone below the knee
Typically affects growing kids
anisotropic
Properties depend on direction
exhibiting properties with different values when measured in different directions
Bone is strongest and stiffest in the direction that bears the most load, while keeping bone mass low.
Bone’s elastic deformation is anisotropic, meaning it’s different when measured parallel to the bone’s long axis, and when measured perpendicular to it.
Trabecular bone’s orientation can change depending on mechanical load, and it can become anisotropic.
