Dynamic Mechanical Analysis
Before going in the deep details of dynamic mechanical system, let me take the space to explain what dynamic mechanical analysis is. You must have heard about the testing response of material to the outside stimulus. In this analysis a deformation is exposed to the material where its response and resistance to the stimulus is studied. This deformation can repeated on the same sample in a cyclic manner. These stimuli can be temperature, frequency, heat and stress as well.
When we need to test a sample commonly termed as geometry, we observe too much extent the surface will absorb the energy and heat. In damping, it is studied how the heat absorption is studied under the cyclic load.
Stress and strain ratio is a central fact in the dynamic mechanics around which the other things take place. Polymers do have viscoelastic properties which according to the classical theory brings the properties of elastic solids. This means that the polymer exhibits both the solid and the liquid properties when the stress response is independent of the strain rate. The theory describes the elastic properties of solid and reveals that the elastic bodies stress is directly proportional to the strain applied. The stress and the strain value and their relationship are studied in the dynamic mechanical analysis.
When a polymer is studied for its liquid and solid like behavior; it’s given a sinusoidal force or you may call it a stress, the response of this stress is the resultant strain of the polymer which is then measured. Now here the polymers are categorized as per their behavior. Perfect elastic solids have the constant stress and the strain phase; the result is always the same. Bodies which are purely viscous, have 90 percent phase lag. Viscoelastic polymers do not give the same results; thus their properties lie in between. You can neither have the same stress and strain phase nor will you get 90 percent phase lag of strain as in liquids or fluids rather you will get the results in between. Thus, here this is important to calculate the phase lag.
For stress
ε = ε0sin(tω) for strain
Oscillating Mechanical System
Oscillation is the system of a mass attached to a spring, the spring is linear. Oscillating mechanical system builds up important kingdom of the engineering regime. Oscillation has brought the resonance disasters in many buildings, so the prime concern of the oscillating mechanical system is to avoid these resonance disasters in the construction of every building.
The disaster comes when the mechanical system starts absorbing more energy when its frequency is matched to any other system’s natural frequency of vibration. For example you must have observed a mechanism in the parade of the soldiers when going on a bridge. The soldiers parade frequency if matches with the vibration of the bridge oscillation; there is a serious danger by having an increase in the amplitude. The same principal is enjoyed by the child taking a swing.
Now mechanical resonance is the study of the matching frequency of the vibration of the two systems. When the energy absorbed by as a result of the matching frequency, the resonance disaster takes place. Here comes the role of the engineers who for taking a precaution recommend the installation of shock mounts which on the detection of any matched frequency dissipate the absorbed energy and hence a system is maintained.
What happens in an earthquake, a building is oscillated as a result of the matched frequency of the ground motion. The danger is of the extreme in the seismic zone where the buildings are vulnerable; here the major construction is made by having an account of the oscillating frequencies. The buildings are constructed and the resonant frequency is made which does not take place with the common ground motion.
Human Ear Principle
You must be amazed to know that the human ear works on the principle of the oscillating mechanical engineering. Basilar membrane vibration and its resonance take place under this category.
Nature Also Works on the Same Principle
Let me add to your knowledge that solar system has some motions of moon which work on this principle.
By: Ammarah Khan
