Hardness

The cutting wheel will be surrounded by transparent guards. These will allow the operator to see the cutting wheel at all times, and will shield the operator from flying metal fragments. The guards must therefore be constructed from material with a high degree

of (1) ........................... hardness, to protect it from impacts.

• abrasion

• indentation

• durable

• hard

As the guards will require regular cleaning, the action of wiping away metal fragments will result in (2) .................................................

• abrasion

• soft

• durable

• hard

The guards must, therefore, have sufficient (3) ............................... hardness in order to retain their transparency and ensure adequate (4) ...............................

• abrasion, durable

• hard, indentation

• scratch, durability

• soft, scratch

the cause of fatigue

• creep

• cyclic loads

• micro-cracking

• fracture toughness

the consequence of fatigue

• creep

• cyclic loads

• micro-cracking

• fracture toughness

a material property that helps to slow down cracking

• creep

• cyclic loads

• micro-cracking

• fracture toughness

permanent changes in shape due to the action of loads over time

• creep

• cyclic loads

• micro-cracking

• fracture toughness

describes a material's ability to resist being scratched. Materials with a high degree of scratch hardness are said to have good abrasion resistance - they are good at resisting damage due to abrasion (the action of two surfaces being rubbed together)

• Indention hardness

• Scratch hardness

describes a material's ability to resist indentations - that is, compressions in the surface of a material caused by impacts.

• Indention hardness

• Scratch hardness

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