Computation of the maximum alternating stress

When you specify that the maximum alternating stress amplitude, ∆s/2, is computed from the specified load cycles, Nf, the durability solver computes it differently depending on the selected fatigue life criterion.

Smith Watson Topper fatigue life criterion

When you use the specified cyclic stress-strain model to convert strain, ∆ε/2, to stress in the life equation, ∆s/2 is computed from the life equation for Nf:

where:

• σm is the mean stress of the cycle along the principal axis.

• σ'f, b, ε'f, c, and E are the durability material properties.

Maximum principal strain life and maximum shear strain life

The strain equivalent of ∆s/2, ∆ε/2 or ∆γm/2, is computed from the life equation for Nf and converted to ∆s/2 using the specified cyclic stress-strain model.

The life equation for maximum principal strain life is:

The life equation for maximum shear strain life is:

where:

• νe is the Poisson's ratio.

• νp = 0.5

Stress life

BWI and TWI fatigue life criteria

where stdev, a, m, and d are weld class parameters.

User-specified S-N curve

When you specify an S-N curve for the material with a stress life, ∆s/2 is determined directly from the specified S-N table data using Nf.

User-specified E-N curve

When you specify an E-N curve for the material with a strain life, the strain equivalent of ∆s/2 is determined directly from the specified E-N table data using Nf and is converted to ∆s/2 using the specified cyclic stress-strain model.

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Static events

Transient events

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Understanding the fatigue safety evaluation

Goodman and Gerber methods

Dang Van fatigue safety factor

Smith-Watson-Topper

Strain life

Stress life

BWI fatigue life criterion

TWI fatigue life criterion

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Computation of the maximum alternating stress, Simcenter 3D 2021.1 Series

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