Materials Flashcards
When a material is deformed what happens?
work is done, transferred into the material and stored as elastic potential energy
What is the area under a force extension graph?
elastic potential energy
What happens if plastic deformation occurs?
work done is not stored as elastic potential it is instead used to rearrange atoms into deformation
What is Hooke’s Law?
for a material within its elastic limit, the tensile/ compressive force applied is directly proportional to the extension of the springs or wires
When does Hooke’s stop applying?
when elastic limit is reached
What is force constant?
measure of stiffness within elastic limit
In which way do the tensile forces act?
away from the centre of the spring in both directions
What do tensile forces cause?
extension
What do the forces acting towards the centre of the spring cause?
compression
What does the application of force on a metal wire cause?
permanent extension past elastic limit
What does the application of force on a rubber band cause?
hysteresis loop- energy lost to stretch material
What does the application of force on a polymer cause?
plastic deformation- easily changes shape
How do you test the force constant of springs, rubber bands and polyethene?
suspend material and measure original length then attach mass and measure extension
How do you reduce the errors within the force constant practical?
read levels at eye level and using a set square to make sure the ruler is straight
How do you calculate the spring constant of springs in series?
(1/k1) + (1/k2) + (1/k3)
How do you calculate the spring constant of springs in parallel?
(k1) + (k2) + (k3)
What is the definition of tensile stress?
force applied to a material per unit cross sectional area (force/area)
What is the definition of tensile strain?
extension or compression of a material per unit of its original length (extension/original length)
What is the definition of Young Modulus?
ratio of stress to strain and measure of stiffness (stress/strain)
How do you determine Young Modulus?
- apply various forces to wire to measure extension
- measure diameter with micrometer and calculate area
- clamp wire and suspend taught over pulley measuring extension with a ruler
What deformation occurs when a brittle material is stretched?
no plastic deformation just breakage
What deformation occurs when an elastic material is stretched?
no plastic deformation, just energy used
What deformation occurs when a ductile material is stretched?
elastic deformation until limit of proportionality and then reaches UTS and breaking point
Define ultimate tensile strength:
maximum stress applied to a material before it breaks
