Durability by Design on Any Budget

Durability by Design

So, you’ve got a tricky durability problem to solve, a budget, and a deadline.  Let’s look at a helpful framework for sorting which Endurica workflows you need.  In the grid below, each row represents a potential approach you can take.  The approaches are, in order of increasing complexity and cost, the Infinite Life approach, the Safe Life approach, the Damage Tolerant approach, and the Fail Safe approach.

Endurica Durability Workflows

The Infinite Life approach is by far the simplest approach.  Here, we say that damage will not be allowed at all.  All locations in the part must operate, at all times, below the fatigue limit (ie intrinsic strength) of the rubber.  The required material testing is minimal: we need only know the fatigue limit T0 and the crack precursor size c0.  We avoid the question of how long the part may last, and we focus on whether or not we can expect indefinite life.  We report a safety factor S indicating the relative margin (ie S = T0 / T) by which each potential failure location avoids crack development.  When S>1, we predict infinite life.  For S<=1, failure occurs in finite time and we must then go on to the next approach…

In the Safe Life approach, the chief concern is whether or not the part’s estimated finite life is adequate relative to the target life.  The material characterization now becomes more sophisticated.  We must quantify the various “special effects” that govern the crack growth rate law (strain crystallization, temperature, frequency, etc.).  We consider the specific load case(s), then compute and report the number of repeats that the part can endure.  If the estimated worst-case life is greater than the target life then we may say that the design is safe under the assumptions considered.  If not, then we may need to increase the part’s load capacity, or alternatively to decrease the applied loading to a safe level.  In critical situations, we may also consider implementing the next level…

The Damage Tolerant approach acknowledges that, whatever the reasons for damage, the risk of failure always exists and therefore should be actively monitored.  This approach monitors damage development via inspection and via tracking of accrued damage under actual loading history.  A standard nominal load case may be assumed for the purpose of computing a remaining residual life, given the actual loading history to date.  Changes in material properties due to cyclic softening or ageing may also be tracked and considered in computing forecasts of remaining life.

The Fail Safe approach takes for granted that failure is going to occur, and obliges the designer to implement measures that allow for this to happen safely.  This can take the form of a secondary / redundant load path that carries the load once the primary load path has failed.  It can take the form of a sacrificial weak link / “mechanical fuse” that prevents operation beyond safe limits.  It can take the form of a Digital Twin that monitors structural health, senses damage, and requests maintenance when critical damage occurs.

The last three columns of the grid show which Endurica fatigue solver workflows align with each design approach.  The Endurica solvers give you complete coverage of all approaches.  Whether you need a quick Infinite Life analysis of safety factors for a simple part, or deep analysis of Damage Tolerance or Fail Safety, or anything in-between, our solvers have just what you need to get durability right.

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Solving the Durability Puzzle

Ever thought about what it takes to deliver the durability you expect from products you use? Durability reflects the combined sum of many decisions made all along the supply chain. What sources to use for raw materials? What dimensions and shape for product features? Are there OEM- or customer-imposed design constraints? What load cases occur in manufacturing, shipping, installation, and operation? Manufacturing processes? OEM-specified qualification and / or regulatory testing requirements? What is the warranty or brand promise? If these decisions are not made well, then durability (as well as cost and weight) will suffer.

The people making these decisions come from many backgrounds.  They are chemists, product engineers, testing engineers, structural analysts.  The big challenge is to organize things so that their contributions all add up to the desired end result: getting durability right, preferably on the first try.  It’s a big challenge because the domain expertise and tools in place today in many organizations were largely built before the science was ready and before the workflows were understood well enough to integrate across disciplines.  This situation can make it quite difficult to solve the durability puzzle.  The pieces don’t all fit together!

  • Oversimplified lab tests whose relationship to actual product use is doubtful
  • Fatigue testing instruments that produce noisy data, or execute with uncontrolled test duration
  • Raw materials suppliers struggling to relate chemistry and process improvements to actual impact on end products
  • Compounders making materials selection decisions based on insufficient / poor information
  • Product engineers missing opportunities to fully leverage material capacity
  • Outdated and inaccurate ‘rule of thumb’ engineering that doesn’t work on new cases
  • Incomplete simulation efforts that fail to forecast or diagnose key durability issues
  • Product qualification tests that under- or over-solicit damage or change failure modes
  • Part suppliers leaving OEMs with too little confidence that durability issues have been handled
  • OEMs and part suppliers struggling to account for actual end-use load cases

Endurica-powered workflows overcome these barriers.  Our training, testing services, testing instruments, and CAE software solutions integrate across disciplines.  Our motto is “Get Durability Right”.

Our classes are geared specifically for your compounders, test engineers, product engineers and analysts.  Your compounder doesn’t need to be a mechanical engineer, but she does need to negotiate the demands on the material.  Your product engineer and your analyst don’t need a PhD in chemistry, but they do need to push for performance that will win for the customer.  Your test engineer needs reliable, productive measurement strategies that get the key information that will power up your materials and product development efforts.  Our classes will pay for themselves many times over when your team confronts the next durability pitfall. 

Our testing services and testing instruments produce a complete picture of what limits durability in your application.  Rubber exhibits many ‘special effects’, and our tests are very useful for quantifying each effect, for building material models, and for solving and diagnosing durability issues.  We partner with leading labs around the world to bring you fast and reliable testing for durability simulation.  We partner with testing instrument maker Coesfeld to bring our protocols directly to your own lab with automated, user-friendly control, measurement and data reduction.  Analysts, designers and materials engineers all need clean, abundant, high-relevance measurements. 

Our software (Endurica CL, Endurica DT, Endurica EIE and fe-safe/Rubber) provides the most complete set of durability analysis capabilities in the world.  Total life, incremental damage, residual life, critical plane analysis, rainflow counting, nonlinear loads mapping, road load signal analysis, stiffness loss co-simulation, self-heating – its all here: documented, supported, validated, with examples and a large user-base.  We support the Abaqus, Ansys and MSC/Marc Finite Element solvers.  Use our software to see how different materials, different geometry, different load / use cases impact durability.  If your materials, product, analysis or testing people can ask the question, chances are that our tools will simulate it and give you new insights. 

Durability doesn’t have to be a difficult puzzle.  It costs way too much when people from different disciplines don’t “speak the same language” and try to go forward with conflicting ideas and tools.  Solve the puzzle by using pieces that fit together.  Get your team speaking Endurican!

Keywords: Compounding, Design, Testing, Analysis, Training

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