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The Sant'Oronzo statue (Lecce, Southern Italy) consists of an internal wooden structure, completely covered with copper sheets, lying on a concrete base about 1.5 m high, which is placed on the top of a Roman column about 29 m high. Lecce may be classified as urban site since it is mainly influenced by vehicular traffic and it is not affected by intense industrial emissions. In the time schedule of the restoration, first of all, non-destructive analyses were planned. In particular, a portable energy dispersive X-ray fluorescence (ED-XRF) was used in order to map the composition of the patinas and to evaluate their degradation. Subsequently, a micro-sampling was performed both of the statue and the column. The collected samples were analysed by using Raman spectroscopy and X-Ray Diffraction in order to evaluate chemical composition. This paper summarizes the archaeometric results and the diagnostic information obtained before of the restoration, which are significant for the restorers’ subsequent work.

A micropolar-based asymptotic homogenization approach for the analysis of composite materials with periodic microstructure is proposed. The upscaling relations, conceived to determine the macro-descriptors (macro displacement and the micropolar rotation fields) as a function of the micro displacement field, are consistently derived in the asymptotic framework. In particular, the micropolar rotation field is expressed in terms of the microscopical infinitesimal rotation tensor and perturbation functions. The micro displacement field is, in turn, obtained by choosing a third order approximation of the asymptotic expansion, in which the macroscopic fields are expressed as a third order polynomial expansion. It follows that the macro descriptors are directly related to both perturbation functions and micropolar two-dimensional deformation modes. Furthermore, a properly conceived energy equivalence between the macroscopic point and a microscopic representative portion of the periodic composite material is introduced to derive the consistent overall micropolar constitutive tensors. It is pointed out that these constitutive tensors are not affected by the choice of the periodic cell. Moreover, in the case of vanishing microstructure the internal-length-scale-dependent constitutive tensors tend to zero, as expected. Finally, the capabilities of the proposed approach are shown through some illustrative examples.

This work aims at studying the mixed-mode delamination process in Moment-Loaded Double Cantilever Beam (MLDCB) specimens. The delamination problem is addressed both analytically and numerically, while considering the interfaces as an assemblage of two sublaminates partly bonded together by an elastic interface. Such interface is modeled as a continuous distribution of elastic-brittle springs acting along the normal and/or tangential direction depending on the interfacial mixed-mode condition. The Timoshenko’s beam theory is here applied to determine the governing equations of the differential problem and the associated boundary conditions, whose solution is not straightforward. The Generalized Differential Quadrature (GDQ) method is then applied as numerical tool to solve directly the differential equations of the problem in a strong form. The capability of the proposed numerical approach is first exploited through a comparative evaluation of the results with the analytical predictions resting on a suitable change of variables for delamination test specimens. The local and global response is determined, in terms of interfacial stresses, internal forces and displacements, as well as in terms of compliance, energy release rate, mode mixity angle, and moment-rotation curves. A further check of the proposed numerical method is performed with respect to a Finite Fracture Mechanics (FFM) criterion, which is able to join both stress- and energy-based approaches. A good agreement between results confirms the good feasibility of the GDQ method when studying delamination phenomena occurring within composite materials or laminated joints, usually subjected to mixed-mode conditions.

Aim:To obtain the first molecular epidemiological survey of Tropheryma whipplei intestinal colonization in Italy. Materials & methods: Retrospective, observational study to assess the prevalence of T. whipplei, the causative agent of Whipple's disease, in stool samples (real-time PCR) of patients attending the Center for Tropical Diseases (Italy) and risk factors associated. Results:Overall prevalence was 6.9% (85/1240). The younger age group showed a significantly higher rate than older age group (12.7 vs 5.9%, p = 0.002). The prevalence was 4.9% for Italians and 9.3% for migrants (p = 0.003). Among the latter, children less than 10 years had higher prevalence than older ones (17.3 vs 7.3%, p = 0.003). The young age, male gender and Giardia duodenalis and Entamoeba histolytica coinfection were risk factors. Conclusion:Our study confirms an increased risk of acquiring T. whipplei infection during childhood, under poor sanitary conditions.

In the framework of energy scavenging for applications in flexible/stretchable electronics, hybrid piezoelectric nanogenerators are investigated. They are made up with zinc oxide (ZnO) nanorods, embedded in a polymeric matrix, and grown on a flexible polymeric support. The ZnO nanorods are arranged in clusters, forming nearly regular distributions, so that periodic topologies can be realistically assumed. Focus is on a dynamic multi-field asymptotic homogenization approach, proposed to grasp the overall constitutive behaviour of such complex microstructures. A set of applications, both in static and dynamic regime, is proposed to explore different design paradigms, related to nanogenerators based on three working principles. Both extension and bending nanogenerators are, indeed, analysed, considering either extension along the nanorods axis, or orthogonally to it. The study of the wave propagation is, also, exploited to comprehend the main features of such piezoelectric devices in the dynamic regime.

Cultural heritage is a complex ecosystem requiring innovative methods and techniques to facilitate its restoration, management and valorization. In detail, restoration processes have to preserve the original characteristics of historical buildings or sites, by involving different professional figures, each one with different roles, responsibilities and skills. In this light, a system that facilitates the information management, supported by new technologies, could allow more precise, efficient and traceable information exchange and could optimize the construction and management operative phase. Starting from these assumptions, the research proposes the application of a new integrated approach to a restoration process of a historical building. It consists of applying Business Process Management (BPM) approach and Building Information Modeling (BIM) methodology to provide valuable insights to optimize the data flow, to gather information and to share knowledge during the restoration process, by optimizing the whole lifecycle management process, by facilitating the ordinary and extraordinary maintenance. All these aspects are essential and strategic for the Italian cultural heritage.

Introduction Neurocysticercosis (NCC) is one of the leading causes of epilepsy worldwide. The majority of cases in Europe are diagnosed in immigrants. Currently in Italy, routine serological screening for cysticercosis is recommended for internationally adopted children (IAC) coming from endemic countries. Methods: We retrospectively analyse the results of the serological screening for cysticercosis in IAC 16 years old or younger, attending two Italian third level paediatric clinics in 2001–16. Results: Of 2,973 children included in the study, 2,437 (82.0%) were screened by enzyme-linked immune electro transfer blot (EITB), 1,534 (51.6%) by ELISA, and 998 (33.6%) by both tests. The seroprevalence of cysticercosis ranged between 1.7% and 8.9% according to EITB and ELISA, respectively. Overall, 13 children were diagnosed with NCC accounting for a NCC frequency of 0.4% (95% confidence interval (CI): 0.2–0.6%). Among the 168 seropositive children, only seven (4.2%) were diagnosed with NCC. Of these children, three were asymptomatic and four presented epilepsy. Among seronegative children (n = 2,805), seven presented with neurological symptoms that lead to the diagnosis of NCC in six cases. The sensitivity, specificity, positive and negative predictive value for the diagnosis of NCC were 54.5%, 98.6%, 14.6%, 99.8% for EITB and 22.2%, 91.1%, 1.4%, 99.5% for ELISA. The yield of the screening programme was 437 NCC cases per 100,000. The number needed to screen to detect one NCC case was 228. The cost per NCC case detected was EUR 10,372. Conclusion: On the base of our findings we suggest the ongoing serological screening for cysticercosis to be discontinued, at least in Italy, until further evidence in support will be available.

In the paper we present a low-order virtual element formulation for modelling the strain-softening response of quasi-brittle materials. For this purpose, a formulation in two-dimensions is considered, with virtual elements having arbitrary shape. The method is based on minimization of an incremental energy expression, with a novel construction of the stabilization energy for isotropic elasto-damage. A set of numerical examples, illustrating the efficiency of the proposed method, complements the paper.

This paper presents a non-local interface mechanical model to describe aortic dissection. In this regard, the mode-I debonding problem based on a cohesive zone modeling is endowed with non-local terms to include long-range interactions that are present in multi-layered biological tissue. Such non-local effects are related to the collagen fibers that transmit forces between non-adjacent elements. Numerical simulations are provided with different values of the non-local parameters in order to show the effect of the non-locality during the debonding processes.

In this paper a non-linear stress-strain relation based on an integral formulation with a power-law kernel is proposed. This constitutive law is able to reproduce both the viscoelastic behavior and the inelastic irreversible phenomenon. It is shown how the proposed stress-strain law is capable to fit experimental data obtained from tensile tests on two kind of metal alloys. Such best-fitting procedure have shown the accuracy of the proposed model and its results are compared to other ones obtained with the aid of classical non-linear constitutive law.

Finding an accurate stress–strain relation, able to describe the mechanical behavior of metals during forming and machining processes, is an important challenge in several fields of mechanics, with significant repercussions in the technological field. Indeed, in order to predict the real mechanical behavior of materials, constitutive laws must be able to take into account elastic, viscous and plastic phenomena. Most constitutive models are based on empirical evidence and/or theoretical approaches, and provide a good prediction of the mechanical behavior of several materials. Here we present a non linear stress–strain relation based on fractional operators. The proposed constitutive law is based on integral formulation, and takes into account the viscoelastic behavior of the material and the inelastic phenomenon that appears when the stress reaches a particular yielding value. A specific case of the proposed constitutive law for imposed strain history is used to fit experimental data obtained from tensile tests on two kind of metal alloys. A best-fitting procedure demonstrates the accuracy of the proposed stress–strain relation and its results are compared to those obtained with some classical models. We conclude that the proposed model provides the best results in predicting the mechanical behavior for low and high values of stress/strain.

The method presented here is a variation of the classical penalty one, suited to reduce penetration of the con- tacting surfaces. The slight but crucial modification concerns the introduction of a shift parameter that moves the min- imum point of the constrained potential toward the exact value, without any penalty increase. With respect to the clas- sical augmentation procedures, the solution improvement is embedded within the original penalty contribution. The problem is almost consistently linearized, and the shift is updated before each Newton’s iteration. However, adding few iterations, with respect to the original penalty method, a reduction of the penetration of several orders of magni- tude can be achieved. The numerical tests have shown very attractive characteristics and very stable solution paths. This permits to foresee a wide area of applications, not only in con- tact mechanics, but for any problem, like e.g. incompressible materials, where a penalty contribution is required.

In this contribution we present a numerical analysis of the Stress Concentration Factor (SCF) KT and the stress distribution around holes and discontinuities in plane state structures. The stress concentration in discontinuous zones is known to be a very significant issue in strength problems. Indeed, the presence of a discontinuity makes even a simple structure model complicated to analyze, regardless of the method being used. The Finite Element Method (FEM) is the most common tool in engineering for treating such problems. However, a very fine mesh is generally required for a realistic prediction of stresses around critical zones as cracks or discontinuities. Despite the large use of the FEM as numerical approach to predict stress concentrations, the problem is still open. Here two innovative numerical techniques are proposed as computationally more efficient alternatives to determine the SCFs with a limited number of degrees of freedom, which may significantly decrease the computation time. A limited number of degrees of freedom is due to a higher order scheme carried out by the SFEM. On the contrary, the standard FEM employs local low order polynomials for the approximation of solution, and special functions are generally implemented for stress concentration problems. More in detail, the local and global strong formulation finite element method (SFEM), and the isogeometric approach (IGA) based on quadratic Non-Uniform Rational B-Spline (NURBS) basis functions, are herein applied for the purpose, as proposed for other applications in [1,2] for the SFEM, and [3-5] for IGA, respectively. In order to demonstrate the accuracy of the two proposed methodologies, some classical examples are studied, which consider rectangular plates with different discontinuities, e.g. circular holes, U-holes, or V-notches. All the numerical results obtained in terms of stress distribution and KT are compared with the theoretical predictions from the literature as well as the numerical solutions provided by FEM. The numerical solutions for the KT are based on a linear interpolation of the stresses near the discontinuities within a certain distance of interpolation, and agree very well with the exact computations available in the handbooks. A comparative evaluation of numerical results based on the IGA, SFEM and FEM approaches is illustrated in Figures 1 and 2, in terms of stress distributions and KT for a U-notched plate subjected to a uniform loading and for different degrees of freedoms (DOFs). The numerical results provided by SFEM and IGA methods are very close to the ones found with FEM, thus confirming the potentials and accuracy of the two proposed methods to capture the stress concentrations in fracture mechanics, also for coarse mesh discretizations.

Nowadays computational frictional contact and fracture mechanics in the regime of large deformations is receiving an increasing attention in many field of engineering and applied science. The non-linear nature of similar problems, as well as their high sensitivity to the geometry accuracy, makes them challenging to analyze, primarily in a computational sense, when robust and stable solutions must be acquired. In such a context, we approach the non-linear contact and debonding problems by applying the isogeometric (IGA) concept based on NURBS and T-Splines interpolations. The IGA technology is here tackled from the finite element point of view, by applying the linear Bèzier operator to map the Bernstein polynomial basis on Bèzier elements to the IGA basis. Thus, the suitable isogeometric discretizations are automatically generated for any CAD geometry and incorporated into a finite element framework.

Nowadays the isogeometric analysis (IGA) represents an innovative method that merges design and numerical computations into a unified formulation. In such a context we apply the isogeometric concept based on T-splines and Non Uniform Rational B-Splines (NURBS) discretizations to study the interfacial contact and debonding problems between deformable bodies in large deformations. More in detail, we develop and test a generalized large deformation contact algorithm which accounts for both frictional contact and mixed-mode cohesive debonding in a unified setting. Some numerical examples are provided for varying resolutions of the contact and/or cohesive zone, which show the accuracy of the solutions and demonstrate the potential of the method to solve challenging 2D contact and debonding problems. The superior accuracy of T-splines with respect to NURBS interpolations for a given number of degrees of freedom (Dofs) is always proved.

T-spline-based isogeometric analysis is applied to frictionless contact problems between deformable bodies in the context of large deformations. The continuum is discretized with cubic T-splines and cubic NURBS. A Gauss-point-to-surface formulation is combined with the penalty method to treat the contact constraints in the discretized setting. It is demonstrated that analysis-suitable T-splines, coupled with local refinement, accurately approximate contact pressures with far fewer degrees of freedom than NURBS. Both two- and three-dimensional examples are presented. Additionally, all T-spline analysis models are generated using commercially available T-spline modeling software without intermediate mesh generation or geometry clean-up steps.

Much of the world's architectural heritage consists of Unreinforced Masonry (URM) structures whose preservation is a topical subject. To prevent possible collapse of multi-block systems in hazardous conditions, a promising tool to investigate their structural response is represented by numerical modelling with the Discrete Element Method (DEM). Gothic buttresses of trapezoidal and stepped shapes are first analysed comparatively under static loading, defining the optimal configurations. Numerical results are verified against the analytical predictions of overturning and sliding resistances, based on a continuum approximation of masonry. The DEM is then successfully adopted to assess the first-order seismic behavior of arches and buttressed arches with different shapes as compared to predictions based on limit analysis. A systematic investigation on dynamic behavior failure domains and on modes of collapse of URM structures is finally performed for varying input parameters, as needed to gain more confidence on the numerical results.

The stress concentration in discontinuous zones is known to be a significant issue in mechanics, since the presence of a discontinuity, even in a simple structure model, makes it complicated to analyze. To this end, the application of numerical methods would require a sufficiently fine mesh for a realistic prediction of stresses around critical zones as cracks or discontinuities. Despite the large effort related to the finite element method as numerical approach to predict stress concentrations, results are still not satisfactory. In this work we propose two innovative numerical approaches to determine the stress concentration factors, with a reduced computational cost. A strong formulation finite element method, its localized version, and the isogeometric approach, are herein applied to study some classical examples, as the plane stress plates with circular holes, U-holes, or V-notches. All the numerical results obtained with both approaches in terms of stress distribution and stress concentration factors are compared to the theoretical and experimental predictions available in the literature and the numerical solutions found with finite element method. A very good agreement between the numerical and the reference results confirms the potentials and accuracy of the proposed methodologies to capture the stress concentrations in fracture mechanics, also for coarse mesh discretizations.

The limitations of sophisticated analytical modelling and experimental investigations for studying complex masonry structures have increased the use of numerical modelling, such as the Discrete Element Method (DEM). Based on this approach, the discontinuous bodies can move freely in space and interact reciprocally with contact forces, leading to an automatic updating of contact detection. In this work, the potential of the DEM is first demonstrated for the assessment of the first-order seismic behaviour of generally shaped vaulted structures in 2D. The relative efficiency of different arch shapes is analysed comparatively such as circular, pointed or basket-handle shapes. The full dynamics and resistance of discrete columns subjected to simple base excitations is additionally studied, with a detailed investigation on failure domains and on modes of collapse of the structures. A parametric evaluation of the sensitivity of the response to the input parameters is numerically performed, which gives more confidence to the DEM predictions.

SUMMARY The penalty method for the solution of contact problems yields an approximate satisfaction of the contact constraints. Augmentation schemes, which can be adopted to improve the solution, either include the contact forces as additional unknowns or are strongly affected by the penalty parameter and display a poor convergence rate. In a previous investigation, an unconventional augmentation scheme was proposed, on the basis of estimating the ‘exact’ values of the contact forces through linear interpolation of a database extracted by the previous converged states. An enhanced version of this method is proposed herein. With respect to the original method, the enhanced one eliminates some numerical problems and improves the regularity of the convergence path by carrying out the estimate through linear regression methods. The resulting convergence rate is superlinear, and the method is quite insensitive to the penalty parameter. The main underlying concept is that, within the iterative solution of a non-linear problem, linear regression techniques may be used as a tool to ‘shoot’ faster to the final solution, on the basis of a set of intermediate data. The generality of this concept makes it potentially applicable to contact problems in more general settings, as well as to other categories of non-linear problems. Copyright © 2012 John Wiley & Sons, Ltd.

Earthquakes represent one of the major threats to the stability of the world architectural heritage, which is mostly constituted by unreinforced masonry (URM) structures. The dynamic behavior of these structures is complex and highly non-linear, as it involves sliding and rocking of the component blocks. As a result, numerical modeling seems to be the most appropriate predictive approach and, in particular, the Discrete Element Method (DEM) has recently emerged as a very promising tool for this purpose. Although multi-drum columns and arches on buttresses are typical components of historic URM structures, their modeling with the DEM has been the subject of relatively limited research. Moreover, a set of input parameters is required for the definition of the numerical model and, due to the uncertainty and difficulty in their experimental evaluation, these parameters are usually set in an arbitrary way. In this paper, a systematic parametric study based on the DEM is adopted to evaluate the dynamic behavior and resistance of multi-drum columns and arches on buttresses subjected to two different base motions, i.e. step and harmonic impulses. A detailed investigation on failure domains and modes of collapse is presented. The main features of the dynamic response of masonry structures and the sensitivity of the response to changes in the excitation, geometry and mechanical parameters are discussed.

NURBS-based isogeometric analysis is applied to 3D frictionless large deformation contact problems. The contact constraints are treated with a mortar-based approach combined with a simplified integration method avoiding seg- mentation of the contact surfaces, and the discretization of the continuum is performed with arbitrary order NURBS and Lagrange polynomial elements. The contact constraints are satisfied exactly with the augmented Lagrangian formula- tion proposed by Alart and Curnier, whereby a Newton-like solution scheme is applied to solve the saddle point prob- lem simultaneously for displacements and Lagrange mul- tipliers. The numerical examples show that the proposed contact formulation in conjunction with the NURBS dis- cretization delivers accurate and robust predictions. In both small and large deformation cases, the quality of the con- tact pressures is shown to improve significantly over that achieved with Lagrange discretizations. In large deformation and large sliding examples, the NURBS discretization pro- vides an improved smoothness of the traction history curves. In both cases, increasing the order of the discretization is either beneficial or not influential when using isogeometric analysis, whereas it affects results negatively for Lagrange discretizations.

This paper focuses on the application of NURBS-based isogeometric analysis to Coulomb frictional contact problems between deformable bodies, in the context of large deformations. A mortar-based approach is presented to treat the contact constraints, whereby the discretization of the continuum is performed with arbitrary order NURBS, as well as C0-continuous Lagrange polynomial elements for comparison purposes. The numerical examples show that the proposed contact formulation in conjunction with the NURBS discretization delivers accurate and robust predictions. Results of lower quality are obtained from the Lagrange discretization, as well as from a different contact formulation based on the enforcement of the contact constraints at every integration point on the contact surface. Copyright © 2011 John Wiley & Sons, Ltd.

This paper proposes a linear elastic fracture mechanics approach for the prediction of plate end debonding in rectilinear and curved plated beams. The analytical model results in simple equations, suitable for immediate design use. The load-deflection curve of a plated beam, from the onset of debonding up to the complete separation of the plate, is obtained by controlling the length of the interfacial debonding crack. Its shape clearly shows that snap-back or snap-through instabilities may arise when the beam is loaded under displacement or force control. Analytical predictions are also compared with finite element results based on an interfacial cohesive crack model. It is shown that the predictions of the proposed analytical model match closely the numerical solution, provided that an effective crack length accounting for the size of the fracture process zone is used in the calculations.

The elastic analysis of interfacial stresses in plated beams has been the subject of several investigations. These studies provided both first-order and higher-order solutions for the distributions of interfacial shear and normal stresses close to the plate end in the elastic range. The notable attention devoted to this topic was driven by the need to develop predictive models for plate end debonding mechanisms, as the early models of this type adopted debonding criteria based on interfacial stresses. Currently, approaches based on fracture mechanics are becoming increasingly established. Cohesive zone modeling bridges the gap between the stress- and energy-based approaches. While several cohesive zone analyses of bonded joints subjected to mode-II loading are available, limited studies have been conducted on cohesive zone modeling of interfacial stresses in plated beams. Moreover, the few available studies present complex formulations for which no closed-form solutions can be found. This paper presents an analytical cohesive zone model for the determination of interfacial stresses in plated beams. A first-order analysis is conducted, leading to closed-form solutions for the interfacial shear stresses. The mode-II cohesive law is taken as bilinear, as this simple shape is able to capture the essential properties of the interface. A closed-form expression for the debonding load is proposed, and the comparison between cohesive zone modeling and linear-elastic fracture mechanics predictions is discussed. Analytical predictions are also compared with results of a numerical finite element model where the interface is described with zero-thickness contact elements, using the node-to-segment strategy and incorporating decohesion and contact within a unified framework.

SUMMARY Several investigations have shown that the classical one-pass node-to-segment (NTS) algorithms for the enforcement of contact constraints fail the contact patch test. This implies that the algorithms may introduce solution errors at the contacting surfaces, and these errors do not necessarily decrease with mesh refinement. The previous research has mainly focused on the Lagrange multiplier method to exactly enforce the contact geometry conditions. The situation is even worse with the penalty method, due to its inherent approximation that yields a solution affected by a non-zero penetration. The aim of this study is to analyze and improve the contact patch test behavior of the one-pass NTS algorithm used in conjunction with the penalty method for 2D frictionless contact. The paper deals with the case of linear elements. For this purpose, several sequential modifications of the basic formulation have been considered, which yield incremental improvements in results of the contact patch test. The final proposed formulation is a modified one-pass NTS algorithm which is able to pass the contact patch test also if used in conjunction with the penalty method. In other words, this algorithm is able to correctly reproduce the transfer of a constant contact pressure with a constant proportional penetration. Copyright q 2009 John Wiley & Sons, Ltd.

The thermo-chemical diffusional process of carburizing and nitriding was modeled in this study. The analysis led to the prediction of surface hardened layers dimensions and hardness in commercial steels. Diffusion model based on Fick’s laws was applied to such steels in order to describe the growth kinetics of layers, then the analytical model was employed to perform finite element calculations. In such way it was possible to calculate the carbon and nitrogen concentration in the cross sections of cylindrical samples and the consequent hardness profiles coupled with the residual stresses ones. The results from analytical model and FE calculations were compared with experimental data.

The contact element formulation presented considers microscopically mechanisms of force transmission and heat exchange together with coupling between thermal and mechanical fields. Experimentally and theoretically well founded micro-mechanical and micro-thermal laws are adapted to FEM consistent linearization necessities. Based on these laws the nonlinear macroscopic related stiffness is calculated as a function of changes in significant parameters. Examples related to industrial applications are shown.

This paper checks the consistency of some published exponential and bilinear mixed-mode cohesive zone models. The effect of coupling on traction-separation behavior and energy dissipation is investigated and the path-dependence of the debonding work of separation and failure domain is evaluated analytically and numerically. All selected models present several inconsistencies, except for the one by van den Bosch et al. (2006), which is, however, not currently formulated within a thermodynamical framework but postulated in an ad-hoc manner. We thus propose a thermodynamically consistent reformulation of this model within damage mechanics, which holds monolithically for loading, unloading, decohesion and contact.

Cohesive zone (CZ) models have long been used by the scientific community to analyze the progressive damage of materials and interfaces. In these models, non-linear relationships between tractions and relative displacements are assumed, which dictate both the work of separation per unit fracture surface and the peak stress that has to be reached for the crack formation. This contribution deals with isogeometric CZ modeling of interface debonding. The interface is discretized with generalized contact elements which account for both contact and cohesive debonding within a unified framework. The formulation is suitable for non-matching discretizations of the interacting surfaces in presence of large deformations and large relative displacements. The isogeometric discretizations are based on non uniform rational B-splines as well as analysis-suitable T-splines enabling local refinement. Conventional Lagrange polynomial discretizations are also used for comparison purposes. Some numerical examples demonstrate that the proposed formulation based on isogeometric analysis is a computationally accurate and efficient technology to solve challenging interface debonding problems in 2D and 3D.

Due to their simplicity, cohesive zone models (CZMs) are very attractive to describe mixed-mode failure and debonding processes of materials and interfaces. Although a large number of coupled CZMs have been proposed, and despite the extensive related literature, little attention has been devoted to ensuring the consistency of these models for mixed-mode conditions, primarily in a thermodynamical sense. A lack of consistency may affect the local or global response of a mechanical system. This contribution deals with the consistency check for some widely used exponential and bilinear mixed-mode CZMs. The coupling effect on stresses and energy dissipation is first investigated and the path-dependance of the mixed-mode debonding work of separation is analitically evaluated. Analytical predictions are also compared with results from numerical implementations, where the interface is described with zero-thickness contact elements. A node-to-segment strategy is here adopted, which incorporates decohesion and contact within a unified framework. A new thermodynamically consistent mixed-mode CZ model based on a reformulation of the Xu-Needleman model as modified by van den Bosch et al. is finally proposed and derived by applying the Coleman and Noll procedure in accordance with the second law of thermodynamics. The model holds monolithically for loading and unloading processes, as well as for decohesion and contact, and its performance is demonstrated through suitable examples., Frattura ed Integrità Strutturale, 8 (29)

The design of a tracking detector for electrons in a magnetic field consisting of a drift chamber is discussed. The chosen materials for its construction must be light to minimize the effects of the subatomic particles interactions with the chamber walls. Low-density materials and very thin wall thicknesses are therefore needed. From a mechanical engineering point of view, it is important to analyse the drift chamber structure and define the conditions to which it is subject in terms of both mechanical loads and geometric constraints. The analysis of the structural response of the drift chamber has been performed through the Finite Element Method (FEM) as implemented in the commercial software ANSYS and its interface for the analysis for composite structures ACP (Ansys Composite Pre/Post).

Background. Tuberous sclerosis is a protean, genetically determined disease that may involve any organ or tissue and lead to a great number of symptoms and clinical features. Objective. Diagnosis can be very difficult in cases with incomplete manifestations (formes fruste) lacking the classic signs of the disease. Materials and methods. We report a case fulfilling the diagnostic criteria for tuberous sclerosis (shagreen patches, hypomelanotic macules, renal cysts and angiomyolipomas, and “migration tracts” in the cerebral white matter) in association with a giant intracranial aneurysm, but lacking mental retardation, epilepsy and facial angiofibroma. Results. Fourteen other cases of tuberous sclerosis and intracranial aneurysms, all but one without any clear sign of polycystic kidney disease, were found in the literature. Conclusion. We suggest that vascular dysplasias in general and aneurysms (mainly intracranial) in particular can be added to the other non-primary diagnostic features for the clinical diagnosis of tuberous sclerosis.

The numerical solution of contact problems via the penalty method yields approximate satisfaction of contact constraints. The solution can be improved using augmentation schemes. However their efficiency is strongly dependent on the value of the penalty parameter and usually results in a poor rate of convergence to the exact solution. In this paper we propose a new method to perform the augmentations. It is based on estimated values of the augmented Lagrangians. At each augmentation the converged state is used to extract some data. Such information updates a database used for the Lagrangian estimation. The prediction is primarily based on the evolution of the constraint violation with respect to the evolution of the contact forces. The proposed method is characterised by a noticeable efficiency in detecting nearly exact contact forces, and by superlinear convergence for the subsequent minimisation of the residual of constraints. Remarkably, the method is relatively insensitive to the penalty parameter. This allows a solution which fulfils the constraints very rapidly, even when using penalty values close to zero.

A recent computational model for tumor growth is presented. The mathematical model, based on thermodynamically constrained averaging theory (TCAT), is shortly summarized in the first part; then the attention is focused on modeling hypothesis and their impact on numerical results. Perspectives for future developments of the presented multiphase model are outlined at the end of the paper. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

A T-spline-based isogeometric analysis is applied to frictional contact problems between deformable bodies in the context of large deformations. The continuum is discretized with cubic T-splines and cubic NURBS (Non-Uniform Rational B-Splines) for comparison purposes. A Gauss-point-to-surface (GPTS) formulation is combined with the penalty method to treat the normal and friction contact constraints in the discretized setting. It is demonstrated that the proposed formulation combined with analysis-suitable T-spline interpolations, is a computationally accurate and efficient technology for local and global solutions of contact problems. T-spline analysis models are generated using commercially available T-spline modeling software without intermediate mesh generation or geometry clean-up steps. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

this paper, a method is proposed to define the geometrical contact constraints. Within this treatment one has the possibility to define locally the contact parameters for an accurate treatment of contact constraints. Local values of the geometrical variables can be determined at the integration points, hence the method permits to integrate contact constitutive laws along contact segments. The weak form for this new formulation is developed. Furthermore, also the consistent linearization is carried out. Finally a technique is proposed to reduce the large number of terms involved. In this case, an almost consistent tangent stiffness is determined. @ 1998 Elsevier Science Ltd. All rights reserved.

In this paper a further method is presented to solve problems involving contact mechanics. The basic idea is related to a special modification of the unconstrained functional to include inequality constraints. The modification is constructed in such a way that minimal point of the unconstrained potential can be exactly shifted to the constraint limit. Moreover, the functional remains smooth and the admissible range of the solution is not restricted. The solution search process with iterative techniques takes advantage from these features. In fact, due to a better control of gap status changes, a more stable solution path with respect to other methods is usually obtained. The characteristics of the method are evidenced and compared to other classical techniques, like penalty and barrier methods. The finite element discretization of the proposed method is included and some numerical applications are shown. © 1998 John Wiley & Sons, Ltd.

Contact between three-dimensional beams which undergo large motions is considered. To formulate the associated constraint conditions the point of contact has to be detected within the beam. Once this is known the contact constraint has to be formulated for a given beam discretization and the associated contribution to the weak form has to be developed. Also, consistent linearization of the contact contribution is derived, which is needed within Newton's method. © 1997 John Wiley & Sons, Ltd.