At this year’s ASIP 2023 Conference in Denver, CO, ESRD provided a 2-hour training course titled “Enhancements in StressCheck v12.0 for DaDT Analysis of 3D Fastened Connections”, presented a technical paper titled “Experimental Validation of DTA Modeling of Bonded Wing Skin Repairs“, and passed out 3D printed F-35 and C-130 models at our booth inside the Gaylord Rockies Resort & Conference Center. The models were a big hit — look out for some new aircraft next year!

Conference Snapshot

ESRD’s Brent Lancaster, Patrick Goulding, and Brian Lockwood spent the week chatting with ASIP attendees and meeting many enthusiastic StressCheck users. The ASIP Conference has become an exciting platform for demonstrating many strong use cases of StressCheck spanning the ASIP community, with around a dozen technical presentations utilizing our technology for their DaDT analyses. We are honored to be such a prominent part of this event and to have so many talented and loyal users in this industry.

We would like to extend our sincerest gratitude to all those who attended Brent’s training, Brian’s technical paper presentation, and/or stopped by our booth to say hello to us. In addition, this was Patrick’s first ASIP Conference and he was thrilled to have the opportunity to meet you all. We really enjoy getting the chance to see you each year and we’re already looking forward to attending ASIP 2024 in Austin, TX.

ASIP 2023 Training Materials Available

On Monday, November 27th, Brent had the pleasure of providing a training course to a large group of attentive ASIP engineers on Enhancements in StressCheck v12.0 for DaDT Analysis of 3D Fastened Connections. We were thrilled with the level of interest and engagement, and the opportunity to present the latest in StressCheck. Thanks to those who attended the training course in person (as well as virtually)!

If you are interested in this topic, you can download Brent’s training presentation (in PowerPoint show or PDF format) and watch the video demo via the below link (note: you must be a registered user to view the training materials):

We are looking forward to receiving your feedback on the training course presentation, as well as your ideas for ASIP 2024 training course topics.

ASIP 2023 Technical Paper Presentation Available

On Thursday, November 30th, Brian had the honor of presenting his technical paper “Experimental Validation of DTA Modeling of Bonded Wing Skin Repairs” to a strong audience of engaged ASIP attendees. The paper was a collaboration between ESRD, AP/ES (Dr. Scott Prost-Domasky) and USAF AFMC WRALC/ENC (Laura Pawlikowski), and continued their project discussed in last year’s presentation (“DTA of Bonded Repairs on the Wing Skin of the C130 Using Finite Elements“) by providing experimental testing data to validate their simulation results.

If you are interested in this topic, you can view Brian’s technical paper presentation (in PowerPoint show or PDF format) via the below link (note: you must be a registered user to view the training materials):

Preview StressCheck v12.0!

Would you like to schedule a preview demonstration of the new features in StressCheck v12?

We would be happy to walk you through the exciting updates to the user interface design, model navigation and visualization tools, and enhanced meshing features.

ESRD, Inc. will be exhibiting, presenting a technical paper (on DTA of bonded repairs) and providing a 2-hour training course in person and virtually at the ASIP Conference 2023 in Denver, CO from November 27-November 30, 2023.  We hope you will drop by our technical presentation, training course and/or booth to check out the latest ESRD developments!

ESRD’s Training Course

A 2-hour training course titled “Enhancements in StressCheck v12.0 for DaDT Analysis of 3D Fastened Joints” will be held Monday, November 27th from 10:00 AM – 12:00 PM MST by ESRD’s Brent Lancaster.  The course description is as follows:

As more DaDT and service life analysis (SLA) engineers look to incorporate the influence of assembly multi-body contact, fastener hole propping and/or fastener load transfer into their beta factor and/or stress intensity factor (SIF) predictions, it is imperative that the numerical simulation of these effects on 3D fracture mechanics parameters can be ascertained without inflicting cumbersome modeling workflows, endless meshing cycles, and high computational costs on the end user. This training course will outline proposed methodologies, guidelines and best practices for ESRD’s StressCheck Professional finite element analysis (FEA) software to perform efficient and accurate DaDT analysis of flawed 3D fastened connections and multi-body contact assemblies, including enhanced automeshing and SIF extraction techniques now available in StressCheck v12.0. In addition, several live demonstrations of technology will be performed for representative use cases.

In this 2-hour training course, we will focus on the following topics:

• StressCheck’s FEA technology implementation for the modeling, meshing and analysis of arbitrarily shaped 3D crack geometries, with and without the local effects of multi-body contact.
• Strategies for automatic meshing of 3D cracks with high-aspect ratio, 3D-solid pentahedral and hexahedral elements to support high-quality SIF extractions at any location on the crack front.
• New StressCheck v12.0 method to support multi-body contact assembly meshing, auto-detection of contact regions, and automatic assignment of contact pairs for 3D solid bodies.

The training course content will be based on concepts from the following resources, available on ESRD’s Resource Library and online documentation:

• ASIP 2018 Training – Modeling Fastened Connections: Hierarchic Approaches Discussion and Demo
• Helpful Hints and Tips: 3D Stiffened Lug Stress + Crack SIF Analyses
• Helpful Hints and Tips: Interference Fit Bushing + SIFs
• StressCheck Demo: Part-Thru Crack SIFs for Stiffened Lug
• StressCheck Tutorial: 3D Elliptical Part-Thru Crack with Multi-Body Contact
• StressCheck Tutorial: Filled vs Open Hole SIF Comparison for 3D Offset Hole

ESRD’s Technical Presentation

A 30-minute technical presentation titled “Experimental Validation of DTA Modeling of Bonded Wing Skin Repairs” and authored by Mr. Brian Lockwood (ESRD), Ms. Laura Pawlikowski (Warner Robins ALC) and Dr. Scott Prost-Domasky (AP/ES) will be presented by Brian Lockwood on Thursday, November 30th at 10:30 AM MST.

As the principal investigator on this USAF SBIR-funded project, Brian will be presenting an update to his work so far in utilizing StressCheck’s finite element analysis implementation to assess the effectiveness of bonded skin repairs on the C-130 center wing. The technical presentation description is as follows:

This presentation is a follow-up to ESRD’s 2022 ASIP presentation titled “DTA of Bonded Repairs on the Wing Skin of the C-130 Using Finite Elements.” That presentation explored a robust method for finite element analysis of bonded skin repairs from the perspective of both static strength and fatigue crack growth. The proposed analysis methodology was presented in a comparative sense, examining a number of criteria in the skin in an undamaged state, a damaged state and a repaired state, in order to allow the analyst to make an assessment of repair effectiveness without detailed knowledge of either the exact boundary conditions of the problem, or of the intricacies of the model itself. One of the criteria for a patch to be deemed effective is that the fatigue life of the skin be at or above that of the pristine configuration.

Given the sparse nature of research on the topic of crack growth under bonded repair patches, ESRD partnered with AP/ES to conduct an experimental program to investigate in detail how a small initial flaw propagates in the aluminum skin under a titanium repair up through failure. Experiments were performed alongside blind predictions of life and crack morphology using ESRD’s research tool, CPAT. Additionally, statistical analysis was performed to assess confidence in the predictions. Given the aleatory uncertainty associated with the available crack growth data for the specimen material, it was important that predictions of fatigue life be accompanied by a confidence level when comparing them with experimental outcomes. Because most of the crack propagation occurred under the repair, a marker band spectrum was used during the test and the crack-cycle data was constructed from fractographic examination. The experimental program covered three specimen configurations:

• Undamaged skin with a surface crack or a corner crack at a hole.
• Skin with a grindout (to remove hypothetical corrosion damage) and either a surface crack at the bottom of the grindout or a corner crack at a hole located at the center of the grindout.
• Same as previous configuration, but including a bonded titanium repair.

Experimental and predicted results will be presented.

ESRD’s Exhibit Booth

ESRD can be found at Booth 5 and will have several staff members available to chat, provide demonstrations, troubleshoot issues (StressCheck Clinic), and answer questions about our training course, our technical presentation, our software products and our composite repair solutions.

We’ll be handing out some fun giveaways at our booth! Stop by early to chat with us and grab one!

Participating ESRD Staff

Contact information for ESRD staff participating in ASIP Conference 2023 is as follows:

• Mr. Brent Lancaster – brent.lancaster@esrd.com
• Mr. Brian Lockwood – brian.lockwood@esrd.com
• Mr. Patrick Goulding – patrick.goulding@esrd.com

ESRD, Inc. will be exhibiting, presenting a technical paper (on DTA of bonded repairs) and providing a 2-hour training course in person and virtually at the ASIP Conference 2022 in Phoenix, AZ from November 28-December 1, 2022.  We hope you will drop by our technical presentation, training course and/or booth to check out the latest ESRD developments!

ESRD’s Training Course

A 2-hour training course titled “Best Practices for the Modeling & Analysis of Bonded Doubler Repairs” will be held Monday, November 28th from 10:00 AM – 12:00 PM local time by ESRD’s Brent Lancaster.  The course description is as follows:

Current methodologies for modeling and analysis of bonded repair patch designs for application to damaged sections of aircraft wing skin can be computationally expensive and difficult to implement in practice, relying instead on accumulated practical experience to determine the effectiveness of a given repair design. These methods, although effective, require a knowledge base acquired over many years of experience making sustainment organizations vulnerable to gaps in knowledge between newer members and more seasoned experts.

This training course will outline proposed methodologies, guidelines and best practices for utilizing ESRD’s StressCheck Professional finite element analysis (FEA) software to parametrically model, analyze and assess the effectiveness of composite or metallic bonded repair patch designs and variations. The effectiveness of repairs regarding static strength and damage tolerance will be addressed. In addition, strategies for efficient solution verification and hierarchic modeling approaches of 3D repair patches will be explored, and a set of representative demonstrations of technology will be provided.

In this 2-hour training course, we will focus on the following topics:

• StressCheck’s FEA technology implementation enabling modeling of very thin domains, including adhesive layers with 3D-solid elements.
• Best practices and guidelines for modeling and analyzing 3D bonded repair doubler variations (e.g. racetrack/rectangular, circular/elliptical, tapered, metallic, ply-by-ply, homogenized, etc.) for circular cutouts and grindouts.
• Performing “what if?” logic-driven studies of a digital 3D bonded repair handbook solution via StressCheck API-powered Engineering Simulation App, in which user-defined input data is passed from Python or Excel VBA to StressCheck Professional to perform scripted “on-the-fly” model adjustments and repair-oriented computations.

The training course content will be based on concepts from the following resources, available on ESRD’s Resource Library and online documentation:

• A System for Simulation Governance of Engineered Repairs of Composite Aircraft Structures
• Bonded Composite Repair Patch for Cracked Hole (Video)
• Laminated Composite Repair Patch Part I – Geometry & Meshing (Video)
• Laminated Composite Repair Patch Part II – Materials, BC’s & Results
• Laminated Composite Repair Patch Part III – Geometric Nonlinear Analysis

ESRD’s Technical Presentation

A 30-minute technical presentation titled “DTA of Bonded Repairs on the Wing Skin of the C-130 Using Finite Elements” and authored by Mr. Brian Lockwood (ESRD), Mr. Ryan Patterson (Warner Robins ALC) and Dr. Scott Prost-Domasky (AP/ES) will be presented by Brian Lockwood on Thursday, December 1st at 3:30 PM local time.

As the principal investigator on this USAF SBIR-funded project, Brian will be presenting his work so far utilizing StressCheck’s finite element analysis implementation to assess the effectiveness of bonded skin repairs on the C-130 center wing. The technical presentation description is as follows:

Current methodologies for the design and application of repairs to damaged sections of aircraft wing skin can be lacking in analytical support, relying instead on accumulated practical experience to determine the effectiveness of a given patch design. These methods are, by their nature, effective, being based on observation, but inefficient, requiring a knowledge base acquired over years of experience. This can make sustainment organizations inflexible and vulnerable to gaps in knowledge between newer members and more seasoned experts. This approach is also problematic in its potential for wasted effort and material, applying repairs that may be more intensive than is required for a given situation.

These problems can all be addressed by the introduction of an accessible, robust analysis methodology cast in the form of an Engineering Simulation Application for the verification of a repair’s performance qualities prior to an actual aircraft application. The finite element method is ideally suited to provide an analysis procedure for this type of problems that can be used by analysts with widely varying degrees of expertise both in numerical simulation and bonded repair application. This presentation will outline a proposed methodology for utilizing finite element analysis to assess the effectiveness of a given bonded repair.

ESRD’s Exhibit Booth

ESRD can be found at Booth 12 and will have several staff members available to chat, provide demonstrations, troubleshoot issues (StressCheck Clinic), and answer questions about our training course, our technical presentation, our software products and our composite repair solutions.

The StressCheck Clinic

StressCheck users may drop by our booth on a first-come, first-served basis to discuss any StressCheck-related questions, issues or feature requests with us. This includes troubleshooting customer models, demonstrating StressCheck features, and providing best practices/tips on how best to optimize StressCheck’s use.

Want to ensure ESRD’s booth staff is well-equipped to answer your StressCheck Clinic request? Click the below button, include “StressCheck Clinic Request” in the message subject, provide a brief explanation, and we will be prepared to discuss your request at our booth. Note: Customer membership level is required.

As a courtesy to other conference participants, we request that StressCheck Clinic visits be capped at 30 minutes.

Participating ESRD Staff

Contact information for ESRD staff participating in ASIP Conference 2022 is as follows:

• Mr. Brent Lancaster – brent.lancaster@esrd.com
• Mr. Brian Lockwood – brian.lockwood@esrd.com

SAINT LOUIS, MISSOURI – April 2, 2018

In our last S.A.F.E.R. Simulation post, we explored the growing importance of Verification and Validation (V&V) as the use of simulation software becomes more wide spread among not just FEA specialists but also the non-FEA expert design engineer. The emphasis on increased V&V has driven a need for improved Simulation Governance to provide managerial oversight of all the methods, standards, best practices, processes, and software to ensure the reliable use of simulation technologies by expert and novice alike.

In this final post of our current series we will profile the stress analysis software product StressCheck and the applications for which it is used in A&D engineering. StressCheck incorporates the latest advances in numerical simulation technologies that provide intrinsic, automatic capabilities for solution verification through the use of hierarchic finite element spaces, and a hierarchic modeling framework to evaluate the effect of simplifying modeling assumptions in the predictions. We will detail what that actually means for engineering users and how StressCheck enables the practice of Simulation Governance by engineering managers to make simulation Simple, Accurate, Fast, Efficient, and Reliable – S.A.F.E.R. – for experts and non-experts alike.

What is StressCheck?

StressCheck live results extraction showing the convergence of maximum stress on a small blend in an imported legacy FEA bulkhead mesh.

StressCheck is an engineering structural analysis software tool developed from its inception by Engineering Software Research & Development (ESRD) to exploit the most recent advances in numerical simulation that support Verification and Validation procedures to enable the practice of Simulation Governance. While StressCheck is based on the finite element method, StressCheck implements a different mathematical foundation than legacy-generation FEA software. StressCheck is based on hierarchic finite element spaces capable of producing a sequence of converging solutions of verifiable computational accuracy. This approach not only has a great effect on improving the quality of analysis results but also in reforming the time-consuming and error-prone steps of FEA pre-processing, solving, and post-processing as they have been performed for decades.

The origins of StressCheck extend from R&D work performed by ESRD in support of military aircraft programs of the U.S, Department of Defense. The motivation behind the development of StressCheck was to help structural engineers tackle some of the most elusive analysis problems encountered by A&D OEM suppliers and their contracting agencies in the design, manufacture, test, and sustainment of both new and aging aircraft. Historically, many of these problem types required highly experienced analysts using expert-only software tools. Yet even then, the results produced were dependent on the same expert to assess their own validity of output.

During the development of StressCheck, ESRD realized that many aerospace contractors were frustrated with the complexity, time, and uncertainty of stress analysis performed using the results of legacy finite element modeling software. As a consequence, it was not uncommon that engineering groups relied upon or even preferred to use design curves, handbooks, empirical methods, look-up tables, previous design calculations, and closed-form solutions. The time to create, debug, and then tune elaborately constructed and intricately meshed finite element models was just too exorbitant, especially early in the design cycle where changes to geometry and loads were frequent.

StressCheck was developed to address these deficiencies. Since its introduction it has now been used by every leading U.S. aircraft contractor along with many of their supply chain and sustainment partners.

What are the applications for StressCheck in the A&D industry?

StressCheck is ideally suited for engineering analysis problems in solid mechanics which require a high-fidelity solution of a known computational accuracy that is independent of the user’s expertise or the model’s mesh. In the aviation, aerospace, and defense industries these application problem classes include: structural strength analysis, detail stress analysis, buckling analysis, global/local workflows, fastened and bonded joint analysis, composite laminates, multi-body contact, engineered residual stresses, structural repairs, and fatigue and fracture mechanics in support of durability and damage tolerance (DaDT). To explore examples of these applications visit our Applications showcase area and click on any of the featured tiles.

StressCheck is not intended to be a replacement for general purpose finite element codes used for internal loads modeling of large aero-structures or complete aircraft. In these global loads models an artisan-like approach of building up a digital structure using an assortment of 2D frame and shell element types, typically of mixed element formulations with incompatible theories, may be sufficient when accuracy beyond that of approximate relative load distributions is unimportant. Most of the strength, stress, and fatigue analyses performed by aerospace structures groups occurs downstream of the global loads modeling. Historically, these analyses workflows required a series of models, each progressively adding in more structural details that had previously been approximated in often crude fashion or ignored all together.

Multi-scale, global-local including multi-body contact analysis of wing rib structure in StressCheck.

Using StressCheck it is now feasible to employ FEA with analysis problems which require modeling large spans of an aero-structure that has widely varying geometric dimensions with numerous joints, fasteners, cutouts, material types and stress concentrations. Before with traditional FEA methods it was often impossible to use solid elements throughout a multi-scale model using geometry directly from CAD data. So much time and often tricks were required to simplify, defeature, approximate, and repair the design topology that engineering managers were reluctant to approve the use of FEA for some analysis types.

Because of its inherent robustness and reliability, StressCheck is also ideal as the solver engine powering a new generation of Simulation Apps which help to democratize the power of simulation. Smart Sim Apps based on StressCheck can help to simplify, standardize, automate, and optimize recurring analysis workflows such that non-expert engineers may employ FEA-based analysis tools with even greater confidence than expert analysts can using legacy software tools.

Request Application Demo

How is StressCheck’s numerical simulation technology different from that used by legacy or traditional FEA softwares?

In a previous S.A.F.E.R. Simulation post we exposed the limitations of finite element modeling as it has been practiced to date. Most of these constraints are attributable to decisions made early in the development of the first generation of FEA software years before high performance computing was available on the engineers desktop. Unfortunately, those limitations became so entrenched in the thinking, expectations, and practices of CAE solution providers such that each new generation of FEA software was still polluted by these artifacts. To learn how this occurred and what makes StressCheck’s numerical simulation technology so different, we encourage you to view the 3.5-minute StressCheck Differentiators video:

What are the key differences and advantages of StressCheck for users?

StressCheck has numerous intrinsic features that support hierarchic modeling, live dynamic results processing, automatic reporting of approximation errors & more.

The most visible difference to the new user is that StressCheck employs a much smaller, simpler, and smarter library of elements. There are only five element types to approximate the solution of a problem of elasticity, whether it is planar, axi-symmetric, or three-dimensional. This compares to the many dozens of element types of legacy FEA software which often require a wizard to know which one to select, where to use or not to use them and more importantly, how to understand their idiosyncrasies and interpret their often erratic behavior.

The second big difference for users is that StressCheck elements map to geometry without the need for simplification or defeaturing. The available higher-order mapping means that the elements are far more robust with respect to size, aspect ratio, and distortion. As such, a relatively coarse mesh created just to follow geometry may be used across variant-scale topologies. There is no loss of resolution or a need for intermediate highly simplified “stick & frame” or “plate & beam” models.

StressCheck meshes are much easier to create, check, and change as the elements and their mesh no longer have to be the principal focus and concern of the analyst’s attention. StressCheck models aren’t fragile nor do they break as easily, and thus have to be recreated, with changes to design geometry, boundary conditions, or analysis types (e.g., linear, nonlinear, buckling). For example, a linear analysis result is the starting point for a subsequent nonlinear analysis, so the analyst simply switches solver tabs to obtain a nonlinear solution. Because of the use of hierarchic spaces during the solution execution, each run is a subset of the previous run, making it possible to perform error estimation of any result of interest, anywhere in the model after a sequence of solutions is obtained.

So, what’s the bottom line? High-fidelity solutions can be obtained from low-density meshes while preserving an explicit automatic measurement of solution quality.  No guesswork is required to determine if the FEA result can be trusted.

Detailed stress concentrations represented on “low-density” StressCheck meshes.

The errors of idealization are separated from those due to discretization/approximation (e.g. do I have ‘enough’ mesh? DOF? Element curvature?). Sources of inaccuracies and errors are immediately identifiable not because an expert catches it, but because the software is intelligent enough to report them. For each analysis users are provided with a dashboard of convergence curves that show the error in any one of a number of engineering quantities such as stress, strain, and energy norm.

Because solutions are continuous, a-priori knowledge or educated guesses of where stress concentrations may occur are no longer needed. Any engineering data of interest can dynamically be extracted at any location within the continuous domain and at any time without loss of precision due to interpolation or other post-processing manipulation necessitated from having nodal results only, characteristic of legacy FEA codes. Proof of solution convergence is also provided for any function at any location regardless of the element mesh and nodal location. As a consequence, the post-processing of fixed solutions common in legacy FEA becomes in StressCheck dynamic instantaneous extraction of live results:

What is the benefit to engineering groups and value to A&D programs from the use of StressCheck?

StressCheck automatically increases the approximation of stresses on a fixed mesh, making solution verification simple, accurate, fast, efficient & reliable.

With the use of StressCheck, the results of FEA-based structural analysis are far less dependent on the user expertise, modeling approximations, or mesh details. High-fidelity stress analysis of complex 3D solid model geometries, with numerous joints and fastener connections typical of aero-structures may be obtained in less time, with reduced complexity and greater confidence.

As a result, the stress analysis function becomes an inherently more reliable and repeatable competency for the engineering organization. FEA-based structural analysis performed with StressCheck is not an error-prone process where every different combination of user, software, elements, and mesh risks generating different answers all to the dismay of engineering leads and program managers.

By using industry application-focused, advanced numerical simulation software like StressCheck it is now possible to simplify, standardize, and automate some recurring analysis tasks to become more robust for less experienced engineers to conduct. New engineers are productive sooner with access to safer analysis tools that are intelligent enough to capture institutional methods and incorporate best practices. The role and value of the expert engineering analyst evolves to a higher level by creating improved methods and custom tools such as automated global local workflow templates and Sim Apps, respectively.

As presented in the first post of this series, the business drivers to produce higher performing damage tolerant aero-structures are requiring a near hyper-level of engineering productivity, precision, and confidence from the use of simulation technologies earlier in the design cycle. This is also true in the later stages as digital simulation replaces more physical prototyping and flight testing to facilitate concurrency of engineering and build.

Status-quo methodologies dependent on expert-only software that risk adding more time, risk, and uncertainty to the project plan is no longer satisfactory to meet these demands. Next generation simulation technologies implemented in software like StressCheck can help to encapsulate complexity, contain cost, improve reliability, mitigate risk, accelerate maturity, and support better governance of the engineering simulation function.

With StressCheck engineering simulation is Simple, Accurate, Fast, Efficient, and Reliable.

Coming Up Next…

We will discuss why StressCheck is an ideal numerical simulation tool for both benchmarking and digital engineering handbook development (i.e. StressCheck CAE handbooks).  In addition, we will provide examples of how StressCheck CAE handbooks are a robust form of Smart Sim Apps that serve to encapsulate both tribal knowledge and state-of-the-art simulation best practices.

To receive future S.A.F.E.R. Simulation posts…

SAINT LOUIS, MISSOURI – May 7, 2018

ESRD President and CEO Dr. Ricardo Actis

Finite element modeling originated in the aerospace industry over 60 years ago. Owing to the level of expertise and experience required, it has remained a practice of analysts. There are many reasons for this, among them getting the right mesh for a problem and getting the mesh right is always near the top of why it takes both an expert and much time to get a solution. Not to mention the expertise required to navigate the minefield of multi-purpose finite element software tools in selecting the “right” elements from an ever-expanding element library, and selecting the “right” value of tuning parameters to overcome various deficiencies in implementations.

Yet, looking at this more closely, the focus should not be the level of experience or modeling skills of the user, but the level of intelligence in the software. Nearly all of the most popular legacy FEA software products were designed to support the practice of finite element modeling and as such none of them have the capability to provide a simple Q/A dashboard to advise the non-expert user if they have a good solution.

Splice joint stress contours generated by ESRD’s Multi-Fastener Analysis Tool (MFAT) Sim App

How then can the vision for expanding the use of numerical simulation by persons who do not have expertise in finite element analysis (FEA) be safely realized? The solution lies in the establishment of Simulation Governance through the development and dissemination of expert-designed Engineering Simulation Apps to ensure the level of reliability and consistency needed for widespread adoption.

The Key Ingredient for FEA-Based Simulation Apps

FEA-based Simulation Apps for the standardization and automation of recurring analysis tasks and process workflows for use by persons who do not have expertise in FEA must be designed by expert analysts to fit into existing analysis processes, capturing institutional knowledge and best practices to produce consistent results by tested and approved analysis procedures. Only by meeting the technical requirements of Simulation Governance can simulation apps have the reliability and robustness needed to support engineering decision-making processes!

Simulation Governance must be understood as a managerial function that provides a framework for the exercise of command and control over all aspects of numerical simulation through the establishment of processes for the systematic improvement of the tools of engineering decision-making over time. This includes the proper formulation of idealizations, the selection and adoption of the best available simulation technology, the management of experimental data, verification of input data and verification of the numerical solution.

Establishing the Proper Framework

Double lap joint inputs for ESRD’s Single Fastener Analysis Tool (SFAT) Smart Sim App.

In the creation of FEA-based Simulation Apps for the application of established design rules, data verification and solution verification are essential. The goal is to ensure that the data are used properly and the numerical errors in the quantities of interest are reasonably small: they must have built-in safeguards to prevent use outside of the range of parameters for which they were designed; they must incorporate automatic procedures for solution verification; and must be deployed with a detailed description of all assumptions incorporated in the mathematical model and a clear definition of the range and scope of application.

To ensure their proper use, Simulation Apps must incorporate estimation of relative errors in the quantities of interest, an essential technical requirement of Simulation Governance. They should not be deployed without objective measures of the approximation errors for all the reported results. The success of the vision of Democratization of Simulation depends on it!

Learn More

Previous S.A.F.E.R. Simulation Posts…

• S.A.F.E.R. Numerical Simulation for Structural Analysis in the Aerospace Industry Part 1: Trends in A&D Driving Simulation
• S.A.F.E.R. Numerical Simulation for Structural Analysis in the Aerospace Industry Part 2: Challenges with Legacy FEA
• S.A.F.E.R. Numerical Simulation for Structural Analysis in the Aerospace Industry Part 3: FEM is not Numerical Simulation
• S.A.F.E.R. Numerical Simulation for Structural Analysis in the Aerospace Industry Part 4: Simulation Governance
• S.A.F.E.R. Numerical Simulation for Structural Analysis in the Aerospace Industry Part 5: An Introduction to StressCheck for High-Fidelity Aero-structure Analysis

To receive future S.A.F.E.R. Simulation posts…

Selecting the simplest model for an analysis is not always trivial for engineers. A Hierarchic Modeling framework eases this burden by providing support for investigating model form errors.

In our previous SAFER Simulation articles, we have explored the concepts of Numerical Simulation, Challenges of Legacy FEA, Finite Element Modeling, Simulation Governance and High-Fidelity Aerostructure Analysis. We worked to establish a lexicon and foundational basis for how ESRD’s technological framework fits into solving the increasingly complex applications facing today’s engineering community.

In this SAFER Simulation article, we explore the concept of Hierarchic Modeling, some practical applications of Hierarchic Modeling, and the importance of implementing a Hierarchic Modeling framework in CAE software tools to support the practice of Simulation Governance.

What Is Hierarchic Modeling?

“Hierarchic models for plates and shells” by Drs. Ricardo Actis, Barna Szabó and Christoph Schwab. Comput. Methods Appl. Mech. Engrg. 172 (1999) 79-107.

The concept of Hierarchic Modeling is not new, it was introduced in the 1990s, and together with hierarchic finite element spaces and hierarchic basis functions it was implemented in StressCheck Professional. From the introduction to the 1999 Computer methods in applied mechanics and engineering technical paper “Hierarchic models of laminated plates and shells” by Drs. Actis, Szabó and Schwab:

The notion of hierarchic models differs from the notions of hierarchic finite element spaces and hierarchic basis functions. Hierarchic models provide means for systematic control of modeling errors whereas hierarchic finite element spaces provide means for controlling discretization errors. The basis functions employed to span hierarchic finite element spaces may or may not be hierarchic. Brief explanations follow:

Hierarchic models are a sequence of mathematical models, the exact solutions of which constitute a converging sequence of functions in the norm or norms appropriate for the formulation and the objectives of analysis. Of interest is the exact solution of the highest model, which is the limit of the converging sequence of solutions. In the case of elastic beams, plates and shells the highest model is the fully three-dimensional model of linear elasticity, although even the fully three-dimensional elastic model can be viewed as only the first in a sequence of hierarchic models that account for nonlinear effects, such as geometric, material and contact nonlinearities.

Hierarchic Modeling makes it possible to identify the simplest model that accounts for all features that influence the quantities of interest given the expected accuracy. This is related to the problem-solving principle, known as Occam’s razor, that when presented with competing models to solve a problem, one should select the model with the fewest assumptions, subject to the constraint of required accuracy.

Not all CAE software tools are capable of supporting Hierarchic Modeling in practice, especially for complex applications for which many modeling assumptions are to be examined.

What Do CAE Software Tools Need to Support Hierarchic Modeling?

As previously discussion in our S.A.F.E.R. Simulation blog article on Numerical Simulation, to enable support for a Hierarchic Modeling framework, and by extension the practice of Simulation Governance, CAE software tools must meet three basic requirements:

1. The model definition must be independent from the approximation.
2. Simple procedures must be available for assessing the influence of modeling assumptions (in support of model validation).
3. Simple procedures must be available for objective assessment of the errors of approximation (in support of solution verification).

The above requirements, and how meeting these requirements are supported in practice, are explained in greater detail in our Brief History of FEA page and its narrated video. The first implementation of model hierarchies in a CAE software tool, as explained in the video, was released in 1991 (ESRD’s StressCheck Professional).

An implementation framework meeting these three requirements enables the practice of Simulation Governance, providing the basis for the creation and deployment of engineering Sim Apps. Democratization of Simulation for standardization and automation of new technologies, such as Sim Apps, can be done with proper safeguards provided that the software tools used for the creation and deployment meet these technical requirements.

Why Should Engineers Care About Hierarchic Modeling?

“On the role of hierarchic spaces and models in verification and validation” by Drs. Barna Szabó and Ricardo Actis. Comput. Methods Appl. Mech. Engrg. 198 (2009) 1273-1280.

Legacy CAE tools used for Finite Element Modeling were not designed to support Hierarchic Modeling. This is because the concept of Hierarchic Modeling was established many years after the infrastructure of legacy FEA tools was created. Their main limitation is that the model definition and the approximation are not treated separately. Different orders of model complexity cannot be objectively compared by engineering analysts, therefore there is no basis for establishing  confidence in the modeling assumptions.

From 2009’s Computer methods in applied mechanics and engineering technical paper “On the role of hierarchic spaces and models in verification and validation” by Drs. Actis and Szabó:

…It is also necessary for the computer implementation
to support hierarchic sequences of models, allowing investigation of the sensitivities of the data of interest and the data measured in validation experiments to the various assumptions incorporated in the model…There is a strong predisposition in the engineering community to view each model class as a separate entity. It is much more useful however to view any mathematical model as a special case of a more comprehensive model, rather than a member of a conventionally defined model class.

For example, the usual beam, plate and shell models are special cases of a model based on the three-dimensional linear theory of elasticity, which in turn is a special case of large families of models based on the equations of continuum mechanics that account for a variety of hyperelastic, elastic-plastic and other material laws, large deformation, contact, etc. This is the hierarchic view of mathematical models.

Comparison of maximum von Mises stress convergence for different hierarchic fastened connection models.

To aid finding the simplest model, sensitivity studies via virtual experimentation are recommended. For example, modeling fastened joints may or may not require full multi-body contact effects if the data of interest are sufficiently far from the region of load transfer; bearing load applications, distributed normal springs or partial contact via “plugs” may be sufficient. By extension, if a structural support is to be approximated by distributed springs, the spring coefficients should be defined parametrically so that sensitivity studies are easy to perform.

The following examples and practical applications illustrate how a Hierarchic Modeling framework leads to increased control over and confidence in the engineering decision-making process.

Applications of Hierarchic Modeling In Engineering Practice

We will focus on two practical applications common to many aerospace engineers: fastened (bolted) joint analysis, and the influences of nonlinear effects such as plasticity. Both engineering applications require high-fidelity analyses to represent the data of interest, and are typically sensitive to the modeling assumptions.

Fastened Joint Analysis

ESRD recently provided a webinar titled “Hierarchic Approaches to Modeling Fastened Connections”, which incorporated the main points from the above discussion. The webinar can be viewed below in its entirety.

Through StressCheck Professional‘s Hierarchic Modeling framework, different modeling assumptions are tested for several classes of fastened joints and connections, including lap joints, splice joints and fittings, and in many cases a simpler model was found that represented the data of interest within a sufficient tolerance:

Some of the fastened joint modeling assumptions explored included the following:

• In-plane only vs out-of-plane bending effects on load transfer and detailed stresses
• 2D structural shear connections vs 3D detailed multi-body contact
• 2D bearing loading vs 3D bearing loading vs 3D multi-body contact
• Compression-only normal springs vs multi-body contact
• Fused fasteners vs multi-body contact
• Linear elastic vs. elastic-plastic materials

Without a Hierarchic Modeling framework, exploring these modeling assumptions would be unfeasible in engineering practice, and create a “simulation bottleneck” for engineering analysts.

Linear vs Nonlinear Effects

In some aerospace engineering applications, it may be necessary to investigate the influence of nonlinearities, such as plasticity and/or large deformations, in the results of interest.  For that reason a linear solution (i.e. small strain, small deformation and linear elastic material coefficients) must be viewed as the first in a hierarchy of models that includes nonlinear constitutive  relations, finite deformation and mechanical contact.

In a Hierarchic Modeling framework, engineering analysts should not need to change the discretization (i.e. mesh, element types and mapping) when transitioning from a linear to nonlinear model analysis for example; the switch should be seamless and simple, allowing the order of the model to increase on demand.

The following demo videos examine two case studies in nonlinear effects, in which the Hierarchic Modeling framework of StressCheck Professional was used to assess the influence of simplifying modeling assumptions without changing the discretization.

Geometric Nonlinearities

In the first case study, a linear vs. geometric nonlinear (large strain/large displacement) analysis for a 3D helical spring was performed:

Performing a geometric nonlinear analysis for the helical spring, in which equilibrium is satisfied in the deformed configuration, required no interaction with the model inputs or discretization parameters. The engineering analyst simply starts from a converged linear solution as the first step in the geometric nonlinear iterations.

The model hierarchies were then compared in live results processing with minimal effort, allowing the engineering analyst to quickly assess how accounting for large displacements/rotations affects the outcome of the results.

Material Nonlinearities

In the second case study, elastic-plastic materials are assigned to a detailed 3D eyebolt geometry, allowing plasticity to develop as the eyebolt is overloaded in tension:

To incorporate plasticity into the model, it was only required to update the material properties from linear to elastic-plastic; no other change in model inputs was required. Then, after a converged linear solution was available, a material nonlinear analysis was seamlessly initiated.

As in the previous case study, both models were available for assessment in live results processing, allowing the engineering analyst to determine whether material nonlinear effects are significant at the given load level (i.e. is the plasticity extensive) or the plastic zone is fully confined by elastic material.

Summary

As demonstrated in the above examples, and articulated in the technical paper excerpts, support for a seamless transition between model orders and theories is made possible by the implementation of a Hierarchic Modeling framework. To implement Hierarchic Modeling, CAE software tools must also allow separation of model definition from the discretization (in legacy FEA software, the definition of the model and the numerical approximation are combined, necessitating large element libraries). Without this clear separation, it is not feasible to reliably perform verification and validation in engineering practice.

Additionally, engineering analysts should expect modern FEA and CAE tools to support “what if” and sensitivity studies, such that modeling assumptions can be easily assessed and the simplest model used with confidence. As more and more engineering organizations look to democratize simulation, and virtual experimentation is increasingly used, it is essential to have numerical simulation tools that treat model definition separately from the approximation.

Finally, through the use of hierarchic finite element spaces and mathematical models it is possible to control approximation errors separately from modeling errors, while providing objective measures of solution quality for every result, anywhere in the model, in support of the increasing simulation demands on engineers.

How We Can Help…

Last week, ESRD wrote a guest contribution for Altair’s Innovation Intelligence blog titled “Hyper-Fidelity Structural Analysis for S.A.F.E.R. Numerical Simulation in the Aerospace Industry“.  Thanks to Altair for their collaboration and support of S.A.F.E.R. Simulation.

This guest contribution was intended to compliment and preview Altair’s October 17th ESRD use case webinar (don’t worry if you missed this webinar, the recording is already available).

Here’s an excerpt from the Innovation Intelligence blog article:

Across the engineering community there is much discussion about the democratization of simulation; meaning the reliable use of numerical simulation by non-simulation experts who may be design engineers, new analysts, or occasional users. The hope is that much of the complexity, time, and risk of performing FEA can be wrung out of simulation in a way that finally allows simulation-driven design to be led by design engineers. Indeed democratization has great potential in the A&D industry to compress the product development lifecycle, but is it realistic? The answer few may want to hear is that this will not be easy to accomplish using legacy FEA technologies, methodologies, and software tools.

The key takeaways are as follows:

• The pressure on engineering organizations to support the increasing complexity, higher performance, shorter design cycles, and longer life expectancy of products they produce and maintain is relentless.
• Legacy computational methodologies, software tools, and simulation processes that have been used for years to perform FEA are slow to master, precarious to use, and unreliable in the hands of the non-expert or infrequent user. Sources of errors are numerous and results are often dependent on the user, model, mesh, and software.
• There is unfortunately a reluctance by some managers and team leaders to support the performance of more computationally-based 3D detail stress analysis due to the perceived time and complexity involved, especially when compared to relying on handbook solutions, design curves, closed form approximations, homegrown spreadsheets, higher margins of safety, or ultimately more time for physical prototyping and testing.
• A different approach to numerical simulation has been developed and commercialized by APA partner ESRD which takes much of the art and craft out of finite element modelling.
• The result is that the performance of structural analysis is more simple, accurate, fast, efficient, and reliable for both the frequent expert and only occasional user (S.A.F.E.R.).

Thoughts? Feedback? Leave us a comment!

ESRD, Inc. will be exhibiting and providing a training course at the ASIP Conference 2019 in San Antonio, TX from December 2-5, 2019.  We hope you will drop by our training course and booth to check out the latest!

ESRD’s Training Course

The training course titled “Automated 3-D Crack Beta Curve Development via Smart Sim Apps” will be held Monday, December 2, 2019 / 6:00 PM – 8:00 PM by Mr. Brent Lancaster.  The description is as follows:

In the past, fatigue crack growth in 3D was typically analyzed with a compounding (or superposition) of beta factors to represent various configurations and loadings for complex components. While compounding approaches can be simulated quickly, many of the beta factors used for DaDT simulations were derived from analytical or empirical models of much simpler configurations, which may not be representative of the 3D case at hand. Thus, a risk of the “unknown” is introduced into the simulation, endangering the ability of DaDT analysts to provide a justifiable assessment of 3D fatigue crack life. To mitigate this risk, recently the numerical simulation community initiated the development of engineering simulation applications, or Sim Apps, to automate parametric finite element analyses (FEA) of complex crack components such that the practice of compounding beta factors could be replaced with fully representative beta factors.

Example Smart Sim App for Automated Computation of Multi-Phase Beta Factors (with Built-In Solution Verification)

This short training course will discuss the creation of Sim Apps for the automatic generation of complex, solution-verified 2D and 3D beta factors via the integration of StressCheck’s parametric FEA engine, the Windows Component Object Model (COM) and Microsoft Excel VBA. This SAFER Simulation approach reduces the error-prone superposition of stress intensity factors (SIF’s) to represent complex beta factors.

Course Outline:

• Overview of fracture mechanics parameters for fatigue crack growth: SIF’s, J-integrals and beta factors.
• Pros and cons of compounding beta factors: what are the risks?
• What is a Sim App, and how can they help DaDT engineers produce more accurate analyses?
• Case studies in Sim Apps for the automation of 2D and 3D beta factor generation
• Live Sim App Demo: automated beta curve generation via an Excel VBA + StressCheck-based Sim App
• Q&A

The training course content will be based on concepts from the following resources, available on ESRD’s Resource Library:

• Automated Beta Curve Development Using Parametric FEA
• StressCheck Demo: Sim App Development via Excel VBA and StressCheck API
• Fracture Mechanics Sim Apps: Sample Visual Basic Application
• Crack Propagation Analysis Tool for 3D Crack Simulation: A Simulation App Case Study
• Deployment of Smart Simulation Apps in Support of DaDT Activities
• 3D Crack Growth Simulation: Advancements & Applications Webinar
• Democratization of Simulation Governance-Compliant Sim Apps Webinar

Register

ESRD’s Exhibit Booth

ESRD’s Brent Lancaster chats with ASIP 2018 attendees.

ESRD can be found at Booth 25 and will have several staff members available to chat and answer questions about our software products and DaDT solutions.

Introducing the StressCheck Clinic

We will also be introducing the StressCheck Clinic at ASIP Conference 2019, where StressCheck users may drop by our exhibit booth (at a communicated time or on a first-come, first-served basis) to discuss any questions, issues or feature requests with a qualified ESRD representative. Stay tuned more more details on this new offering!

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Participating ESRD Staff

Contact information for ESRD staff participating in ASIP Conference 2019 is as follows:

• Mr. Gordon Lehman, PE – gordon.lehman@esrd.com
• Mr. Brent Lancaster – brent.lancaster@esrd.com

ESRD is hosting joint webinars on July 17th and July 29th, both at 1:00 pm EST.

Want to learn from the experts in FEA-based Simulation Application (Sim App) development for standardization & automation of complex engineering analysis tasks, such as 3D fatigue crack growth, 3D ply-by-ply laminated composite analysis or other challenging applications you’d like to safely put into the hands of non-experts?

This July, ESRD will be partnering with several industry leaders to provide not one but TWO stimulating webinars on the latest in FEA-based Sim App development.

The Latest Developments in Sim Apps for 3D Crack Growth Simulations

BAMF Example Crack Front Estimate via StressCheck/AFGROW Integration (courtesy Hill Engineering).

First, ESRD is pleased to join Hill Engineering, LLC (developers of BAMF) and LexTech, Inc. (developers of AFGROW) for a joint webinar on Wednesday July 17, 2019 @ 1:00 pm EST. This collaborative webinar will be titled “3D Crack Growth Simulation: Advancements & Applications“, and will detail the latest technological advancements in Sim Apps for accurate simulation of three-dimensional metallic crack growth via coupled finite element analysis (FEA) and fatigue life computations.

During this webinar, you will see the latest in 3D crack growth predictions via Hill Engineering’s Broad Application for Modeling Failure (BAMF) Sim App, which provides a robust integration between StressCheck’s high-fidelity DaDT/fracture solutions and AFGROW’s crack growth life prediction capabilities.

Additionally, ESRD, LexTech & Hill Engineering representatives will explain how each of their respective technologies seamlessly fit together to enable automated, verified & validated (i.e. backed by experimental data) fatigue crack propagation.

Register Now

The Importance of Simulation Governance in Sim App Development & Deployment

This joint ESRD/Rev-Sim webinar will explore Sim-Gov compliant Sim Apps for democratization of simulation.

Then, on Monday July 29, 2019 @ 1:00 pm EST, ESRD will join the thought leaders at Revolution in Simulation (Rev-Sim) for a joint webinar on why Simulation Governance compliance is essential to the development & deployment of Sim Apps titled “Democratization of Simulation Governance-Compliant Sim Apps“.

In this timely webinar, we will discuss why it is essential that Sim Apps implement Numerical Simulation technologies which enable the practice of Simulation Governance in order for the vision of democratization of simulations to be realized, as well as why it is important for engineering managers to get on the Simulation Governance train sooner rather than later. Strategies will be explored for democratizing engineering simulations via Sim Apps which are: 1) based on the latest Numerical Simulation technologies, 2) available in Commercial Off the Shelf (COTS) form, and most importantly 3) Simulation Governance-compliant.

Register Now

More ESRD Webinars…

Interested in the complete ESRD webinar listing, including on-demand recordings from past ESRD webinars? Visit our webinars page here:

View Webinar Listing

Demo of BAMpF/StressCheck interation as run through an AFGROW plug-in (courtesy Hill Engineering)

Announcing Hill Engineering and ESRD Agreement to Jointly Market BAMpF & StressCheck Professional

March 12, 2020

Hill Engineering and Engineering Software Research and Development, Inc. (ESRD) have executed a joint marketing agreement to collaboratively promote the combined use of our software tools Broad Application for Multi-Point Fatigue (BAMpF) and StressCheck Professional, respectively, for the engineering applications of fatigue and damage tolerance analysis.

ESRD is pleased to join forces with Hill Engineering and LexTech, Inc. (an ESRD technology partner and developers of AFGROW) to enable state-of-the-art fatigue crack growth capabilities for DaDT engineers.

BAMpF is a software tool developed by Hill Engineering for predicting the growth of fatigue cracks in 3D parts. Starting from an assumed initial flaw, BAMpF automatically combines fracture mechanics solutions from StressCheck with fatigue life calculations from AFGROW to assess fatigue crack growth performance.

Read Hill Engineering’s announcement.

BAMpF Resources

The following are helpful resources for learning more about the BAMpF/StressCheck/AFGROW integration for fatigue crack growth:

• BAMpF Home page (via Hill Engineering)
• ESRD/Hill Engineering/LexTech Joint Webinar recording (recorded July 2019)
• AFGROW/BAMpF Training workshop (courtesy LexTech/Hill Engineering/ASIP Conference 2019)
• BAMpF Use Case presentation PDF (courtesy Brian Boeke/AFGROW User’s Conference 2019)

BAMpF Case Study Example

The figure below shows a comparison between the fatigue crack growth predicted near a hole (using BAMpF and StressCheck Professional + AFGROW) and results from a fatigue crack growth test for similar conditions. In this case there is an initial flaw at the edge of the hole and the hole has been cold-expanded to introduce compressive residual stress.

Predicted crack front evolution (blue) compares favorably with the observed experimental result (red):

Want to Learn More? Contact Us:

• Hill Engineering
• ESRD