Mechanical Properties Of Polymer

Mechanical Properties of Polymers

Polymers:

Polymer means many parts. Polymers are the long chain compounds.

A chemical compound that is made up of many small molecules that are arrange in simple molecular structure to form a large molecule.

Types of Bonding in Polymers:

i) Cross Linkage ii) Bonding

Examples:

Polyester, Acrylic, Polypropylene, Teflon Bakelite, Phenol Formaldehyde, Melamine, Duraplastetc

What is Mechanical behavior?

Mechanical behavior is basically the properties that are use d to define a material i.e. hardness, stiffness, toughness strength, thermal stability, color resistance. Etc.

Mechanical Behavior in Polymers:

Polymers are the compounds that are used widely in a variety of applications from structure materials

Metals and polymers are mechanically dissimilar to each other in many cases but here we will discuss only the range of modulus of elasticity and tensile strength of both materials.

The range of modulus of elasticity for polymers may be as low as 7MPa and as high as 4GPa .But for metals it ranges between 48 TO410 GPa. The maximum value of tensile strength for polymer is 100 MPa and for metal alloys is 4100 MPa. The elastic elongations in polymers are more than 1000 % but for metals it is rarely more than 100%.

Effect of Temperature

The temperature has also great influence on mechanical properties of polymers. These properties are much more sensitive near room temperature. The temperature has inverse relation with tensile strength and modulus of elasticity but possess direct relation with ductility. As temperature increase the tensile strength and modulus of elasticity decreases but ductility increases.

Viscoelasticity deformation:

At different temperature the amorphous polymer acts differently. It is glass like structure at low temperature, behaves like a rubber at intermediate temperature and is a viscous liquid at high temperature. At low temperature the behavior is totally elastic which move towards viscous liquid as the temperature

Stress relaxation tests are performed to identify the behavior. In the test the specimen is strained rapidly in tension and in low strain level. The temperature is kept constant and the stress used to maintain strain is measured. In polymer molecular relaxation process occurs due to which stress is reduced.

Viscoelasticity Creep:

Viscoelasticity creep is basically a time dependent deformation when the stress level is kept constant. This deformation is significant at room temperature and at the stresses that lie below yield strength. Creep test are applied in the same way as for metals. These tests are performed under isothermal conditions and stress is maintained at constant level while strain is measured as a function of time. It is also a temperature sensitive and diminishes with the rise of temperature.

Impact Strength

Polymers show ductile or brittle fracture under impact loading circumstances. Both semi crystalline and amorphous polymers are brittle at low temperature and both have relatively low impact strength. They practice a ductile to brittle shift over a relatively slight temperature