3.4.2 Materials Flashcards
What is the formula for density and what are the units?
Density (kgm-3) = Mass (kg) / Volume (m3)
What is 1cm in ml?
1cm=1ml
What is 1ml in cm?
1ml=1cm
What is an alloy?
An alloy is a mixture of two or more metals
How do you work out the volume of a irregular solid?
Submerge it in water and the increase in level is equivalent to it’s volume
How do you work out the mass of a liquid?
The measurement of the mass of the liquid and container minus the mass of the same but empty container
What is 1kg equal to in g?
1kg=1000g
What is 1000g equal to kg?
1000g=1kg
What is 1m3 equal to in cm3?
1m3=10 power of 6 cm3
What is 10 to the power of 6cm3 equal to in m3 ?
10 power of 6 cm3=1m3
What is F=ke
Force = spring constant * extension
F k e
What is Hooke’s Law?
Hooke’s Law is the force applied to a body is proportional to the extension that it experiences up to the elastic limit (limit of proportionality)
When does Hooke’s Law only apply?
Hooke’s law only applies within the elastic region of a material (before the force permanently deforms it)
What does F∝e mean?
Force is directly proportional to the extension
F∝e
What are the 4 types of forces?
- Tensile
- Compressive
- Shear force
- Torsional force
When in a series, what is the spring constant?
In a series, the spring constant is less that that of 1 spring
1/k1 + 1/k2 = 1/kseries
When in a parallel, what is a spring constant?
When in a parallel, the spring constant is more than that of 1 spring
k1 + k2 = kparallel
What is elasticity?
Elasticity is the ability of an object to resume to its original shape after it has been deformed or distorted and the forces that deformed it has been released
What is plasticity?
Plasticity is being able to be shaped easily
What is the elastic limit?
The elastic limit is the maximum extent to which an object can be stretched without permanent alteration and will return to its original dimension after the applied stress is removed
What is stiffness?
Stiffness is the extent to which an object resists deformation in response to an applied force
What is ductility?
Ductility is when a solid object stretches under tensile stress
What is brittleness?
Brittleness is when subjected to stress, a material breaks without significant plastic deformation
What is the plastic region?
Plastic region is when an applied stress is so great, the material is unable to return to it’s original dimensions therefore it is permanently deformed
What are materials with no plastic region often?
Materials with no plastic region are often very brittle
What is mechanical stress?
Mechanical stress is when a stress applied to a material depends not only on the force applied but also the area to which it is applied - pressure felt by material
What is the symbol for stress?
σ
What is the equation for stress?
Stress(σ) = Force (F) / Area (A)
Nm-2 N m2
What is Ultimate Tensile Stress (UTS)?
Ultimate Tensile Strength is the maximum value of stress that a material can withstand and occurs at the breaking point
What occurs to brittle materials during Ultimate Tensile Stress?
Brittle materials fracture under Ultimate Tensile Stress
Why do brittle materials fracture under Ultimate Tensile Stress?
Brittle materials fracture due to cracks rapidly spreading throughout the material
What happens to ductile materials under Ultimate Tensile Stress before fracturing?
Ductile material tend to ‘waist’/’neck’ before fracturing
After fracturing, what do ductile materials look have?
Upon fracturing, ductile materials have a cup and cone fracture
What is mechanical strain?
Mechanical strain is the measure of the effect an applied stress has had on a material
What is the symbol for strain?
ε
What is the equation for strain?
Strain (ε) = extension (e) / original length (l)
Where is the force and extension on Force-extension graphs?(Hooke’s Law)
Y axis - Force (F)
X axis - extension (e)
Where is the Stress and Strain on Stress-Strain graphs?
Y axis - Stress(σ)
X axis - Strain(ε)
Describe what occurs to a brittle material on a Stress-Strain graph?
- Has a elastic region but no plastic region
- Once reaches Elastic limit and limit of Hooke’s law, it reaches Ultimate Tensile Stress and has its breaking point
- Material snaps without any noticeable yield
Describe what happens to a ductile material (copper) on a Stress-Strain diagram?
- Elastic region
- Elastic Limit and limit of Hooke’s law
- Plastic region
- Ultimate Tensile Stress and Breaking point
Describe what happens
- Elastic region
- limit of Hooke’s law
- Elastic limit
- Plastic region
- Yield point
- Ultimate Tensile Stress
- Breaking point, extends while it snaps
What is Young’s Modulus?
A constant of proportionality which takes into account the dimensions of a materials properties and is hence a material property
What is Young’s Modulus measured in?
Nm-2
What is Young’s Modulus equal to?
E = Stress/Strain
What is energy stored in stretched wires?
When a wire extends, a force does work causing it to extend. The work done on the wire is stored in it as potential energy and it is this energy which allows it to spring back once the load is removed
Why do springs have the ability to ‘spring back’?
When a wire extends, work is done causing it to extend. The work done is stored as potential energy which allows it to spring back once the load is removed
What is energy stored equal to?
Energy stored = 1/2 Force * extension
area underneath a Force-extension graph
What occurs when a material is taken beyond it’s elastic limit?
Slip occurs between atomic layers when a material is taken beyond it’s elastic limit. Movement caused by friction between layers causes the material to internally heat up, so some of the energy is lost as heat. The energy stored is less than the work done so the molecules cannot return to it’s original shape.
In a force-extension graph, what is the total work done on a material that is take beyond it’s elastic region?
The total work done is when the work done by the spring is less than the work done by the load
What is strain energy?
The energy stored is sometimes known as strain energy expressed as strain energy per unit volume
What are the equations for strain energy per unit volume?
1/2 Fe/V
1/2 Fe/Al
1/2 σ*ε
What is an equation for Young’s Modulus?
E = Fl/eA
What is an example of a perfectly plastic material?
Plasticine
What are examples of materials with no plastic region?
Glass, Cast iron, Nylon
How is spring energy transformed to kinetic and gravitational potential energy?
Elastic potential energy is stored in a stretched spring. If the spring is released, the elastic energy is transferred into kinetic energy
How to increase the tension of a material?
Increase the weight the material supports to increase the tension of a material
What is plastic deformation?
Permanent deformation occurs in a material so it cannot return to it’s original shape, beyond elastic limit
What is the unit for the spring constant (K)?
Nm-1
What is density?
The density of a substance is defined as it’s mass per unit volume
What is tensile stress?
Force per unit of cross-sectional area
What is tensile strain?
Extension per original length
How do you work out the density of an alloy?
- Work out mass of each metal
- Work out total mass
The bigger the spring constant in a spring?
The greater the value of K (spring constant), the stiffer the spring is
What is tension in a spring being stretched?
Tension in a spring is equal and opposite to the force needed to stretch the spring
What happens during and after the yield point of a ductile material (mild steel) being stretched on a Stress-Strain diagram?
- The material weakens temporarily
- A small increase in tensile stress causes a large increase in tensile strain
- Beyond maximum ultimate tensile stress, the material loses strength, extends and becomes narrower at its weakest point
- Increase of tensile stress occurs due to reduced area
- Breaking point, extends while it snaps
What is the ultimate tensile stress also sometimes known as?
Ultimate tensile stress sometimes called the breaking stress
On a stress- strain graph, what does a steeper gradient represent?
On a stress- strain graph, the steeper the gradient, the stiffer the material
What is a permanent extension?
- Sign of plastic deformation
- Material no longer returns to original shape
In a metal wire (spring), how is loading compared to unloading curve while in elastic limit?
Loading curve = Unloading curve
Metal wire (spring) while in elastic limit
In a metal wire (spring), how is loading compared to unloading curve beyond the elastic limit?
Unloading curve parallel to Loading curve
Metal wire (spring) beyond the elastic limit
In a rubber, how is loading compared to the unloading curve?
Change in extension in unloading more than loading for a given tension
- Loading curve less except at 0 and maximum extension
(Rubber)
In polythene, how is loading compared to the unloading curve?
Change in extension in unloading more than loading
- Low limit of proportionality
- Plastic deformation
