What is a relaxation spectrum?
The relaxation spectrum and the retardation spectrum are the distributions of the spectrum intensity with respect to relaxation and retardation time. They are an essential characteristic of LVE materials, from which all other viscoelastic functions and their responses can be obtained [4].
What is viscoelastic relaxation?
Viscoelastic material exhibits both elastic and viscous characteristics, and its deformation is temperature dependent. Relaxation modulus E(t) is a characteristic of material viscoelasticity as used to describe the stress relaxation of materials with time (t).
What is relaxation time viscoelastic?
Relaxation time is the characteristic time in which a system relaxes under certain changes in external conditions. Here, it refers to the characteristic time required for the polymer coil to relax from a deformed state to its equilibrium configuration. It is a key parameter for characterizing a viscoelastic fluid.
What is relaxation time in rheology?
In other words, Non-Newtonian fluids have a characteristic memory time scale which is referred to as the relaxation time. When the applied rate of deformation is reduced to zero, these materials relax over their characteristic relaxation time – a constitutive property of each material.
How can I get my relaxation time?
Thus, the relaxation time can be determined, by measuring the time it takes for X0 to decrease to X0/2.718. In other words, it is the time in which the relaxation process carries the system a fraction 1/e toward the equilibrium position. Thus, τ is a time interval like the half-life t1/2.
What is relaxation time physics?
The relaxation time is a measure of the time it takes for one object in the system (the “test star”) to be significantly perturbed by other objects in the system (the “field stars”). It is most commonly defined as the time for the test star’s velocity to change by of order itself.
What is meant by stress relaxation?
Stress relaxation is a time-dependent decrease in stress under a constant strain. This characteristic behavior of the polymer is studied by applying a fixed amount of deformation to a specimen and measuring the load required to maintain it as a function of time.
What is an example of stress relaxation?
An example of stress relaxation is when a rubber band, which is a polymer, is wrapped around a newspaper for an extended period of time. The rubber band is held at a constant displacement, however the force that it is applying to the newspaper decreases over time and it loses its integrity.
What is the best relaxation technique?
Six relaxation techniques to reduce stress
- Breath focus. In this simple, powerful technique, you take long, slow, deep breaths (also known as abdominal or belly breathing).
- Body scan.
- Guided imagery.
- Mindfulness meditation.
- Yoga, tai chi, and qigong.
- Repetitive prayer.
What is the meaning of relaxation time?
1 : the time required for an exponentially decreasing variable (as the amplitude of a damped oscillation) to drop from an initial value to 1/e or 0.368 of that value (where e is the base of natural logarithms)
What is called the relaxation time?
What is relaxation process?
Relaxation processes allow nuclear spins to return to equilibrium following a disturbance, e.g. a radiofrequency pulse. The first is closely related to spin–lattice relaxation, and arises from the finite lifetime of the spin states, through the uncertainty principle.
What are the assumptions for the relaxation time spectrum?
The procedure to calculate the relaxation time spectrum, for a given MWD, using the four assumptions made by Bersted and Slee: The relaxation time spectrum is truncated at high shear rates; τ m is the maximum allowable relaxation time at a specific shear rate γ m.
Are there molecular models for relaxation time spectra?
Molecular models for relaxation time spectra based on molecular theory were introduced by Rouse [9], de Gennes [10], and Doi and Edwards [11]. The models start out with the most simple molecular geometry, that of long, linear, flexible chains of uniform length.
Which is the maximum allowable relaxation time?
The relaxation time spectrum is truncated at high shear rates; τ m is the maximum allowable relaxation time at a specific shear rate γ m. The relationship between τ m and γ m is τ m ≅ 1 / γ m.
How is the relaxation time spectrum expressed as a Laplace transform?
The relaxation modulus can be expressed as a Laplace transform of a continuous relaxation time spectrum H (λ): H (λ), called the spectrum from here on, is an alternative to the directly observ-able relaxation modulus G° ( t ). Each of these material functions alone is sufficient for describing the viscoelastic behavior of a material.