License Queueing

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Design optimization studies are driving a need to support the efficient management and execution of many jobs.  This is why we are announcing that Endurica’s software license manager now supports queueing for licenses. This allows a submitted job to automatically wait to start until enough licenses are available, instead of the prior behavior of exiting with a license error. Now you can submit many jobs without worrying about license availability.

License queueing is only available for network licenses (not node-locked). It is currently supported for Katana CL/DT jobs and EIE jobs submitted from a command prompt.

To enable queueing, set the environment variable RLM_QUEUE to any value. This environment variable must be set on the client machine (not the license server).

To learn more about license queueing, search for “How to Queue for Licenses” in the RLM License Administration documentation here: https://www.reprisesoftware.com/RLM_License_Administration.pdf

 

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Defining the Temperature Dependence of Strain Crystallization in Endurica

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Crystallization requires the suppression of molecular mobility, which in natural rubber can happen either by reducing the temperature or by increasing the strain.  Crystallization of natural rubber can be extremely beneficial to durability.  Nonrelaxing conditions (ie R>0) can increase life by factors of more than 100!  So, what happens if you have both high mean strain and high temperature?

This was the question studied in 2019 by Ruellan et al.  They constructed Haigh diagrams for a filled natural rubber at 3 temperatures: 23 degC, 90 degC and 110 degC.  They completed a large experimental study using dumbbell shaped specimens with a matrix consisting of approximately 4 R ratios x 4 amplitudes x 3 temperatures = 48 conditions.  Their results show that the increase of fatigue life with increasing mean strain at constant amplitude disappears as temperature is increased.  In particular, notice how at 23 degC each life contour (shown in red) has a strongly defined minimum force amplitude that lies near the R=0 line.  Also notice how, at higher temperatures, the life contours start to reflect a decrease of life with increasing mean strain.

This interesting effect can easily by replicated in the Endurica fatigue solver by letting the strain crystallization effect depend on temperature.  The material definition we have used in this quick demo is given below in both the old hfi format and the new Katana json format.  I have highlighted in yellow those parts of the definition which reflect the temperature dependence.

In the material definition, we have reflected two behaviors:

  1. the increase of crack growth rate with temperature (ie the RC parameter), and
  2. the decrease of strain crystallization with temperature (ie the Mars-Fatemi exponential strain crystallization parameter FEXP).

We have plotted the resulting Haigh diagrams in the Endurica viewer, and directly overlaid Ruellan’s results for comparison.  Although the x and y scales in Ruellan’s results are shown in terms of total specimen force and ours are shown in terms of strain, a quite satisfying match is nonetheless achieved for the interaction of temperature with the mean strain effect.  It is especially satisfying that such rich behavior is so compactly and so accurately described by means of the Mars-Fatemi crystallization parameter.

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What is the Price of Standing Still?

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What if we don't change at all and something magical just happens? Technical equation for entropy

“We have always done it this way.” No longer simply a hated phrase, this statement is a warning of impending disaster. Entropy – the disorder that happens when energy disperses and systems simply fall into chaos – happens when things do not change. But it’s a slow process you don’t see day-to-day. Continuing with traditional “build and break” development methods instead of embracing CAE and simulation has many long-term risks but it will only be after stagnating for some time that rubber parts manufacturing firms, and even the entire rubber industry, will realize the pitfalls:

Talent Loss
People are the key to it all and we start here since intelligent, hard-working, productive people are the fundamental reason any business succeeds. When the best and brightest employees leave a company, the fundamental reasons often include the lack of opportunity, learning, and career development. When not allowed to work with emerging technologies and are no longer challenged to grow, top performers find new opportunities taking not only raw potential but also institutional memory with them. And if they don’t see the industry as a viable long-term option, switching companies can also mean leaving the sector completely.

Warranty Issues/Payouts
Liability issues arise when product usage, applications and environments bring risks that may not have been factored in to the original designs and/or production methods. Traditional testing methods cannot be used to investigate “what if?” scenarios the way CAE and simulation can. Recalls and litigation can be significantly more costly than new technology implementations.

Lost Opportunity Costs
While harder to measure than fixed and variable business costs, there is an expense to every choice known as opportunity cost. Refusing to enter a new business sector may result in significant loss of revenue and profit. Taking on a big client project may strain production capabilities. “Standing still” eliminates those risks, but at what potential gain? As the rubber industry wrestles to “go green” we are all weighing and measuring the opportunity costs involved. The real lost opportunity is in refusing to embrace a fundamentally better design platform.

Incompatibility or Obsolescence
At some point, everything being produced right now will become obsolete. Even if you produce the best “widgets” anywhere, the environment around that “widget” will change and will no longer be needed in its current form. The rubber industry standard procedure of building a product then breaking it in physical testing to determine the next design rendition is incompatible with the time available for new product development. It just does not work anymore.

How quickly your business can adapt to or anticipate change is a key factor in continued success. The reasons companies do not make continued progress often include:

Change is expensive
Investments in training, new production systems, updated software and computers add up, but these numbers are not insurmountable when factored against the ongoing and often increasing costs of waste, repairs and downtime associated with outdated systems and equipment.

Learning new technology is time-consuming
Remember when you were thinking about going to college and four (6-8-10) years seemed like FOREVER? What was your ROI? What will it be now? Time invested in learning reaps many rewards beyond the subject at hand and often provides renewed overall energy.

The status quo works
For today, yes. For a brighter future for you company and the industry, NO. Companies that don’t evolve face certain death. Day-to-day operations may appear stable, but firms who do not keep up with technology do not stay in business. Covid forced many to embrace technology in new ways and those firms continuing to provide progressive working arrangements are gathering more than their fair share of the best and brightest talent. Enabling people to work beyond traditional geographic boundaries requires accountability and processes for measuring valued contributions rather than simply time at a desk.  Firms embracing CAE and simulation technologies have realized this and are at the top of the leading rubber industry rankings.

 Six reasons to adopt Endurica workflows

  1. Technically superior (click for details)
  2. Save big on development out of pocket costs (click for details)
  3. Reduce the need for physical testing (see page 2, blue box on right)
  4. Speed to market (able to use the tools immediately)
  5. Accuracy in meeting client needs (click for details)
  6. Easier answers down the road (click for details)
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Introducing Tom Ebbott, the new Vice President at Endurica!

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Thomas G. Ebbott, Ph.D. Vice President Endurica LLC

Hello everyone. I am really excited to be writing this as the newest member to Team Endurica! I am really enjoying my on-boarding with Will and the team thus far. I continue to learn all the capabilities that the Endurica software has to offer, along with all the services that Endurica the company offers. I’m looking forward to using my knowledge and experience with modeling and simulation combined with expertise in fatigue and fracture in polymers to bring value to Endurica’s customers.

Endurica’s software and services enable customers to monitor, predict and improve the endurance of products. This has a positive impact on many of today’s contemporary questions. For example, for sustainability, customers need to evaluate the durability impact of using a material with a more sustainable source, or one with better recyclability or re-useability in place of an existing material. Even re-designing a component to use less material, or to last longer is more sustainable. For electric vehicles, many of the elastomeric components are called on to carry higher loads and higher torques in the case of tires. And, for fleet operations, Endurica can be used to monitor the health of elastomeric systems and predict when maintenance will be needed.

I feel I have a good background to help both Will and the team at Endurica as well as Endurca’s many and wide-ranging customers. As many of you know, I recently retired from Goodyear after nearly 36 years with that great company. While I was at Goodyear, I worked with many wonderful and capable people, and I was fortunate to have many fulfilling experiences and roles. Some include developing fundamental technology, developing products–specifically Aviation Tires and Retreads, various people leadership roles, and finally a high-level technical leader role responsible for technical strategy. While at Goodyear, I was able to publish several papers on topics such as fracture mechanics of rubber in tires, temperature distribution and rolling resistance prediction for tires, crack growth in twisted rubber disks, and continuum damage analysis of cord-rubber structures. I served on The Tire Society Executive Committee for 8 years as Treasurer. One of my long-term contributions at Goodyear was to the 30-year partnership with Sandia National Laboratories.

For my formal training, I spent 10 years at the University of Wisconsin-Madison that culminated in a PhD in Engineering Mechanics. My masters work focused on structural dynamics while my PhD research was on crack growth in polyethylene. The application of my PhD work was for the durability evaluation of natural gas distribution pipelines. The crack growth evaluation in (high density, high molecular weight) polyethylene required development of viscoelastic material laws and characterization as well as crack growth measurement systems, means to measure strain distributions, and use of viscoelastic crack growth theories.

On a personal note, my wife Sheri and I have two adult children. Amanda is teaching 2nd grade at a school near Columbus, OH, and Zachary is a junior pursuing a Finance degree at Regis University in Denver. One of my passions is flying, and I’ve had my private pilot’s license for many years. One of my most memorable flying trips was to New Mexico and Colorado. The photo shows my plane with the sun rising over the Sandia mountains in Albuquerque, NM.

I’m looking forward meeting and talking with Endurica’s customers in the coming months and learning about their needs and challenges concerning the use of elastomers and polymers for component design.

 

 

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The View on ‘22 – The Top 10 Happenings for Endurica in 2022

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  1. Expanded our team! We welcomed 35-year Goodyear veteran Tom Ebbott to our team as Vice President, and at one point we had 3 interns working with us this year.  It wasn’t all hard work – we enjoyed our first company canoe trip / picnic in July.
  2. Solved much bigger problems. We set a record this summer for the largest rubber fatigue analysis ever. Ford Motor Company gave us multi-channel recorded road load histories from the full schedule of 144 distinct test track events that they use to qualify a motor mount for durability. We used Endurica EIE to map the load space and generate 3.2 Terabytes of stress-strain history for fatigue analysis. The new Katana multi-threading architecture of our Endurica CL fatigue solver enabled us to process 152k elements through all 15,693,824 timesteps of the schedule.  Check out our presentation at RubberCon 23 in Edinborough UK.
  3. Made analysis of block cycles easier. The Endurica CL and DT solvers’ Katana architecture now enables multiple blocks of load history to be specified in a single analysis.WoD 6 - Strain Crystallization
  4. Added a Haigh diagram visualization to the Endurica Viewer. Use it to quickly understand your material’s dependence of fatigue life on mean strain and strain amplitude.
  5. Implemented a channel reduction algorithm to Endurica EIE. It will analyze your multi-channel loading history to check for opportunities to reduce the dimensionality of your analysis through a change of coordinate basis.  Often, a 6-channel signal can be reduced to 3, 4 or 5 channels, greatly reducing computational requirements for building the map for EIE’s interpolation process.
  6. Expanded our licensing model to offer local, regional and global options. If your organization uses Endurica at multiple sites around the world, ask us about the advantage of regional or global licenses. These licenses allow any number of users to share a pool of solver threads for maximum flexibility and compute power.
  7. Added an experimental characterization for ozone cracking. Ozone is a trace gas that strongly reacts with some rubbers to produce surface cracking. It limits useful product life, even for loads below the fatigue threshold.Ozone Module. quantify ozone attack critical energy and rate Our testing method gives you the parameters you need to set up the ozone attack model in your Endurica CL / DT analyses. Perfect for analysis of tire sidewall endurance.
  8. Were honored when our founder and president, Will Mars, received the Herzlich Medal – the highest award in the tire industry – at the International Tire Exhibition and Conference. This honor is bestowed every other year to recognize an individual whose career and accomplishments have changed the tire industry for the better and left a lasting impact on tire design, development and manufacturing.
  9. Strengthened our documentation. New and experienced users alike will find it easier than ever to find the theory, procedures and examples that will yield rapid success in applying our software workflows. Check out the new sections on Mullins Effect, Ageing, Safety Factor, and Block Cycle analysis.
  10. Celebrated our client’s success. Technetics Group (Pierrelatte, France Maestral® R&D Sealing Laboratory) and Delkor Rail (New South Wales, Australia) shared their Winning on Durability success in case studies.
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Necessity and Invention: Getting Durability Right and Winning

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Will Mars Delivering Keynote Presentation as Herzlich Medal Winner 2022

William V. Mars, Ph.D., P.E.
2022 Harold Herzlich Award Winner
Acceptance Speech
at ITEC 2022, Akron, Ohio on 15 September 2022

Three key takeaways from our founder’s acceptance speech of the tire industry’s highest award.

  1.  There is a point at which commercial simulation code outcompetes internally developed simulation code. Will talks about how this played out in the early days of finite element technology in the tire industry, and how the lessons learned apply to durability simulation today.
  2. Traditional is not the same as conservative. Will talks about the tension between the tire industry’s conservatism and the necessities that drive its progress, and how Endurica navigated its entry to the industry with its disruptive technology.
  3. The industry is going through a transition from scientific discovery and invention towards the empowerment of product developers to leverage advances in durability simulation. Will talks about the integration of testing and simulation workflows, and some of the capabilities that open new channels for gaining competitive advantage.

Check out the full talk here to enjoy some fun insights about Will’s personal journey through the years.

 

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The 5-50-500 Rule

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The 5, 50, 500 Rule with dice showing Chance to Change

2 Minute Read | 400 Words

I ran a marketing consulting business for 30 years before joining Endurica and tried to save clients from learning the hard way. When brochures were the only way to convey a company’s message (pre-internet), it was critical that people understood the $5, $50, $500 rule.

  • $5 = cost for changes during the earliest design phase. This is the point where everything is on the table as you develop the look, feel, message, and content of the brochure.
  • $50 = cost to make changes at the first mock-up of the brochure. No big deal. At this stage, changes take a bit of work and may impact multiple pages or sections – but it’s a LOT better to make changes now than later and I encouraged people to speak up about anything/everything because change was still pretty easy. Approval at this stage sends us into production.
  • $500 = cost to make changes after we sent the brochure to the printer. That’s the cost to change even one LETTER, let alone a photo or – heaven forbid – an entire page. It was at this point that one client said “ok, now I’ll read it” and I had to stop myself from throwing a file at him.

All of this came up as we talked about the value of our software in rubber product development. The concept’s the same but the numbers are SO MUCH BIGGER. “Add about 3 zeroes to each of those steps,” remarked Tom Ebbott, Endurica’s VP and newest team member. “It’s the same concept in tire development but the impact is just so much bigger.”

From a technical side, one of our client’s says it best: “In optimizing a geometry to extend the fatigue life of a product I ran a few iterations of inner-cavity geometries, and found one specific geometry with Endurica that achieved 500,000 cycles to failure in contrast to the 30,000 I had before. It’s more than a 10-time improvement and that’s really significant. These concrete numbers are really powerful in helping us and our customers to make good decisions.” Francois Rouillard, R&D Mechanical Engineer, Maestral Sealing Laboratory, Technetics, Pierrelatte, France.

WHY IT MATTERS: Endurica’s users find THE BEST solution to their client’s problem early — at the $5,000 stage of design. They can skip the multiple iterations that easily run $50,000 each and go right into the $500,000 production testing cycle with complete trust in the product’s success.

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Tension / Compression Cycles, R ratio and a Discussion of Wohler Curve for Rubber

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Fatigue Life of Rubber with different strain constraints

In fatigue testing, R is the ratio of the minimum to the maximum occurring during one period of a cycle.  If the mean value is zero (ie the cycle is centered on zero), then the minimum is equal and opposite in sign to the maximum.  In this case, we say that R=-1.  The cycle can be defined by various parameters.  If we define R in terms of the stress or the strain, then R may take either positive or negative values.  We might hear, for example, that R=-1 uniaxial loading is a symmetric tension / compression cycle.

Be careful about definitions, however! The Endurica material models define R in terms of the tearing energy (ie T = – dU/dA, where T is the tearing energy, U is the elastic potential energy and A is the crack area).  The tearing energy is the driving force responsible for crack growth.  It is always greater than or equal to zero.  When R is defined in terms of tearing energy, its range is 0 ≤ R ≤ 1.

This leads to the following question that we often hear:  how can Endurica compute fatigue in compression if it does not admit a negative R ratio?

Let’s look at a series of signals, all having the same strain amplitude, and each with a different mean strain.  We will set the mean strain so that it is at most equal to the amplitude (corresponding to fully relaxing R=0 tension), and at least equal to the negative of the amplitude (corresponding to fully relaxing R=0 compression).  In the middle of the range, we have fully reversed tension/compression (what some call “R=-1” loading when defining R in terms of strain).  The principal engineering strains are plotted below for each case.  This gives a smooth progression from a cycle that is only compression to a mixed cycle with both tension and compression and finally to a cycle that is only tension.

Series of signals with same strain amplitude but different Tension/Compression levels

Even for these simple uniaxial cases, the critical plane for simple compression is not the same as the critical plane for simple tension.  In simple compression, due to crack closure, the critical plane is the plane that maximizes shearing.  These planes make a 45-degree angle with the axis of loading (x direction).  In simple tension, however, the critical plane is perpendicular to the load (x direction).  In the figure below, the change in the critical plane as the mean strain increases from compression to tension is evident.  On each sphere, the arrows indicate the perpendicular of a critical plane.

Mean strain increase as compression to tension is evident with change in the critical plane

The next figure shows the cracking energy density (units of mJ/mm3, and proportional to tearing energy) as a function of time on the critical plane for each case.  The symbols on each line indicate the times at which the identified crack plane is open or closed.  Now we can see clearly that fully reversed tension/compression (ie “R=-1” loading in terms of strain) is really R=0 when viewed in terms of tearing energy on the critical plane.

Graphs showing the cracking energy density as a function of time on the critical plane. Fully reversed tension/compression is really R=0 when viewed in terms of tearing energy.

The computed fatigue life is given in the last figure for each case using this material definition:

MAT=RUBBER
ELASTICITY_TYPE=ARRUDABOYCE
SHEAR_MODULUS=1 ! MPa
LIMIT_STRETCH=4
BULK_MODULUS=3000 ! MPa
FATIGUE_TYPE=THOMAS
FLAWSIZE=0.025 ! mm
FLAWCRIT=1 ! mm
TCRITICAL=10 ! kJ/m^2
RC=3.42E-2 ! mm/cyc
F0=2
X(R)=LINDLEY73

The computed fatigue life depending on different percentages of tension/compression

The moral of the story:

  1. Fully reversed tension/compression cycles (“R=-1” in stress or strain terms) are really fully relaxing cycles (R=0 in tearing energy terms) from the perspective of the crack precursor on the critical plane.
  2. The critical plane depends on whether you have tension or compression. Wohler curve analysis completely misses the fact that the failure plane is not always perpendicular to the loading direction!
  3. A simple sinusoidal history that crosses through zero results in separate tension and compression events, each of which has its own peak and valley, and each of which influences the critical plane selection. Wohler curve analysis based on max principal stress or strain amplitude completely misses these physics.
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Busting Myths About Endurica

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Myths vs Facts on Endurica, Test your knowledge about Endurica

True or False? Test your knowledge about Endurica

Endurica is only a software company.
False. While Endurica is perhaps best known for its game-changing fatigue solver software, we also deliver industry-leading testing services, testing instruments, and training.  If you need durability for elastomers, we are uniquely positioned to bring you winning capabilities.

Endurica is used by the majority of top rubber product makers.
True.  As of the 2021 Rubber News global rankings report, 6 of the top 9 global rubber product makers are using Endurica solutions to characterize and simulate durability.

Endurica invented Critical Plane Analysis.
False, but...  Critical Plane Analysis – the technology that gives best accuracy fatigue life predictions under complex multiaxial loading – was originally pioneered by the metals fatigue community.  But Endurica does hold the patent on the first Critical Plane Analysis algorithm suitable for elastomers, and we are the world leaders in making the technology available to product developers.

Wohler curve based methods are just as accurate and competitive as Endurica’s Critical Plane / Fracture Mechanics-based method.
False. Wohler curve based methods suffer from many problems that are solved by the Critical Plane Method.  1) they often assume a wrong crack orientation rather than searching for the most damaging scenario, 2) they do not account properly for mode of deformation effects, 3) the testing program required to populate a Wohler curve scales poorly and has poor repeatability.

I don’t need Endurica software if I already have a metal fatigue code (nCode DesignLife, FEMFAT, MSC Fatigue, and fe-safe).
False. Metals and elastomers have completely distinct molecular structures and behaviors.  While metals operate at small strain, elastomers tend to operate at large strain.  Where metals exhibit linear elasticity, elastomers exhibit nonlinear behavior.  Using a metal fatigue code for analyzing elastomer fatigue is like trying to use a car as a boat: you can certainly drive the car into the water, but you end up on the bottom of the lake.

Endurica solvers work with Ansys, Simulia, and Hexagon simulation platforms
True. We maintain software development partnerships with the major finite element software vendors so that we can offer easy to use pre-and post- integrations with Ansys, Abaqus, and MSC/Marc.  You can use the Endurica workflows with the finite element code that works for you.  We also develop the fe-safe/Rubber plugin.

Everyone knows you can simulate durability.
False. We’re always surprised by the number of people at conferences and trade shows who don’t know that simulating the durability of rubber is even possible.  Our tools simulate everything from basic constant amplitude cyclic loading, to variable amplitude, multiaxial loading (up to 6 input channels!), ageing, strain crystallization, ozone attack, cyclic softening, creep crack growth, self-heating, block cycle schedules, residual life.  Our multi-threading capabilities mean that large jobs can execute quickly.  Our solvers are fast enough to compute damage in real-time for a full finite element model!

Endurica solutions have had significant commercial impact.
True.  Endurica was founded in 2008 to reduce rubber product launch cost and risk and we have saved our clients millions of dollars.  Endurica’s impact was recognized with the prestigious U.S. Small Business Administration Tibbetts award.

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My SAE WCX 2022 Top Takeaway

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SAE WCX | Detroit, Michigan | April 5-7, 2022

There were several papers on fatigue life prediction for elastomers at SAE WCX 2022, but the highlight for us was this one from Automotive OEM Stellantis: “Fatigue Life Prediction and Correlation for Powertrain Torque Strut Mount Elastomeric Bushing Application” by Dr. Touhid Zarrin-Ghalami, Durability Technical Specialist at FCA US LLC Fiat Chrysler Automobiles logowith coauthors C Elango, Sathish Kumar Pandi, and Roshan N. Mahadule from FCA Engineering India Pvt, Ltd.  Check out the abstract or buy the paper here…

The study shows that very accurate fatigue life prediction results are possible for elastomeric components under block cycle loading using Critical Plane Analysis.  A key feature of the analysis is the characterization and modeling of rubber’s hyperelastic properties, fatigue crack growth properties, crack precursor size, and strain crystallization behavior.  Careful measurement of these analysis ingredients led to a nearly perfect correlation of the predicted life (520 blocks) with the tested life (523 blocks, average of 4 replicate tests), and of predicted failure mode with observed failure mode.

Endurica users like Stellantis are developing a solid track record of routine and successful fatigue life prediction.  We soon expect to see the day when CAE fatigue life prediction for rubber components is regarded as obligatory, given the risk and cost avoided with “right the first time” engineering.

Congratulations to the Stellantis team on this impressive success!

Fatigue Life (block) demonstrating the accuracy of the CAE Virtual Simulation compared to a physical test

Citation: Elango, C., Pandi, S.K., Mahadule, R.N., and Zarrin-Ghalami, T., “Fatigue Life Prediction and Correlation of Engine Mount Elastomeric Bushing using A Crack Growth Approach,” SAE Technical Paper 2022-01-0760, 2022, doi:10.4271/2022-01-0760.

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