AFGROW User Workshop 2017

Davis Conference Center

An AFGROW Workshop will be held at the Davis Conference Center in Layton, UT
on September 19-20, 2017.

The purpose of the Workshop is to provide a forum for AFGROW Users to exchange information and ideas, network with peers from industry, and gain access to the AFGROW developers.

The Conference Center is adjacent to the Hilton Garden Inn Hotel, and is very close to several other hotels in Layton. Continental breakfast and afternoon refreshments will be provided.

Group discussions will also provide direction for new capabilities and improvements, best practice methods and tips and tricks from the experts. AFGROW team will also provide information on the latest development efforts.

Who should attend: Engineers, researchers, technologists, and managers who are users of AFGROW and/or have an interest in Crack Growth Analysis tools.

The cost will be: $460.00/person until July 31, $495.00/person thereafter (continental breakfast and refreshments are provided).

The Workshop registration form is available to download.

AFGROW Workshop 2017 Round-Robin Life Prediction Invitation for Centered & Offset Holes with a Single Corner Crack

Purpose: The purpose of this round robin exercise is to predict the evolution of the crack aspect ratio (a/c) and total life of an initial corner crack at a centered and offset hole. The loading spectrum, material data, and Initial Flaw Size (IFS) are provided for each test specimen. Participants will use the AFGROW framework as the life prediction tool. Certain aspects of the AFGROW framework are also provided for common use by each participant, and all other aspects will be left to the user’s discretion. It is important that each participant follow this guidance so that variability in the predictions is limited to the aspects left to user discretion. Test data from this Round Robin will be presented at the 2017 AFGROW Workshop along with predictions made by each participant. Each participant is invited to give a short presentation (10 -15 minutes) outlining the pertinent details of their analyses. A group discussion will follow to help identify which analysis options worked best for this study, and what improvements to AFGROW may be helpful in the future. The results will be published on the AFGROW Web Page following the Workshop in a manner that will not identify who performed each prediction.

Day 1, 19th September

Day 2, 20th September

8:00 - 8:30Welcome and Introductions (Continental Breakfast)
8:30 – 10:00TBD
James Harter, Alex Litvinov (LexTech, Inc.)
10:00 – 10:30Group Discussion
10:30 – 10:45Break
10:45 – 11:15Stress Ratio Influence on da/dN with the Generalized Willenborg Model – Updated Material Data & Fitting Processes
Robert Pilarczyk (Hill Engineering, LLC)
11:15 – 11:45Quantifying the Impact of the Modified Residual Stress State at a Cold Expanded Hole, Due to the Presence of a Fatigue Crack, on a Fatigue Life Prediction Using BAMF
Scott Carlson (SwRI)
11:45 – 12:00Group Discussion
12:00-1:00 Lunch Break
1:00 – 1:15Round-Robin Life Prediction Effort Introduction
Jim Harter (Senior Consultant, LexTech, Inc.)
1:15 – 2:15Round-Robin Testing
Scott Fawaz (SAFE, Inc.)
2:15 – 3:15Fractography and Crack Growth Rate Data
Tom Mills (AP/ES)
3:15 – 3:30Break
3:30 – 4:00Prediction Results
4:00 – 5:00Presentations by Participants
8:00 - 8:30Continental Breakfast
8:30 – 9:30 TBD
Cordell Smith, James Harter (LexTech, Inc.)
9:30 – 10:00 TBD
Alex Litvinov (LexTech, Inc)
10:00 – 10:15Break
10:15 – 10:45 Deployment of Smart Simulation Apps in Support of DaDT Activities
Ricardo Actis (Engineering Software Research & Development, Inc)
10:45 – 11:15 Prediction of Full Field Residual Stress in Arbitrary Bodies Using ERS-toolbox®
Caleb Morrison, Michael R. Hill, Adrian T. DeWald (Hill Engineering, LLC, Rancho Cordova, CA )
11:15 – 11:45The Future of BAMF
Joshua Hodges, Bob Pilarczyk, Michael R. Hill, Adrian T. DeWald
(Hill Engineering, LLC, Rancho Cordova, CA)
11:45 – 12:00Group Discussion
12:00 – 1:00Lunch Break
1:00 – 1:30Demonstration of Normalized Stress Correction Factor to Compute the Stress Intensity Factors for an Elliptical Surface Crack in a Stepped Flat Tension Bar
Scott Prost-Domasky (APES, Inc.)
1:30 – 2:00TBD
2:00 – 2:45TBD
James Harter, Alex Litvinov (LexTech Inc.)
2:45 – 3:00Break
3:00 – 5:00Group Discussion and Adjourn
Stress Ratio Influence on da/dN with the Generalized Willenborg Model – Updated Material Data & Fitting Processes
Robert Pilarczyk - Hill Engineering, LLC

Previous AFGROW presentations discussed the influence of retardation models and the resulting effective stress ratio, highlighting the need for additional crack growth rate data at negative stress ratios. As a result of these investigations, a test program was executed to develop crack growth rate data for common T-38 materials at multiple negative stress ratios. The presentation will review this new data, comparing and contrasting to previous material model extrapolations, as well as revisiting RLO. Concurrently, a structured material fitting process was utilized. Damage Tolerant Analysis comparisons will be presented to review impacts from new crack growth rate data and the material fitting process.

Quantifying the Impact of the Modified Residual Stress State at a Cold Expanded Hole, Due to the Presence of a Fatigue Crack, on a Fatigue Life Prediction Using BAMF
Scott Carlson - SwRI

Research has been underway for the past few years to quantify the effect a fatigue crack has on the residual stress field introduced by the Cold Expansion (Cx) process. In an effort to quantify this impact the Contour Method has been employed to determine the residual stress state in two aluminum alloys (2024-T351 and 7075-T651) after a fatigue crack has been propagated in it. Each coupon had a 0.50inch centered Cold Expanded (Cxed) hole that was designed to hit the “Low” end of FTI’s applied expansion specification. Eight (8) coupons were produced for each alloy and a range of fatigue crack sizes were propagated in them. This presentation will discuss how the residual stresses obtained through the Contour Method have been implemented into BAMF to provide a prediction of a fatigue condition and compare those results to fatigue test data. Two different methods were developed to define the modified residual stress traction stress equations which were utilized in the fatigue life predictions. The effects of the residual stress statistical distribution, as discussed at last year’s AFGROW Workshop, was also be implemented into the life prediction matrix, thus showing the effect of both the modified residual stress traction equation and the statistical distribution of the residual stress state on the final life prediction.

Deployment of Smart Simulation Apps in Support of DaDT Activities
Ricardo Actis, (Engineering Software Research & Development, Inc.)

Democratization of numerical simulation through the development and dissemination of expert-designed “engineering simulation apps” is rapidly gaining attention for durability and damage tolerance (DaDT) applications. Such apps must satisfy certain technical requirements to ensure their reliable use due to the high accuracy requirements in the computation of fatigue crack propagation life. Proper application of numerical simulation procedures requires expertise in computational engineering that is not widely or readily available. Standardization deployed by means of Smart Engineering Simulation Apps (SESA) can leverage this expertise for recurring analysis tasks, similar to the expertise of specialists in applied mechanics made available through engineering handbooks. Because classical handbooks have limitations in model complexity and scope, SESA developed by expert analysts can deploy verified solutions obtained by numerical means allowing models of much greater complexity for users who do not need to have expertise in numerical simulation technology.

By Smart Engineering Simulation Apps we mean FEA-based software tools developed for standardization and automation of recurring analysis tasks and process workflows for use by non-specialists. Designed to fit into well-defined analysis processes, engineering simulation apps capture institutional knowledge and best practices, can be shared by engineering groups at different geographic locations and produce consistent results by tested and approved analysis procedures. When designed to meet the requirements of Simulation Governance, simulation apps for engineering use are “smart” because their embedded intelligence enables simple, accurate, fast, efficient, and reliable (S.A.F.E.R.) simulations with built-in quality assurance, essential for the non-expert user.

This is particularly important in the area of DaDT where life estimate procedures require accurate computation of stress intensity factors along the crack front and the shape of the propagating crack is solution-dependent. An example of a simulation app for the prediction of fatigue life for cracks emanating from cold-worked holes, developed in support of the AFRL-SBIR Phase III project “Deep Residual Stress Method Demo Program”, and to accelerate the transition of new technology into professional practice, will be presented. The example simulation app has been connected to a residual stress database to facilitate the input of residual stress profiles and communicates with AFGROW via COM to determine the crack growth rate (da/dN) by interpolation, from the available da/dN-K curves of the material, using the values of SIFs for the mechanical load and the residual stresses determined by the app along the crack front.

Prediction of Full Field Residual Stress in Arbitrary Bodies Using ERS-toolbox®
Caleb Morrison, Michael R. Hill, Adrian T. DeWald (Hill Engineering, LLC, Rancho Cordova, CA)

Engineered residual stress (ERS) is increasingly being applied as a way to extend the durability and damage tolerance performance of primary structure in various industries including aerospace and power generation. To reduce development costs, reduce the development time, and increase the effectiveness of the final design, methods that accurately predict residual stress for surface treatments are being developed. ERStoolbox® is a software suite which predicts full field residual stress for a variety of processes including conventional shot peening (SP), laser shock peening (LSP), and cold hole expansion (CX). An overview of ERS-toolbox® will be presented along with example applications.

The Future of BAMF
Joshua Hodges - USAF, T-38 ASIP Analysis Group, Hill AFB, UT

The BAMF software, developed by the USAF (A-10/T-38), has evolved over the past seven years to take on unique and challenging fatigue crack growth analysis problems. Recent technological advancements include: complex geometries/crack scenarios, multi-point multi-crack analysis, and inclusion of residual stresses. Hill Engineering plans to facilitate the continued viability of BAMF for internal and external use. Hill Engineering plans to continue to update and maintain the software and support customer needs. This presentation will discuss the current state of BAMF, the near-term transition plan, and long-term thoughts to keep the capability relevant, viable, and growing. The presentation will also provide an opportunity to get input from the user community, similar to the framework established by LexTech with AFGROW.

Demonstration of Normalized Stress Correction Factor to Compute the Stress Intensity Factors for an Elliptical Surface Crack in a Stepped Flat Tension Bar
Scott Prost-Domasky - APES, Inc.

AFGROW is a very powerful crack growth analysis tool which allows the fracture mechanics analyst to efficiently access dozens of standard crack scenarios (with tension, bending, and/or bearing loads) in both through and part-through crack geometries. Stress Intensity Factors (SIFs) for each crack scenario are computed with either curve fits or table lookups—normally derived from finite element solutions or classic crack handbook solutions such as Tada, et al, “The Stress Analysis of Cracks Handbook.” Each of these methods assumes a specific far field load profile which causes a particular uncracked stress state on the intended crack plane—for instance, the tension loading of a plate with an elliptical surface crack assumes a constant tension far field, and causes a constant tension field in the uncracked state at the intended crack plane.

However, the fracture mechanics analyst will often need to have the SIFs for a crack embedded in a non-standard stress field; that is, the uncracked stress state does not match the uncracked stress state of any AFGROW standard solution geometry. Fortunately, AFGROW has an efficient method for adjusting the computed SIFs for the new, nonstandard stress field, either with Normalized Stress correction or Beta Corrections Factors in the Beta Correction Factor interface.

We demonstrate the use of the Normalized Stress correction on an elliptical surface flaw in the fillet of a 3D stepped flat tension bar. First, the uncracked stress at the intended crack plane in the fillet is calculated. Second, some minor calculations and curve fits are made to fit the data to the AFGROW specific format. Lastly, the data is read into the Beta Correction Factor interface and SIFs are computed for a few cracks. For comparison, SIFs are also computed with the p-version finite element software StressCheck.

If you would like to make a 20 or 40 minute presentation, please submit an abstract to . If you have a topic that requires more time, let us know and we will do our best to accommodate you.