Features of MSC Fatigue

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MSC Fatigue allows the designer or analyst to carry out fatigue calculations early in the design process. It takes the detailed stress distributions produced by a finite element analysis and a description of the variation of the loading with time, carries out fatigue calculations using state-of-the-art fatigue life estimation methods, and produces fatigue life results in the form of contour plots. These life plots can be displayed using standard MSC Patran imaging tools as well as imaging tools from other popular pre- and post-processing systems.

MSC Fatigue offers a unique integration between finite element analysis (FEA) and fatigue life estimation by enabling the user to select areas of the finite element (FE) model for fatigue life analysis with specific tools provided in the display postprocessor. All three commonly used fatigue life estimation techniques are supported: total life or nominal stress-life (including analysis of welded structures), crack initiation (otherwise known as strain-life), and crack growth or Linear Elastic Fracture Mechanics (LEFM) life estimation techniques.

Both the crack initiation and total life approaches provide the capability to investigate the effect of local changes in surface finish and treatment. A comprehensive materials database is provided that has sophisticated search facilities. Full elastic-plastic transformations are carried out in the crack initiation modeling. Multiple or single static and/or offset load cases may be defined. Fatigue results may be presented in a number of different ways including scaling the results in terms of user-defined units such as hours, miles, flights, etc. Full‑color life contour plots may be produced providing a rapid assessment of fatigue critical areas.

Detailed analysis may be carried out to establish sensitivities to variation in material, manufacturing process or loading, using the Design Optimization analyzer. Crack growth may be investigated using the cycle-by-cycle linear elastic growth analysis facilities.

The link between finite elements and fatigue introduces a control on fatigue life performance at an early stage in the design cycle. This integrated approach promotes a total quality policy enhancing the design/development process within a company.

1. Total Life analysis (S-N) based on the nominal stress-life method using rainflow cycle counting and Palmgren-Miner linear damage summation. Various analysis parameters may be chosen such as mean stress correction methods and confidence parameters. Both component and material S-N curves may be accessed. Material S-N curves allow for specification of material surface finish and treatment.

2. Crack Initiation analysis (ε-N) or the local strain method using cyclic stress‑strain modeling and Neuber elastic-plastic correction. The mean stress correction method, surface finish and treatment factors may be adjusted to investigate the effect of these fatigue dependent parameters.

3. Crack Growth analysis using linear elastic fracture mechanics (LEFM) and cycle-by-cycle modeling of crack closure due to overloads, the effect of chemical environment, the loading rate and history effects. On-line displays of crack progress report the rate of crack growth, and postprocessing menus enable interpolation of results.

4. Factor of Safety analysis for structures designed for infinite life (such as powertrain and engine components) is available also for the crack initiation and the total life methods.

5. Fatigue analysis of steel or aluminum welded structures using the total life approach as defined in the British Standard, BS7608, design code including a Weld Classifier.

6. A state-of-the-art Spot Weld analyzer is also available as a separate module where spot welds are modeled in MSC Nastran as stiff bars between two sheets. The forces in the bars are then converted to stress and used in a S-N analysis using the Rupp-Stoerzel-Grubisic method. The method calculates fatigue life on the basis of structural stresses around each spot weld which are then calculated on the basis of the cross-sectional forces and moments in the CBAR elements. A relatively coarse mesh is required, and results can be visualised to good effect using INSIGHT.

7. Vibration Fatigue analysis calculates fatigue lives directly from Power Spectral Density Functions (PSDF or PSD) using the S-N method. This is a very powerful capability when it is not convenient to analyze a structure in the time domain, making it necessary to do a random vibration analysis.

8. Global life estimates presented as color fringe contour plots enable the rapid assimilation of the Results and easy identification of the fatigue critical areas.

9. Interactive Design Optimization allowing the rapid assessment of analysis parameters and design options including alternative geometries, surface finishes, surface treatments, weld details, or materials.

10. Materials Database loaded with standard fatigue data sets. Access to the database is provided by a sophisticated materials database which offers loading, editing, creating, searching, and data visualization.

11. Loading Time History Database manager provides a method of archiving loading time histories together with their details. In addition, full graphical editing and signal creation facilities offer the ability to prepare time histories, spectrums and PSDs from measured field data or artificially synthesized data.

12. The combined effect of Multiple Loading histories may be explored together with Multiple Materials datasets on one structure. Substructures may be analyzed by selecting specific geometric entities within MSC Patran.

13. A Biaxiality Analysis feature helps in determination of necessary fatigue analysis methods when complex multi-axial loadings are involved and the validity of an associated fatigue analysis. Corrections can be made for proportional loading and if non-proportional loading is determined a separate module allows for Multiaxial Fatigue life calculations.

14. Finite element stress/strain results may be used from either Linear Static/ Transient Dynamic/Forced Vibration or Frequency Response/Random Vibration analyses. Results are read directly from the MSC Patran database or from either a MSC Patran FEA results file or external MSC Patran results files. This architecture supports results from virtually any analysis code that is supported by PATRAN 2.5 or MSC Patran. In addition results may be read from other external results files from analysis codes such as MSC Nastran and I-deas.

15. An interface to NASA/FLAGRO is also featured within MSC Fatigue via the MSC Patran PCL forms. NASA/FLAGRO is a two dimensional crack growth code developed by NASA which is complimentary to the crack growth module featured in MSC Fatigue.

16. A Software Strain Gauge module allows the MSC Fatigue user within the MSC Patran environment to simulate an actual strain gauge. This allows for extraction of time varying strain results from a fatigue analysis in the coordinate system(s) of the strain gauge for test/analysis comparison and correlation.

17. A number of useful Utilities are include as a separate module of MSC Fatigue. These include many time history manipulation and display utilities and additional fatigue life analysis features such as calculations from measured stress or strain data and time correlated damage.