Published: Jan 2007
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PLASTICS ARE POLYMERIC MATERIALS THAT CAN be molded into shape by flow at some elevated temperature. Elastomers are polymeric materials that have high elongation (more than 100% in a tensile test) and forcibly return from elongation/deformation; they have high restitution. It is current practice to combine moldable plastics with elastomers to make thermoplastic elastomers; essentially, these are injectionmoldable rubbers. There is a plastic phase and a rubber phase in the microstructure.
To make this subject a bit more complicated, plastics are often filled with substances that run the gamut from extremely hard aluminum oxide to unctuous polytetrafluoroethylene (PTFE, or Teflon). In addition, some plastics are commonly reinforced with continuous (woven) or nonwoven materials such as cotton, canvas, glass, plastic filaments, carbon fiber, boron fiber, ceramic whiskers, and nanoparticles. In other words, they can be very heterogeneous, and many formulations, probably more than 20,000, are commercially available.
How do these materials wear? The short answer is that they wear differently than metals, ceramics, and other traditional engineering materials. And that is the reason why there is a chapter dedicated to them. Their differences compared with metals and ceramics often lead to problems in diagnosing wear type and in simulating service conditions in laboratory testing.