What are Units of Stress and Strain - Definition

Tensile stress is measured in units of force per unit area. The unit is newton per square meter (N/m^2), kilogram (force) per square centimeter (kg/cm^2) or pascal. Strain is dimensionless quantity.

Tensile stress is measured in units of force per unit area. The unit is newton per square meter (N/m^2), kilogram (force) per square centimeter (kg/cm^2) or pascal.

Most commonly used unit of stress is pascal, which is defined as force of 1N that is exerted on unit area.

1 Pascal = 1 N/m²

However, for most engineering problems it is fairly small unit, so it is convenient to work with multiples of the pascal: the GPa, and the MPa.

1 MPa 10⁶ N/m²
1 GPa 10⁹ N/m²

The ultimate tensile strength (UTS) of a material is the force per unit area at which it breaks in two. Tensile stress is that type of stress in which the two sections of material on either side of a stress plane tend to pull apart or elongate. The capacity of a material or structure to withstand loads tending to elongate is known as ultimate tensile strength (UTS). Ultimate tensile strength is measured by the maximum stress that a material can withstand while being stretched or pulled before breaking. In the study of strength of materials, tensile strength, compressive strength, and shear strength can be analyzed independently. Because tensile and compressive loads produce stresses that act across a plane, in a direction perpendicular (normal) to the plane, tensile and compressive stresses are called normal stresses.

Strain is dimensionless quantity which expresses a proportional dimensional change (intensity or degree of the distortion) and is measured as the total deformation (elongation) per reference length of material due to some applied stress.

References:

Materials Science:

U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
Gaskell, David R. (1995). Introduction to the Thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:

Strength

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