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Delivered as part of the RAPRA technical session at the
Plastics Design & Moulding (PDM)Tradeshow 2015
Justin TaylorPrincipal Consultant
Ipolytech
www.ipolytech.com
© 2015 Independent Polymer Technology Ltd
Failure
Failure
Failure
It doesn’t just happen!
“With few exceptions we cannot blame an inanimate material or hold it responsible for our failures” –DC Wright- Failure of Plastics and Rubber Products
© 2015 Independent Polymer Technology Ltd
Will my product fail?
All products will fail at some point in time.
• The time to failure and mode of failure can, to a significant extent, be controlled / predicted
• Balance of cost of testing versus consequence of failure
Why bother?
Understanding how plastic products fail allows us to reduce premature failures and enhance performance and profit.
• Reduce product warranty claims and recalls• Avoid litigation• Wasted time on failed designs and concepts• Improve market confidence and sales• Avoid over engineering
Assessing Failure of Plastic Products
• Rarely is there a single cause of failure
• Failure is often the result of a chain of events from product conception to the end user.
• We have control over many of the factors affecting product performance.
Failure doesn’t just happen
Failure of Plastic Products
Rarely is there a single cause of failure
Control handle failing in a brittle manner.
Failure of Plastic Products
Rarely is there a single cause of failure
Poor design including sharp corners at regions of peak stress.
Stress concentration
Failure of Plastic Products
Rarely is there a single cause of failure
Flow path from thick to thin back to thick sections.
High moulded in stress and void formation
Failure of Plastic Products
Rarely is there a single cause of failure
Polycarbonate - mouldings exhibited silver streaking due to moisture from poor drying of granules.
Hydrolytic degradation
Failure of Plastic Products
Rarely is there a single cause of failure
Control handle failing in a brittle manner.
MaterialsMaterials selectionAdditive selectionMaterial SupplyAdditive SupplyDegradation in CompoundingStorage of materialsContamination
ProcessingIncorrect conditionsDegradationPoor process controlContaminationDispersion of fillersDefects – voids etc.Moulded in stressAssembly processes
StorageUV AgeingThermal Ageing /CyclingHumidityMicrobial attackChemical Attack/ ESC Interaction with Packaging etc
Service LoadsMechanical StressElectrical StressTolerance stack-up
EnvironmentUV
RadiationThermalChemicalGases and Vapours Migration
UnplannedChemicalsTemperature spikesLoad spikes
“The perfect storm”
Human FactorMisuseMalicious damagePoor designLack of knowledge of material /process limits
Failure to follow manufacturing proceduresSecondary intervention – after market modsInstallation errorsUse of internet published data
Servicing of product (positive intervention)
Key Control Points
• Design• Specification• Testing• Quality Control• Product monitoring – verification of test
Control Points• Design–Material selection–Avoid stress concentrations– Long term creep and fatigue data for long
term performance–Awareness of the effect of working
environment on physical performance–Design for manufacturing
Control Points
• Testing– Select test methods appropriate to the
application.–Understand the test methods specified in
industry guidelines and what they achieve.– Test to failure not to an acceptance level–Be careful of over accelerating tests
Control Points• Specification–Define a detailed specification of
requirements–Where possible set realistic quantified
requirements–Where possible specify grade and quality of
material. If you allow alternate grades, then verify their performance
Control Points• Quality Control – in addition to a robust quality auditing system– Identify check points at design stage and
review throughout prototyping and production– Ensure QC tests prevent failure –Retain samples at all stages of manufacture– If relying on supplier documentation
read it /confirm it
Control Points• Product monitoring – verification of test
– Test products obtained from service to verify performance is as predicted
– Subject product to long term testing with record of environment and corresponding performance to verify accelerated testing
– Test failures against your retained samples– Determine all factors in failures do not just assign
one cause e.g. impact and then stop.– Feedback lessons learnt into the design, test
protocols, specification and quality systems
Control Points
• Design• Testing• Specification• Quality Control• Product monitoring – verification of test
Failure it doesn’t just happen
• Understand your materials• Accept your power to control life expectancy
of products• Learn from failures in your industry and others• Keep improving
Suppliers
Materials
TestingManufacturingTraining
