Welcome and Introduction (Continental Breakfast)

AFGROW, Release 5.3 includes several new features and capabilities. The most important new capabilities/features include:

• A new, advanced solution for through crack(s) at holes under bearing loading
• Ability to use different crack growth rate data for each growth direction (a and c)
• Ability to use different crack growth rate data for spectrum defined temperature tags
• Solution for corner cracks at the “knuckle” of a C/S hole
• Bearing solution for advanced through crack(s) at a hole

The fracture mechanics database (AFMAT) on the AFGROW web site has been expanded to include data for several additional materials. The search engine has been improved to allow additional search capabilities, and new tabular crack growth rate curve fits for over 50 materials have been added.

A new Spectrum Management Tool is also available for AFGROW, Version 5.3 licensed users. This software simplifies creation and modification of load history data. Users create individual sub-spectra which may be sequenced in any desired order. Loading data may be entered manually, or by copy/paste from any Windows application. Loading data for a single channel are currently supported by AFGROW, but spectra for three load channels (axial, bending, and bearing) may be created with this software for use in a future release of AFGROW. Spectrum clipping/truncation capabilities are included, and users may add environmental tags to any spectrum level to trigger the use of alternative crack growth rate data in AFGROW for the given environment. The resulting load spectra are saved in XML format.

Break

An important part of crack growth prediction with variable amplitude loading is to utilize crack growth retardation. The Generalized Willenborg retardation model, most commonly used for T-38 analyses modifies the effective stress ratio of cycles following an overload. Recent examinations by USAF demonstrated that this retardation model can significantly adjust the stress ratios used to calculate crack growth rates. For certain fatigue critical locations on the T-38, over 80% of the effective stress ratios used to calculate growth rate are negative despite the applied stress ratios being largely positive. This revelation has focused material characterization efforts on negative stress ratios for fatigue crack growth rate testing. Test programs completed by Southwest Research Institute and USAF have provided the necessary data to accurately determine material behavior at negative stress ratios. Due to the large amount of cycles at negative effective stress ratios when modeling, small differences in fatigue crack growth rate characterization in this regime lead to significant differences in life predictions. USAF has developed novel methods to quantify Rlo from test data. The results of the analysis suggests that Rlo may be significantly higher than values that have been considered best practice.

Constant amplitude countersunk hole fatigue testing was recently performed by SwRI in order to validate the new K solutions for countersunk holes added to AFGROW v5.3. The follow-on analysis of the test data show correlation between the Ks from AFGROW v5.3 and the Ks developed from the test data, with a few issues that were then corrected by LexTech. This presentation will review the results of the testing & analysis.

Lunch Break

In general, fatigue crack growth rate testing is performed using one of a handful of standard specimens, all of which have a through-thickness crack. Testing was performed to develop near-threshold growth rates for 2024-T351 plate and 2024-T3511 extrusion at two different stress ratios (0.1 and -0.3) and two different specimen geometries. The specimens included an edge cracked plate and a centered hole in a plate, both with a corner crack instead of the typical through crack. This presentation will include some background information leading to the motivations for the testing, a description of the testing including the unique requirements necessitated by the two-dimensional nature of the crack, test results, and potential impact on analysis.

This presentation will give an overview of all updates and added features scheduled to be released in Spectrum Manager v.1.1. Some of the updates include improved data handling for large spectra, a redesigned Exceedance Plot, and improvements to the Preview Spectrum tab. There will also be a discussion of upcoming features that will be added to Spectrum Manager in future versions.

In part one of the presentation, non-dimensional geometric correction factor, ß, data for stress intensity factor, K, calculations are generated through finite element analyses and collected from the literature for axially loaded single-edge cracked plates with rotationally free and constrained loaded edges typically used in fatigue crack growth experiments. The solutions are valid for crack length-to-width ratio, a/W, in the range of 0.01 ⩽ a/W ⩽ 0.975 and plate height-to-width ratio, H/W, in the range of 0.8 ⩽ H/W ⩽ 10.0. Comparisons are made between the literature reported data and the present effort’s results with generally satisfactory correlation. However, differences as large as 12.7% exist for short cracks in small H/W valued plates.

In part two of the presentation, we’ll revisit the environmentally assisted crack growth analyses presented in 2015 with crack growth rate data that has come available since that time.

This presentation will provide an overview of new updates made to the AFMAT database. This presentation will also review the material data added to the online database. Future plans for database development and integration with AFGROW will be also discussed.

Group Discussion

Continental Breakfast

SwRI recently completed fatigue crack growth rate testing in the L-T and L-S directions for four aluminum alloys/product forms: 2024 plate and extrusion, 7075 plate, and 7175 forging. This testing was performed using a combination of standard ASTM E647 through-crack geometries [e.g., C(T) and M(T)] and part-through corner crack test axially loaded specimens. Testing was also performed in the diagonal direction between L-T and L-S, defined by ASTM E399 as L-TS, for the 2024 and 7075 materials. Presentation of the results includes a discussion of the impacts of implementing the tested rates in typical two-dimensional (a-tip and c-tip) part-through crack analysis and the potential impacts on multipoint analysis for which the analytical growth is often not orthogonal to the material directions.

Life predictions for the 2017 AFGROW blind round-robin test effort were in good agreement with the test results in terms of life. The predictions for the centered hole specimens were better than the offset hole specimens, but the crack shape predictions for the corner cracks did not match the trends seen in the any test case. The test data seemed to indicate that crack growth in each direction was following a different growth rate curve. This presentation will summarize the result of using the test specimen fractography data to estimate the growth rate curves for the c and a-directions and applying the result to “post-dictions” for the three center hole tests.

Break

Accurate characterization of crack aspect ratio (a/c) behavior for corner cracks at fastener holes has proven to be problematic with differing trends between observed test behavior and analytical predictions. Recent investigations as a result of the AFGROW Round Robin effort, utilizing an inverse analysis method to derive crack growth rate properties in the a- and c-directions, have proven to increase to correlation between test and analysis. Results derived for this same approach for the ERSI Round Robin baseline cases were compared to historical test data to understand the influence of multi-directional material properties of predicted versus test aspect ratio correlation. These comparisons as well as future considerations will be discussed.

Group Discussion

Post processing life prediction output information can help verify input data, promote a better understanding of the life prediction process, and provide a detailed summary of the various elements of the analysis. Our initial approach to post processing, issues and challenges discovered during development will be presented. This presentation will also describe the software architecture and demonstrate the capabilities of the beta version of the software.

Group Discussion

Lunch Break

Information on the latest research and development efforts and plans beyond AFGROW Release 5.3.

Group Discussion

This will be a discussion of the current release of BAMF v5.0 (Feb 2, 2018)

• Features (users’ manual, installation packages)
• Reported bugs and issues
• Current output format/post processing
• Current BAMF default user options
• Local system crack creation

Break

Accounting for Thermal Process Induced Residual Stress in Additive Manufacturing Based Laser Cladding Repair of High-strength AerMet®100 Steel-Kevin Walker Multi-Crack Multi-Point BAMF-An implementation case of a generic milled pocket crack

This will be a discussion of items slated for the next release of BAMF v5.1 (Jan 2019)

This is an open discussion of items we would like to go after in the future. We would like to rack and stack this list based on desire/interest/feedback from the community. The community will be able to add to this list as well. These are items we would like to incorporate if funding becomes available.

Group Discussion