A polymer is a visco-elastic materials. Which means, its elastic property is time dependent. Simply, the elastic modulus of a polymer will be different if the rate of loading is changed from very low to very. At high rate of loading, the elastic modulus measured will be high and vice versa. This is because a polymer always carries viscous behaviour along with the elastic nature.
Another important effect of visco-elastic behaviour can be seen when there is dynamic loading, that is, the load is continuously changing from low to high and then to low. Dynamic Loading of plastics (viscoelastic materials) gives rise to a phase lag between the stress and the strain. Therefore, the complex modulus of a viscoelastic materials is defined by two terms - Storage Modulus and Loss Modulus. Storage modulus is the modulus of the polymer that corresponds to the true elastic recovery of the materials. Loss modulus is the modulus term that is not going to be recovered and in fact lost in viscous energy dissipation.
Dynamic Mechanical Test (DMT) can be used to characterize a polymer for its many properties such as creep, stress-relaxation, glass transition temperature, dynamic stress-strain etc. Applications of viscoelastic materials include vibration control, shock absorbance, sound proofing, earthquake proofing, prevention of fatigue failure due to vibration etc.
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31 июл 2024
