Molded plastic couplings used in an industrial application exhibited abnormally brittle properties, as compared to previously produced components. The couplings were specified to be molded from a custom-compounded glass-filled nylon 6/12 resin. An inspection of the molding resin used to produce the discrepant parts revealed that the pellets were of two general types, neither of which matched the pellets from a retained resin lot. Investigation included visual inspection, micro-FTIR in the ATR mode, and analysis using DSC. The thermograms supported the conclusion that the brittle couplings contained a significant level of contamination, polypropylene and nylon 6/6. The source of the polypropylene was likely the purging compound used to clean the compounding extruder. The origin of the nylon 6/6 resin was unknown but may represent a previously compounded resin.

A component of a water filtration unit failed while being used in service for approximately eight months. The filter system had been installed in a commercial laboratory, where it was stated to have been used exclusively in conjunction with deionized water. The failed part had been injection molded from a 30% glass-fiber and mineral-reinforced nylon 12 resin. Investigation, including visual inspection, 118x SEM images, 9x micrographs, energy-dispersive x-ray spectroscopy, micro-FTIR in the ATR mode, and TGA, supported the conclusion that the filter component failed as a result of molecular degradation caused by the service conditions. Specifically, the part material had undergone severe chemical attack, including oxidation and hydrolysis, through contact with silver chloride. The source of the silver chloride was not established, but one potential source was photographic silver recovery.

A nylon oil-lubricated driving gear showed pitting upon visual inspection. The pitting produced numerous surface microcracks. Further investigation (visual inspection and 37x images) supported the conclusion that failure occurred in association with large-scale fragmentation (frictional wear). No recommendations were made.

A production lot of mechanical hinges used in an automotive application had failed during incoming quality-control routine actuation testing. A change in part supplier had taken place between the approval of the prototype parts that performed acceptably and the receipt of the first lot of production parts. The mechanical hinges were specified to be injection molded from an impact-modified, 13% glass-fiber-reinforced nylon 6/6 resin. Investigation of samples representing the failed components and the original prototype parts included visual inspection, 118x SEM images, micro-FTIR, DSC analysis, and TGA. It supported the conclusion that the hinge assemblies failed through brittle fracture associated with stress overload during the actuation of the parts. The failed part material was found to be degraded, most likely occurring during the compounding of the resin or during the actual molding of the parts. While resins for both failed and non-failed parts produced results characteristic of a 13% glass-fiber-reinforced, impact-modified nylon 6/6, the failed part material, contained a significantly lower level of rubber, which rendered the parts less impact resistant and subsequently lowered the ductility of the molded hinge assemblies. No recommendations were made.

A production lot of plastic wire clips was failing after limited service. The failures were characterized by excessive relaxation of the clips, such that the corresponding wires were no longer adequately secured in the parts. No catastrophic failures had been encountered. Parts representing an older lot, which exhibited satisfactory performance properties, were also available for reference purposes. The clips were specified to be injection molded from an impact-modified grade of nylon 6/6. However, the part drawing did not indicate a specific resin. Investigation included visual inspection, micro-FTIR in the ATR mode, and analysis using DSC. The spectrum representing the reference parts showed a relatively higher level of a hydrocarbon-based impact modifier, while the results obtained on the failed parts showed the presence of an acrylic-based modifier. Also, the reference clip thermogram showed a melting transition attributed to a hydrocarbon-based impact modifier. The conclusion was that the control and failed clips had been produced from two distinctly different resins. It appeared that the material used to produce the failed clips had different viscoelastic properties, which produced a greater predisposition for stress relaxation.

Plastics or polymers are used in a variety of engineering and nonengineering applications where they are subjected to surface damage and wear. This article discusses the classification of polymer wear mechanisms based on the methodologies of defining the types of wear. The first classification is based on the two-term model that divides wear mechanisms into interfacial and bulk or cohesive. The second is based on the perceived wear mechanism. The third classification is specific to polymers and draws the distinction based on mechanical properties of polymers. In this classification, wear study is separated as elastomers, thermosets, glassy thermoplastics, and semicrystalline thermoplastics. The article describes the effects of environment and lubricant on the wear failures of polymers. It presents a case study on nylon as a tribological material. The article explains the wear failure of an antifriction bearing, a nylon driving gear, and a polyoxymethylene gear wheel.

This article presents the mechanisms of polymer wear and quantifies wear in terms of wear rate (rate of removal of the material). Interfacial and bulk wear are discussed as well as a discussion on the wear study of "elastomers," "thermosets," "glassy thermoplastics," and "semicrystalline thermoplastics." The article also discusses the effects of environment and lubricant on the wear failures of polymers. It presents a case study on considering nylon as a tribological material and failure examples, explaining wear resistance of polyurethane elastomeric coatings and failure of an acetal gear wheel.

An antifriction bearing made from a nylon/ polyethylene blend failed. The bearing came into contact with a steel shaft. Investigation (visual inspection and 417X images) supported the conclusion that movement of the shaft against the bearing caused abrasion due to fine iron oxide particles. No recommendations were made.