6 Materials Flashcards
Name the two spring forces?
Tensile forces - producing an extension
Compression forces - producing a compression
What regions are Hooke’s Law true?
Until the limit of proportionality - elastic limit of the material
State Hooke’s Law
The extension of the spring is directly proportional to the force applied - as long as the elastic limit of the spring is not exceeded.
What does the force constant measure?
F∝𝑥
Measure of stiffness of the spring
gradient of a force against extension graph
What is elastic and plastic deformation?
Elastic deformation means that the spring will return to its original length when the force is removed. Plastic deformation means that it doesn’t go back to its original length.
Formula for elastic potential energy
E= area under graph
E=1/2F𝑥
work done = average force x final extension
Doubling extension does what to energy stored?
E=1/2k𝑥^2
Quadruples the energy stored.
What happens to the length of a 1cm spring if put in series with another
Both have a 1cm extension
What happens to the length of a 1cm spring if put in parallel with another
Shared the extension, both have 0.5cm extension
Area of a force extension graph?
Work done (elastic potential energy)
Difference between loading and unloading? Area of graph
Thermal energy
Loading is adding a force, unloading is removing a force.
What does a hysteresis loop do/look like?
Elastic/ rubber graph of force against extension. Doesn’t have an elastic limit. Return to original shape after force removed - elastic deformation.
Theory behind warming up rubber
Rubber consists of squashed and tangled long-chain molecules. Untangled easily with small forces, but need large forces to extend fully. Rubber is poor at storing energy - ideal material for impact forces.
What does the force-extension graph look like for a metal?
loading=unloading until the elastic limit.
What does the force-extension graph look like for a polythene?
Doesn’t follow Hooke’s Law - not straight proportional. Suffer plastic deformation with little force.
Define tensile stress
Force applied per unit cross-sectional area of the wire.
Define tensile strain
Fractional change in the original length of the wire
Equation for tensile stress and strain
stress - σ=F/A
strain - ε= 𝑥/L
Stress-Strain graph: Define P, E, Y1 and Y2, UTS, B
P - limit of proportionality
E - elastic limit (plastic deformation after this)
Y1 and Y2 - yield points, material extends rapidly with little stress.
UTS - ultimate tensile strength, maximum stress before it breaks.
B - breaking point, stress value at point of fracture.
Define Young modulus
stress ∝ strain
gradient of the linear region of the stress-strain graph
measure of the ability of a material to withstand changes in length when under tension or compression.
What is work hardening a material
Getting the material to the Y2 point on the graph for predictable use in structures.
Define necking of a material
When the decreasing area increases the stress of the material after the point of Ultimate Tensile Strength
What is Ultimate Tensile Stress equal to?
The stress value at that point - the force in σ=F/A.
