Plastics are viscoelastic materials, meaning that they exhibit both viscous and elastic characteristics when undergoing deformation. This is due to their unique molecular structure. The polymer molecules consist of long chains with high molecular weight. Those individual polymer chains are and tangled into each other, but are mobile and can slide past each other because they do not share chemical bonds with the other chains.

Because of their viscoelastic nature, the mechanical properties of plastics vary depending on the conditions under which stress is applied. Most commonly, the mechanical properties of plastics will vary with temperature, time under load, and strain rate.

Their viscoelastic nature is important to those designing, manufacturing, or using plastic components. and is a fundamental concept of plastic behavior that needs to be understood. It is important to recognize the viscoelastic nature of plastic materials so that their behavior in the intended application can be understood.

This course will expose the attendees to the following concepts:

• The viscoelastic nature of plastics is attributed to their molecular structure.
• Thermoplastic materials have both long-term and short-term properties – they flow due to the application of stress over time.
• Most mechanical testing of plastic materials is actually testing the material’s viscoelasticity – how the plastic flows when different stresses are applied.
• Plastics are time, temperature, and strain rate sensitive.