What is strain amplitude?
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 basquin equation?
Basquin’s equation is a power law relationship which describes the linear relationship between the applied stress cycles (S) in the y-axis and the number of cycles to failure in the x-axis plotted on a log-log scale.
How do you calculate strain life parameters?
The equations used for stress-strain and strain life are:
- Ramberg-Osgood equation:εtot=σE⏟elastic+(σK)1n⏟plastic.
- Hysteresis curve equation:Δε=ΔσE⏟elastic+2(Δσ2K)1n⏟plastic.
- Coffin-Manson equation:εtot=σfE(2Nf)b⏟elastic+εf(2Nf)c⏟plastic.
- Morrow Mean Stress Correction:εtot=σf−σmE(2Nf)b⏟elastic+εf(2Nf)c⏟plastic.
Which stage of the fatigue crack is most significant in the low cycle fatigue?
LCF due to transient thermal stresses. Hence, an LCF crack starts and propagates at the surface where the tensile stresses are the highest and the stress risers are more prominent.
What is stress amplitude?
One-half the range of fluctuating stress developed in a specimen in a fatigue test. Stress amplitude often is used to construct an S-N diagram.
What is transition fatigue life?
If the stress amplitude equals the transition stress of the specimen (i.e., if x = x t , α ), then the fatigue life of the specimen can be referred to as the Transition Fatigue Life (TFL) of the specimen (i.e., then y = y t , α ).
What is basquin’s law?
Abstract. Basquin’s law of fatigue states that the lifetime of the system has a power-law dependence on the external load amplitude, tf∼σ−α0, where the exponent α has a strong material dependence. On the microlevel, the fatigue fracture proceeds in bursts characterized by universal power-law distributions.
What is Coffin Manson Law?
The Coffin–Manson law relates for a metal uniaxially and cyclically loaded the plastic strain amplitude ɛp to the cycle number of fracture Nf through a two-parameter power law(1) ε p = ε f N f c where ɛf and c (<0) are the fatigue ductility coefficient and exponent, respectively [1], [2].
What is strain life method?
The Strain Life approach predicts how long a product will survive due to for both elastic and plastic loads. The Strain Life approach requires a local stress-strain time history (observed at same location) to determine the cycles and corresponding damage to the product.
What is high cycle fatigue and low cycle fatigue?
High cycle fatigue require more than 104 cycles to failure where stress is low and primarily elastic. Low cycle fatigue is characterized by repeated plastic deformation (i.e. in each cycle) and therefore, the number of cycles to failure is low.
What is Coffin-Manson Law?
What is Coffin-Manson?
The Coffin-Manson model considers the effects of dwell time and ramp time using frequency of usage f. It cannot tell the difference between dwell time and ramp time. Dwell time and ramp rate are critical factors in temperature cycle test. Dwell time is important for creep development, especially at high temperature.
Why does the plastic strain amplitude decrease with increasing number of cycles?
The monotonic decrease in the plastic strain amplitude with increasing number of cycles reflected that cyclic hardening occurred in the entire process, from the first cycle at a high strain amplitude of ±6000 με ( Fig. 3.15A ).
What is plastic strain amplitude in LCF?
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 the time lag of the stress-strain response?
The time lag or phase shift of the strain response is used to quantify its viscous behavior; the slope of the stress-strain response relates to its elastic behavior. These properties are often described as the ability to lose energy as heat (damping) and the ability to recover from deformation (elasticity).
What is time-dependent strain in viscoelastic materials?
Viscoelastic materials have elements of both of these properties and, as such, exhibit time-dependent strain. Meaning the strain response to a stress input is delayed, resulting in a loss of energy. Viscoelastic behavior normally occurs at different time scales in the same material.