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Advanced Crack Growth Analyses of Heat Exchanger Components

A major manufacturer of heat exchanger components for airframe and high-temperature jet engine applications contacted CAE Associates when they needed advanced crack growth analyses to certify their products to meet military requirements.  A new application design and prototype construction was moving forward rapidly.  Without the certifying analysis to meet customer specifications, the project schedule would be extensively delayed.

As a mission critical component on military aircraft, the heat exchanger had to be shown by analysis to be damage tolerant per strict military specification. Damage tolerance analysis confirms that peak operating stresses will be low enough such that the largest flaw size that can escape detection by inspection techniques will not be catastrophic. The analysis must demonstrate that various flaw types will not propagate at all, or slowly enough such that the calculated life will exceed a specified service life or inspection interval.

The client was familiar with performing finite element analysis on their components, but had limited experience with crack growth analysis. In addition, the timing of a critical design review made a fast solution imperative. CAE Associates was engaged to help, based on their extensive experience with both finite element stress analysis and fracture mechanics methods.

CAE Associates worked with the customer's existing CAD geometry and performed static structural finite element analysis to predict detailed stresses and material response based on the prescribed loading requirements.  After determining the critical regions of the parts, CAE performed crack growth calculations based on assumed initial flaws.  These procedures include linear elastic fracture mechanics via NASA's crack growth prediction tool, NASGRO.

Crack Growth vs. Cycles

With CAE Associates’ ANSYS customization and analysis process automation experience, a concise, fast method of determining critical bending and in-plane stresses within the part was implemented.  This saved the client both time and money by automating the stress spectrum input process for critical crack growth calculations.  The final results were delivered on-time to meet the critical design review date, and to allow production to continue on schedule.