How Does Stuff Break?

Corrosion

Metals are strong, but they corrode or rust. Paint helps protect the metal from water and air which are the ingredients of corrosion.

Fatigue

Repeated loading opens and closes tiny defects over and over, and eventually those defects become cracks which propagate and fracture or tear. Under repeated loading, structures ultimately fail at much lower loads than originally thought. Take a paperclip and try unfolding and refolding it in different directions (rotating vs. bending). Try cycling with different ranges of deflection and count the number of cycles needed to break the paper clip. Is there a relationship between deflection angle and number of cycles before breakage?

Plastic Man or the Man of Steel?

Plastics are cheap, easy to shape, light, and pretty strong for their weight, but they easily soften with temperature. Their strength-to-weight ratio is not as good as steel, a popular structural material. Steel, however, is quite heavy and subject to corrosion.

What about these materials?

Ceramic is brittle, aluminum is ductile. Concrete is usually reinforced with metal bars inside, so the total structure has mixed properties.