# Materials engineering

There are multiple factors to consider when engineering *anything*, and the quality of an engineered item has a *profound* impact on the quality of the item:

- Accessibility to the material itself (e.g., diamonds are harder to get than dirt).
- The load-bearing capacity of the object during normal use.
- Lateral loads on the object (i.e., the angle where it'll be weakest).
- The structural integrity of the object when under tension, both from a strong impact and from sustained tension.
- The structural integrity when the object is torqued (i.e., one part of it is rotated while the other is still or rotated the *other* way).
- The flexibility of the object when exposed to stress.
- Its ability to combine with other materials to create composites and alloys, and what the combined material looks like.
- How the material connects to other materials (bolts, ropes, hinges, etc.).
- The possible ways to permanently make it part of another material of the same (e.g., gluing, welding).
- Types of connections that work in various capacities (e.g., moment connections, bracing and truss connections).
- The effect of long-term vibrations on the material.
- Structural design that takes the most advantage of the materials' tradeoffs (e.g., girders, A-frames).

Each material has its tradeoffs:

- Wood is easily accessible and easy to work with, but breaks down easily when stressed and is flammable.
- Stones vary by geological type, tend to be easy to chip and plane into tools, but also easily break, especially under prolonged stress.
- Gemstones are *very* durable, but can be rare and expensive.
- Some metals are naturally occurring and simple to work with (e.g., bronze) while others need extra treatment to work with (e.g., iron). Since alloys are hybrid mixes of metals, they often can reinforce each other's weaknesses (e.g., steel).
- Plastic is derived from crude oil, and is *very* cheap, but is flimsy and can be bio-hazardous in some implementations.

*Acquiring* those materials is often another form of engineering:

- Wood is a *completely* renewable resource (which is why it's so ubiquitous), and there are ways to farm it even more easily without having to cut the trees down.
- Most materials require some form of refining before they can be worked into an engineered solution, which can dramatically affect the cost.
- Mining materials (e.g., coal, iron, aluminum) are geography-specific, so they require [logistical considerations](logistics.md) for refining.
- Drawing oil out of the ground requires refining into diesel (and further refining creates gasoline), but can also be refined into plastics for a vast range of uses.

Stressors affect organic and inorganic components differently:

- Organic
  - No stress: either recovery or decay
  - Low stress: Hormesis (gets stronger)
  - High stress: Trauma (either medical or psychology)
- Inorganic
  - No stress: low-level entropy
  - Low stress: Material fatigue (gets weaker)
  - High stress: Breakage

Designing for physical reality is difficult, so engineers *must* accommodate imperfection into the structure of inorganic objects:

- Keep it simple, since complexity has more points of potential failure and there are fewer parts to maintain.
- Heavily reinforce the parts of the object that will take the worst beating.
- Make the most likely failure happen at the most accessible place for a technician.
- Have redundant systems in place to prepare for a likely breakage.
- Add random problems to the system during testing *on purpose* to see what might break.
- Create backup systems that can *thrive* when the first things break.
- If you need a complex system, string together multiple simple systems.

## Metal: Ironworking

Steel is a specific form of ironwork:

- Wrought iron is an iron alloy with very little carbon (~0.08%).
  - It simply involves heating iron, then working with it.
- Steel is an alloy composed of iron, carbon (~2-4%), and several other elements that reinforce its structure.
  - It requires a unique firing process that involves adding and removing various components to create the final alloy.

Steel goes through the entire range of color as it heats:

- ~199°C: tan
- ~241-249°C: brown
- ~271°C: purple
- ~302°C: blue
- ~427°C: dark grey
- ~593°C: slight red
- ~815°C: bright red
- ~927°C: orange
- ~1093°C: yellow