Strip-electromechanical model solution for piezoelectric plate cut along two semi-permeable collinear cracks

A strip electric saturation and mechanical yielding model solution is proposed for a piezoelectric plate cut along two equal collinear semi-permeable mode-I cracks with electrical polarization reaching a saturation limit and normal stress reaching a yield stress along a line segment in front of the cracks. By using Stroh formalism and complex variable technique, we derived the analytical solution for the field quantities. Three different situations are investigated when developed electrical saturation zone is bigger/smaller or equal to the developed mechanical yield zone. Numerical results show that the effect of different electric boundary conditions on the crack opening displacement and crack opening potential drop is significant and should not be ignored. The influence of electric load displacement on the energy release rate is also investigated for PZT-4, PZT-5H and BaTiO₃ ceramics, and it may assists for the correct choosing of ceramic for specific job.     

A thermodynamics-based cohesive model for interface debonding and friction

A constitutive model for interface debonding is proposed which is able to account for mixed-mode coupled debonding and plasticity, as well as further coupling between debonding and friction including post-delamination friction. The work is an extension of a previous model which focuses on the coupling between mixed-mode delamination and plasticity. By distinguishing the interface into two parts, a cracked one where friction can occur and an integral one where further damage takes place, the coupling between frictional dissipation and energy loss through damage is seamlessly achieved. A simple framework for coupled dissipative processes is utilised to derive a single yield function which accurately captures the evolution of interface strength with increasing damage, for both tensile and compressive regimes. The new material model is implemented as a user-defined interface element in the commercial package ABAQUS and is used to predict delamination under compressive loads in several test cases.     

A continuum model for fiber reinforced materials with debonding

A continuum theory for a fiber-reinforced material with debonding between the constituents is presented. The debonding phenomenon is simulated by imposing the continuity of the normal displacements at the fiber-matrix interfaces while allowing free tangential slip there. The derived theory is of the lowest order and is obtained by using a first order expansion in the displacements in the fiber and matrix phases. The theory is applied to investigate the effect of debonding on the propagation of waves in a boron/epoxy fiber reinforced material. It is shown that an additional mode of propagation is obtained as compared with the usual case of perfect bonding     

A novel time dependent cohesive zone model for the debonding interface between solid propellant and insulation

A novel time dependent cohesive zone model (CZM) is proposed in this paper based on two main assumptions. Firstly, ultimate cohesive parameters are inherent and fixed for a given non-aging bond interface. The apparent cohesive parameters are time related variables. Secondly, relaxation response of the interface is the main reason for the time dependent traction. Numerical simulation shows that the traction, critical displacement as well as damage initiation displacement will increase with imposed loading rate and parameter λ for single Maxwell box based model. N single Maxwell box connected in parallel construct the N Maxwell box based model, and each Maxwell box bears 1/N traction of the interface. Double cantilever beam (DCB) is utilized to investigate the structure response with the single Maxwell box based model including constant stretch and relaxation test. Quite good agreement between the numerical and experimental reaction force–displacement curves is obtained from stretch test of Double cantilever sandwich beam (DCSB) specimen with four different N Maxwell box based model, especially when the number of the Maxwell box is 7. It is a fact that the model will be more adaptive with more Maxwell box connected in parallel which can be revealed by the verification test.     

On the interaction between two inclined cracks under biaxial load

Summary An analysis of the in-plane biaxial loading of an infinite homogeneous and isotropic elastic plate with two inclined collinear cracks of equal length is performed. The boundary value problem is solved by using the complex potentials method. The influence of the lateral load on the local stress distributions as well as on the crack tips behaviour is analyzed and the features of the interaction are described.

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Sommario Viene studiato il problema piano di due fessure inclinate ed allineate, di uguale lunghezza, in una lastra piana infinita di materiale elastico omogeneo ed isotropo, in regime di carico biassiale. Il problema dei valori al contorno viene risolto mediante la tecnica di potenziali complessi. Vengono analizzati gli effetti del carico laterale sia sui campi locali degli sforzi che sul comportamento delle estremitá delle fessure e descritte le modalità di interazione.

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Financial support of the National Research Council (C.N.R.) through research contribution N. 80.02203.07.     

An investigation on two cracks perpen-dicular to the interfaces in a piezolectric layer bonded to two half spaces by the schmidt method

The behavior of two collinear anti-plane shear cracks in'a piezoelectric layer bonded to two half spaces is investigated by the Schmidt method. The cracks are vertically to the interfaces of the piezoelectric layer. By using the Fourier transform, the problem can be solved with two pairs of triple integral equations. These equations are solved using the Schmidt method. This process is quite different from that adopted previously. Numerical examples are provided to show the effect of the geometry of the interacting cracks and the piezoelectric constants of the material upon the stress intensity factor of the cracks. Project supported by the Post Doctoral Science Foundation of Heilongijang Province, the Natural Science Foundation of Heilongjing Province and the Science Research Foundation of Harbin Institute of Technology(HIT. 2000. 30).     

Investigation of the stability of a composite in compression along two parallel structural cracks at the layer interfaces

The scientific results of this paper were obtained by means of a program written with the support of the Alexander von Humboldt Foundation (Bonn-Bad Godesberg, Germany).     

Theoretical model for elliptical tube laterally impacted by two parallel rigid plates

An analytical model is developed to study the crushing behavior and energy absorption capability of a single elliptical tube impacted by two parallel rigid plates, with and without consideration of the strain hardening effect. The four-hinge collapse mechanism is used, and the governing equation is derived from Lagrange equations of the second kind. The numerical simulation of the dynamic response of the elliptical tube under impact using the finite element explicit code LS-DYNA is performed. The reaction force-displacement curve and displacement-time curve of the plate obtained from the two methods are in good agreement.     

A planar problem of failure of structural materials in compression along two parallel cracks

Institute of Mechanics of the Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Prikladnaya Mekhanika, Vol. 27, No. 4, pp. 29–38, April, 1991.     

A capillary force model for interactions between two spheres

Based on the method of energy principle, an analytical approach for computing the capillary force for sphere/sphere geometry is presented in this paper. In modeling the capillary force, we consider spheres with both equal and non-equal radii, for both symmetric and asymmetric configurations at liquid/solid interfaces. We use numerical analysis to investigate the validity and efficiency of the derived model. The effect of various parameters including humidity, distance between two spheres, radii of spheres and contact angles on the meniscus force are investigated. Finally the results obtained from the model are compared with experimental measurements, and the accuracy and precision of the presented approach is verified.     

Two-parameter failure criterion for elastoplastic bodies with mode I cracks

The generalized Dugdale crack model is used to formulate two-parameter failure criteria for the cases of quasibrittle state and developed plastic zones at a mode I crack tip. The failure criteria relate the fracture strength characteristics and the stress mode at the crack tip through the plastic constraint factor. The critical state of bodies with cracks under uni-and biaxial loading is analyzed in the cases of plane stress and plane strain using the Tresca and von Mises yield criteria. A small-scale yield criterion, which is an analytic relation between the critical stress intensity factor and T-stresses, is established __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 7, pp. 47–57, July 2007.     

Relations between a micro-mechanical model and a damage model for ductile failure in shear

Gurson type constitutive models that account for void growth to coalescence are not able to describe ductile fracture in simple shear, where there is no hydrostatic tension in the material. But recent micro-mechanical studies have shown that in shear the voids are flattened out to micro-cracks, which rotate and elongate until interaction with neighbouring micro-cracks gives coalescence. Thus, the failure mechanism is very different from that under tensile loading. Also, the Gurson model has recently been extended to describe failure in shear, by adding a damage term to the expression for the growth of the void volume fraction, and it has been shown that this extended model can represent experimental observations. Here, numerical studies are carried out to compare predictions of the shear-extended Gurson model with the shear failures predicted by the micro-mechanical cell model. Both models show a strong dependence on the level of hydrostatic tension. Even though the reason for this pressure dependence is different in the two models, as the shear-extended Gurson model does not describe voids flattening out and the associated failure mechanism by micro-cracks interacting with neighbouring micro-cracks, it is shown that the trends of the predictions are in good agreement.     

An interaction integral method for 3D curved cracks in nonhomogeneous materials with complex interfaces

This work derives an interaction integral for the computation of mixed-mode stress intensity factors (SIFs) in three-dimensional (3D) nonhomogeneous materials with continuous or discontinuous properties. The present method is based on a two-state integral by the superposition of actual and auxiliary fields. In 3D domain formulation of the interaction integral derived here, the integrand does not involve any derivatives of material properties. Furthermore, the formulation can be proved to be still valid even when the integral domain contains material interfaces. Therefore, it is not necessary to limit the material properties to be continuous for the present formulation. On account of these advantages, the application range of the interaction integral can be greatly enlarged. This method in conjunction with the finite element method (FEM) is employed to solve several representative fracture problems. According to the comparison between the results and those from the published lectures, good agreement demonstrates the validation of the interaction integral. The results show that the present interaction integral is domain-independent for nonhomogeneous materials with interfaces.     

Dynamic behavior of two collinear interface cracks between two dissimilar functionally graded piezoelectric/piezomagnetic material strips

The dynamic interaction of two collinear interface cracks between two dissimilar functionally graded piezoelectric/piezomagnetic material strips subjected to the anti-plane shear harmonic stress waves was investigated. By using the Fourier transform, the problem can be solved with the help of a pair of triple integral equations in which the unknown variable is jump of displacement across the crack surfaces. These equations are solved using the Schmidt method. Numerical examples are provided to show the effect of the functionally graded parameter, the circular frequency of the incident waves and the thickness of the strip upon stress, electric displacement and magnetic flux intensity factors of cracks.     

Viscoplastic approach for rate-dependent failure analysis of concrete joints and interfaces

In this work, a new rate-dependent interface model for computational analysis of quasi-brittle materials like concrete is presented. The model is formulated on the basis of the inviscid elastoplastic model by [Carol, I., Prat, P.C., López, C.M., 1997. “A normal/shear cracking model. Interface implementation for discrete analysis”. Journal of Engineering Mechanics, ASCE, 123 (8), pp. 765–773.]. The rate-dependent extension follows the continuous form of the classical viscoplastic theory by [Perzyna, P., 1966. “Fundamental problems in viscoplasticity”. Advances in Applied Mechanics, 9, pp. 244–368.]. According to [Ponthot, J.P., 1995. “Radial return extensions for viscoplasticity and lubricated friction”. In: Proceedings of International Conference on Structural Mechanics and Reactor Technology SMIRT-13, Porto Alegre, Brazil, (2), pp. 711–722.] and [Etse, G., Carosio, A., 2002. “Diffuse and localized failure predictions of Perzyna viscoplastic models for cohesive-frictional materials”. Latin American Applied Research (32), pp. 21–31.] it includes a consistency parameter and a generalized yield condition for the viscoplastic range that allows an straightforward extension of the full backward Euler method for viscoplastic materials. This approach improves the accuracy and stability of the numerical solution. The model predictions are tested against experimental results on mortar and concrete specimens that cover different stress paths at different strain rates. The results in this work demonstrate, on one hand, the capabilities of the proposed elasto–viscoplastic interface constitutive formulation to predict the rate-dependency of mortar and concrete failure behavior, and, on the other hand, the efficiency of the numerical algorithms developed for the computational implementation of the model that include the consistent tangent operator to improve the convergence rate at the finite element level.     

Finite-part integral and boundary element method for interaction between two parallel planar cracks in three-dimensional finite bodies

By using the Somigliana representation and the concepts of finite-part integrals, a set of hypersingular integral equations of the interaction between two parallel planar cracks in a three-dimensional finite body subjected to arbitrary loads is derived, and then its numerical method is proposed by the finite-part integral method combined with the boundary element method. According to the analytic theory of hypersingular integral equations, the square root models of displacement discontinuities in the elements near the crack front are applied, and thus the computational precision is raised. Based on this, the stress intensity factors can be directly calculated. Finally, the stress intensity factors of several typical interaction problems are calculated.     

Higher order model for soft and hard elastic interfaces

The present paper deals with the derivation of a higher order theory of interface models. In particular, it is studied the problem of two bodies joined by an adhesive interphase for which “soft” and “hard” linear elastic constitutive laws are considered. For the adhesive, interface models are determined by using two different methods. The first method is based on the matched asymptotic expansion technique, which adopts the strong formulation of classical continuum mechanics equations (compatibility, constitutive and equilibrium equations). The second method adopts a suitable variational (weak) formulation, based on the minimization of the potential energy. First and higher order interface models are derived for soft and hard adhesives. In particular, it is shown that the two approaches, strong and weak formulations, lead to the same asymptotic equations governing the limit behavior of the adhesive as its thickness vanishes. The governing equations derived at zero order are then put in comparison with the ones accounting for the first order of the asymptotic expansion, thus remarking the influence of the higher order terms and of the higher order derivatives on the interface response. Moreover, it is shown how the elastic properties of the adhesive enter the higher order terms. The effects taken into account by the latter ones could play an important role in the nonlinear response of the interface, herein not investigated. Finally, two simple applications are developed in order to illustrate the differences among the interface theories at the different orders.     

Closed-form solution for two collinear cracks in a piezoelectric strip

Under the permeable electric boundary condition, the problem of two collinear anti-plane shear cracks lying at the mid-plane of a piezoelectric strip is investigated. By using the Fourier transform, the associated problem is reduced to a singular integral equation. Solving the resulting equation analytically, the electro-elastic field intensity factors and energy release rates at the inner and outer crack tips can be determined in explicit form. Numerical results for PZT-5H piezoelectric ceramic are also presented graphically. The results reveal that the effect of electric field on crack growth in piezoelectric materials is dependent on applied elastic displacement.     

Meso cell model of fiber reinforced composite: Interface stress statistics and debonding paths

The primary goal of this work is to develop an efficient analytical tool for the computer simulation of progressive damage in the fiber reinforced composite (FRC) materials and thus to provide the micro mechanics-based theoretical framework for a deeper insight into fatigue phenomena in them. An accurate solution has been obtained for the micro stress field in a meso cell model of fibrous composite. The developed method combines the superposition principle, Kolosov–Muskhelishvili’s technique of complex potentials and Fourier series expansion. By using the properly chosen periodic potentials, the primary boundary-value problem stated on the multiple-connected domain has been reduced to an ordinary, well-posed set of linear algebraic equations. The meso cell can include up to several hundred inclusions which is sufficient to account for the micro structure statistics of composite. The presented numerical examples demonstrate an accuracy and high numerical efficiency of the method which makes it to be a promising tool for studying progressive damage in FRCs. By averaging over a number of random structure realizations, the statistically meaningful results have been obtained for both the local stress and effective elastic moduli of disordered fibrous composite. A special attention has been paid to the interface stress statistics and the fiber debonding paths development, which appear to correlate well with the experimental observations.