Fractional signal processing: scale conversion

In Proceedings of the “ECCTD '01 - European Conference on Circuit Theory and Design, Espoo, Finland, August 2001Scale conversion of discrete-time signals are studied taking as base the fractional discrete-time system theory. Some simulation results to illustrate the behaviour of the algorithms will be presented. A new algorithm for performing the zoom transform is also described

Fractional discrete-time signal processing: scale conversion and linear prediction

Nonlinear Dynamics, Vol. 29A generalisation of the linear prediction for fractional steps is reviewed, widening well-known concepts and results. This prediction is used to derive a causal interpolation algorithm. A reconstruction algorithm for the situation where averages are observed is also presented. Scale conversion of discrete-time signals is studied taking as base the fractional discrete-time system theory. Some simulation results to illustrate the behaviour of the algorithms will be presented. A new algorithm for performing the zoom transform is also described

Environmentally-assisted fatigue crack growth in prestressing steel wires

This paper presents the evolution of the surface crack front in prestressing reinforced concrete steel wires subjected to fatigue in air and to corrosion-fatigue in Ca(OH)₂+NaCl. To this end, a numerical modelling was made on the basis of a discretization of the crack front (with elliptical shape), considering that the crack advance at each point is perpendicular to such a front according to a Paris-Erdogan law, and using a threeparameter solution for stress intensity factor (SIF). Each analyzed case (a particular initial crack geometry) was characterized by the evolution of the semielliptical crack aspect ratio (relation between the semiaxes of the ellipse) with the relative crack depth and by the variation of the maximum dimensionless SIF at the crack front.Описано еволюцію фронту поверхневої тріщини в сталевих дротах для переднапруженого стану залізобетону, підданих втомному навантаженню на повітрі і корозійній втомі в середовищі Ca(OH)₂ + NaCl. На основі дискретизації чисельно змодельовано фронт тріщини, який приймали еліптичним, і вважали, що тріщина в кожній точці просувається перпендикулярно до її фронту згідно з законом Періса–Ердогана. Використовували трипараметричний розв’язок для коефіцієнта інтенсивності напружень (КІН). Кожний з аналізованих випадків, якому відповідала певна початкова геометрія тріщини, характеризувався еволюцією форми напівеліптичної тріщини (відношення півосей еліпса) і відносної її глибини, а також варіацією значень максимального безрозмірного КІН вздовж фронту тріщини.Описана эволюция фронта поверхностной трещины в стальных проволоках для преднапряженного состояния железобетона, подвергаемых усталости на воздухе и коррозионной усталости в среде Ca(OH)₂+ NaCl. На основе дискретизации численно смоделирован фронт трещины, который принимали полуэллиптическим, и считали, что трещина в каждой точке движется перпендикулярно к ее фронту согласно закону Пэриса– Эрдогана. Использовали трехпараметрическое решение для коэффициента интенсивности напряжений (КИН). Каждый из анализированных случаев, которому соответствовала определенная начальная геометрия трещины, характеризовался эволюцией формы полуэллиптической трещины (отношение полуосей эллипса) и относительной ее глубины, а также изменением значений максимального безразмерного КИН вдоль фронта трещины

Crack tip field in circumferentially-cracked round bar (CCRB) in tension affected by loss of axial symmetry

In this paper, the stress intensity factor (SIF) is computed in a circumferentially-cracked round bar (CCRB) subjected to tensile loading, considering that the resistant ligament is circular and exhibits certain eccentricity in relation to the cylinder axis. The computation was performed by means of the finite element method (FEM) using a three dimensional (3D) model and the J-integral, the analyzed variable being the eccentricity of the circular ligament. Results show that the SIF is higher at the deepest point of the crack and that an increase of eccentricity (in relation to the bar axis) raises the difference between the SIF values along the crack front. From a certain value of the misalignment a bending effect appears, so that the crack remains closed in the area near the point of lower depth

Crack tip fields and mixed mode fracture behaviour of progressively drawn pearlitic steel

This paper deals with the influence of the cold drawing process on the fracture behaviour of pearlitic steels. To this end, fracture tests under axial loading were performed on steel wires with different drawing degree (from a hot rolled bar to a commercial prestressing steel wire), transversely pre-cracked by fatigue, analyzing in detail the changes in fracture micromechanisms. The deflection angles of the fracture path were measured by longitudinal metallographic sections and the characteristic parameters of the loaddisplacement plot were related to different fracture events. Results allowed a calculation of critical stress intensity factors for different fracture angles and drawing degrees, thus evaluating the strength anisotropy and obtaining a sort of directional toughness

Influence of crack micro-roughness on the plasticity-induced fatigue propagation in high strength steel

This article deals with the locally multiaxial fatigue behaviour of high strength steel. To this end, the influence of the cracking path deflections (at the micro level) on the plasticity-induced fatigue crack growth is analyzed. With regard to this, a modelling by means of the finite element method was performed for a given stress intensity factor in the Paris regime, considering the existence of micro-roughness in the crack path (local micro-deflections with distinct micro-angles as a function of the microstructure of the material). The numerical results allow one to obtain the fatigue crack propagation rate and compare it with that for the same material in the absence of micro-roughness (with no micro-crack deflections, i.e., uniaxial fatigue behaviour)

Evolution of crack paths and compliance in round bars under cyclic tension and bending

The aim of this paper is to calculate how the surface crack front and the dimensionless compliance evolve in cracked cylindrical bars subjected to cyclic tension or bending with different initial crack geometries (crack depths and aspect ratios). To this end, a computer application (in the Java programming language) that calculates the crack front’s geometric evolution and the dimensionless compliance was made by discretizing the crack front (characterized with elliptical shape) and assuming that every point advances perpendicularly to the crack front according to the Paris law, and using a three-parameter stress intensity factor (SIF). The results show that in fatigue crack propagation, relative crack depth influences more on dimensionless compliance than the aspect ratio, because the crack front tends to converge when the crack propagates from different initial geometries, showing greater values for tension than for bending. Furthermore, during fatigue crack growth, materials with higher values of the exponent of the Paris law produce slightly greater dimensionless compliance and a better convergence between the results for straight-fronted and circular initial cracks

Role of the microstructure on the mechanical properties of fully pearlitic eutectoid steels

This paper analyses how the microstructure of an eutectoid pearlitic steel affects its conventional mechanical properties (obtained by means of a standard tension test) and the associated micromechanisms of fracture. Results show how the yield strength, the ultimate tensile strength (UTS) and the ductility, increase as the continuous cooling rate rises, whereas on the other hand the strain at UTS decreases. The fracture surface exhibits more brittle features when the continuous cooling rate decreases, in such a manner that in the fractureprocess zone an increasing area appears where the pearlite lamellae can be detected and less regions of microvoids are observed

Magnetic Field Dependent Behavior of the CDW ground state in Per2M(mnt)2 (M = Au, Pt)

The Per2M(mnt)2 class of organic conductors exhibit a charge density wave (CDW) ground state below about 12 K, which may be suppressed in magnetic fields of order 20 to 30 T. However, for both cases of counter ion M(mnt)2 species studied (M = Au (zero spin) and M = Pt (spin 1/2)), new high field ground states evolve for further increases in magnetic field. We report recent investigations where thermopower, Hall effect, high pressure and additional transport measurements have been carried out to explore these new high field phases.Comment: 6 pages, 10 figures, 27 reference