lies that the component no longer fulfils its function. Frequently, the ability to withstand mechanical stress or strain (and thereby store or absorb mechanical energy) is the most important criterion in service and consequently mechanical failure is usually a primary concern. However failure may be attributed to loss of attractive appearance or shrinkage etc.

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 mater

In an age of consumer champions, regulatory agencies and alert attorneys the plastics designer, manufacturer, fabricator and ultimate retailer are under drastic pressure to assure themselves, their customers, and the general public that their product can do what it is supposed to do throughout a prolonged life span and furthermore, do it in a safe and trouble-free manner. Whilst it is accepted that nothing lasts forever, the key to performance of plastics products is that it must remain serviceable for a reasonable life cycle, and failure must not occur in a manner that could jeopardise the equipment or individual it services. At the end of a useful service life it should ideally expire peacefully having no detrimental effect on its surrounding environment.

Plastics failure can cause economic and legal problems, as well as contributing to personal injury and death. The ‘owners’ of plastic products that have failed are, for obvious reasons, generally reluctant to publicise the fact. Failure diagnosticians tend to be restricted from doing so by confidentiality agreements and for this reason the activity is predominately covert. As a consequence the potential benefits such as learning from the mistakes and misfortunes of others, and identifying priorities for research and critical issues in product development are far from being fully exploited.

It is clear from the extent of plastic failures received by Rapra that this limited dissemination of plastic failure knowledge within the public domain has resulted in a continual cycle of plastic failure incidents from all industrial sectors. The lessons of good plastic product design are not being learnt even in light of the enormous growth in product liability cases that have imposed an entirely new dimension on the consumer product environment. It is now well established in law that manufacturers are liable for injuries resulting from defective product; for injuries from a hazard associated with a product against which the user should have been warned; or for damages caused by misapplication of a product which could have been foreseen by the manufacturer.

It is a practical necessity to understand why plastics fail in order to minimise the failure scenario. Rapra Technology has acquired this knowledge due to 80 years dealing with a diverse clientele providing technical services aimed at problem solving and in particular failure diagnosis.

Failure is a practical problem with a product and implies that the component no longer fulfils its function. Frequently, the ability to withstand mechanical stress or strain (and thereby store or absorb mechanical energy) is the most important criterion in service and consequently mechanical failure is usually a primary concern. However failure may be attributed to loss of attractive appearance or shrinkage etc.

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 mater

services. At the end of a useful service life it should ideally expire peacefully having no detrimental effect on its surrounding environment.

Plastics failure can cause economic and legal problems, as well as contributing to personal injury and death. The ‘owners’ of plastic products that have failed are, for obvious reasons, generally reluctant to publicise the fact. Failure diagnosticians tend to be restricted from doing so by confidentiality agreements and for this reason the activity is predominately covert. As a consequence the potential benefits such as learning from the mistakes and misfortunes of others, and identifying priorities for research and critical issues in product development are far from being fully exploited.

It is clear from the extent of plastic failures received by Rapra that this limited dissemination of plastic failure knowledge within the public domain has resulted in a continual cycle of plastic failure incidents from all industrial sectors. The lessons of good plastic product design are not being learnt even in light of the enormous growth in product liability cases that have imposed an entirely new dimension on the consumer product environment. It is now well established in law that manufacturers are liable for injuries resulting from defective product; for injuries from a hazard associated with a product against which the user should have been warned; or for damages caused by misapplication of a product which could have been foreseen by the manufacturer.

It is a practical necessity to understand why plastics fail in order to minimise the failure scenario. Rapra Technology has acquired this knowledge due to 80 years dealing with a diverse clientele providing technical services aimed at problem solving and in particular failure diagnosis.

Failure is a practical problem with a product and implies that the component no longer fulfils its function. Frequently, the ability to withstand mechanical stress or strain (and thereby store or absorb mechanical energy) is the most important criterion in service and consequently mechanical failure is usually a primary concern. However failure may be attributed to loss of attractive appearance or shrinkage etc.

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 mater

, and identifying priorities for research and critical issues in product development are far from being fully exploited.

It is clear from the extent of plastic failures received by Rapra that this limited dissemination of plastic failure knowledge within the public domain has resulted in a continual cycle of plastic failure incidents from all industrial sectors. The lessons of good plastic product design are not being learnt even in light of the enormous growth in product liability cases that have imposed an entirely new dimension on the consumer product environment. It is now well established in law that manufacturers are liable for injuries resulting from defective product; for injuries from a hazard associated with a product against which the user should have been warned; or for damages caused by misapplication of a product which could have been foreseen by the manufacturer.

It is a practical necessity to understand why plastics fail in order to minimise the failure scenario. Rapra Technology has acquired this knowledge due to 80 years dealing with a diverse clientele providing technical services aimed at problem solving and in particular failure diagnosis.

Failure is a practical problem with a product and implies that the component no longer fulfils its function. Frequently, the ability to withstand mechanical stress or strain (and thereby store or absorb mechanical energy) is the most important criterion in service and consequently mechanical failure is usually a primary concern. However failure may be attributed to loss of attractive appearance or shrinkage etc.

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 mater

cturers are liable for injuries resulting from defective product; for injuries from a hazard associated with a product against which the user should have been warned; or for damages caused by misapplication of a product which could have been foreseen by the manufacturer.

It is a practical necessity to understand why plastics fail in order to minimise the failure scenario. Rapra Technology has acquired this knowledge due to 80 years dealing with a diverse clientele providing technical services aimed at problem solving and in particular failure diagnosis.

Failure is a practical problem with a product and implies that the component no longer fulfils its function. Frequently, the ability to withstand mechanical stress or strain (and thereby store or absorb mechanical energy) is the most important criterion in service and consequently mechanical failure is usually a primary concern. However failure may be attributed to loss of attractive appearance or shrinkage etc.

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 mater

lies that the component no longer fulfils its function. Frequently, the ability to withstand mechanical stress or strain (and thereby store or absorb mechanical energy) is the most important criterion in service and consequently mechanical failure is usually a primary concern. However failure may be attributed to loss of attractive appearance or shrinkage etc.

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 from a theoretical standpoint. Brittle fracture is a low energy process characterised by failure at low strain, with little or no deformation. Components contain small, crack like defects which can act as stress concentration features; these micro-cracks grow under load and may eventually lead to rapid catastrophic failure.

When considering the design and development of a plastic product it is imperative that a designer fully understands the fundamental limitations of plastics. A designer must be aware that plastics are:-

· Non-linear, visco-elastic materials
· Temperature dependant
· Materials that physically age
· Susceptible to chemical attack and environmental stress cracking
· They will, under the action of a tensile stress, eventually fail
· The time to fail will diminish as the stress increases
· The time to fail will diminish as the temperature increases
· The time to fail will diminish in the presence of certain environments
· The time to fail will diminish under the action of cyclic loading
· The moulding process can result in significant levels of residual stress in components
· Weld lines are planes of weakness, particularly in fibre filled materials
· Most plastics are highly notch sensitive.
· Mechanical anisotropy due to the alignment of fibre reinforcement
· Moulded articles rarely achieve theoretical material properties


Rapra’s experience has shown that many designers do not consider and / or are aware of these issues when considering the use of plastic materials. We have designers who can design but have no real appreciation for the material they are proposing to use. Rapra has found that Poor product design is endemic to all plastic sectors including the medical, pharmaceutical, automotive, rail, aerospace, packaging, oil / gas, energy, engineering and construction industries.

More than 5,000 failures have been the subject of study at Rapra. Interestingly the number of failures evaluated has increased significantly during the past five years.

Rapra Technology Plastic’s consultancy provides a range of services which allow engineers to prove designs at an early stage, ensuring that their product will be right first time inclusive of finite elemental analysis (FEA - ABAQUS), material selection (Plascams), evaluation of design aspects, injection