What is amplitude strain?

Plastic strain amplitude (the half-width of the stress–strain hysteresis loops at zero stress) is a key parameter in LCF tests, because it is directly associated with the fatigue life of structural components via the well-known Coffin–Manson relationship [34].

What is amplitude in rheology?

Rheology > Oscillatory tests. During an amplitude sweep the amplitude of the deformation – or alternatively the amplitude of the shear stress – is varied while the frequency is kept constant. The amplitude is the maximum of the oscillatory motion.

What amplitude sweep tells us?

Amplitude sweeps are useful in practice to describe the behavior of dispersions, pastes, and gels; for example, for use in the food, cosmetics, pharmaceutical, and medical industries, and for coatings, sealing compounds, and lubricating greases.

Why does storage modulus increase with frequency?

As the frequency increases the rate of shear also increases, which also increases the amount of energy input to the polymer chains. Therefore storage modulus increases with frequency.

What is Cox Merz rule?

The Cox–Merz rule is an astonishingly simple relationship that predicts that the com- plex viscosity * and steady shear viscosity ( ˙ ) are equivalent when the angular frequency is equal to the steady shear rate ˙ . The viscosity functions of the silicone oils used in this study also obey the Cox–Merz rule.

What is stress amplitude?

[′stres ‚am·plə‚tu̇d] (mechanical engineering) One half the algebraic difference between the maximum and minimum stress in one fatigue test cycle.

What is frequency sweep in rheology?

In a frequency sweep, measurements are made over a range of oscillation frequencies at a constant oscillation amplitude and temperature. Below the critical strain, the elastic modulus G’ is often nearly independent of frequency, as would be expected from a structured or solid-like material.

What is strain in rheology?

Strain in rheology is somewhat different from its everyday meaning: it’s a purely geometrical quantity, a way to quantify the amount of deformation in a given material, and has no units. Much of the complexity of rheology relates to defining or measuring strain.

What is strain sweep?

The strain sweeps tests, employed in the 80’s to characterize viscoelastic materials, consist of applying a cyclic strain signal with increasing amplitude. Initially they were used to establish the linear viscoelastic domain of these materials in terms of strains.

Is storage modulus the same as Young’s modulus?

E’ Storage modulus A measure of the elastic response of a material but not the same as Young’s modulus.

Is flexural modulus the same as Young’s modulus?

Ideally, the flexural modulus of a material is equivalent to its Young’s modulus. In practical terms, the higher the flexural modulus of a material, the harder it is to bend. Conversely, the lower the flexural modulus is, the easier it is for the material to bend under an applied force.

What is steady shear viscosity?

Theoretical analysis on the relationship of complex viscosity (η*) and steady shear viscosity (η) indicates that viscous viscosity (η′) measured under linear viscoelastic region equates with steady shear viscosity at low shear rates, and the Cox‐Merz Rule applies only to the suspension whose viscous viscosity of the …

What is complex viscosity?

It is also possible to define a complex viscosity η*, which is a measure of the total resistance to flow as a function of angular frequency (ω) and is given by the quotient of the maximum stress amplitude and maximum strain rate amplitude.

How do you calculate amplitude stress?

The applied nominal stress amplitude on the bolt is determined: σ a = F SAo − F SAu 2 A S = φ ( F A max − F A min ) 2 A S = 0.098 ( 15,000 − 0 ) 2 × 0.25 × π × 8.60 2 = 12.65 N / mm 2 .

How do you calculate stress amplitude?

It is sometimes called as alternating stress is calculated using Stress amplitude = (Maximum Stress at Crack Tip-Minimum Stress)/2. To calculate Stress Amplitude, you need Maximum Stress at Crack Tip (σmax) & Minimum Stress (σmin).

What is the purpose of a frequency sweep?

Frequency sweeps are only defined for linear time-invariant circuits. With a frequency sweep, you can extract the bandwidth of a circuit or system, and you can generate a transfer function. Nonlinear circuits require more sophisticated simulations, or they require complex iteration in the time-domain.

How do you sweep frequency?

Start Frequency and Stop Frequency The sweep is phase continuous over the full frequency range. The default start frequency is 100 Hz. The default stop frequency is 1 kHz. To sweep up in frequency, set the start frequency less than the stop frequency.

What is G and G in rheology?

The G’ refers to the elastic modulus, and reflects elastic behavior of a material when deformed. The G” refers to the viscous modulus, which reflects the flow of a material while it is deformed.

What is frequency in DMA?

The modern DMA systems are nearly always fixed frequency systems operating at frequencies between about 0.01 and 100 Hz. and in a temperature region ranging from about −150°C to 300°C.

What is the difference between flexural modulus and flexural strength?

Modulus of rupture is the behaviour of a material under direct tension. Where as, Flexural strength is the behaviour of a structure in direct bending (like in beams, slabs, etc.) Bending occurs due to development of tensile force on tension side of the structure.

What is constant strain amplitude testing?

In constant strain amplitude testing, either increasing or decreasing stress amplitude can be seen, depending on whether the material is cyclic strain hardening or softening, although in many cases this stabilises to a constant value after a number of cycles.

What is plastic strain amplitude and why does it matter?

Plastic strain amplitude (the half-width of the stress–strain hysteresis loops at zero stress) is a key parameter in LCF tests, because it is directly associated with the fatigue life of structural components via the well-known Coffin–Manson relationship.

What is the relation between endurable stress amplitudes and permissible stress amplitude?

Permissible stress amplitudes are derived from endurable stress amplitudes on the basis of eq. (2.8), introducing the safety factor jσ, which depends on the scatter bandwidth and on what failure probability is acceptable.

How do you find the a stress amplitude?

A stress amplitude of Sa = 171 MPa is determined by the input of 2N f = 2 × 10 6 reversals to the previous equation. Note that this point ( Sa = 171, 2 Nf = 2 × 10 6) on the median S−N curve is arbitrarily chosen.