Allowable Stress

on . Posted in Classical Mechanics

Allowable stress, abbreviated as S, also called allowable working stress or design stress, is the maximum stress that a material can safely withstand under specific operating conditions.  It is determined by considering various factors such as the material's strength, its mechanical properties, and the desired level of safety.

The selection of the allowable stress depends on several factors, including the type of material, its manufacturing method, intended application, and any applicable codes or standards.  The codes and standards provide guidelines and limits for allowable stresses based on extensive testing, research, and industry experience.  Design engineers consider the allowable stress when determining the appropriate dimensions and thicknesses of structural components such as pipes, pressure vessels, and other equipment.  By ensuring that the operating stress levels remain below the allowable stress, engineers can maintain the structural integrity and safety of the components throughout their intended service life. 

It's important to note that different materials and applications may have different factors affecting the determination of allowable stress.  However, the actual determination of allowable stress may involve more complex considerations, such as load combinations, temperature effects, and specific design codes or standards.  Therefore, consulting the relevant codes, standards, and material specifications is crucial to accurately determine the allowable stress for a particular scenario.


Allowable stress formula

\(\large{ S = \frac{\sigma}{FS} }\)     (Allowable Stress)

\(\large{ \sigma =  S \; FS   }\)

\(\large{ FS = \frac{\sigma}{S} }\)

Solved for S

yield strength, σ
factor of safety, FS

Solved for σ

allowable sterss, S
factor of safety, FS

Solved for FS

yield strength, σ
allowable stress, S

Symbol English Metric
\(\large{ S }\) = allowable stress \(\large{\frac{lbf}{in^2}}\) \(\large{Pa}\)
\(\large{ \sigma }\)  (Greek symbol sigma) = yield strength \(\large{\frac{lbf}{in^2}}\) \(\large{Pa}\)
\(\large{ FS }\) = factor of safety \(\large{dimensionless}\)


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Tags: Strain and Stress