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.

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…

Verifying the accuracy of FEA solutions is straightforward when employing the following Key Quality Checks.

In a recent ESRD webinar, we asked a simple but powerful question: if you routinely perform Numerical Simulation via finite element analysis (FEA), how do you verify the accuracy of your engineering simulations? During this webinar, we reviewed ‘The Four Key Quality Checks’ that should be performed for any detailed stress analysis as part of the solution verification process:

• Global Error: how fast is the estimated relative error in the energy norm reduced as the degrees of freedom (DOF) are increased? And, is the associated convergence rate indicative of a smooth solution?
• Deformed Shape: based on the boundary conditions and material properties, does the overall model deformation at a reasonable scale make sense? Are there any unreasonable displacements and/or rotations?
• Stress Fringes Continuity: are the unaveraged, unblended stress fringes smooth or are there noticeable “jumps” across element boundaries? Note: stress averaging should ALWAYS be off when performing detailed stress analysis. Significant stress jumps across element boundaries is an indication that the error of approximation is still high.
• Peak Stress Convergence: is the peak (most tensile or compressive) stress in your region of interest converging to a limit as the DOF are increased? OR is the peak stress diverging?

When the stress gradients are also of interest, there is an additional Key Quality Check that should be performed:

• Stress Gradient Overlays: when stress distributions are extracted across or through a feature containing the peak stress, are these gradients relatively unchanged with increasing DOF? Or are the stress distribution overlays dissimilar in shape?

In this S.A.F.E.R. Simulation blog, we’ll explore each of the above Key Quality Checks as well as additional best practices for verifying the accuracy of FEA solutions. To help us drive the conversation in a practical manner, we selected a widely available and well understood benchmark problem to model, solve and perform each Key Quality Check using ESRD’s flagship FEA software, StressCheck Professional.

Note: the following Key Quality Checks for FEA Solution Verification focus on results processing for linear and nonlinear detailed stress analyses applications. Webinars containing solution verification best practices have been previously presented for fracture mechanics applications, global-local analysis (co-hosted by Altair), and fastened connection and bolted joint analysis.

Benchmark Problem: Tension Bar of Circular Cross Section with Semi-Circular Groove

Benchmark problem for Key Quality Checks for FEA Solution Verification.

The benchmark problem for the following discussion focuses on accurately computing a very common stress concentration factor, the classical solution(s) of which may be found in myriad engineering handbook publications and used often by many practicing structural engineers: tension bar of circular cross section with a semi-circular groove.

Since the available literature supports numerous classical solutions, we will limit our coverage to three (3) of the most popular classical stress concentration factor approximation sources: Peterson, Shigley and Roark.

Classical Source #1: ‘Peterson’s Stress Concentration Factors’ (Pilkey)

Our first classical source comes from Section 2.5.2 and Chart 2.19 (‘Stress concentration factors K_tn for a tension bar of circular cross section with a U-shaped groove’) in ‘Peterson’s Stress Concentration Factors’, 2^nd Edition, by Walter D. Pilkey:

Courtesy ‘Stress Concentration Factors’, 2nd Edition (Pilkey).

Courtesy ‘Stress Concentration Factors’, 2nd Edition (Pilkey).

The curve marked ‘Semicircular’ will be used for the classical stress concentration factor approximation.

Note: as is documented in Section 2.5.2 above, Chart 2.19 is computed from the Neuber 3D case K_tn curve (Chart 2.18, see below) for a nominal Poisson’s ratio of 0.3:

Courtesy ‘Stress Concentration Factors’, 2nd Edition (Pilkey).

Pilkey notes in Section 1.4 (‘Stress Concentration as a Three-Dimensional Problem’) that the Poisson’s ratio will have an effect on the K_tn for cases such as the above.

Classical Source #2: ‘Shigley’s Mechanical Engineering Design’ (Budnyas & Nisbett)

Our second classical source comes from Figure A-15-13, Table A-15, in ‘Shigley’s Mechanical Engineering Design’, 9^th edition, by Richard G. Budnyas & J. Keith Nisbett:

Courtesy ‘Shigley’s Mechanical Engineering Design’, 9th edition (Budnyas & Nisbett).

Classical Source #3: ‘Roark’s Formulas for Stress and Strain’ (Young & Budynas)

Our third source comes from the equation in Table 17.1, ’15. U-notch in a circular shaft’, ‘Roark’s Formulas for Stress and Strain’, 7^th Edition, by Warren C. Young and Richard D. Budynas:

Courtesy Roark’s ‘Formulas for Stress and Strain’, 7th Edition (Young & Budynas).

We will use the equation for the semi-circular notch (h/r = 1) for the classical stress concentration factor approximation.

Classical Stress Concentration Factor Comparison:

For this benchmark case study, the dimensions and axial tension force were defined as following (in US Customary units):

• D = 9″
• d = 6″
• h = 1.5″
• r = 1.5″
• P = 10,000 lbf
• σ_nom = 4*P/π/d² = 354 psi
• r/d = 0.25
• D/d = 1.5
• h/r = 1.0

These values result in the following classical solutions for the stress concentration factor:

The above classical solutions are noted by the authors as approximations of the stress concentration factor, given the configuration of geometric and axial loading parameter values; the exact solution can be obtained by solving the 3D elasticity problem. An approximation to the solution of the elasticity problem can be obtained using the finite element method (e.g. via StressCheck Professional or another FEA implementation).

A reasonable goal of our benchmark case study is to determine which (if any) of the classical solutions best approximates this particular configuration.

Modeling Process: CAD + Automesh + BC’s + Material Properties

The solid geometry for the benchmark case study was constructed in StressCheck Professional using 3D solid modeling techniques, an automesh of 3665 curved tetrahedral elements was generated, and boundary conditions (axial loads, rigid body constraints) were applied:

Curved Tetrahedral Automesh (courtesy StressCheck Professional)

The linear elastic material properties selected for the benchmark case study are representative of a 2014-T6 aluminum extrusion (i.e. E = 10.9 Msi, v = 0.397).

Solution Process: Linear P-extension + Fixed Mesh

The model was analyzed in StressCheck Professional’s Linear solver via an hierarchic p-extension process, in which the orders of all elements on the fixed mesh were uniformly increased from 2^nd order (p=2) to 8^th order (p=8) for a total of seven (7) runs.

Note: before executing the solution, the mesh was converted to geometric (blended) mapping, which ensured the optimal representation of the geometric boundaries. This conversion was required for the solution order to exceed p=5, as by default StressCheck Professional’s tetrahedral elements are curved using 2^nd order functions (Isopar).

Since StressCheck Professional automatically stores all completed runs of increasing DOF for results processing, we can determine the minimum DOF for which the benchmark case study was well approximated for each Key Quality Check.

Note: it is not necessary to always increase the order of all elements to 8^th order, unless the mesh is a) generated manually and is a minimum mesh of high-aspect ratio elements, or b) a solution of exceedingly low discretization error in the data of interest is the goal (our reason). Many times a sufficiently refined mesh at a lower order (p<6) will achieve an acceptable discretization error for most practical engineering applications.

Results Extraction: Do We Pass Each Key Quality Check?

After the solution process completed, the estimated relative error in the energy norm (EREEN) was automatically reported as 0.01%, indicating no significant discretization errors but telling us very little about our data of interest, the stress concentration factor.

Then, how do we determine if we have an accurate enough FEA solution to approximate the stress concentration factor for the benchmark case study? Let’s go through each Key Quality Check to determine if our discretization is sufficient.

Key Quality Check #1: Global Error

Key Quality Check #1: Global Error (courtesy StressCheck Professional)

Studying how the global error (% Error column), as represented by EREEN, decreases with increasing DOF is our first ‘Key Quality Check’. This value is a measure of how well we are approximating the exact solution of the 3D elasticity problem in energy norm.

Additionally, a Convergence Rate of >1.0 is also a good indicator of the overall smoothness of the solution. Note: in problems with mathematical singularities, such as the simulation of cracks in fracture mechanics applications, the convergence rate is typically <1.0.

VERDICT: Pass

Key Quality Check #2: Deformed Shape

Key Quality Check #2: Deformed Shape (courtesy StressCheck Professional)

Since the benchmark case study was loaded axially under self-equilibrating loads of P=10,000 lbf, rigid body constraints were applied to three nodes at the leftmost side to cancel the six rigid body modes in 3D elasticity.

The deformed shape for the highest DOF run indicates the model is behaving as expected at a 2,000:1 deformed scale (red outlines are the undeformed configuration).

VERDICT: Pass

Key Quality Check #3: Stress Fringes Continuity

Key Quality Check #3: Stress Fringes Continuity (courtesy StressCheck Professional)

When assessing the stress fringes for quality, it is important to ensure that there are no significant “jumps” across element boundaries (edges/faces) in regions where the stresses are expected to be smooth, continuous and unperturbed. This assessment requires that the stresses be plotted without any averaging or blending features enabled.

The 1^st principal stress (S1) fringe continuity for the highest DOF run is quite smooth across element boundaries, with no significant “jumps” detected in the region of interest (root of the notch). The maximum 1^st principal stress value (S1_max) is computed as 619.3 psi.

However, we will need to verify that this value has converged to a limit (e.g. independent of DOF) before it is compared with the benchmark case study’s theoretical K_tn and σ_max.

VERDICT: Pass

Key Quality Check #4: Peak Stress Convergence

Key Quality Check #4: Peak Stress Convergence (courtesy StressCheck Professional)

For this benchmark case study, our data of interest was the peak stress at the root of the circumferential groove. Since StressCheck Professional automatically keeps all solutions for ‘deep dive’ results processing, it is very simple and easy to ‘check the stress’.

Selecting the StressCheck model’s curve which encircles the root of the groove, an extraction of maximum 1^st principal stress (S1_max) vs. each run of increasing DOF was performed. Even though we have a fairly refined mesh in the groove, note the large differences between the first three runs (p=2 to 4) and the final four runs (p=5 to 8). For this reason, it is simply not enough to have a “good mesh” or smooth stress fringes that pass the “eyeball norm”; the peak stress values must be rigorously proven to be independent of mesh and DOF.

It can be observed from the table that convergence in S1_max was achieved by the 4th or 5th run, with a converged value of S1_max = 619.3 psi. Here is a summary of how the classical stress concentration factor approximations K_tn rate for this particular configuration:

% Relative Difference = 100*(σ_{max –} S1_max)/S1_max

It appears that Peterson’s classical stress concentration factor approximation is most appropriate, with a relative difference of 1.75% when compared to the estimated exact solution from the numerical simulation.

Note: the S1_max convergence table confirms that it was not necessary to continue increasing the DOF by p-extension past the 5th run (p=6 in this particular case); we could have stopped the p-extension process once the error in the S1_max was sufficiently small for our purposes.

VERDICT: Pass

A Note on the Poisson’s Ratio Effect

Recalling the derivation of the Peterson K_tn, the value use in the benchmark case study assumed a v=0.3 for its approximation, while a v=0.397 as was used in StressCheck Professional. This highlights the importance of understanding the derivation and limitations of classical solutions.

If we “eyeball” Chart 2.18 for r/d = 0.25 and a v~0.4, we get a K_tn of ~1.78 (vs. K_tn~1.81 for v=0.3). We then multiply the Peterson K_tn by 1.78/1.81 to get an ‘adjusted’ Peterson K_tn ~1.75 for v=0.397. This results in a σ_max = 619.67, a difference of 0.06%.

That being said, it is always up to the engineer and management to determine an acceptable classical solution error in practical engineering applications.

Key Quality Check #5: Stress Gradient Overlays

Key Quality Check #5: Stress Gradient Overlays (courtesy StressCheck Professional)

As an additional Key Quality Check, we should ensure that the stresses nearby the location of peak stress are also well-represented and do not change much with increasing DOF. In StressCheck Professional we can dynamically extract the stresses across or through any feature, for any resolution and available solution, and overlay these stress gradients on the same chart for an assessment of quality.

The stress gradient extraction was performed across the groove for the final three runs (p=6 to 8), and the automatic stress gradient overlay showed that there was practically no difference between the point-wise values. Again, this proves that the 5th run (p=6) was sufficient for representing both the peak stress and the groove stress gradient.

Note: as for the stress fringe continuity check (Key Quality Check #3), it is important to perform this extraction without averaging features enabled.

VERDICT: Pass

In Summary…

Example of the democratization of classical engineering handbook methods via FEA-based digital engineering applications.

Solutions of typical structural details in 2D and 3D elasticity obtained by classical methods are approximations obtained using various techniques developed in the pre-computer age. This benchmark case study shows that in order to rank results obtained by classical methods, they have to be compared with the corresponding values obtained from the exact solution of the problem of elasticity. Alternatively, when the exact solution is not available, classical methods can be compared with the results from an approximate solution of the same problem of elasticity obtained by FEA.

It was also shown that strict solution verification procedures are required to provide evidence that the approximation error in the quantities of interests are much smaller than the difference observed among the results obtained by classical solutions, an essential technical requirement of Simulation Governance and any benchmarking-by-FEA process.

Finally, this example also highlights another important point: Classical engineering handbooks and design manuals are examples of democratization practiced in the pre-computer age. With the maturing of numerical simulation technology it is now possible to remove the manifold limitations of classical engineering solutions and provide parametric solutions for the problems engineers actually need to solve. This is the main goal of democratization.

There is a fundamentally important prerequisite, however: The exceptionally rare talents of engineer-scientists who populated conventional handbooks have to be democratized, that is, digitally mapped into the world of modern-day analysis.

The time has come for democratization to be reinvented.

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!

On February 12, 2020 a webinar on tips & resources for enhancing our users’ StressCheck Professional knowledge, titled “Mastering StressCheck: Practical Training Approaches & Online Resources for A&D Engineers”, was provided by ESRD’s Brent Lancaster. Thanks to all who attended! In case you missed it, the webinar slides and on-demand recording are now available.

Keys to mastering StressCheck Professional are explored.

In this user-oriented webinar, we discussed the latest StressCheck training options for Aerospace & Defense (A&D) engineering analysts, how to improve your mastery of StressCheck via the Getting Started page, software FAQ’s, on-demand video tutorials & best practices in the ESRD Resource Library, and why investing in StressCheck for detail analyses is well worth your time. We also provided a live demo of a sample Introduction to StressCheck training course topic (“Tips for Practical StressCheck Usage”).

Here was the webinar agenda:

• The “Nuts & Bolts” of ESRD’s StressCheck.
  • Typical Aerospace & Defense (A&D) engineering applications solved by StressCheck.
• Why get StressCheck training?
  • StressCheck training topics and options.
• Introduction to StressCheck training course preview.
  • Tips for Practical StressCheck Usage.
• Accessing & navigating StressCheck resources:
  • Getting Started with StressCheck.
  • FAQ Articles.
  • ESRD Resource Library and on-demand video tutorials.

View Webinar Recording

Click the button below to view the 1 hour 20 minute webinar recording (scroll to the bottom of the webinar landing page to find the videos):

View Webinar Slides

Click the button below to view the webinar slides (PowerPoint Show):

Want to Set Up an Instructor-Led Training?

Click the below button to get a quote for an on-site, off-site or web-based training course:

StressCheck User Experience Survey v2.0

If you have not already, please take a few minutes to give us some feedback about how you use, or would like to use, StressCheck Professional. Your answers are very valuable to us!

After completing the survey, you will automatically be entered into a random drawing for a $50 Amazon gift card:

SAINT LOUIS, MISSOURI – December 5, 2017

In ESRD’s November S.A.F.E.R. Simulation post we summarized the business trends in A&D that are driving the need for higher-performing aerostructures that are more efficient, lighter-weight, and more durable and damage-tolerant over longer life spans. This in turn is driving the requirement for higher-fidelity engineering analysis that brings increased accuracy and reliability to the structural engineering function without adding more time and risk to the program schedule.

In this second of our multi-part series on “S.A.F.E.R. Numerical Simulation for Structural Analysis in the Aerospace Industry” we will distill what this means to stress analysis groups and the challenges experienced when using legacy simulation and analysis technologies based on the finite element method (FEM).

Aerospace & Defense budgets are squeezed ever tighter, yet simulation demands and complexities keep increasing…

The Democratization of Simulation

As discussed in our last post on the state of simulation in aerospace, the capabilities of FEA-based software tools have become increasingly more advanced in functionality and richer in features. Not surprising, they have also become more sophisticated to use and difficult to master, even by expert analysts. Training analysts in FEA-based simulation software is a laborious, expensive process, and the results are not always transferable as analysts move to new programs or employers which have their own set of tools, processes, and best practices.

Across the engineering software community there is much discussion about the democratization of simulation; meaning the reliable and routine use of numerical simulation software by non-simulation experts. These non-experts may be mechanical design engineers, occasional users, or new engineering graduates. The hope of democratization is that much of the complexity and risk of FEA-based simulation can be distilled out such that simulation-driven design may be performed with greater confidence by engineers earlier in the design cycle.

Excerpt from “The Role of Simulation Governance in the Democratization of Simulation Through Sim Apps in the A&D Industry” presented by ESRD’s CEO Dr. Ricardo Actis at NAFEMS 2017 Aerospace Simulation Engineering: The Big Issues

Indeed, democratization has great potential to compress the product development lifecycle, but is it a realistic objective for the demanding aviation, aerospace, and defense industries? The answer few may want to hear is that it will not be easy to accomplish using legacy FEA-based simulation technologies along with the software tools based upon these technologies.

The results when reviewing the previous attempts to put FEA tools into the hands of the non-expert have not been encouraging.  These schemes included embedding solvers into CAD software to hide complexity, employing scripted templates to insulate users from making errors, and exercising wizards to automate processes. None of these have yet to move most FEA work off of the expert analyst’s desktop and place it into the hands of the design engineer.  Upon closer inspection, most of these approaches failed not because they were bad ideas, but because they were still based on legacy FEA methodologies where creating, debugging, running, and post-processing finite element models was a complex error-prone art form for the expert.

Challenges with Legacy FEA Software

Simulation software providers have continually sought ways to compensate for – and in some cases hide – the inherent complexity of the finite element method (FEM) when applied to analysis problems in computational solid mechanics.  There have certainly been many advancements in the functionality, user interfaces, pre/post processors, high-performance computing, delivery platforms, and licensing options of FEA software over recent years. Yet, none of these individually or collectively removed the intrinsic complexity and challenges of learning and performing FEA by either the expert or novice user.

There are many good reasons why this is so. The underlying theory and methods employed “under the hood” of nearly all FEA software products on the market today are in fact many decades old. As a result, there are near endless sources of assumptions, idealizations, approximations, manipulations and judgement calls, each that add complexity, time, and uncertainty to engineering simulations.

Example of loading fastener holes via Rigid Body Elements (RBE’s). Using RBE’s and other element libraries may be acceptable for expert users, but for non-experts they can be a source of unknown errors.

As an example, the element libraries of most FEA software products contain dozens of variants and odd mutants that must be carefully selected and deployed. When these overly-sensitive elements are used in fragile meshes it is not uncommon for a finite element model to break with even small changes to design geometry or boundary conditions. Rarely can the same elements and meshes be used for different types of physics modelling such as non-linear, contact, heat transfer, dynamics, or fracture analysis.

Often more time is spent in the pre-processing steps of constructing “bad” models, to finally arrive at the “good” ones, than in post-processing the results or optimizing a design. While CAD data is increasingly 3D solid-based, it must often be repaired, defeatured, re-created, or reduced before meshing. It is often unrealistic in legacy FEA simulations to use solid finite element models of large-spanning, multi-scale geometries of built-up components, which are common in aerostructures. Often a series of increasingly granular models must painstakingly be constructed to perform a sequence of multi-fidelity, multi-scale global/local analyses.

Extracting and validating results in traditional FEA is an equally laborious process that is inherently error-ridden. In legacy FEA software mathematical degrees of freedom are nodal based, which means quantities of interest at other locations must be interpolated, extrapolated or massaged in a way that potentially injects additional inaccuracies in engineering data. High-density meshes must be used in areas of stress gradients, which often requires a-priori knowledge of the results and locations of interest, or changing the model once the results are produced and then iterating. It is not uncommon that models are tuned and tweaked such that the computational results align with empirical test data.

Averaged vs. Not Averaged results for Legacy FEA Simulation Technology. Which stress concentration (Kt) is more accurate, if either one? Is this the right mesh density?

All of the above limitations and challenges are so well understood by the expert analyst, who typically has advanced engineering degrees and many years of experience, that they rarely think twice about whether it has to be this complex. They know all the traps, fixes, tricks, and workarounds of finite element modelling. Yet, there is a more fundamental challenge often overlooked; legacy generation finite element methods do not provide a fool-proof measurement of the quality of their solutions. There is no inherent quality assurance, much less explicit support of solution verification. As such, it is up to the individual analyst to assess the applicability, accuracy, and completeness of the computed results. It is no wonder that it always takes an expert in the loop to determine if the results are good and more importantly when they are deficient.

It All Ends Up On The Engineer’s Desktop…

The confluence of demanding A&D business drivers, higher product performance requirements, and increasing complexity of digital simulation all end up on the structures engineer’s desk. The stress analyst on a modern A&D program ends up owning the burden to produce a larger volume of higher-fidelity analyses, earlier in the NPD cycle, spanning an expanded optimization solution space of structural design variations.

In doing so they are expected to create all-encompassing 3D digital models, with few details left behind to support virtual prototyping and reduce testing, while using more sophisticated tools that take longer to learn and master. And they are expected to perform these analyses in less time with a greater level of confidence in the results and with less tolerance for uncertainty or “fat” factors of safety that were once acceptable in yesteryear’s aerostructure designs.

Compounding the above pressures, today’s analysts may no longer have access to internal support from engineering methods groups which historically provided training, troubleshooted problems, captured institutional knowledge, and shared best practices. It is little surprise that industry associations like NAFEMS report that providing oversight of the simulation function through the practice of Simulation Governance is one of “The Big Issues” for engineering managers who often see their simulation teams struggle to deliver with so many conflicting requirements.

These pressures are not letting up, and current trends do not appear sustainable. The evidence speaks for itself that FEA-based structural analysis often adds so much more time and complexity to engineering processes such that project managers seek to minimize its use when there are other faster methods available. Fortunately, a new generation of simulation software is emerging where that is no longer the case.

Coming Up Next…

In Part 3 of this series we will explain why Numerical Simulation is not the same as Finite Element Modeling and what this means to engineering analysis within the A&D industry. We will describe how the practice of Simulation Governance, enabled by the next generation of software based on numerical simulation, is helping engineering groups respond to an avalanche of complexity in products, processes, and tools.

In our final segment we’ll profile the capabilities of ESRD’s numerical simulation software StressCheck™ and Smart Sim Apps deployed in a Digital CAE Handbook built using StressCheck. Finally, we’ll share use-case examples from A&D that document the benefits to engineers and value to their programs from the use of this newer generation of analysis software that is Simple, Accurate, Fast, Efficient, and Reliable – S.A.F.E.R – for both the expert and non-expert user alike.

Next Week’s Webinar…

On Thursday, December 14th @ 1:00 pm EST an Aerospace & Defense-oriented webinar titled “High-Fidelity Stress Analysis for S.A.F.E.R. Structural Simulation Webinar” will be provided by ESRD’s Brent Lancaster and Gordon Lehman.

Sign Up for Next Week’s High-Fidelity Stress Analysis Webinar

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

We would like to thank NAFEMS for allowing us to co-sponsor, exhibit and present at the NAFEMS 2017 Aerospace Simulation Engineering conference in Wichita, KS on November 8th.  It was a pleasure to meet the other vendors, co-sponsors, attendees and NAFEMS community.

ESRD’s President and CEO Dr. Ricardo Actis presented on how Simulation Governance is a requirement for Democratization of Simulation, and ESRD Project Engineer Mr. Eric Buettmann presented on improving global-local simulation workflows for detailed Aerospace Simulation Engineering.  Both presentations spent time addressing several Big Issues in the Aerospace & Defense industry.

These presentations are now available to download from our ESRD Resource Library:

• The Role of Simulation Governance in the Democratization of Simulation Through Sim Apps in the A&D Industry.
• Improving Global-Local Simulation Workflows for High-Fidelity Stress and Damage Tolerance Analysis.

Reminder: ESRD will be attending and exhibiting at ASIP 2017 next week.  We hope to see you there!

Comparison of von Mises stress distributions for fastened connection model hierarchies.

ESRD’s June 20th @ 1:00 pm EST webinar titled Hierarchic Approaches to Modeling Fastened Connections will focus on best practices for accurately modeling & analyzing fastened connections and joints, including appropriate simplifying assumptions based on the data of interest:

Modeling of fastened connections, including Planar-only (fastener elements), multi-body contact (load transfer between all parts), fastened plugs (load transfer between notable parts), & normal springs (compression-only single part analysis) approaches. Pros and cons of each approach will be analyzed.

A live demo will be provided to demonstrate the process of checking reactions in contact regions, as well as how to perform live-dynamic processing of detailed stresses in multi-part assemblies.

We hope you will join us to discuss these modeling approaches.

Webinar Teaser

Examples of hierarchic modeling of fastened joints are shown in the videos below:

Sign Up for This Webinar

To sign up for this webinar, please provide your contact details and submit!  You will be sent a confirmation e-mail with details on how to join:

On Thursday, December 14th @ 1:00 pm EST an Aerospace & Defense-oriented webinar titled “High-Fidelity Stress Analysis for S.A.F.E.R. Structural Simulation Webinar” will be provided by ESRD’s Brent Lancaster and Gordon Lehman. This is a continuation on the S.A.F.E.R. Simulation theme introduced during our previous webinar, Durability and Damage Tolerance (DaDT) Analysis Best Practices Webinar.

We will share advancements in numerical simulation that make the performance of finite element analysis S.A.F.E.R. – Simple, Accurate, Fast, Efficient, and Reliable. We will focus on what makes us uniquely-qualified to enable and deliver high-fidelity detailed stress analysis for aerostructures engineers, as well as provide use cases to solidify our claim.

Register

To learn more details and register for the webinar: High-Fidelity Stress Analysis for S.A.F.E.R. Structural Simulation Webinar

We hope you’ll join us for this event!

Not already subscribed to S.A.F.E.R. Simulation news?

On Thursday, December 14, 2017 an Aerospace & Defense-oriented webinar titled “High-Fidelity Stress Analysis for S.A.F.E.R. Structural Simulation Webinar” was provided by ESRD’s Brent Lancaster and Gordon Lehman. This was a continuation on the S.A.F.E.R. Simulation theme introduced during our previous webinar, Durability and Damage Tolerance (DaDT) Analysis Best Practices Webinar.

In this 36-minute webinar, we shared advancements in numerical simulation that make the performance of finite element analysis S.A.F.E.R. – Simple, Accurate, Fast, Efficient, and Reliable. We discussed what makes us uniquely-qualified to enable and deliver high-fidelity detailed stress analysis for aerostructures engineers, as well as provided use cases and a demo of “live processing” solution results.

Watch Webinar

To watch the 36-minute webinar: High-Fidelity Stress Analysis for S.A.F.E.R. Structural Simulation Webinar

Not already subscribed to S.A.F.E.R. Simulation news?

WATCH THIS WEBINAR

Part 1: Nuts & Bolts of StressCheck, Why Get StressCheck Training?

Part 2: Intro to StressCheck Training Course Preview, Self-Training Resources

Want to Set Up an Instructor-Led Training?

Click the below button to get a quote for an on-site, off-site or web-based training course: