Materials Flashcards
(21 cards)
Density of water
1g per cm^3 (1gcm^-3)
Define Hookes law
The extension is directly proportional to the force applied up to the lim it of proportionality
On a force extension graph, what is the gradient and what is the point called after it becomes linear
Gradient = spring constant
Point = Elastic limit (Hookes law only works before this point)
For a springs in parallel, explain principles
Force is split between the two springs
Extension is the same for both springs
Force = F1 + F2 (K1L1+K2L2)
Keff = K1 = K2
Energy is conserved when stretching
For springs in series, explain principles
Forces in spring is the same
Total extension = L1 + L2
Keff = (1/K1 + 1/K2)^-1
Explain elastic deformation
Material can return to its original shape after force
Atoms are pulled apart but can move small distances whilst still in equilibrium
They then return to original positions
Only happens when below elastic limit
Explain plastic deformation
Material is permanently stretched
Atoms move apart and can’t move back
Only happens after elastic limit
Explain brittle
A material that fractures with little elastic deformation and no (little) plastic deformation
Explain stiff
The extent to which an object resists deformation in response to an applied force (ratio of force to extension)
Explain strong
Can take a lot of force before breaking
Explain tough
Resists failure, after deformation (amount of energy before breaking)
Explain malleable
Can be moulded by force
Explain hardness
Can resist surface abrasions (scratches)
Explain endurance
Can withstand repeated stress cycles
Explain ductile
Able to plastically deform without breaking along its length
What is meant by breaking stress
Stress big enough to break a material
What is meant by ultimate tensile stress
Maximum stres a material can withstand
On a force extension graph, what does the area under the graph represent
Elastic strain energy
Explain a practical for Youngs Modulus
Setup: Wire, marker, pulley, weight, ruler
Method; Measure diameter of wire, 3x find average and find cross sectional area.
Measure length of wire from fixed end to marker
Add weights 100g per time and measure extension
Plot a graph of stress against strain
Line of best fit, gradient = E
On a stress strain graph, name the 2 main points
Limit of proportionality (Until it stops being linear)
Yield point - material starts to stretch (stress at which plastic deformation takes place)
Why doesn’t an unloading line on a stress strain graph doesn’t go through the origin
Material has plastically deformed (parallel to loading line)
