Stress, Strain & Tensile Strength (OCR AS Physics): Revision Note

Stress, Strain & Tensile Strength

• Opposite forces can deform an object

• If the forces stretch the object, then they are tensile forces

• Tensile forces lead to the two properties of materials known as tensile stress and tensile strain

Tensile Stress

• Tensile stress is defined as the force exerted per unit cross-sectional area of a material

• The ultimate tensile stress is the maximum force per original cross-sectional area a wire is able to support until it breaks

• Stress has the units of pascals (Pa), which is the same units as pressure (also force ÷ area)

Tensile Strain

• Strain is the extension per unit length

• This is a deformation of a solid due to stress in the form of elongation or contraction

• The strain is a dimensionless unit because it’s the ratio of lengths

• Sometimes strain might be written as a percentage

  • For example, extending a 0.1 m wire by 0.005 m would produce a strain of (0.005 ÷ 0.1) × 100 = 5 %

Ultimate Tensile Strength

• The ultimate tensile strength of a material is defined as:

  The maximum amount of load or stress a material can handle until it fractures and breaks

• The table lists some common materials and their tensile strength:

Tensile strength of various materials