3.4 Materials Flashcards
what is tensile force
forces that produce extension
what is a compressive force
forces that shorten an object
state Hooke’s law
the force of a load on a material is proportional to its extension provided the proportion limit is not exceeded
what equation relates the force applied to a spring and its extension
F=kx
springs in series and parallel
series: 1/Ktot= 1/K1 +1/K2 +…
parallel: Ktot= k1+k2+…
what does the spring constant (force constant) tell you about the spring
its a measure of the stiffness of the spring
explain what elastic limit means
if E is exceeded then material will not revert back to its original shape and size when the load is removed
explain what plastic deformation means
permanent structural changes to the spring occur and it does not return to its original length when the force is removed
how can you determine the elastic potential energy stored in a stretched elastic material from the force-extension graph
the area under the graph
state two equations that can be used to calculate elastic potential energy
E=1/2Fx
E=1/2kx2
How is Epe related to the extension
E is directly proportional to extension2
If you double the extension of the spring, what happens to the energy stored
The energy stored quadruples
What is a hysteresis loop
The loop formed by the loading and unloading curves (rubber band)
Describe the molecular structure of a rubber band
Rubber consists of squashed and tangled long-chain molecules
Define tensile stress
The force applied per unit cross sectional area of the wire
State the equation for tensile stress
tensile stress= force/ cross sectional area (σ=F/A)
What are the units of tensile stress
Pascals Pa
Define tensile strain
Fractional change in the original length of the wire
State the equation for tensile strain
Tensile strain= extension/original length (ε=x/L0)
What are the units of tensile strain
Ratio or % so no unit
What is meant by ‘ultimate tensile strength’
The maximum stress that a material can withstand when being stretched before it breaks
Define Young’s modulus in words
Ratio of stress and strain
State the equation for Young’s modulus
Young’s modulus= stress/ strain E=σ/ε
What are the units for Young’s modulus
Nm-2 or Pa
What is a polymeric material
a material that is composed of many monomers (from 10s to 1000s) all linked together to form chains.
What is meant by the limit of proportionality
The region where the material obeys Hooke’s law
What is a yield point on a stress-strain graph
Y1 and Y2 are lower and upper yield points- where the material extends rapidly
What is the difference between ultimate tensile strength and breaking strength
UTS is the maximum stress that a material can withstand when being stretched before it breaks
Breaking strength is the stress value at the point of fracture of the material
What is a ductile material
A material that can be easily drawn into a wire or hammered into a thin sheet
What is a strong material
A material with a high ultimate tensile strength
