Hardness
Any material which can resist wear and tear, denting and twisting and bending is said to have the quality of hardness. Drills, files emery cloth and glasspaper  have these qualities.

Fatigue
Fatigue is caused by repeated bending or stressing in some way. Corrosion can cause fatigue as can temperature and surface finish. Collapsing bridges with the constant weight of cars is an example.

I'm well hard !
Huh! Suffering from fatigue.

Toughness
The ability to withstand sudden shocks or blows without it fracturing. It can also be applied to the ability of a material to withstand cracking if it is subjected to bending forces or shear forces.

Brittleness

This is the opposite of toughness. Materials that are brittle cannot withstand any strain before they crack or break. Two good examples of this type of material would be acrylic and glass.

Durability
If a material withstands wear and tear, the weather and corrosion it is durable (long lasting). It usually is noticed by a change in appearance when it starts to wear out. Corrosion is the main area affecting durability and can often be overlooked which can have serious effects on structures such as bridges whose durability can be affected by rust. Ultra violet light can affect materials, particularly plastics which can become very brittle with the effects of the sun. In general though, plastics are less likely to corrode than most materials but strength is not usually associated with plastics.

Stability
Materials which are stable resist changes in size and shape, which can often be caused by weather, particularly wet or dry conditions. Wood tends to warp and twist if it gets too wet or dry. Plastic tends to bend and stay bent if it is subject to constant force. This stretching due to force is called 'creep'. It is most important that certain objects such as turbine blades resist 'creep' because they are subjected to a lot of rotational force and high temperatures which are known to cause 'creep'.

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