Maximum damage approach

When you use the maximum damage approach, the durability solver follows these steps:

1. It identifies and processes only the element faces on the surface of the structure or on the displayed group of elements.

2. It generates a coordinate system located at the centroid of the element face. Its Z-axis points outward and normal to the face. The other two axes are on the element face, and tangent to the face at the element centroid.

3. It calculates the stress time history at the centroid of each element face with respect to the element coordinate system. For static durability analysis, the stress time history is calculated by superposition of static solution results and the load patterns. For transient durability analysis, the stress time history is taken from the transient solution.

4. It calculates the principal stresses at every time step.

5. It sets up a given number of search angles,θ, in the range between 0° and 180°.

6. It determines the directions of the two effective principal axes on element face, i and j as follows:The effective principal axis i is located at the search angle θ from the X-axis of the element coordinate system.The effective principal axis, j is perpendicular to the effective principal axis i.

7. It performs a 2D tensor transformation to calculate the stress histories σi(t) and σj(t) along the two effective principal axes and the normal stress σk(t).For strain-based fatigue life criteria, the durability solver also calculates the strain histories in the three principal directions, εi, εj, and εk.

8. It chooses the primary loading axis as follows:For all fatigue life criteria except maximum shear strain life, the primary loading axis is chosen between i and j as follows:The solver calculates the two stress biaxial ratios:r1 = σi/σj**r2 = σj/σiThe solver compares r1 and r2.If r1 is smaller, the direction j is the primary loading direction, and σ1 = σj, σ2 = σi, ε1 = εj, and ε2 = εi.If r2 is smaller, the direction i is the primary loading direction, and σ1 = σi, σ2 = σj, ε1 = εi, and ε2 = εj.The stress biaxial ratio that is used later in the calculations is r = min(r1,r2).For maximum shear strain life, the durability solver uses the principal strains to calculate the shear strain history γm(t) in the maximum shearing direction (γm = max(γij,γik,γjk)). The corresponding normal strain history εn(t) and the strain biaxial ratio rε = εn(t)/γm(t) are calculated for biaxial analysis.

9. It uses the stress ,σ1, or strain, ε1, in the primary loading direction or in the case of maximum shear strain life, the shear strain γm to calculate the stress or strain amplitudes and mean values using rainflow counting. See Rainflow counting and Fatigue life criteria for more information.

10. It calculates damage and life:For uniaxial loading fatigue, it uses the stress or strain amplitudes and means in the S-N curve of the selected life criterion for damage calculation. See Fatigue life criteria for more information.For biaxial loading fatigue, it uses the biaxial ratio r or rε to update the S-N curve of the life criterion for damage calculation. See Biaxial fatigue evaluation on element free faces for more information.

11. It saves the damage and the life only if the damage in the given direction θ from step 6 is the greatest compared to the damages in the other loading directions.

12. It repeats steps 6 through 11 for maximum damage, and calculates life.

Learn more

Static events

Transient events

Analyzing strain gage rosette data

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Fatigue evaluation on element free faces

Principal axes approach

Critical plane approach

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Maximum damage approach, Simcenter 3D 2021.1 Series

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