Tissue Mechanics Flashcards
what is mechanical stress?
the internal force divided by the cross-sectional area of the surface on which the internal forces act
How is mechanical stress calculated?
Internal force divided by cross sectional area of the area on which the internal force is acting on
what is stress?
the force between molecules resisting the molecules being pulled apart
What are the three principle types of stresses?
tensile, compressive, and shear
what is tensile stress
tensile stress is an axial stress (stress changing length of body) that occurs at the analysis plane as a result of a force or load that tends to pull apart the molecules bonding the object together at that plane
*think of someone hanging with a 20lbs weight attached to them, they are experiencing a tensile stress
when a tensile stress is applied, how does the object deform?
when a tensile stress is applied, the body of the object is axially loaded in tension and the object tends to deform by stretching/elongating in the direction of the external load
what is a compressive stress
an axial stress (stress that changes length of body) that results when a load tends to push/squash molecules of a material more tightly together at the analysis plane
when a compressive stress is applied, how does it deform the object?
When an object is axially (length changing) loaded in compression, the object tends to deform by shortening in the direction of these external forces
what is a shear stress?
a shear stress is a transverse stress that acts parallel to the analysis plane as a result of forces acting parallel to this plane
what does a shea stress do to the molecules of an onject?
A shear is the result of forces that push ,molecules past eachother - so it would push the molecules past eachother
what is a simple (uniaxial) mechanical load?
It is a load that produces one type of stress that is uniform across the analysis plane
is bending a uniaxial stretss?
NO - it is expericing multiple stypes of stress (both compression and tensile)
why can a larger diamater object withstand greater bending loads?
This is because a larger diameter means is has more cross sectional area - meaning the counteracting tensile and compressive stresses are lower because they have a larger moment arm (because the distance from the axis of rotation to the force is larger)
what is a combined load?
often experienced by bones and cartilage as they can be loaded in a variety of ways, that produce unifom stress to bending and tortion loads producing more complex stress patterns. It is these complex stress patterns that are a combined load
what is mechanical strain
quantification of the deformation of a material
what is linear strain
change in length of a material as a result of tensile or compressive stress
what is shear stran?
a change in orientation of adjacent molecules as a result of these molecules slipping past each other due to shear stress
What is elastic modulus (Young’s modulus)?
the ratio of stress to strain (which is shown graphically as the slope of the strain-stress curve)
what is elastic behaviour?
stretching under tensile load, but returning to its original shape when a load is removed
what is plastic behavior?
when a permanent deformation of the object occurs under a load
what is maximal strength?
the maxium stress (or strain) the material is able to witstand before failure
what is the yield point with regards to material strength?
the point of the stress-strain curve where further stress will cause permanent deformation
what is ultimate strength with regards to material strength
ultimate strength is the maximum stress the material is capable of withstanding
What is failure strength with regards to material strength
stress where failure actually occurs - it corresponds to the endpoint of the stress-strain curve
describe failure strain of ductile materials
large failure strain
describe failure strain of brittle materials
small failure strain
Describe failure stress of hard materials
large failure stress
Describe failure stress of soft materials
small failure stress
what is toughnes?
the ability to absorb energy - the more energy required to break it - the tougher it is.
How can we estimate the toughness of a material?
By calculating the area under the stress-strain curve
