AFGROW User Workshop 2023

Davis Conference Center Davis Conference Center
1651 North 700 West
Layton, Utah 84041

The next AFGROW Workshop will be held at Davis Conference Center in Layton, UT on September 12-13, 2023.

Are you, or someone you know, interested in learning about the latest developments happening right now in Fracture Mechanics? Would you like the chance to meet a wide range of experts from across the industry? Do you want to know more about the uses and capabilities of Crack Growth Analysis tools? All of these opportunities and more are available to you at the AFGROW Users Workshop.

The purpose of the Workshop is to provide a forum for AFGROW Users to come together to exchange information and best-practices, network with peers from the industry, and get a chance to talk with the AFGROW developers and community.

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

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

The Davis Conference Center is close to the Hill AFB South Gate, and is conveniently close to several hotels in Clearfield and Layton. Continental breakfast and afternoon refreshments will be provided.

You can register for the User Workshop online or alternatively you can download the registration form and fax or email it to us.

Register Online for Workshop

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.

Workshop Agenda (in progress)

8:00 AM
9:00 AM
10:00 AM
11:00 AM
12:00 PM
1:00 PM
2:00 PM
3:00 PM
4:00 PM
5:00 PM
Current AFGROW Release Overview 8:30AM- 9:30AM

 James Harter, Alexander Litvinov, James Lambert (LexTech, Inc)

CAStLE Continued K-Solutions Support 8:30AM- 9:00AM

 Gregory A. Shoales (USAF, CAStLE )

Fracture Analyses of Thin-Ductile Aerospace Materials 10:30AM- 11:30AM

 J. C. Newman (Fatigue & Fracture Associates, LLC)

Developing plugin models for offset loaded lug geometry 10:30AM- 11:30AM

 Adrian Loghin*, Alexander Litvinov**, James Harter** (*Simmetrix Inc., **LexTech, Inc.)

Recent Development in AFGROW COM and Plug-In Capabilities 1:30PM- 2:00PM

 James Lambert, Alexander Litvinov (LexTech, Inc.)

Cold-Expanded Hole Tolerance Effects: Pre-Test Predictions 2:00PM- 2:30PM

 Trevor Shoemaker (USAF, A-10 ASIP Analysis Group)

MSD Implementation in AFGROW 3:00PM- 3:30PM

 James Harter, Alex Litvinov (LexTech, Inc.)

Spectrum Manager overview 3:30PM- 4:00PM

 Matthew Gross (LexTech, Inc.)

AFGROW Future Development Discussion 4:00PM- 4:30PM

 James Harter, Alex Litvinov (LexTech, Inc)

Current AFGROW Release Overview
James Harter, Alexander Litvinov, James Lambert - LexTech, Inc

3D fatigue crack path deflection and residual stresses in 17-4PH stainless steel rod
Trevor Shoemaker - USAF, A-10 ASIP Analysis Group

Damage tolerant structures require accurate fatigue crack growth rate models for life prediction. Central to these models are fracture mechanics similitude and empirically gathered growth rates. In this work, standard test methods failed to achieve similitude for 17-4PH stainless steel round-rod but succeeded for plate. Material product form differences are interrogated through constant dK tests, crack path analysis, residual stress (RS) characterization, and growth rate simulation. Analyses revealed that quench-induced RS in the round-rod promoted a non-planar, 3D crack path with closure effects. Strategies to mitigate the RS/path effects are evaluated by controlling constraint, closure, environment, and heat treatment.

Fracture Analyses of Thin-Ductile Aerospace Materials
J. C. Newman - Fatigue & Fracture Associates, LLC

The critical crack-tip-opening angle or displacement (CTOA/CTOD) fracture criterion is one of the oldest fracture criteria applied to metallic materials. Improved computer-aided photographic methods have been developed to measure CTOA during the fracture process; and elastic-plastic, finite-element analyses (ZIP2D) with a constant CTOA and a plane-strain core have been used to simulate fracture of laboratory specimens. The fracture criterion has been able to link the fracture of laboratory specimens to structural applications. This paper analyzes fracture of cracked thin-sheet 2219 aluminum alloy over an extremely wide range in width, crack-length-to-width ratio, and applied loading (tension, bending, and combined tension-bending loads). The results from the critical CTOA fracture analyses on the thin-sheet material showed that the stress-intensity factor at failure (KIe) was linearly related to the net-section stress (Sn), as predicted by the Two-Parameter Fracture Criterion (TPFC).

A-10 Aft Cowl Cracking Analysis: An Example of Structural Digital Engineering
Brian Boeke - USAF, A-10 ASIP Analysis Group

The A-10 program office performed an urgent action TCTO to inspect fittings that attach the aft cowl of the nacelle to the main center section. This was done in response to an aft cowl departure in flight and subsequent preliminary crack findings. The TCTO revealed an extensive cracking issue with this interface and an analysis team was tasked to determine the root cause and subsequent inspection requirements for cracking.

The presentation shows how organic Air Force capabilities were leveraged to perform failure analysis, Finite Element Modeling (FEM), and multi-point crack growth analysis to validate results and determine a way forward for fleet management. The materials lab at Hill AFB was able to perform striation counting at multiple points along the fracture surface to correlate crack growth rates to analysis. Siemens Simcenter was used to build a Nastran FEM of the area near the attach fittings. The legacy stress analysis was used to determine appropriate loads. The forces on the attach fitting calculated with the Nastran model were then transferred over to the ESRD StressCheck to model the cracking geometry found in the failure analysis and correlate stress intensities to what would have been required to achieve the measured crack growth rates. The loads were scaled to create the appropriate stress profiles to match failure analysis. Then a multi-point fracture mechanics model was created to grow multiple cracks within the fittings as was seen in the data. The resulting crack growth curves and the detectable flaw sizes from inspection were used to reduce risk and manage the fleet.

Evaluation of T38 DTA Methods
Teresa Moran - SwRI

Overview of the Implementation of API 579 Stress Intensity Factor Solution for Cylinders in AFGROW
Alexander Litvinov - LexTech, Inc.

MSD Implementation in AFGROW
James Harter, Alex Litvinov - LexTech, Inc.

Various Cracking Patterns, Scenarios and Stages for Crack Growth Analysis
Dr. Patrick Safarian P.E. - FAA

In 1978, The Code of Federal Registry, Title 14 § 25.571 - Damage-tolerance and fatigue evaluation of structure, was published and mandated damage tolerance based inspections to ensure that the principal structural elements (PSE) of the airplanes remain safe throughout the operational life of the airplane. The threat associated with this risk mitigation was associated with the fatigue stresses that the structures experience during the operation. To satisfy the requirements of § 25.571, damage tolerance evaluations are carried out for every PSE and maintenance actions are developed and included in the airworthiness limitation section. For the damage tolerance evaluation, fracture mechanics is the common means to set the maintenance program. As part of fracture mechanics, crack growth analysis is performed to determine how many flight cycles or flight hours it takes for a crack to grow from a certain length to the critical length. The assumption of the location and modes of the lead crack and the associated adjacent cracks in the detail design points of the PSE are the key to a meaningful damage tolerance evaluation and suitability of the maintenance program to detect the crack before it reaches the critical length. In this presentation, acceptable cracking scenarios and patterns that are based on test and service history are presented to help the analyst establish suitable inspections to detect a crack in a timely manner and to meet the safety requirements prescribed by the aforementioned regulations.

CAStLE Continued K-Solutions Support
Gregory A. Shoales - USAF, CAStLE

For more than two decades CAStLE has been facilitating the creation of high-fidelity stress intensity factors for millions of crack configuration through the work of Börje Anderson. While this work had been supported by various USAF ASIP organizations in the past, since before 2010 CAStLE has obtained sufficient discretionary funds from a variety of DoD sources to continue this work independent of any direct project funding. Additionally, CAStLE has facilitated the in-person participation of Börje in the annual AFGROW Users meeting as a way of sharing the new solution space created over the previous year and to help steer the priorities of the remaining solution space in the years to come. As a way of introduction to this year’s presentation by Börje, this presentation will briefly summarize the accomplishments of the recent previous years.

New K-databases for straight shank and countersunk hole geometries developed 2022/2023
Börje Andersson - BARE, AB Sweden

Novel high-accuracy KI (φ)-solutions developed during 2022/2023 are reviewed.

  • For straight-shank hole geometries, the most important developments are new crack solutions for 19 different plate widths. A recent benchmark 2020 emphasized an urgent need for these solutions.
  • For countersunk hole geometries, two different hole depths are considered namely b/t = 0.50 and b/t=0.05 (almost knife-edge countersunk holes) for 19-30 different plate widths.
  • A difficulty with the KI(φ)-solutions is that KI(φ) goes to infinity near crack-vertices located at the conical surface, or upper plate surface, at almost half of the crack shapes. A special filtering technique was therefore developed which is based on the mathematical vertex theory, a technique that is used at each crack vertex when generating all KI (φ)-databases.
  • The solution accuracy is very high for all solutions, in all databases, with a relative error in K_I (φ) less than 0.05% at every point φ on the crack fronts. That includes all the vertex regions where KI → ∞, or, KI → 0, where the abovementioned filtering technique have been used.

The lecture describes analysis techniques, filtering techniques, schemes for control of solution accuracy and contents of new KI (φ)-databases.

Current A-10 Approach for Multi-Point Analysis and Residual Stresses
Jake Warner - USAF, A-10 ASIP Analysis Group

With the recent publication of a USAF Structures Bulletin on including residual stresses in analysis (EZ-SB-17-001 Revision A), the A-10 team has developed ground rules for utilizing residual stresses in analysis as well as ground rules for utilizing multi-point analysis methods. The presentation provides an overview of these ground rules as well as a brief summary of test validation for some applications.

Developing plugin models for offset loaded lug geometry
Adrian Loghin*, Alexander Litvinov**, James Harter** - *Simmetrix Inc., **LexTech, Inc.

Restarting BAMpF with Variable Amplitude spectra and Load interaction
Joshua Hodges - Hill Engineering

Recent Development in AFGROW COM and Plug-In Capabilities
James Lambert, Alexander Litvinov - LexTech, Inc.

Cold-Expanded Hole Tolerance Effects: Pre-Test Predictions
Trevor Shoemaker - USAF, A-10 ASIP Analysis Group

Compressive residual stresses (RS) imparted to structures via cold-expansion (Cx) of fastener holes are critical for fatigue life extension of airframes. Recently, there has been progress in predicting the fatigue life of Cx holes with RS measured using the contour method and multi-point stress intensity simulations. However, the Cx process has several factors that cause significant variation in the RS field and associated lifing predictions. One critical factor is the Cx applied expansion (Ia), but manufacturing tolerances (e.g., hole size, mandrel size, etc.) can result in Ia variations up to ~25% from nominal. The current work examines fatigue life prediction variations due to Ia differences in contour-based Cx hole RS fields. Over 50 simulations were performed representing both in- and slightly out-of-tolerance Cx processes. Predictions for in-tolerance Cx holes (Ia = 3.0-4.5%) showed a wide life improvement factor (LIF) ranging from 2.5-31. With the large number of unique RS fields analyzed, results from this work may serve as a benchmark for Cx predictions utilizing contour-method based RS fields.

Spectrum Development for Complex Loading in Aircraft Structures
James Burd - Aeronautica

Spectrum Manager overview
Matthew Gross - LexTech, Inc.

This presentation will give an overview of the upcoming Spectrum Manager v 1.3.

AFGROW Future Development Discussion
James Harter, Alex Litvinov - LexTech, Inc

Information on the latest research and development efforts and plans beyond AFGROW Release 5.4

The previous workshop proceedings are available online ↷