biomechanics- stress/strain

compression load

- a pressing or squeezing force - seen in bones and fibrocartilage

failure (in stress-strain curve)

- point at which stress leads material to fail (break/tear/rupture) -stress quickly falls to zero

plastic region

-curve past yield point -material is permanently deformed in this region (if stress removed, material will not return to original state)

strain

-deformation of materials in response to stress -resulting deformation of tissues caused by applied stress (%) -strain =change in length/ initial length = ((Lf-Li)/Li)x100

Elastic region of stress-strain curve

-linear portion of curve -if stress is removed in this region, the material is able to return to its original state (not deformed)

bending load

-opposite ends loaded in same direction -compressive stress on one side -tensile stress on the other side

stress

-pressure or tension exerted on a material object -force applied to deform a structure per unit area (N/m^2 or Pascal (Pa)) -internal resistance to deformation that occurs inside the tissue -stress=force/area=F/A

Elastic Modulus (Young's Modulus)

-slope of elastic region (change in stress/change in strain) - measure of a material's intrinsic ability to resist deformation -"stiffness" of a material

hysteresis

Energy loss during loading and unloading energy converted (heat) when material deforms energy dissipation (the area in b/w the 2 lines of the graph)

How does temperature affect the stress-strain curve?

It moves the curve to the right creep property if tissue is warmed

toughness

Mechanical property of a material that indicates the ability of the material to handle overloading before it fractures.

resilience

ability to absorb forces in the elastic range and return to original shape

deformation

change in length or structure of a material

cartilage is made by

chondrocytes

fibrous connective tissue is made up of....

collagen elastin

residual strain

difference between original length and length resulting from stress into the plastic region (the line b/w O and D)

load

external force applied to a material or tissue

loading rate-dependent

faster rate of loading the tissue = greater resistance to deformation

collagen is made by

fibroblasts

non-fibrous connective tissue is made up of.... (aka "ground substance" / extracellular matrix)

glycoproteins (water + proteoglycans) water solutes

isotropic behavior

material properties are the same regardless of the direction force is applied

anisotropic behavior

material properties differ depending on direction force is applied (stress stain curve looks different depending on load orientation) ex) bone

viscoelastic properties

non-linear relationship between stress and strain includes: creep, stress relaxation, hysteresis, rate-dependent loading, isotropic/anisotropic behavior

bone is made by

osteoblasts

yield point of stress-strain curve

point where slope eventually decreases as greater force is applied (transition point from elastic region to plastic region)

stress relaxation

time dependent decrease in stress over time that occurs under constant strain ( if a tissue is stretched to a fixed length, over time the force to maintain that fixed length decreases e.g. a long static stretch or yoga)

creep

time-dependent permanent deformation that occurs under constant stress strain reaches a maximum higher loads and temperatures increase the effect

torsion load

twisting Occurs when torques act about the long axis of the object at each end

shear load

two forces acting parallel to each other but in opposite directions so that one part of the object is moved or displaced relative to another part

tension load

two forces pull on an object in opposite directions