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Foundation ::
CAD CAM CAE ::
FATPLUS
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FATPLUS
The Automated Fatigue Calculation Program
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SOURCE CODE AVAILABLE
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The Automated Fatigue Calculation Program (FATPLUS) is a menu driven, interactive design tool that provides basic calculation of fatigue life and design trade study capability. The program was developed to provide an interactive program for fatigue life predictions. FATPLUS can be used to independently validate proprietary fatigue methodologies, identify fatigue sensitive parts, and train engineers in fatigue life prediction.
FATPLUS provides interactive capability for trade studies and analysis in fatigue life, stress spectrum effects, design change effects, material change effects and stress concentration changes. Additionally, FATPLUS allows the user to create, save, and modify specific stress spectra and materials properties. FATPLUS provides a conservative methodology which, combined with reasonable engineering practices, yields a valid prediction of fatigue life.
Fatigue life estimation is a function of four factors:
- stress spectrum (i.e. loadings performed as a percentage of total time, or numbers of stress cycles per activity unit),
- loading per stress event,
- material fatigue properties, and
- safety factors applied.
The stress spectrum and loading are integrally related. A misestimation in either count leads to severe errors in the estimation of fatigue life. Material properties have inherent scatter because the microstructure of every manufactured item is different. Additionally, certain processes such as coating or chemical etching can affect the material structure significantly. Safety factors are one of the largest variables in estimating fatigue life. There are two typical reductions: life reduction (which multiplies the total damage, or reduces the cycles allowable by a constant factor), or a statistical reduction factor (which reduces the allowable stress by a percentage based on materials variability constants.)
FATPLUS uses online or preprogrammed spectrums which are then applied to a materials curve. The materials curve is actually a complex curve composed of the more conservative of a constant life reduction or a statistical life reduction. User inputs are then summed to calculate the total damage and allowable life. The allowable life is determined from the cycles in the input spectrum. Since the user may not have access to corporate or private fatigue data, MIL-HNDBK-5 data is used for materials constants inputs. The user inputs the fatigue data for the material in use, and the program calculates the statistical variation of the data. Alternatively, a numerical equation for fatigue properties may be entered. This equation can be derived from non-MIL-HNDBK-5 resources.
FATPLUS carries the NASA case number MSC-22537. It was originally released as part of the NASA COSMIC collection.
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