Troubleshooting article about print strength

[Ghostkeeper]

I'd like to add a troubleshooting article that helps the user to create parts that are stronger. While it's not technically a print defect, it's still a common question that people have.

Topics to discuss in this article are:

• Terminology between different types of strength: Hardness/Young's Modulus, yield strength, toughness, etc. And how prints can be strong in one direction but weak in another. How we want to increase strength without increasing printing time and material usage. This serves as an introduction as to why you'd want to optimise this as well, and to make the reader realise that simply going for 100% density might as well be the best solution.
• How to adjust the model to make it tougher.
• The walls normally provide the majority of the strength of the part, rather than the infill. So increase the wall thickness.
• Increasing infill density, and different patterns.
• Improving layer adhesion.
• Improving horizontal adhesion between infill and walls (requires #61).
• Optimising the direction of the layers and lines to improve strength in a certain direction. Also using the Infill Line Directions and Top/Bottom Line Directions settings.
• Stiffness, for the case of flexible filaments.