Tensile Stress, Strain and Modulus

The SI unit of stress is newton per square meter (N/m ), which also is called the pascal (Pa). However, a tensile stress of 1 pascal is extremely small, and hence the unit of megapascal (MPa) often is used for convenience. 

The tensile stress causes the elongation of the fiber. The fractional amount a fiber elongates when it is subject to a tensile stress is called the tensile strain. Mathematically, the tensile strain (e) can be written as  

According to the Hooke s law, the amount of tensile strain experienced by a fiber is directly proportional to the tensile stress. The tensile modulus ( ) can then be defined as  

Tensile modulus is also called Young s modulus or elastic modulus. The unit of tensile modulus also is pascal, or more often gigapascal (GPa) for the purpose of convenience. Fibers with high tensile modulus are stiff and deform veiy little under stress, whereas fibers with low tensile modulus are soft and deform significantly. 

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