Influence of oscillation localization on film detachment from a substrate

In modern constructions, thin-layer coats are often used as protecting or strengthening elements. Deformations of such constructions may cause significant stresses on the interface between the base and the coat because of the difference in their physical-mechanical properties, which leads to the destruction or detachment of the cover. Of special interest is strength analysis under dynamical or vibrational impacts because of the possibility of localizing oscillations in a neighborhood of the initial inhomogeneities (such as inclusions, defects, construction elements, etc.). In this paper, on the example of the detachment of a string from an elastic substrate, the possibility of localizing oscillations on a detachment defect is demonstrated and the effect of this localization on the growth of the detachment zone is analyzed. A simplified setting of the problem is considered. The possibility of localizing oscillations on a detachment defect is demonstrated and an approximate analytical solution is constructed, which takes into account only the first symmetric form of oscillations describing the development of the initial detachment. A numerical modeling of the problem is performed, and the results of modeling are compared with the approximate analytical solution.     

Delamination growth of laminated circular plates under in-plane loads and movable boundary conditions

An investigation is made on interlaminar delamination growth of composite laminated circular plates under in-plane loads and movable delamination boundary conditions. A four-dissociated-region model is developed on the basis of von-Karman plate theory. The model is geometrically nonlinear and the laminated circular plate considered is subjected to axisymmetrical delamination. The effects of transverse shear deformation and contact effect of the delamination on the laminated plates are taking into account in the development of the governing equations of the laminated circular pates with random axisymmetrical delamination. The formulas for describing the total energy release rate and its individual mode components along the delamination front are also derived with considerations of Griffith criterion for fracture. Based on the model established, the delamination growth is numerically studied; and the influences of the parameters such as delamination radii and depths, together with material properties of the plates on the energy release rate are analyzed in detail.     

外部压力作用下复合材料层合圆柱壳的脱层扩展分析

含脱层的层合圆柱壳在承受外部压力作用时,容易发生脱层扩展,进而引起结构失效．基于可动边界变分原理并考虑脱层间的接触效应对圆柱壳在外部压力作用下的脱层扩展进行了分析,同时应用Griffith准则,导出了脱层前缘各点处的能量释放率表达式,且以轴对称脱层层合圆柱壳为例进行了数值计算,讨论了脱层大小、脱层深度、几何尺寸、材料性质及纤维铺层方式等因素对脱层扩展的影响．     

Numerical Analysis of a Cyclical Loaded Construction under Corrosion Degradation

A contribution for analytical and numerical tools that permits of a deterministic evaluation of structure behavior in external conditions, under multiparameter and/or cyclic mechanical, thermal and chemical loads, is the aim of this paper. Particular structure elements undergo the plastic and corrosion degradation and they dissipate energy, which consists of irreversible contributions, like a work on the inelastic strains. The construction and its unit lifetime are estimated according to a dissipated energy criterion. The paper emphasizes the modeling and numerical implementation of degradation effects, such as cyclic plasticity, generated by mechanical and thermal loads, stress corrosion, electrochemical corrosion and low-cyclic corrosion. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A bifurcation-based decohesion model for simulating the transition from localization to decohesion with the MPM

Based on recent experimental observations on the formation of localization before delamination, a bifurcation-based decohesion approach is proposed in this paper to simulate the transition from localization to decohesion involved in the delamination process of compressed films. The onset and orientation of discontinuous failure are identified from the discontinuous bifurcation analysis. A discrete constitutive model is then formulated based on the bifurcation analysis to predict the evolution of material failure as decohesion or separation of continuum. The Material Point Method, that does not employ fixed mesh-connectivity, is developed as a robust spatial discretization method to accommodate the multi-scale discontinuities involved in the film delamination. To demonstrate the potential of the proposed approach, a parametric study is conducted to explore the effects of aspect ratio and failure mode on the evolution of failure patterns under different boundary conditions, which provides a better understanding on the physics behind the film delamination process.     

A bifurcation-based decohesion model for simulating the transition from localization to decohesion with the MPM

Based on recent experimental observations on the formation of localization before delamination, a bifurcation-based decohesion approach is proposed in this paper to simulate the transition from localization to decohesion involved in the delamination process of compressed films. The onset and orientation of discontinuous failure are identified from the discontinuous bifurcation analysis. A discrete constitutive model is then formulated based on the bifurcation analysis to predict the evolution of material failure as decohesion or separation of continuum. The Material Point Method, that does not employ fixed mesh-connectivity, is developed as a robust spatial discretization method to accommodate the multi-scale discontinuities involved in the film delamination. To demonstrate the potential of the proposed approach, a parametric study is conducted to explore the effects of aspect ratio and failure mode on the evolution of failure patterns under different boundary conditions, which provides a better understanding on the physics behind the film delamination process.Received: January 16, 2003; revised: August 11, 2003     

Dynamic loading of layered composite beams with damage of delamination type

Failure of composite beams containing initial delamination is investigated under low-speed impact by a dropping weight. Bolotin's theory of dynamic failure (1992) is used. The start and stop time of growth of a nonsymmetric delamination crack is studied. It is found that the initial extension starts and subsequently continues at the crack tip, which is located closer to the impact point. Then extension is observed on the second crack tip, and finally a synchronous growth of delamination occurs at both crack tips. With constant impact energy, the final size of delamination does not depend on its initial size. The start and stop time of delamination growth increases as the initial defect approaches the beam surface.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Moscow Power Engineering Institute, Technical University, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 787–794, November–December, 1998.     

On some regularities in dynamic response of cyclic periodic structures

The paper deals with cyclic periodic structures modelling bladed disk assemblies of blades with friction elements for vibration damping. These elements placed between adjacent blades reduce the vibration amplitudes by means of dry friction resulting from centrifugal forces acting on the elements and relative displacements of the blades. However, the application of these friction elements results in an additional dynamical coupling which together with mistuning of some system parameters (e.g., blade eigenfrequency or contact parameters) may cause localization of vibration. In the present paper a linear approximation of such a system is investigated. The structure composed of cyclic periodic cells modelled each as a clamped-free beam interacting with each other by means of viscoelastic elements of complex stiffness is applied for dynamic system analysis. In case of free vibrations as well as in case of steady-state dynamic response to a harmonic pressure field, a perfect periodic structure and the structures with periodically mistuned parameters (blade eigenfrequencies and contact parameters) are studied. Some regularities in the dynamic response of the systems with mistuning have been noticed. Despite the fact that only a linear approximation has been used, the results and conclusions can be applied for models which describe the blade interaction in a nonlinear way.     

Delamination of composite plates under tensile load

Conclusions Among the two configurations discussed, the beam has a rather theoretical importance, as an extension and generalization of the cracked beam problem. Unlike this, embedded delaminations can be found often in real constructions. The fact that the maximum value of SERR vs. fibre orientation angle curve for the circular embedded delamination is surpassed by that for the split beam only by three times and by that for the split beam under mode II loading approximately six times means that an embedded delamination can lead to difficulties when the plate is tensed (or compressed — even in an underbuckled state — within the linear approach the non-opening modes of stress concentration will just change their signs when the load changes its sign), especially under a cyclic loading. Of course, the shell model used is fairly rough and does not take in account several features or real delaminations extension and does not allow one to evaluate properly the stress field near the crack front; thus, more analytical and experimental studies would be needed, to establish the crack development process. The 3D analysis is necessary when initiating delaminations are studied, for the beam/plate assumptions can no longer be regarded as necessary since the delamination linear dimensions are comparable to or less than the thickness of the sublaminate.Published in Mekhanika Kompozitnykh Materialov, Vol. 31, No. 1, pp. 45–50, January–February, 1995.     

Compressive stability of multilayered delaminations in composites

The behavior of defects of the near-surface crack type was investigated in laminated composites. Multilayered delaminations in compressed elements were examined on the assumption that cylindrical bending of the delamination is accompanied by shear within the framework of a model similar to the Timoshenko model. The effect of the mechanical properties and thickness and number of layers in the delaminated section on the critical buckling strain and strain corresponding to the beginning of growth of the delamination was investigated. It was shown that when the delaminated section contains several bearing layers and the rigidity of the composite with respect to interlaminar shear is small, consideration of the shear in the delaminated section can lead to a significant change in the critical compressive strains and/or critical size of the delamination.Translated from Mekhanika Kompozitnykh Materialov. Vol. 33, No. 3, pp. 312–320, May–June, 1997.     

On FF-rings

In this paper, we study the class of rings in which every flat ideal is finitely generated. We investigate the stability of this property under localization and homomorphic image, and its transfer to various contexts of constructions such as direct products, pullback rings, and trivial ring extensions. Our results generate examples which enrich the current literature with new and original families of non-Noetherian rings that satisfy this property.     

Numerical Assessment of Stabilization Techniques for Coupled Poro-plastic Analysis using Low-Order Finite Elements

For the numerical modeling of geomaterials in general, and soft, water saturated soils in particular, the nonlinear constitutive behavior of the skeleton and its strong coupling with the pore fluid must be considered. In the limit of zero compressibility of water and soil grains and very low permeability (which correspond to the classical “undrained” assumption in soil mechanics), the functions used to interpolate displacements and pressures must fulfill either the Ladyženskaja-Babuška-Brezzi inf-sup condition [1] or the much simpler patch test proposed by Zienkiewicz and Taylor. These requirements exclude the use of elements with equal order of linear interpolation for pressures and displacements, for which spurious oscillations may appear. Low-order elements with linear approximation of displacements and pressure variables may be used if stabilization techniques are employed. The work is concerned with the numerical assessment and investigation of several stabilization techniques and their application to strain localization problems in coupled poro-plastic analyses of soft, saturated soils [2,3]. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Explicit stability conditions for integro-differential equations with periodic coefficients

New explicit stability conditions are derived for a linear integro-differential equation with periodic operator coefficients. The equation under consideration describes oscillations of thin-walled viscoelastic structural members driven by periodic loads. To develop stability conditions two approaches are combined. The first is based on the direct Lyapunov method of constructing stability functionals. It allows stability conditions to be derived for unbounded operator coefficients, but fails to correctly predict the critical loads for high-frequency excitations. The other approach is based on transforming the equation under consideration in such a way that an appropriate ‘differential’ part of the new equation would possess some reserve of stability. Stability conditions for the transformed equation are obtained by using a technique of integral estimates. This method provides acceptable estimates of the critical forces for periodic loads, but can be applied to equations with bounded coefficients only. Combining these two approaches, we derive explicit stability conditions which are close to the Floquet criterion when the integral term vanishes. These conditions are applied to the stability problem for a viscoelastic bar compressed by periodic forces. The effect of material and structural parameters on the critical load is studied numerically. © 1998 B. G. Teubner Stuttgart–John Wiley & Sons Ltd.     

Non-linear buckling for the surface rectangular delamination of laminated piezoelectric shells

An analytical method is presented to study the non-linear buckling characteristic of rectangular local delamination near the surface of fiber-reinforced piezoelectric lamination shells under coupled mechanical and electric loads. The stacking sequence of fiber reinforced lamination shells with piezoelectric layers is considered as symmetry, but the stacking sequence of rectangular local delamination sub-shells is arbitrary. Based on the nonlinear displacement mode of delaminated sub-shells, the effects of electric fields, the geometrical, physical parameters and stacking sequences of piezoelectric laminated shells on the non-linear local buckling for rectangular delamination near the surface of piezoelectric laminated base-shells are solved.     

Shorter identity-based encryption via asymmetric pairings

We present efficient identity-based encryption (IBE) under the symmetric external Diffie–Hellman (SXDH) assumption in bilinear groups; our scheme also achieves anonymity. In our IBE scheme, all parameters have constant numbers of group elements, and are shorter than those of previous constructions based on decisional linear (DLIN) assumption. Our construction uses both dual system encryption (Waters, CRYPTO 2009) and dual pairing vector spaces (Okamoto and Takashima, Pairing 2008; ASIACRYPT 2009). Specifically, we show how to adapt the recent DLIN-based instantiation of Lewko (EUROCRYPT 2012) to the SXDH assumption. To our knowledge, this is the first work to instantiate either dual system encryption or dual pairing vector spaces under the SXDH assumption. Furthermore, our work could be extended to many other functional encryption. In Particular, we show how to instantiate our framework to inner product encryption and key-policy functional encryption. All parameters of our constructions are shorter than those of DLIN-based constructions.     

Combinatorial and accessible weak model categories

In a previous work, we have introduced a weakening of Quillen model categories called weak model categories. They still allow all the usual constructions of model category theory, but are easier to construct and are in some sense better behaved. In this paper we continue to develop their general theory by introducing combinatorial and accessible weak model categories. We give simple necessary and sufficient conditions under which such a weak model category can be extended into a left and/or right semi-model category. As an application, we recover Cisinski-Olschok theory and generalize it to weak and semi-model categories. We also provide general existence theorems for both left and right Bousfield localization of combinatorial and accessible weak model structures, which combined with the results above gives existence results for left and right Bousfield localization of combinatorial and accessible left and right semi-model categories, generalizing previous results of Barwick. Surprisingly, we show that any left or right Bousfield localization of an accessible or combinatorial Quillen model category always exists, without properness assumptions, and is simultaneously both a left and a right semi-model category, without necessarily being a Quillen model category itself.     

Prime and primitive algebras with prescribed growth types

Bartholdi and Smoktunowicz constructed in 2014 finitely generated monomial algebras with prescribed sufficiently fast growth types. We show that their construction need not result in a prime algebra, but it can be modified to provide prime algebras without further limitations on the growth type.Moreover, using a construction of an inverse system of monomial ideals which arise from this construction, we are able to further construct finitely generated primitive algebras without further limitations on the growth type.Then, inspired by Zelmanov’s example in 1979, we show how our prime algebras can be constructed such that they contain non-zero locally nilpotent ideals; this is the very opposite of the primitive constructions.     

Generalizing pairs of complementary sequences and a construction of combinatorial structures

Pairs of complementary sequences such as Golay pairs have zero sum autocorrelation at all non-trivial phases. Several generalizations are known where conditions on either the autocorrelation function, or the entries of the sequences are altered. We aim to unify most of these ideas by introducing autocorrelation functions that apply to any sequences with entries in a set equipped with a ring-like structure which is closed under multiplication and contains multiplicative inverses. Depending on the elements of the chosen set, the resulting complementary pairs may be used to construct a variety of combinatorial structures such as Hadamard matrices, complex generalized weighing matrices, and signed group weighing matrices. We may also construct quasi-cyclic and quasi-constacyclic linear codes which over finite fields of order less than 5 are also Hermitian self-orthogonal. As the literature on binary and ternary Golay sequences is already quite deep, one intention of this paper is to survey and assimilate work on more general pairs of complementary sequences and related constructions of combinatorial objects, and to combine the ideas into a single theoretical framework.     

Thermo-mechanical modeling of turbine blades taking into account structural defects

In turbine blades of aero-engines typical defects are cracks due to high mechanical and thermal loads. The extended finite element method (XFEM) is used for simulations of fracture mechanics problems with cracks. Discontinuities in the displacement and temperature field are allowed and the crack opening displacement and crack tip stress field are reproduced accurately. Since crack closure and non-physical penetration of the crack surfaces may occur under certain load conditions, it becomes necessary to enforce the non-penetration condition for crack surfaces. This contact formulation is assumed to be frictionless. The node-to-segment approach proposed in [3] is extended to ten-node tetrahedral elements with quadratic shape functions. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tabu search and GRASP for the maximum diversity problem

In this paper, we develop new heuristic procedures for the maximum diversity problem (MDP). This NP-hard problem has a significant number of practical applications such as environmental balance, telecommunication services or genetic engineering. The proposed algorithm is based on the tabu search methodology and incorporates memory structures for both construction and improvement. Although proposed in seminal tabu search papers, memory-based constructions have often been implemented in naïve ways that disregard important elements of the fundamental tabu search proposals. We will compare our tabu search construction with a memory-less design and with previous algorithms recently developed for this problem. The constructive method can be coupled with a local search procedure or a short-term tabu search for improved outcomes. Extensive computational experiments with medium and large instances show that the proposed procedure outperforms the best heuristics reported in the literature within short computational times.