11.3- DEFORMATION OF SOLIDS Flashcards
What is needed to stretch or twist or compression a material?
pair of forces
What is the elasticity of a solid material?
it’s ability to regain its shape after it has been deformed or distorted + forces that deformed it have been released
What is deformation that stretches an object?
tensile
What is deformation that compresses an object?
compressive
How are different material tested to see how easily they stretch?
materials held at its upper end + loaded by hanging weights at its lower end
set sq or pointer attached to bottom of weights may be used to measure extension of material, as weight of load increased in steps then decreased to 0
What is the extension of strip of material at each step? (different material tested to see how easily they stretch)
its increase of length from its unloaded length
What is the tension in the material equal to? (different material tested to see how easily they stretch)
the weight
What line on a tension-extension graph does steel give?
straight line in accordance with Hooke’s law
What line on a tension-extension graph does rubber band give?
at first extends easily when it’s stretched
but becomes fully stretched + very difficult to stretch further when it has been lengthened considerably
What line on a tension-extension graph does polythene strip give?
stretched easily after its initial stiffness overcome
but after ‘giving’ easily, it extends little + becomes difficult to stretch
With what apparatus can the extension of a wire under tension be measure using?
Searle’s apparatus
How to use Searle’s apparatus?
micrometre attached to control wire adjusted so spirit level between control + test wire horizontal
when test wire loaded, it extends slightly, causing spirit level to drop to one side
micrometre then readjusted to make spirit level horizontal again
What is the change of the micrometre reading in Searle’s apparatus equal to?
the extension
How can the extension be measure for different values of tension in Searle’s apparatus?
by increasing test weight in steps
Equation for tensile stress?
σ = T/A
T- tension
A- area of cross section
What unit is tensile stress measured in?
pascal (Pa)
Equation for tensile strain?
ε= ∆L/L
∆L- extension
Why does tensile strain not have a unit?
as it’s a ratio
What is the value of stress/strain known as?
Young modulus of material
Equation for Young modulus?
tensile stress/ tensile strain = TL / A∆L
What is the area of a cross section for a wire of uniform diameter d?
A= πd^2/4
What is the yield point of the graph?
where the wire weakens temporarily
What is the elastic limit on the graph?
point beyond which wire permanently stretched + suffers plastic deformation
Beyond Y2 on the graph what happens?
small increase in tensile stress causes large increase in tensile strain
Why does a small increase in tensile stress causes large increase in tensile strain beyond Y2 on graph?
as material of wire undergoes plastic flow
What happens beyond maximum tensile stress on wire?
ultimate tensile stress (UTS), wire loses its strength, extends + becomes narrower as its weakest point
Why does the tensile stress occur- graph?
due to reduced area of cross section at this point until wire breaks at point B
What is the ultimate tensile stress sometimes called?
breaking stress
How can the stiffness of different materials be compared?
using gradient of stress-strain line which is equal to Young modulus of material
What is the strength of a material?
its ultimate tensile stress (UTS)
What is the ultimate tensile stress (UTS)?
its maximum tensile stress
What does a brittle material do?
snaps without any noticeable yield
What can be done to a ductile material?
can be drawn into a wire
