2b.2 Stress, strain and the young modulus Flashcards
what is stress
the proportionate measure of the force on a sample
what is the formula for stress
omega Nm-2 = Force N/area m-2
what is stress measured in
Nm-2 or pascal (pa) is the same unit as pressure
what is strain
the proportionate measure of the extension or (compression) on a sample
what does stain = to
extension (m) /oringnal length (m)
what is young modulus
it is the measure of the stiffness of a constant
what is young modulus = to
tensile stress/tensile strain
what is young modulus measured in
Nm-2 or pa
from a stress-strain graph, how can we tell if an object is flexible or not
if an object as a low gradient it is more flexible
what is the similarities and difference between f=ke and E = omega/strain
similarities:
1. both the k and E measure the stiffness of an object
2. they both apply within the limit of proportionality (when the material is obeying Hooke’s law)
Differences:
1. k applies to a specific object and depended on the dimensions of that object
2. E applies to materials and it doesn’t depend on the dimensions of that object
3. E is measured in pa and k is measured in Nm-1
what are strain and stress graphs
Stress-strain graphs have the same shape as force-extension ones
They are preferable to force-extensions graphs as stress and strain are properties of the material and so do not depend on the dimensions of the sample
Thus, these graphs can provide an ideal format to compare the relative properties of materials rather than objects.
what is ultimate tensile stress
is the maximum stress a material can ithstand before fracturing.
describe the 3 points that happen in the stress x strain graph
point p is the limit of proportionality, now the material still behaves elastically but it can not increase proportionally anymore
point E is the elastic limit beyond that point the material won’t return to its original shape even when the stress is removed
point Y the yield point, where the material undergoes a sudden increase in extension as its atomic structure is significantly re-organised as the atoms in the material would slip past each other to new potions where stress is reduced
point UTS or ultimate tensile stress which is the highest stress within the material
point fs is the fracture stress, it is the value of stress the material would have when it breaks
