Fatigue Life Prediction Division Unconfirmed Minutes

April 19, 20 & 21, 1999 -DaimlerChrysler - Auburn Hills, MI

Tuesday, April 20, 1999 - Divisional Progress Meeting

1. October 1998 Structural Analysis Division minutes were approved as written.

2. C.C. Chu opened the session by saying that some committee members had expressed some confusion about how the committee was organized. She offered one overhead, which shows the relationships between the divisions: One of the functions of the Road Loads Data Division is to provide the load data used by the Component Test and Structural Analysis Divisions. One of the functions of the Component Test Division in testing components is to provide nominal and local strain gage measurements to be used by the Fatigue Life Prediction Division (FLPD). One of the functions of the Structural Analysis Division is to provide the stress analysis of remotely loaded complex structures. The elastic stress-strain results, along with multiaxial notch correction routines can be used by the FLPD. One of the functions of the Material Properties Division is to produce material characterizations to be used in the fatigue analysis by the FLPD. As Chu presented it, the divisions support each other with results from each funneling to FLPD for stress-strain tracking and life predictions.

3. John Bonnen ("Multiaxial Fatigue Life Response of Normalized 1045 Steel Subjected to Periodic Overloads") presented an overview of part of his thesis. He also incorporated research from other U of Waterloo researchers (Conle, Dequessney, Topper, and others) in his presentation. John noted that we often do not consider low amplitude cycle damage in our fatigue calculations, but this can be in error, if field variable amplitude loading includes overloads. He showed a 4X difference in life compared to constant amplitude tests when the variable amplitude history contained a 1% strain overload. There is a parabolic relationship between crack opening stress and overload stress, whereas our constant amplitude test specimen data would lead us to believe that the relationship is linear. John proposed using "overload" strain-life data in life predictions. This data includes the effect of the overload, and John noted that it produces a curve similar to the method used by Tom Cordes for fitting properties. John showed results for bending overload followed by low amplitude torque cycling and also for bending overload followed by holding the bending load constant and applying low amplitude torque cycling. He saw a 2X drop in the endurance strain, regardless of the B/T ratio, when the histories included overloads. He saw a 5X-scatter band when plotting max shear strain or Brown-Miller vs.Life. The best parameter for correlating the data was the Fatemi-Socie-Kurath parameter. Contact John at 313-322-9127 for more details.

4. Al Conle ("Fatigue Analysis Modules and more on FD&E Web Site") noted that we have put in place several standard file formats to facilitate quick transfer of data between companies. He showed that a standard wrapper (a header and a tail) can be cut/pasted to these files to allow us to do processing of the data on the Internet. The processing can include plotting, life calculations, curve fitting, and more. This is a way to extend the value of the raw data and to set up shared material databases. Al encouraged members to look at examples he has set up on fde.uwaterloo.ca. Al can be contacted at aconle(at)ford.com.

Wednesday, April 21, 1999 - Divisional Planning Session

Web tool development and testing - There seems to be wide enough interest in the web tools Al Conle Presented in the progress meeting. To encourage more participation and development, most attendees agreed to provide Al or Chin-Chan through email (aconle(at)ford.com, cchu(at)ford.com) a material file, such as the stress-strain or strain-life curve. Any suggestion as to what fatigue analysis tools are beneficial to FD&E members is also welcome.