Mechanics of materials Flashcards
define stress
intensity of the force
- how much of the force is distributed over a given area
what is axial / normal stress
component of force perpendicular to the area of interest
- can be compressive (-) or tensile (+)
what is shear stress
component of force parallel to the area of interest
during stress on an inclined plane, how far apart are the max and min normal stresses
always 90deg apart
during stress on an inclined plane, where will max shear stress occur
45deg between max and min normal stress
what are the principal stresses
max and min normal stresses
define strain
change in length divided by the original length
- can be compressive or tensile
what is the difference between the axial and shear components of strain
axial - want to change the size of the object
shear - want to change the shape of the object
what is poissons ratio
ratio of transverse to axial strain
- material loaded in one direction will undergo strains both parallel and perpendicular to the direction of load
what is hooke’s law
linear relationship between stress and strain
what does the elastic / youngs modulus depend on
bonding types between atoms and molecules
what is yield strength
stress at which the material will no longer go back to its original shape when unloaded
- deviates from linear because the material is being damaged (bonds being broken)
what is ultimate strength
max stress a material can withstand before failure
what occurs at the point of failure
material fractures or ruptures (unable to withstand or carry any load)
- can be lower than the ultimate strength in a tougher material
what is the difference between toughness and strength
stronger material = can experience more stress
tougher material = can experience more deformation and still carry load after yield prior to failure
what is toughness
area under the stress strain curve
- total energy a material can absorb prior to failure
- broken into elastic and plastic components
what are material properties
calculated from stress strain curve
independent from structure (don’t depend on size and shape)
what are structural properties
calculated from area under force displacement curve
are material properties specific to loading mode
yes - often don’t behave the same in compression, tension, and shear
what are the three different types of materials
isotropic
tranversely isotropic (anisotropic)
orthotropic (anisotropic)
what is an isotropic material
doesn’t exist in biomechanics
material properties are independent of loading direction
(always behaves the same)
what is a tranversely isotropic material
one direction has material properties different from the other
two directions behave similarily
ex = cortical bone (due to longitudinal osteons) and tendons (direction of fibres)
what is an orthotropic material
material properties are different about every axis
behaves differently in every loading direction
ex = trabecular bone and cartilage
what is elastic deformation
when the stress applied is < or = to the yield strength
- deformation will be completely recovered when the load is removed
what is plastic deformation
when stress applied is beyond the yield strength
- deformation is permanent
