Characteristics of polymer mechanical properties
1. Polymer materials have the widest range of mechanical properties of all known materials, ranging from liquids, soft rubbers to very hard solids. The response of various polymers to mechanical stress varies widely, for example:
PS products are very brittle, broken when knocked (brittle)
Nylon products are very tough, not easily deformed, and not easily broken (toughness)
When the lightly crosslinked rubber is stretched, it can be stretched several times, and the force is basically restored to its original state (elasticity).
After the clay is deformed, it completely retains its new shape (stickiness)
This diversity of polymer mechanical properties provides a wide range of options for different applications.
2. The most characteristic of the mechanical properties of polymers is high elasticity and viscoelasticity.
(1) High elasticity of the polymer: Due to the extremely large molecular weight of the polymer, the polymer chain has many different conformations, and the conformational change causes the polymer chain to have its own flexibility. The performance of the chain flexibility is the high elasticity of the polymer. The difference between it and the general elasticity of general materials is due to the change of conformation; the conformational entropy decreases during deformation and increases upon recovery. Internal energy does not play a major role in high elastic deformation (it is the main cause of general deformation)
(2) Viscoelasticity of a polymer: It means that the polymer material not only has the general characteristics of an elastic material, but also has some characteristics of a viscous fluid. Elasticity and viscosity are particularly pronounced on the polymer material at the same time.
The viscoelasticity of a polymer is manifested by its outstanding mechanical relaxation. The relationship between stress, strain and time must be considered when studying its mechanical properties. Temperature is also a very important factor for mechanical properties
Describe the mechanical behavior of viscoelastic polymer materials must consider four parameters of stress, strain, time and temperature. The strong dependence of the mechanical properties of polymer materials on time and temperature is a problem that should be clarified in the study of its mechanical properties. It is also a problem that must be paid attention to when testing and using polymer materials.
Characteristics of polymer mechanical properties