Fatigue Striations - polycarbonate

Failure Analysis

Determining the exact cause of a component failure is the first step towards defining corrective action. ipolytech have extensive experience in polymer failure analysis of products manufactured from all major thermoplastic materials over all end user sectors. Understanding of why a plastic product has failed requires detailed knowledge of the long term performance of polymers together with a thorough understanding of their interaction with specific service environments (chemical, temperature, stress and time).

The majority of plastic component failures occur in the mid to long term. Even in normally tough, ductile plastic materials failures are invariable brittle in nature and result in a short service life. Such brittle failures are most commonly caused by the following factors:

Incorrect Materials Selection
the use of an incorrect material for an application is a common cause of polymer failure, lack of understanding of the interaction of polymers with chemicals and environments and long term response commonly leads to premature failure

Response to long term loads
Plastic and rubber products are sensitive to long term loads. These can be either static loads through creep or fatigue mechanisms. These processes mean that the strength and stiffness of plastic components in service conditions are frequently significantly lower than quoted on a standard data sheet. A lack of understanding of the significance of the long term mechanical effects is a common cause of failure

Notches and defects
Polymers are notch sensitive material, that is the say the effect of notches and defects induces brittle failure of the material. Such notches can be produced by poor component design but inclusions, voids and other defects can act as notch like defects and induce brittle failure.

Chemical and Environmental Interactions
interaction of polymers with chemicals and environments can lead to degradation or cracking of polymers. For many materials specific interactions with common household products can lead to rapid crazing, cracking, fracture and product failure

Processing Error
Correct processing of materials is vital in ensuring long term durability.  Incorrect processing causes thermal/oxidative and hydrolytic degradation and embrittlement process, the introduction of high residual stresses, material inhomogeneity, moulding defects or contaminants.  Such factors will not only affect product appearance but will also have a significant effect on durability.  

 Inappropriate design
Product design is fundamental to ensuring plastic component long term durability. incorrect design will highlight polymeric material weaknesses to long term loads, chemical environments, high speed loading, fatigue loads resulting in brittle failure of the product within a short service life

Product failure is often caused by a number of interacting factors;

Factors Contributing to Product Failure