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Mechanical testing determines properties of a material when force is applied, therefore indicating its appropriate use in mechanical applications. The mechanical properties of metals can be expressed in numerous ways: strength, ductility, hardness, toughness, etc. The hardness and the strength of a material are closely related. Hardness is useful for estimating wear resistance and approximate strength; and is defined as the resistance of a material to surface indentation. Rockwell hardness is the most widely used method for determining hardness and several different Rockwell scales are utilized for materials of a variety of hardness ranges. Aluminum alloys, brass, and soft steels are often measured on the Rockwell B scale or HRB, whereas harder steels and titanium are measured on a Rockwell C scale or HRC. Other ways to obtain mechanical properties include tensile testing, compression testing, impact testing, fatigue testing, and fracture toughness testing, etc., depending on the application and performance requirements of the component.