Lateral strain

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Lateral strain, also called transverse strain, is how much a material’s diameter changes compared to its original diameter when it is deformed along its length. Under tensile stress, the object lengthens and its diameter becomes smaller; under compressive stress, it shortens and its diameter becomes larger. Lateral strain is a dimensionless quantity. Poisson's ratio, ν, relates lateral and longitudinal strain: ε_lateral = -ν ε_longitudinal. Most materials have a positive Poisson's ratio, so lateral strain has the opposite sign to longitudinal strain. Some materials, called auxetics, have a negative Poisson's ratio. For them, stretching makes the diameter larger (positive lateral strain) and compression makes it smaller (negative lateral strain).