Materials Goodnotes Recap Flashcards
Density?
How much space an objects mass occupies otherwise the mass per unit volume of a material
Density and Power?
The relationship between these 2 values is they both have the same SI units of kgm-3
Density Equation?
p = m / v
Density = Mass / Volume
Float Conditions?
For an object to float on a fluid it has to have an average density lower than the density of the fluid it is attempting to float on.
Water Density?
Water has a density of 1.00 gcm-3 at room temperature. This means at room temperature 1cm3 will have a mass of 1g to achieve this density
Density factors?
Density depends on what an object is made of not its size or shape
Hooke’s Law Discovery?
Discovered in 1676 by Robert Hooke. This was identified if a weight is attached to a wire it will cause it to stretch. The weight pulls down. It then achieves equilibrium at the support where the weight is attached
Hooke’s Law Definition?
The extension of a stretched wire is proportional to the load otherwise force exerted upon it
“K”?
K in Hooke’s Law is the stiffness constant and this depends on the object being stretched
Hooke’s Law Equation?
F = k∆L
Force= Stiffness Constant x Extension
Metal Spring and Hooke’s Law?
A metal spring also changes in length with a pair of opposite forces applied to it. The extension otherwise compression has to be proportional to force applied to obey Hooke’s Law
Metal Spring and Hooke’s Law formula?
The “k” in the Hooke’s Law formula instead of being referred to as stiffness constant it is instead called a springs stiffness or spring constant
Hooke’s Law and Compressive Forces?
Hooke’s Law can be applied to a compressive force as well as a tensile force. “k” has the same value whether it’s a tensile or compressive force. Not all objects and springs are able to compress
Hooke’s Law on Force-Extension Graph?
Hooke’s law being obeyed is where a proportional relationship cutting through the origin is present
Stiffness Constant on Force-Extension Graph?
The gradient of the straight line part of a force-extension graph is the stiffness constant
Limit of Proportionality on force-extension graphs?
Where force exceeds extension causing an end to the straight line relationship and causing the gradient of the force-extension graph to curve
Elastic Limit on force-extension graph?
The point at which an object cannot return to its original shape, the origin, and is permanently deformed after the force is applied and removed on a force-extension graph
Elastic Limit?
A material is permanently stretched and when the load force is removed the material will be longer than the start
Limit of Proportionality?
Also referred to as Hooke’s Law Limit, this is the point where force is no longer proportional to extension and the point at which Hooke’s Law stops being obeyed
Hooke’s Law suitable conditions?
The clamp stand should be supported to stabilize the equipment. The best results have a large amount of mass before breaking. Trilling with different sized masses allow most suitable weight to be applied to the object
Hooke’s Law Investigation?
A ruler is used to measure the original length of the spring with no mass. Weight is added in regular intervals to the spring that is clamped. The recorded results are put on a load-extension graph
Extension in Hooke’s Law investigation?
Subtracting the new length against the original length
Elastic Deformation?
The material returns to the original shape one forces are removed leaving no permanent extension
Elastic Deformation on Force-Extension Graph?
The unloading leads to extension returning to 0 as force also becomes 0
Atoms behavior loading and unloading forces?
When a material is under tension the atoms of material are pulled apart from one another. Atoms can move small distances relative to their equilibrium without changing position in the material. Once load is removed atoms return to equilibrium position
Metal Elastic Deformation?
Elastic deformation only happens in a metal whilst Hooke’s Law is obeyed
Plastic Deformation?
The material is permanently stretched after the force has been removed and has stretched past its elastic limit
Atom behavior in plastic deformation?
Some atoms move relative to each other and when load is removed the atoms don’t return to their equilibrium position indicating plastic deformation has occurred
Deform?
A material subjected to a pair of opposite forces might change shape
Tensile Force?
A force which will stretch a material
Compressive Force?
A force which squashes a material
Tensile Stress?
The force applied divided by the cross-sectional area and has the units Pascals (Pa) or Newton Meters Squared (Nm-2)
Tensile Stress Formula?
Stress = Force / Area
Tensile Stress = F / A
Stress and Strain Factors?
A stress will always cause a strain. Strain has no units because it is a ratio. The equations for stress and strain are not dependent on the type of force. Tensile Forces produce positive values and compressive forces produce negative values
Tensile Strain?
Tensile Strain is defined as the change in length divided by the original length of the material
Tensile Strain Formula?
Tensile Strain = ΔL / L
Strain = Change in Length / Original Length
Atom Behavior in breaking stress?
The greater tensile force the more stress occurs. This causes the atoms to pull apart from each other. The stress becomes so great atoms separate completely and the material breaks
Breaking Stress?
The stress at which a material breaks
Ultimate Tensile Stress?
The maximum stress a material can withstand before breaking
Graphing Stress and Strain trends?
Breaking stress is the end of the curve on a stress-strain graph. The ultimate tensile stress is the last point stress and strain are increasing
Elastic Strain Energy?
When a material is stretched work has been done in stretching the material. Before the elastic limit all work done is stored as potential energy in the material
Elastic Strain Energy on a Force-Extension Graph?
The area under the graph is the elastic strain energy inside the material and this energy can be worked out if the material obeys Hooke’s Law
Elastic Potential Energy Trends?
The energy stored by the stretched material is equal to the work done on stretching the materiel if the material obeys Hooke’s Law
Work Done?
This is equal to the force multiplied by the displacement of an object
Force on a force-extension trend?
Force acting on a material is not a constant value. This means the average force acting on the material needs to be calculated
Energy on a Force-Extension Graph?
The area under the graph from the origin to the extension is energy if the material obeys Hooke’s Law. The area represents energy stored otherwise the work done which is referred to as elastic strain energy
Hooke’s Law affect on force?
Because Hooke’s Law is obeyed the force can be substituted into the change in length, force, spring constant equation
Energy effect on atoms?
If the material goes past its elastic limit some work done is used changing the position of the atoms. The energy will not be stored as strain energy so isn’t available when the force is released as its used to reposition the atoms
Elastic Potential Energy Equation?
Work Done = 1/2 x Force x Change in Length
W = 1/2 x F x ΔL
Energy = 1/2 x Spring Constant x Extension ^2
Energy = 1/2 x k x ΔL^2
Energy Conservation in deformation?
Energy is always conserved whilst stretching. A material being stretched has work done stored as elastic strain energy in the material. The removal of the stretching force transfers the elastic strain energy to other forms
Energy and Plastic Deformation?
If deformation is plastic work done is used to separate the atoms. Plastic deformation doesn’t have energy stored as strain energy so dissipates the energy through other forms but most often as heat
Energy Store behavior in elastic spring deformation?
A vertical spring with a mass below has elastic strain energy stored. The mass released causes the energy store to transition into kinetic energy. The spring contracting turns the energy stored then into gravitational potential energy. The spring compressing again reverts it back into kinetic energy where it ends up back again as elastic strain energy
Energy in safety?
The dissipation of energy in plastic deformation is used to design safer vehicles and an example of these is crumple zones
Crumple Zones?
A requirement of modern vehicles to reduce impact upon occupants. This is done by energy of impact being used to transform shape of the car so less energy is transferred inside the car reducing risk to passengers as the energy impact they endure is now lower
Stress and Strain relationship with limit of proportioanlity?
When load is applied to a stretched material it experiences a tensile stress and strain and when these are proportional to each other it is the limit of proportionality
Young’s Modulus?
Has the symbol E and is located below the limit of proportionality for a particular material where the stress divided by strain is constant
Young’s Modulus Equation?
E = FL / ΔL
Young’s Modulus = Tensile Stress/ Tensile Strain
Units in Young’s Modulus Equation?
Strain has no units so Young’s Modulus takes the units of Strain. Young’s Modulus has the units Nm^-2 or Pa. Force in Young’s Modulus equation is measured in Newtons and cross-sectional area in m^2
Conditions for Young’s Modulus Investigation?
A thin and long wire has higher extension for the same force and also a lower uncertainty. Cross-sectional area is found using a micrometer by finding diameter at several points and putting average reading into circle formula. Straighten wire by adding and removing weight and allow weights to hang off surface.
Method for Young’s Modulus Investigation?
Measure distance between end of wire and marker to work out distance of unstretched wire. Add regular intervals of weight and record the amount of weight suspended and the extension from the change in marker position. Calculate stress and strain of these results after a suitable amount obtained and plot a stress-strain curve
Stress-Strain Graph trends?
The gradient is the Young’s Modulus. The area under the graph is the strain energy per unit volume
Strain Energy Per Unit Volume?
The energy stored in 1m^3 of a wire
Stress-Strain Graphs and Hooke’s Law?
The stress-strain graph has a straight line relationship if Hooke’s Law is obeyed
Strain energy per unit volume equation?
Energy Per Unit Volume = 1/2 x stress x strain
Limit of Proportionality trends?
After the limit of proportionality an object could still potentially return to its original shape and size when stress is removed
Gradient behaviour on stress-strain graphs?
Obeying Hooke’s law has a straight line through the origin before the limit of proportionality. Where the gradient is constant it will be the value of Young’s Modulus. After the limit of proportionality the gradient changes to cause the line to bend
Elastic Limit Behaviour?
The elastic limit is when an object starts to behave elastically. After the elastic limit the object no longer returns to its original shape and size when stress is removed
Yield Point?
Where a material suddenly starts to stretch without additional load. It is also called yield stress. It is the stress at which a large amount of plastic deformation takes place at a reduced load
Force-Extension graph results trends?
Different wire lengths with different dimensions of the same material can produce different force-extension graphs
Force-Extension graphs compared to Stress-Strain Graphs?
Force-Extension graphs are specific for the tested object and depend on its dimension. Stress-Strain graphs describe general behaviours of materials as stress and strain are independent of dimensions
Trend behaviour on Force-Extension graphs?
Graphs can be plotted when weight is gradually added or removed. This means the unloading line cannot match with the loading line. If the material has deformed plastically it will not return to the original shape
Object past elastic limit?
This means the object has been stretch to a level where it deforms plastically and remains permanently stretched
Atom behaviour for plastic deformation?
The forces between atoms would be the same in unloading as loading if the object doesn’t deform plastically. The unloading line doesn’t go through the origin if the object has deformed plastically
Loading trends on a force-extension graph?
The unloading line will be parallel to the loading line as the stiffness constant otherwise the “k” value remains unchanged. When load is removed the amount of extension will decrease
Curve on a force-extension graph?
When a force-extension graph starts to curve it means the metal wire has been stretched beyond its limit of proportionality
Loading affect on area of graph?
The area between loading and unloading is the work done required to permanently deform a wire
Stress-Strain graphs for brittle materials?
The stress-strain graph for a brittle material doesn’t curve. Brittle materials obey Hooke’s Law producing a straight line gradient going through the origin
Brittle Materials behaviour?
Brittle materials when they stretch to a certain point will snap due to material fracturing and this shows brittle materials do not deform plastically
Force-Extension compared to Stress-Strain graphs for brittle materials?
The trends are similar as there is no plastic deformation which means the gradient is a straight line until the material fractures
Brittle material properties?
If a force is applied it will not deform plastically. Brittle objects suddenly snap when stress gets to a certain magnitude. Brittle materials can be quite weak if they have cracks in them.
Examples of brittle materials?
A chocolate bar and an example of it being brittle is parts can be broken off without changing the whole shape. Ceramics are brittle as they can shatter with certain magnitudes of stress
Ceramics Structure?
Ceramics are made by melting certain materials and letting them cool. The arrangements are crystalline or polycrystalline. The structure is based on regions otherwise grains of crystalline structures. The bonding is a giant rigid structure. The strong bond make it stiff while rigid makes them brittle
Metals and brittle property?
Most metals are not brittle and this is because atoms within metals are able to move apart preventing cracks from getting larger
Brittle material cracks?
When stress is applied to a brittle material the cracks get larger because they have a rigid structure and when they become large enough they cause the material to break
Brittle Fracture?
When stress is applied to a brittle material any cracks at the materials surface get larger until the material completely breaks
