Number Of Transient Cycles Research Articles

Alternating Shear Orientation During Cyclic Loading Facilitates Yielding in Amorphous Materials

The influence of alternating shear orientation and strain amplitude of cyclic loading on yielding in amorphous solids is investigated using molecular dynamics simulations. The model glass is represented via a binary mixture that was rapidly cooled well below the glass transition temperature and then subjected to oscillatory shear deformation. It was shown that periodic loading at strain amplitudes above the critical value first induces structural relaxation via irreversible displacements of clusters of atoms during a number of transient cycles, followed by an increase in potential energy due to the formation of a system-spanning shear band. Upon approaching the critical strain amplitude from above, the number of transient cycles required to reach the yielding transition increases. Interestingly, it was found that when the shear orientation is periodically alternated in two or three dimensions, the number of transient cycles is reduced but the critical strain amplitude remains the same as in the case of periodic shear along a single plane. After the yielding transition, the material outside the shear band continues strain-induced relaxation, except when the shear orientation is alternated in three dimensions and the glass is deformed along the shear band with the imposed strain amplitude every third cycle.

Structural transformations during periodic deformation of low-porosity amorphous materials

Atomistic simulations are employed to study microstructural evolution of pore ensembles in binary glasses under periodic shear deformation with varied amplitude. The consideration is given to porous systems in the limit of low porosity. The initial ensembles of pores are comprised of multiple pores with small sizes, which are approximately normally distributed. As periodic loading proceeds, the ensembles evolve into configurations with a few large-scale voids and significantly reduced number of small pores. These structural changes are reflected in skewed shapes of the pore-size distribution functions and the appearance of a distinct peak at large length scales after hundreds of shear cycles. Moreover, periodic shear causes substantial densification of solid domains in the porous systems. The structural evolution of pore ensembles is found to stem from the formation of shear band like regions of enhanced particle mobility after a number of transient cycles. The spatial extent of regions with increased atomic mobility depends strongly on the strain amplitude. A simple theoretical model is developed to qualitatively describe the transformation of the initial configurations of small-size voids into larger-scale void agglomerates.

The yielding transition in periodically sheared binary glasses at finite temperature

Non-equilibrium molecular dynamics simulations are performed to investigate the dynamic behavior of three-dimensional binary glasses prepared via an instantaneous quench across the glass transition. We found that with increasing strain amplitude up to a critical value, the potential energy approaches lower minima in steady state, whereas the amplitude of shear stress oscillations becomes larger. Below the yielding transition, the storage modulus dominates the mechanical response, and the gradual decay of the potential energy over consecutive cycles is accompanied by reduction in size of transient clusters of atoms with large nonaffine displacements. In contrast, above the yield strain, the loss modulus increases and the system settles at a higher level of potential energy due to formation of a system-spanning shear band after a number of transient cycles.

Relationship Between Free-Running Period and Minimum Tolerable Light Pulse Interval of Skeleton Photoperiods in Field Mice Mus Booduga

The entrainment of the circadian rhythm of locomotor activity was studied in the field mouse Mus booduga in order to examine the relationship between the free-running period (τ) and minimum tolerable light pulse interval of the skeleton photoperiods. The animals were entrained under three different light/dark (LD) schedules, each out of phase with the other. They were then subjected to various skeleton photoperiods created by two repeated light pulses (LPs) interrupting darkness. Animals that selected the shorter interval between the LPs as their “subjective night” had significantly shorter τ (23.13 ±0.38h) as compared to those that selected the longer dark interval as subjective night (τ = 23.87 ± 0.18h). When the longer dark interval was 12h, animals selecting that interval as their subjective night included both long-τ and short-τ individuals. When both intervals of darkness were of equal duration, no difference in the selection of subjective night was seen between short and long-τ animals. When the “dusk” LP for the animals that selected the longer dark interval as subjective night was advanced by 2h to create a new skeleton photoperiod, the number of transient cycles appearing before steady-state entrainment was found to depend on the duration of the photoperiods. When the night defined by the two LPs was reduced below 6h, a dramatic “phase jump” in the activity rhythm was observed, and the initial phase relationship was restored after a relaxation in the night duration. We observed considerable interindividual variation in the “minimum tolerable light pulse interval of skeleton photoperiods,” which we suggest may be due to the observed variation in τ among individuals. (Chronobiology International, 14(3), 237–245, 1997)