PRobability Of Failure (PROF) Software
Overview
Under contract to the Air Force, UDRI has developed a structural risk analysis program, Probability of Failure (PROF) that synthesizes the hazard rate and probability of fatigue failure as a function of flight hours based on data largely available from the USAF Aircraft Structural Integrity Program.
A basic run of PROF estimates the single flight probability of failure and probability of failure between inspections as a function of flight hours for a population of critical locations as defined by the unique damage tolerance analysis (DTA) for the location. There are three major aspects of the process:
- Estimating the crack size distribution as a function of light hours.
- Estimating the distribution of time to reach a pre-defined crack size.
- Calculation the probability that a stress will exceed residual strength during a flight.
Capabilities
PROF comprises a comprehensive graphical user interface (GUI), a data management system and computation modules. The following is a brief listing of the key GUI/data management features:
- A tree for saving, recalling and organizing information related to control points and analysis.
- Wizards that provide step-by-step procedures for entering and updating information.
- A standards library for quick recall of crack size distribution and inspection capability information with drag-and-drop entry for analyses.
- Data organization by user-defined groups of analyses, such as Model/Design/Series (MDS).
- Grouping of control point information by user-defined classes.
- Storage of descriptive information concerning input and analysis results in a Microsoft Access database.
- Provisions for exporting results to Microsoft Excel for user-specific analyses.
PROF Software Window Screenshots
Figure 1
Single flight probability of failure
Figure 2
Failure probability between inspections
Figure 3
Crack distribution at inspection (before/after)
A basic PROF analysis run calculates the probability of failure as a function of flight hours due to the growth of fatigue cracks at a population of locations defined by a single damage tolerance analysis, such as a control point. Failure is defined in terms of the Irwin fracture criteria. For the control point, PROF calculates tables and plots of:
- The SFPOF as a function of flight hours for the combination of all similar control points (see Figure 1).
- The probability of failure as a function of flight hours for the combination of all similar control points (see Figure 2).
- The expected percentage of sites at which cracks will be found at each inspection.
- The predicted distribution of crack sizes immediately before each inspection (see Figure 3).
- The predicted distribution of crack sizes immediately after each inspection (see Figure 3).
- The predicted distribution of crack sizes that are missed at each inspection.
- The predicted distribution of crack sizes that are found at each inspection.
- The probability of failure as a function of crack size.
The results of an analysis can be exported to an Excel file for further use.
The SFPOF and probability of failure results from a basic PROF run can be combined in post-processing phases to describe failure risks for more complex structural configurations and to calculate fleet summaries. In particular, it:
- Facilitates such calculations by providing the ability to perform multiple analyses and export the results from the multiple analyses to an Excel file.
- Combines SFPOFs from independent (non-interacting) control points to obtain failure probabilities for the combination.
- Calculates the expected number of fleet failures at selected combinations of control points as a function of calendar time from the projected number of flight hours for calendar periods of the individual aircraft in a fleet.
Contact
PROF is proprietary to the University of Dayton but is freely available for U.S. government applications. For applications not directly related to the U.S. government, a license for the use of PROF can be arranged.
Mr. Chris Buck
Phone: 937-229-4013
E-mail: christopher.buck@udri.udayton.edu