Search results for "Creep"
showing 10 items of 167 documents
Magnetization relaxation in the flux-creep annealing regime across the second magnetization peak of disordered YBa2Cu3O7− crystals
2001
Abstract The relaxation of the irreversible magnetization of disordered YBa 2 Cu 3 O 7− x crystals measured in the “flux-creep annealing” regime reveals that across the second magnetization peak (SMP) the barriers against flux motion remain finite at low current densities, which supports the existence of a crossover to a dissipation process involving the plastic deformation of the vortex system. In our experiments, the vortex creep process appears to be exclusively controlled by collective pinning barriers (diverging at low current densities) only below the onset of the SMP, where the vortex system is stable against dislocation formation. The (elastic) collective pinning barriers observed f…
Analysis of magnetization relaxation in MgB2 bulk samples obtained by electric-field assisted sintering
2008
Abstract The relaxation of the irreversible magnetization of MgB2 bulk samples obtained by electric-field assisted sintering was investigated using the SQUID magnetometry for a magnetic field H up to 50 kOe applied in zero-field-cooling conditions. We observed a crossover plastic creep at high temperatures T-elastic creep at low T, described by H ∝ T−2 in the low T range, which appears to be caused by the macroscopic currents induced in the sample during magnetization measurements. By decreasing T below this line the determined creep exponent rapidly overcomes the widely accepted theoretical values for elastic (collective) pinning. This behaviour can easily be explained through the occurren…
Mechanical behaviour of natural cow leather in tension
2009
We study experimentally the microstructure and mechanical behavior of natural cow leather. Tensile tests are performed using leather strips to observe their deformation, creep and failure. It is found that the microstructure of cow leather is a layered, complicated network of fibers of different sizes from a few to a few hundreds of nanometers in diameter. They show nonlinear stress-strain relations and viscoelastic behavior. The effect of humidity is also examined. A simple theoretical model of a multilayered beam is proposed to describe the most basic behavior in tension.
Influence of the Mean Load Value in Fatigue Block Loading on Strains
2014
This paper presents the results of the fatigue tests of the specimens made from S3555 steel and aluminum alloy AlCu4MgSi subjected to bending block loading with mean load value. The influence of the changes of the mean load conditions was investigated. During the tests strains were registered and relation between the load and the strains was analyzed. In the case of S355 steel it was observed, that additional hardening occurs when higher value of the mean load is applied at the beginning of the block loading. Other case, when the mean load was increased from zero to maximum, a creep effect of the material was registered. For the specimens made from aluminum alloy similar processes were not …
A micro-mechanical model for grain-boundary cavitation in polycrystalline materials
2015
In this work, the grain-boundary cavitation in polycrystalline aggregates is investigated by means of a grain-scale model. Polycrystalline aggregates are generated using Voronoi tessellations, which have been extensively shown to retain the statistical features of real microstructures. Nucleation, thickening and sliding of cavities at grain boundaries are represented by specific cohesive laws embodying the damage parameters, whose time evolution equations are coupled to the mechanical model. The formulation is presented within the framework of a grain-boundary formulation, which only requires the discretization of the grain surfaces. Some numerical tests are presented to demonstrate the fea…
Relaxation of remnant magnetisation in YBa2Cu3O7−δ films
2007
Abstract The relaxation of the remnant magnetisation in optimally doped disk-shaped YBa2Cu3O7−δ films with the initially applied magnetic field H oriented along the c axis was measured using dc SQUID magnetometry. The temperature (T) dependence of the experimentally observed normalised magnetisation relaxation rate S exhibits three distinct regions. At high T, S(T) increases with increasing T, which can be explained in terms of plastic vortex creep. The well known plateau in the S(T) variation at intermediate T appears to be caused by collective (elastic) creep in a dynamically ordered vortex system. At low T, where S increases again with increasing T, the magnetisation relaxation is not in…
Creep–recovery and oscillatory rheology of flour-based systems
2023
The chapter reviews the application of creep-recovery and oscillatory rheological tests in flour based systems, including simple flour water systems, and more complex ones, such as bread, cookies and biscuits. A theoretical introduction about the fundaments and methods of linear viscoelastic rheology is presented, including general mathematical models and their application in flour based systems. A summary of experimental conditions to perform the rheological tests is covered. Functionality of flour based systems is extremely dependent on their viscoelastic properties. Processes like mixing, pumping, lamination, baking performance have been found to be strongly dependent on the system visco…
A comparative study of fatigue behaviour of flax/epoxy and glass/epoxy composites
2012
Experimental investigations on flax and glass fabrics reinforced epoxy specimens, i.e. FFRE and GFRE, submitted to fatigue tests are presented in this paper. Samples having [0/90]3S and [±45]3S stacking sequences, with similar fibre volume fractions have been tested under tension–tension fatigue loading. The specific stress-number of cycles to failure (S–N) curves, show that for the [0/90]3S specimens, FFRE have lower fatigue endurance than GFRE, but the [±45]3S FFRE specimens offer better specific fatigue endurance than similar GFRE, in the studied life range (<2 × 10^6). Overall, the three-stage stiffness degradation is observed in all cases except for [0/90]3S FFRE specimens, which prese…
Analysis of Fractional Viscoelastic Material With Mechanical Parameters Dependent on Random Temperature
2017
It is well known that mechanical parameters of polymeric materials, e.g., epoxy resin, are strongly influenced by the temperature. On the other hand, in many applications, the temperature is not known exactly during the design process and this introduces uncertainties in the prevision of the behavior also when the stresses are deterministic. For this reason, in this paper, the mechanical behavior of an epoxy resin is characterized by means of a fractional viscoelastic model at different temperatures; then, a simple method to characterize the response of the fractional viscoelastic material at different temperatures modeled as a random variable with assigned probability density function (PDF…
Elasticity and long-term behavior of recycled polyethylene terephthalate (rPET)/montmorillonite (MMT) composites
2014
Abstract Recycled polyethylene terephthalate (rPET) nanocomposites with various amounts of montmorillonite clay (MMT) have been manufactured by using twin screw extrusion. By rising MMT weight content Wf up to 1 wt.% it is possible to increase yield strength and ultimate strength of the composite by 17% and 27% respectively in comparison to neat rPET. Introduction of MMT in the rPET leads also to considerable increase of the modulus of elasticity E. Relationship E(Wf), however, is non-linear and is characterized by slow-down in E growth along with increasing MMT content. At low nanofiller content experimental results are sufficiently well described by using the method of Mori–Tanaka and the…