notes on diffusion, deformation processes

uni/mmme/1029_materials_and_manufacturing/manufacturing.md

@@ -131,3 +131,50 @@ $$C = \frac{mC_m}{1-f} + \frac{C_t}{n} + \frac{1}{\dot n} \left[ \dot C_{oh} + \
 - Low thermal capacity and high conductibity
 - Low solubility
 - Not contaminated by air
+
+## Deformation
+
+When a metal is plastically deformed, dislocations move and multiply.
+
+Annealed aluminium may have a dislocatio density of around 200 m per mm$^3$.
+This is a very low amount.
+A heavily cold worked piece may have a density of up to 270 km per mm$^3$.
+
+As dislocation density increases, the dislocations impede the motion of other dislocations.
+This means that to continue plastically deforming, more stress has to be applied.
+
+The stress goes down towards the end of the graph due to the material necking, meaning the
+material gets thinner.
+This means that the engineering stress is lower as the true area is lower.
+The true stress, however, is going up:
+
+![](./images/vimscrot-2022-02-28T20:01:59,453437307+00:00.png)
+
+### Effect of Prior Deformation (*Work Hardening*)
+
+![](./images/vimscrot-2022-02-28T20:02:42,050513187+00:00.png)
+
+See
+[here](materials.html#work-hardening-and-cold-working)
+for more information
+
+### Effect of Temperature (Diffusion)
+
+In an alloy, atoms tend to migrate from regions of high concentration to low concentration.
+This is diffusion.
+
+More information on diffusion [here](materials.html#diffusion).
+
+### Annealing
+
+Annealing is a process by which a component is heated to reduce work hardening.
+
+![](./images/vimscrot-2022-02-28T20:32:47,838820599+00:00.png)
+
+These are diffusional processes and only occur at higher temperatures.
+
+When the temperature of a material, $T > 0.55T_m$, it is said to be hot.
+A material being worked on hot has its deformations eliminated as fast as they are created.
+
+A material is said to be cold when $T < 0.35T_m$.
+

uni/mmme/1029_materials_and_manufacturing/materials.md

@@ -1140,7 +1140,74 @@ You can apply the Arrhenius equation for all thermally activated diffusion:
 
 $$D = D_0 \exp{\left( - \frac{Q}{RT} \right)}$$
 
-where $Q$ is the activation energy and $R$ is the ideal gas constant (8.31 J k$^{-1}$ mol$^{-1}$).
+where $D$ is the diffusion coefficient, $D_0$ is the frequency factor, $Q$ is the activation energy,
+$R$ is the ideal gas constant (8.31 J k$^{-1}$ mol$^{-1}$).
+
+You can find the diffusion distance, $x$, with the following equation:
+
+$$x ~ \sqrt{Dt}$$
+
+![](./images/vimscrot-2022-02-28T20:31:12,395307966+00:00.png)
+
+
+# Materials in Sustainable Transport
+
+- Concerns over use of fossil fuels, climate change
+- Const of energy
+- Energy use in making and moving vehicles
+- Rising energy prices mean cost of fuel is comparable to cost of car
+- 1/4 of energy used in UK is to transport goods and people
+- Legislation and voluntary targets set by EU to improve fuel efficiency
+- In 2015 average CO2 emmisions as 130 g / km
+- Engine powerhas gone up significantly from 2001 to 2018 (~30%) yet engine displracement has gone
+  down ~10% and CO2 emissions down ~18% while weight has gone up ~10%
+
+## Is the car emissions reduction target significant?
+
+Overall CO2 emissions in 2016 is 466 Megatonnes.
+
+Does a reduction from 130 g / km to 95 g / km (a 35 g/km reduction) make a significant difference?
+
+There are 33 million registered cars in the uk.
+
+If they average around 8000 miles each (~13000 km) per year that's a ~15 Megatonne reduction,
+or about 3% of the annual C02 emmissions, a significant reduction.
+
+## Materials in Cars
+
+- Most of the energy used by cars is during driving (71%)
+- This means the mass of the vehicle has a great effect on its emmissions across a lifetime
+- The body, suspension, drivetrain, and interior all contribute roughly a quarter to the mass of the
+  car
+- However, the mass of cars are increasing
+
+### Material Substitution
+
+- The material will likely have performance requirements:
+
+  - It may need to be a physical size
+  - It may need to operate at certain temperatures
+  - It may need to bear a certain load
+
+- The component mustalso be designed for convenient manufacturing, assembly, servicing, disposal,
+  remanufacturing and/or disassembly
+
+#### Case Study --- 2012 Honda Accord
+
+- Body --- opted to stay with steel --- aluminium intense and multi-material approaches were both
+  rejected due to higher costs and limitations in manufacturing and assembly.
+  Recyclability was also noted as an issue due to different grades of aluminium needing to be
+  separated at end of life.
+- Doors and bonnets --- move to aluminium from steel --- more costly but the mass savings made this
+  option worth it
+- Wiring --- aluminium to copper --- lower mass for same conductivity, copper is more expensive
+  (I think)
+- Seats --- steel to composites or magnesium structural components --- very high weight savings
+
+## Choosing a Material
+
+
+
 
 # Glossary