Composite material identification as micropolar continua via an optimization approach

A strategy based on material homogenization and heuristic optimization for the structural identification of composite materials is proposed. The objective is the identification of the constitutive properties of a micropolar continuum model employed to describe the mechanical behaviour of a composite material made of rigid blocks and thin elastic interfaces. The micropolar theory (Cosserat) has been proved to be capable of properly accounting for the particles arrangements as well as their size and orientation. The constitutive parameters of the composite materials, characterized by different textures and dimensions of the rigid blocks, are identified through a homogenization procedure. Thus, the identification is repeated exploiting the static or modal response of the composite materials and using the Differential Evolution algorithm. The benchmark structures assumed as target are represented by discrete models implemented in ABAQUS where the blocks and the elastic interfaces are modelled by rigid bodies and elastic interfaces, respectively. The obtained results show that proposed strategies provide accurate results paving the way to the experimental validation and in field applications

Optimal sensors placement in dynamic damage detection of beams using a statistical approach

Structural monitoring plays a central role in civil engineering; in particular, optimal sensor positioning is essential for correct monitoring both in terms of usable data and for optimizing the cost of the setup sensors. In this context, we focus our attention on the identification of the dynamic response of beam-like structures with uncertain damages. In particular, the non-localized damage is described using a Gaussian distributed random damage parameter. Furthermore, a procedure for selecting an optimal number of sensor placements has been presented based on the comparison among the probability of damage occurrence and the probability to detect the damage, where the former can be evaluated from the known distribution of the random parameter, whereas the latter is evaluated exploiting the closed-form asymptotic solution provided by a perturbation approach. The presented case study shows the capability and reliability of the proposed procedure for detecting the minimum number of sensors such that the monitoring accuracy (estimated by an error function measuring the differences among the two probabilities) is not greater than a control small value

Fast statistical homogenization procedure (FSHP) for particle random composites using virtual element method

Mechanical behaviour of particle composite materials is growing of interest to engineering applications. A computational homogenization procedure in conjunction with a statistical approach have been successfully adopted for the definition of the representative volume element (RVE) size, that in random media is an unknown of the problem, and of the related equivalent elastic moduli. Drawback of such a statistical approach to homogenization is the high computational cost, which prevents the possibility to perform series of parametric analyses. In this work, we propose a so-called fast statistical homogenization procedure (FSHP) developed within an integrated framework that automates all the steps to perform. Furthermore within the FSHP, we adopt the numerical framework of the virtual element method for numerical simulations to reduce the computational burden. The computational strategies and the discretization adopted allow us to efficiently solve the series (hundreds) of simulations and to rapidly converge to the RVE size detection

Torsional characteristics of carbon nanotubes: Micropolar elasticity models and molecular dynamics simulation

Efficient application of carbon nanotubes (CNTs) in nano-devices and nano-materials requires comprehensive understanding of their mechanical properties. As observations suggest size dependent behaviour, non-classical theories preserving the memory of body’s internal structure via additional material parameters offer great potential when a continuum modelling is to be preferred. In the present study, micropolar theory of elasticity is adopted due to its peculiar character allowing for incorporation of scale effects through additional kinematic descriptors and work-conjugated stress measures. An optimisation approach is presented to provide unified material parameters for two specific class of single-walled carbon nanotubes (e.g., armchair and zigzag) by minimizing the difference between the apparent shear modulus obtained from molecular dynamics (MD) simulation and micropolar beam model considering both solid and tubular cross-sections. The results clearly reveal that micropolar theory is more suitable compared to internally constraint couple stress theory, due to the essentiality of having skew-symmetric stress and strain measures, as well as to the classical local theory (Cauchy of Grade 1), which cannot accounts for scale effects. To the best of authors’ knowledge, this is the first time that unified material parameters of CNTs are derived through a combined MD-micropolar continuum theory

Micromodels for the in-plane failure analysis of masonry walls with friction: Limit analysis and dem-fem/dem approaches

Despite its complexity, the accurate structural modelling of masonry still represents an active field of research, due to several practical applications in civil engineering, with special reference to the preservation and restoration of cultural heritage. In this work a comparison of different models and techniques for the assessment of the mechanical behaviour of two-dimensional block masonry walls subjected to the static action of in-plane loads is presented. Panels are characterized by different height-to-width ratio as well as various masonry textures. Brick-block masonry, perceived as a jointed assembly of prismatic particles in dry contact, is modelled as a discrete system of rigid blocks interacting through contact surfaces unable to carry tension and resistant to sliding by friction, modelled as zero thickness elasto-plastic Mohr-Coulomb interfaces. Different approaches and numerical models are considered: Limit Analysis (LA), Discrete Element Model (DEM) and Finite Ele-ments/Discrete Element Model (FEM/DEM). Limit Analysis is able to provide fast and reliable results in term of collapse multiplier and relative kinematism. Here a standard Limit Analysis is adopted via an own made procedure based on Linear Mathematical Programming, taking into account friction at interfaces

Statistical Assessment of In-Plane Masonry Panels Using Limit Analysis with Sliding Mechanism

Historical masonry structures have a great interest in civil engineering because they constitute a large part of the world's building heritage. In this paper, the effects that different geometrical (panel ratio, block ratio, and bond type) and mechanical (friction ratio) parameters have on the in-plane structural response of brick masonry panels are investigated. A discrete modeling approach, based on a limit analysis and capable of reproducing sliding mechanisms, formulation by one of the authors has been adopted, enhanced, and implemented. Results, in terms of collapse multipliers and collapse mechanisms, are presented and analyzed following a systematic statistical approach. Statistically significant effects have been found for each factor considered. Furthermore, the statistical model adopted included nonlinear terms that allowed the identification of whether the effect of one parameter on the response depends on the level of any other parameters. Thus, it was observed that two-way factor interactions played an important role in the in-plane response of masonry panels. The panel ratio-friction ratio two-way factor interaction was the one with a more significant effect

Flexural characterization of a novel recycled-based polymer blend for structural applications

The use of recycled plastic in construction fields, among others, is becoming a turning point for resolving significant related problems such as resource management, sustainability and plastic waste generation. Hence, in the context of sustainability, the "Three R’s": reduce, reuse and recycle, are getting more attention day after day. There has been a huge surge in the recycling and reuse of plastic composites due to their eco-friendliness, lightweight, life cycle superiority and low cost. However, because of a lack of knowledge of their performance and behavior, their application is still limited in the real world. The aim of this research is to understand the behavior of recycled plastic and derive its material properties which can be used in the design of structural and non-structural elements. In the present study, three stiffened plates are manufactured from 80% of recycled plastic (around 50% of recycled Polypropylene rPP, and around 50% of High Density Polyethylene PEHD with a little part of Low Density Polyethylene PELD) and 20% of virgin polypropylene PP Copolymer. Three-point bending test is performed on the three specimens. In the experimental campaign, the behavior of these stiffened plates under pure bending loads has been studied. After that, the material properties are extracted from the data collected during the experiment using Ramberg–Osgood equation. Then, once implemented in finite elementcmodels, it was observed that the simulated material shows similar behavior to the one registered during the experiment. As a conclusion, the derived material properties show reliability and they can be used to study a design of a structural or non-structural component including recycled plastic

Carbon nanomaterials-based electrically conductive scaffolds to repair the ischaemic heart tissue

Ischaemic heart diseases are the leading causes of morbidity around the world and pose serious socio-economic burdens. Ischaemic events, such as myocardial infarction, lead to severe tissue damage and result in the formation of scar tissue. This scar tissue, being electrically inert, does not conduct electrical currents and thus generates lethal arrhythmias. The ventricle dilates with time due to asynchronous beating due to the scar, and it eventually leads to total heart failure. The current pharmacological approaches only cure heart failure symptoms without inducing tissue regeneration. Therefore, heart transplant remains the gold standard to date, but the limited organ donors and the possibility of immune rejection make this approach elusive. Cardiac tissue engineering has the potential to address this issue by engineering artificial heart tissues using 3D scaffolds cultured with cardiac stem cells. Compared with the traditional non-conductive scaffold, electroconductive scaffolds can transfer feeble electric currents among the cultured cells by acting as a "wire". This improves intercellular communication and synchronisation that otherwise is not possible using non-conductive scaffolds. This article reviews the recent advances in carbon nanomaterials-based electroconductive scaffolds, their in vitro/in vivo efficacy, and their potential to repair ischaemic heart tissue

LIMIT ANALYSIS FOR THREE-DIMENSIONAL STONE MASONRY STRUCTURES WITH FRICTION

Abstract The paper deals with the limit analysis of structures made of rigid blocks interacting through no-tension and frictional contact surfaces performed using mathematical programming methods. The presence of friction makes the problem non-linear and non-convex. It is shown that a proper choice of the initial guess for the variables of the non-linear program enables the convergence to the optimal solution. The initial variables are evaluated as the outputs of a linear program performing the limit analysis of the same assembly of blocks with dilatancy along the joints, instead of friction. Various analyses show the validity of the procedure and the effectiveness of the limit analysis approach for studying the collapse behaviour of real three-dimensional stone masonry structures. Key Words Block-Masonry Structures, Limit Analysis, Mathematical Programming, Friction Introduction In this work a computer procedure for the detection of the collapse behaviour of stone masonry assemblages, based on non-standard limit analysis method, is proposed. The procedure elaborated provides a computational tool suitable to be used in practical structural analyses for assessing the safety of ancient masonry buildings, with particular references to the seismic actions. In spite of the many sophisticated tools of analysis available for the analysis of masonry structures at this time, most of them based on Finite Element codes, appropriate and simple tools for the structural analysis of ancient masonries, generally made of stones dry assembled together or with joints filled by poor and scattered mortar, are still lacking. In particular, non-linear finite elements approaches, both for generalised homogeneous classical and micropolar continu