Strength calculations for orthotropic failure criteria

For orthotropic materials, the durability solver computes the strength safety factor, SSF, and the margin of safety, MS, using the failure index expression of the orthotropic or laminate failure criterion with static strength limits. The static strength limits are orthotropic material properties.

• XT_static is the tensile static strength stress limit in 1–direction.

• XC_static is the compressive static strength stress limit in 1–direction.

• YT_static is the tensile static strength stress limit in 2–direction.

• YC_static is the compressive static strength stress limit in 2–direction.

• Sstatic is the static in-plane shear stress limit.

The following table lists the equations that the durability solver uses to compute the strength safety factor and margin of safety results.

	Strength safety factor equation	Margin of safety equation
Hill failure criterion	SSF = ((σxx/X)2 – σxx**σyy/X2 + (σyy/Y)2 + (σxy/Sstatic)2)-1	MS = (SSF1/2/FS – 1) x 100
Hoffman failure criterion	SSF = (F1σxx + F11σ2xx + F2σyy + F22σ2yy + 2F12σxx**σyy + F66σ2xy)-1where:F1 = 1/XT_static – 1/XC_static**F11 = 1/XT_static XC_static**F2 = 1/YT_static – 1/YC_static**F22 = 1/YT_static YC_staticHoffman failure criterion, F12 = –1/2(XT_static XC_static**YT_static YC_static)1/2For the Tsai–Wu failure criterion, the value for F12 is the specified Tsai–Wu interaction coefficient. If you do not specify this property, F12 is set to zero.F66 = 1/S2static	MS = (min(max(0, β1), max(0, β2))/FS – 1) x 100where:β1,2 = (-B±(B2+4A)1/2)/2A**A = F11σ2xx + F22σ2yy + 2F12σxx**σyy + F66σ2xy**B = F1σxx + F2σyy
Tsai–Wu failure criterion
Maximum stress failure criterion	SSF = min((	σxx

For the Hill failure and maximum stress failure criteria, the durability solver determines the values for the stress limits X and Y as follows:

• X = XT_static if σxx > 0

• X = XC_static if σxx < 0

• Y = YT_static if σyy > 0

• Y = YC_static if σyy < 0

Look up more details

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Understanding the strength evaluation

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Fatigue life criteria

Biaxial fatigue evaluation on element free faces

Using a notch factor for modeling the local plastic behavior

Understanding cyclic stress-strain behavior

Understanding the fatigue safety evaluation

Cumulative damage

Random fatigue methods

Strain and stress calculations from strain gage leg data

Strain gage transverse corrections for rosette legs

Scientific literature references for durability

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Strength calculations for orthotropic failure criteria, Simcenter 3D 2021.1 Series

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