Best Practice Expert Witness for Polymer Products
Smithers Rapra is one of the world’s largest independent investigators of failed plastic and rubber components and products. Over 5000 plastic product failures have been undertaken by Smithers Rapra over the last 25 years. The company provides a comprehensive expert witness support service relating to polymer based failures, quality issues, disputes over design and manufacturing processes.
We can independently review the reasons for premature failure in plastics and rubber products and we recognize the importance of systematic failure analysis when preparing scientific and engineering evidence.
In depth technical capability combined with experience preparing and presenting evidence to court
- The Smithers Rapra consulting team includes plastic materials engineers, polymer chemists, rubber specialists and manufacturing consultants each with typically over 20 years’ experience in their field.
- Expert witness services extend to a wide range of industry sectors including; pharmaceutical, transport, automotive, industrial and consumer.
- Recent cases have included products such as medical devices, packaging materials, building components, toys and tires.
- The laboratories at Smithers Rapra are accredited in accordance to ISO17025 and the majority of our projects are carried out to this quality standard.
Our Failure Investigation Process
- In undertaking failure investigations at Smithers Rapra, a wide range of testing and polymer analysis tools can be called upon to get a true picture of the reasons for failure.
- A typical analysis on a failed product may require microscopic examination followed by chemical analysis to confirm material and additive type, examination of polymer molecular distribution to determine material degradation status, and thermal analysis to understand temperature transition responses.
- A manufacturing process audit may be appropriate to determine any influences on the failure. The product under load, or its manufacturing process may be modeled using computer simulation.
- Components or products are sometimes subjected to mechanical testing in creep or fatigue modes in specific operating environments to simulate in service conditions.
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Common Failures in Polymer Products
Reasons for Failure
Over 5000 plastic product failures have been undertaken by Smithers Rapra over the last 25 years. These have been classified below into root cause to highlight how and why failure occurs.
It has been found that although it is common for a combination of effects to contribute to failure there is often a human factor to its cause. The pie chart below shows 45% of the plastic failures investigated resulted from a poor material selection choice or a misunderstanding of the performance specification required for the product at its design stage.
Common factors that are often overlooked where products fail include:
- Long-term behavior - rubber and plastics mechanical properties are both time and temperature dependent.
- Environmental effects - exposure to chemical environments and elevated temperature can reduce long term performance.
- Product manufacturing effects - errors in manufacturing polymer products can introduce complications that have a detrimental effect on the performance of the product.
Many polymer product manufacturers are often unaware of the consequences of their process on part performance.
Many applications for plastics are for metal replacement components and the design requirements are becoming more arduous with the operating environment having higher continuous operating temperatures and more aggressive chemicals.
The two main forms of mechanical failure are ductile and brittle failure. Ductile failure is, by definition, failure at high strain. It is relatively straightforward to design plastic components to avoid ductile failure. However, in practice, ductile materials often fail in a brittle manner, which becomes much more difficult to predict. Brittle fracture is a low energy process characterised by failure at low strain, with little or no deformation. Components can contain small, crack-like defects which can act as stress concentration features; these micro-cracks grow under load and may eventually lead to rapid failure.