Delivered as part of the RAPRA technical session at the Plastics Design & Moulding (PDM)...

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