AFGROW User Workshop 2021

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 13-14, 2021.

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
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
AFGROW release 5.4 8:30AM- 9:30AM

 James Harter, Alex Litvinov (LexTech, Inc.)

Assessing Limited Pedigree da/dN Crack Propagation Data 8:30AM- 9:00AM

 Mark Thomsen ( USAF, A-10 ASIP Analysis Group)

A-10 durability analysis method development 9:30AM- 10:00AM

 Richard Lammons, Luciano Smith (SwRI)

Continuing Damage Testing and Analysis 10:30AM- 11:00AM

 Matt Andrus ( USAF, T-38 Structural Integrity & Analysis Group)

Kt free CX test program 11:00AM- 11:30AM

 Jake Warner ( USAF, A-10 ASIP Analysis Group)

Investigating SIF Extractions using Solver Agnostic Tools 2:00PM- 2:30PM

 Lawrence “Charlie” Stoker ( Denmar Technical Services, Inc.)

Rapid 2 Point RS Predictions in AFGROW 2:00PM- 2:30PM

 Jake Warner (USAF, A-10 Analysis Group)

AFGROW BEASY Integration For Improved Life Prediction 3:00PM- 3:30PM

 Ryan Butchers, Sharon Mellings, Tom Curtin, John Baynham and Robert Adey (CMI BEASY )

AFGROW Future Development Discussion 3:00PM- 3:30PM

 James Harter, Alex Litvinov (LexTech, Inc.)

Spike Overload Crack Growth Challenge 4:00PM- 4:30PM

 Kevin Walker (QinetiQ Australia – Melbourne, Australia)

Spectrum manager overview 4:30PM- 5:00PM

 Matthew Gross (LexTech, Inc.)

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.

AFGROW release 5.4
James Harter, Alex Litvinov - LexTech, Inc.

Compression Pre-cracking Methods to Generate Near-Threshold Fatigue-Crack-Growth-Rate Data
J. C. Newman, Jr. - Fatigue and Fracture Associates, LLC;

This presentation will review the current ASTM load-reduction test method and discuss issues of possible concern. An explanation of a compression pre-cracking threshold test methodology will also be provided. A comparison of near threshold crack growth rate data will be made for several materials. Finally, a proposed annex to ASTM E-647 will be presented.

Cross-Comparisons of Stress Intensity Factors from Various Sources: The Pathway to Improved SIF Solutions
Robert Pilarczyk - Hill Engineering

Building Block Testing As Applied to Crack Growth Methods, (BAMF)
Juan Perez, Adam Morgan - Northrop Grumman

A building block test effort is a vital and necessary component to certifying aircraft structure. In this presentation, the application of coupon and element level building block test results to identifying analysis parameters, used as part of an air vehicles crack growth methodology, are examined. The applicability of key analysis parameters, such as available stress intensity solutions, angles at which stress intensities are evaluated (f-angles), closure correction factor (ßr), and load interaction models, to the analysis method in general and/or to specific usages/control points are discussed. Both quantitative and qualitative metrics used in assessing the validity of the parameter settings are discussed. Finally, the overall correlation of the final set of analysis parameters are discussed along with the validity of applying applicable parameters settings to analyses using BAMF V7 is presented.

Part through crack at hole finite width correction
James Harter - LexTech, Inc.

A-10 DTA ground rules refinement studies
Luciano Smith - SwRI

The A-10 ASIP team has performed a number of analytical studies recently to help in refinement of the DTA ground rules. Typically, these studies have involved reviewing the function in question, determining the impact of incorporating the function on A-10 analyses, and investigating the relative accuracy of the different options. This presentation summarizes the studies performed that investigated the use of varying vs constant corner crack aspect ratios, standard vs advanced models, net section yield as a failure criterion, and the Generalized Willenborg compressive cycle yield zone correction.

A-10 Auxiliary Longeron Damage Modeling and Repair
Brian Boeke - SwRI

The A-10 program has recently discovered a trend in the fleet showing damage in the upper auxiliary longeron. Four aircraft have been discovered with severed longerons, and many with crack indications. The load path in the area is unique and poorly designed. The intended load path is shear transfer through a skin panel due to a step up from the forward fuselage longeron section to the center fuselage section. Due to the presence of a removable panel, this skin panel is attached with clearance fit holes and nut plates. The consequence of this is load gets transferred through the frame section common to the two longeron segments instead of the skin panel. The interest related to AFGROW is two fold. First, there is a large off-axis load component since the load has to transition vertically through the frame and skin panel. Secondly, there is significant variation in the TSF and BSF for the critical hole for different load levels within the spectrum. At about 25% max spectrum load, the TSF is approximately 0.78 and BSF is 13.5, and at max spectrum load the TSF is about 0.89 and BSF is 5.51. This presentation intends to drive discussion within the group on how best to handle these scenarios within AFGROW.

Investigating SIF Extractions using Solver Agnostic Tools
Lawrence “Charlie” Stoker - Denmar Technical Services, Inc.

Many FEA programs offer Stress Intensity Factor (SIF or K) calculations for certain crack shapes. A notable exception is Siemens NASTRAN. MSC PATRAN requires additional solver add-ons to determine SIFs. ANSYS and StressCheck have the most robust SIF calculation tools but have limited capability with very large, multi-material assemblies. A general solution to determine SIFs based on nodal values of displacement and stress around the crack tip was desired. Using standard 2nd order elements (hexahedral, pentahedral, pyramid, and tetrahedral), models were built in Siemens Simcenter/NASTRAN. Both the Displacement Interpretation Method (DIM) and Contour Integral Method (CIM) were explored. A crack construction methodology, data extraction methodology, and exploration into the underlying formulas were also studied and will be presented.

AFGROW BEASY Integration For Improved Life Prediction
Ryan Butchers, Sharon Mellings, Tom Curtin, John Baynham and Robert Adey - CMI BEASY

Work has recently been completed to establish an integration of AFGROW with the BEASY Fatigue & Crack Growth software. Utilizing the AFGROW COM Interface, developments have been undertaken to support efficient communication between the two software platforms. This integration has significant value in that the BEASY software provides, highly accurate and structurally representative stress intensity factors, that can be used in conjunction with crack growth equations and fatigue crack growth material data available in AFGROW. By leveraging the unique capabilities of each software platform we can offer the engineering community, higher fidelity fatigue crack growth simulations based on more realistic structural models and loading conditions. Ultimately, the more accurate capture of crack shape evolution, coupled with vetted material data and crack growth relationships, will provide improved structural lifing prediction capability.

Quantifying sources of experimental and numerical variability using a 3D FE modeling validation process
Adrian Loghin - Simmetrix Inc.

Fatigue crack growth round robin challenges can provide very useful verification and validation benchmarks for the damage tolerance design community. A corner crack at a fastener hole is a common round robin example due to its relevance in aircraft structural integrity assessment. Various tools are available to the analyst to perform fatigue crack growth life assessments that resemble specimen level testing conditions, compare against measurement data for reaching validation requirements and apply the same modeling technique with confidence at component or structure level. 3D finite element modeling is one of the techniques that can be employed in simulating incremental crack growth. Using SimModeler Crack, nominal experimental conditions from two fatigue crack growth test procedures (made available to the ERSI working group) were simulated using 3D FEA and, fatigue crack growth predictions were compared to the corresponding physical measurements. One advantage of employing readily available 3D modeling techniques over reduced order models is the ability to deterministically evaluate sources of variability related to modeling assumptions (one example is crack front shape), experimental procedure (specimen misalignment) or geometric dimensions (interference fit allowance). Off-nominal conditions were simulated to quantify the sensitivity of crack growth prediction (remaining useful life) to different sources of variability and therefore, provide a broader modeling validation assessment.

Spike Overload Crack Growth Challenge
Kevin Walker - QinetiQ Australia – Melbourne, Australia

A key challenge generally for predicting fatigue crack growth is the use of baseline constant amplitude (CA) data to predict the behaviour under spectrum loading. Predicting CA behaviour for a given geometry and loading should be relatively simple and accurate. In the case discussed here, a compact tension specimen manufactured from 7075-T6 aluminium alloy was subjected to tension-tension R=0.1 loading. After a period of sustained and stable growth, a single factor 2.0 spike overload was applied and then the CA loading was resumed. The crack did continue to grow, and after another period of sustained stable growth, another single factor 2.0 overload was applied. The CA loading was again resumed and growth continued. This scenario was recently offered up to the fatigue and fracture community as a blind prediction challenge. Several submissions were received. The results from this challenge case are presented and discussed here.

Spectrum manager overview
Matthew Gross - LexTech, Inc.

Assessing Limited Pedigree da/dN Crack Propagation Data
Mark Thomsen - USAF, A-10 ASIP Analysis Group

Obtaining and assessing the utility of crack propagation data, specifically with limited documentation for how the data were generated, is a challenge. One option is to disregard the data altogether and develop your own based on ASTM E647 in combination with test expertise. This can prove prohibitive for many analysts due to lack of funding, lack of experience, or both. Another is to analyze data available and see how various data sets compare to each other and as a group. In this example, a couple options were evaluated. First, da/dN distributions were determined incrementally at fixed ranges of delta K. The second approach was to develop delta K distributions based on fixed ranges of da/dN. It was determined that the latter approach was impractical because a fixed range of da/dN, i.e. a scatter factor, is not consistent across the range of delta K. In contrast, choosing a fixed range of delta K, for conversation sake, could be justified by an acceptable load uncertainty. Although a 5% variation, positive and negative, was chosen, the concept could be adapted based on unique analysis criteria. A two parameter Weibull analysis process was applied to each of the various data groups for a collection of 7050 crack propagation data. In addition to highlighting how the data varied through a range of delta K, other observations will be highlighted for further discussion.

Material comparisons to justify the nacelle hanger frame material substitution from forging to machined plate
Kaylon Anderson - USAF, A-10 ASIP Analysis Group

A-10 durability analysis method development
Richard Lammons, Luciano Smith - SwRI

Durability analysis is in work on A-10 control points with crack indications from fatigue tests. SwRI began with both a strain-life approach and a crack growth life approach. For the crack growth calculation, each CP was assigned an initial flaw size of 0.01” and the COM was used following the A-10 DTA ground rules. For the strain-life analyses, a new COM was developed. The strain-life approach saw significant increase in durability life compared to the damage tolerance analysis. In order to understand and verify the results, SwRI performed a sensitivity study on the parameters required for the strain-life method.

Continuing Damage Testing and Analysis
Matt Andrus - USAF, T-38 Structural Integrity & Analysis Group

A fatigue test program is being conducted for the continuing damage scenario (two cracks growing on opposite sides of a hole). The test matrix includes some coupons that are pre-cracked and some that are not. Various analytical models will be used to predict the crack growth and comparison will be made to the measured cracking in the coupons. It is desired to gain insight into several questions related to the analytical models (such as: what is an appropriate secondary flaw size?) and to compare the multi-phase approach vs the simultaneous crack growth approach.

Kt free CX test program
Jake Warner - USAF, A-10 ASIP Analysis Group

Interference fit hole testing
Tomas Mills - APES Inc.

Development of an Analytical Methodology for Taper-Lok Fastener Holes
Robert Pilarczyk - Hill Engineering

Sensitivity Study on Cold Expanded Fastener Hole Damage Tolerance Life
Laura D. Hunt - SwRI

This presentation summarizes a cross-committee effort within the ERSI Working Group to help identify the driving factors in the Cx process that contribute to extended damage tolerance life. FTI modeled 29 coupons with varying parameters using their ABAQUS process simulation model and the resulting residual stress fields were extracted. AFGROW-BAMpF models were then created for each individual geometry and stress field. A surrogate model was created by fitting the input variables to the output (life). Global sensitivity analysis revealed that sleeve thickness was dominant; however, results should be interpreted with caution since the input data was from observed measurements and not a DOE.

Rapid 2 Point RS Predictions in AFGROW
Jake Warner - USAF, A-10 Analysis Group

Fatigue predictions that include residual stresses have historically required iterative type analyses with FEA. A complete fatigue prediction would often take many hours. Alternatively, AFGROW has a built in capability to include residual stresses on a traditional analysis, completed in seconds. An overview of recent comparisons using the AFGROW built in capability to test data, and FEA based predictions is shown with lessons learned and recommendations for applicability of each approach.

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

BAMF Consortium Group Meeting

The previous workshop proceedings are available online ↷