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Foundation ::
Failure Analysis ::
PFAFAT
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PFAFAT
Probabilistic Failure Assessment for Fatigue
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SOURCE CODE AVAILABLE
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Probabilistic Failure Assessment for Fatigue (PFAFAT) is a package which utilizes the Probabilistic Failure Assessment (PFA) methodology to model high and low cycle fatigue failure modes of structural components. It consists of nine programs to perform probabilistic fatigue analysis using the PFA method. Three of the programs perform probabilistic fatigue analysis by means of Monte Carlo simulation. The other six programs are used for generating random processes, characterizing materials fatigue life data, and processing the simulation output.
PFAFAT includes routines for the simulation of both High Cycle and Low Cycle Fatigue cases. The example applications for the High Cycle Fatigue analysis software include the Space Shuttle Main Engine's (SSME) High Pressure Oxidizer Turbopump (HPOTP) main discharge duct, Low Pressure Fuel Turbopump (LPFTP) turbine drive duct, and (HPOTP) heat exchanger coil. The PFAFAT package includes programs to analyze elbow ducts with welds and straight ducts with welds having large temperature differences across the duct wall. The example application for the Low Cycle Fatigue analysis software is a high pressure fuel turbopump turbine disk.
The PFAFAT package includes other programs for fatigue analysis. MATCHR is a program for simulating the cyclic fatigue behavior of a material using fatigue test data. This program contains both the stress and strain formulations of the materials characterization model in a standalone form. PFAFAT also includes a set of programs which compute the prior failure distribution parameters and assurance calculations. Routines to implement the Bayesian statistical procedure are supplied. This procedure is used to combine operating experience with the prior failure distribution obtained from the probabilistic failure modeling. A number of random number generators are provided, including uniform, normal, gamma, beta, and Weibull distributions.
The Probabilistic Failure Assessment (PFA) methodology, which is utilized by PFAFAT, is an advanced approach for evaluating failure risk, assessing service life, and establishing design parameters for structures subject to fatigue failure. This technique combines engineering analysis with experience from tests and service to quantify failure risk. The PFA methodology is particularly valuable when information on which to base design analysis or failure prediction is sparse, uncertain, or approximate and is expensive or difficult to acquire.
The PFA methodology is a prescribed statistical structure in which engineering analysis models that characterize failure phenomena are used in conjunction with uncertainties about analysis parameters and/or modeling accuracy to establish failure probability distributions for specific failure modes. These distributions can then be modified by means of statistical procedures of the PFA methodology to reflect test or service experience.
The PFA methodology is applicable to failure modes of structures that can be analytically or empirically modeled. Engineering analysis models employed for design or prediction of failure due to specific failure modes are used in PFA. PFA can be applied at any time in the design, development, or operational phases of a program using the information available. Sensitivity analyses conducted as a part of PFA can be used to evaluate alternative measures to control risk, such as design changes, testing, or inspections, thereby enabling limited program resources to be allocated more effectively.
PFAFAT carries the NASA case number NPO-18965. It was originally released as part of the NASA COSMIC collection.
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