Zencrack can readily be used to conduct parametric studies of crack sizes. Cases where this type of parametric study may be important include:
- through-thickness crack analysis of welds in pipelines
- leak before break studies
- investigations to determine critical crack size
- comparison against theoretical solutions where the crack shape is defined by an equation.
In the example shown here an investigation of stress intensity factors is carried out for an elliptic surface crack in which the depth is fixed and the length along the surface is varied. This results in stress intensity factor as a function of surface crack length for the deepest point and the surface point.
K at surface and deepest point as a function of aspect ratio
This analysis is conducted using the same initial mesh for all crack sizes. The only change is in the initial crack specification in the Zencrack input file. Once a suitable initial mesh is generated the analysis can therefore be conducted very quickly and efficiently.
This example has used the crack-block method but the mesh independent remeshing method provides an even more powerful capability for parametric studies because of the independent nature of the geometric crack definition and the underlying mesh.
Another situation in which a parametric study can be required is comparison with existing published solutions. In some cases the approach of modifying the Zencrack input is not the most convenient and instead the various crack shapes can be developed by carrying out a "pseudo-crack-growth" analysis. For this type of analysis the initial crack is defined and instead of advancing by the normal means of stress intensity factors and a crack growth law, the crack is advanced in a user subroutine in order to control the shape of each generated crack profile.
The example below shows such an analysis in which an initial surface elliptic defect in a circular cross section shaft is loaded by cyclic bending. In order to compare stress intensity factors against published data for different specified ellipse sizes a pseudocrack-growth run is carried out to generate a sequence of elliptic profiles in a single Zencrack analysis. The "true" profiles based on stress intensity factors and a crack growth data, in this case a Paris law, are somewhat different.
Ellipse with a/c=0.5
Ellipse with a/c=2
Ellipse with a/c=3
Ellipse with a/c=5
Ellipse with a/c=7
Profiles forced to an elliptic shape
Growth using actual K solution and a Paris law
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