Measuring the Complex Modulus of Polyethylene Using Instrumented Indentation

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The mechanical properties of a material determine manufacturability, performance, and longevity; thus, knowing mechanical properties is essential for making good design decisions. Polymers are exceptionally complex materials—mechanical properties depend on chemistry, processing, and thermo-mechanical history. Specifically, mechanical properties depend on the type and length of the parent chain, branching, cross-linking, strain, temperature, and frequency, and these dependencies are generally interrelated. Further, it is likely that mechanical properties also depend on volume constraints. That is, we should not be surprised if a certain polymer manifests different mechanical properties depending on whether it is in the form of a thin film or a large block, because volume constraints can affect molecular mobility. Thus, in order to gain useful information for making sound decisions when designing with polymers, mechanical property measurements should be made on a relevant sample in a relevant context. Instrumented indentation testing makes such context-specific measurements more accessible, because samples can be small and minimally prepared.