Adhesive joint modeling using compatible element formulation

Fiber-reinforced polymer (FRP) composites offer several advantages in relation to traditional materials, such as high specific strength, good corrosion resistance, low thermal conductivity and rapid component installation. Despite the great potential of these materials, two major disadvantages limit their acceptance in civil engineering applications: their lack of inherent ductility and the fact that their fibrous and anisotropic character makes the joining of structural components difficult. The purposes of this research are to develop ductile structures using brittle all-FRP materials and to provide a corresponding design method assuring robustness and structural safety. The proposed concept for all-FRP structures incorporates system ductility through the use of ductile, adhesively-bonded joints and redundant (statically indeterminate) structural systems. The concept envisages adhesives with an initially elastic behavior sufficiently stiff to meet short- and long-term serviceability requirements. When serviceability and ultimate loads are exceeded, however, adhesive behavior should change and become plastic, or at least highly non-linear inelastic, with much lower stiffness. The ductile connections effect a favorable redistribution of internal and external forces in the redundant system in the same way as plastic hinges in statically indeterminate systems with ductile materials. In case of joint failure, the redundant system allows the creation of alternative load paths and redistribution of section forces preventing structural collapse. Numerical and experimental investigations of adhesively-bonded double-lap joints demonstrate that using an appropriate bilinear adhesive is more advantageous than using a traditional structural and stiff epoxy adhesive. These investigations show that ductile adhesives generate a linear axial strain distribution and consequently a constant shear stress distribution along the overlap. Numerical and analytical modelings are validated with experimental results. The numerical modeling allows evaluation of the effect of ductile adhesive behavior on joint behavior and establishment of recommendations for the selection of adhesive mechanical properties, according to serviceability and failure limit state requirements. Based on numerical modeling results, joints can also be classified according to stiffness (stiff or flexible). An analytical model, based on numerical and experimental results, is developed for predicting joint stiffness when using ductile adhesives, assuming that the adhesive deforms only and uniformly in shear and that adherends deform only in tension. The design method is developed in accordance with the new structural concept and Eurocode design philosophy. It is based on both numerical and analytical model results for adhesively-bonded double-lap joints. A case study illustrating the adhesively-bonded joint design and appropriate adhesive selection is carried out on continuous beams with adhesively-bonded joints at mid-support. Corresponding bending experiments on beams with ductile, adhesively-bonded connections demonstrate the new structural concept's feasibility and validate the proposed design method. An energy factor defined as the ultimate strength to serviceability limit state energy ratio is proposed to quantify and compare the robustness and safety of structures built from both ductile and brittle materials.

Structural Health Monitoring (SHM) systems are widely regarded as capable of significantly reducing inspection costs of safety-critical structures in industries such as aerospace, nuclear, and oil and gas, among others. Successful SHM systems can be considered those which combine good sensitivity to defects, preferably with the capability of localization and identification, with a low sensor density. Techniques based on sparse arrays of sensors which generate and receive guided waves are among the most promising candidates. Guided waves propagate over large distances and certain modes have the ability to transmit through a variety of structural features leading to a relatively small number of distributed sensors being able to cover the structure. In complex structures, which contain high densities of structural elements, the timetraces obtained are often too complex to be directly interpreted due to the large number of overlapping reflections. In this case, the Baseline Subtraction technique becomes attractive. In this method a current signal from the structure is subtracted from a signal which has been acquired during the initial stages of operation of the structure. This eliminates the need for interpretation of the complex raw time signal and any defects will be clearly seen provided the amplitude of the residual signal obtained after subtraction of the baseline signal is sufficiently low when the structure is undamaged. However, it is well known that environmental effects such as stress, ambient temperature variations and liquid loading affect the velocity of guided waves; this modifies the time-traces and leads to high levels of residual signal if a single baseline, taken under different conditions, is used. Of these effects, temperature variations are the most commonly encountered and are critical since they affect not only the wave propagation but also the response of transducers. The present work aims to demonstrate the potential of guided wave health monitoring of large area complex structures. It starts with a general literature review on inspection and monitoring of large area structures, in which the advantages and disadvantages of this technique compared to other well-established SHM techniques 2 are presented. The design and behaviour of two different temperature-stable transducers generating high A0 or S0 mode purity in the sub-200kHz frequency region are described. The efficiency of different signal processing techniques aimed at reducing or eliminating the influence of temperature on wave propagation is evaluated and a temperature compensation signal processing strategy is proposed. Finally, a large metallic structure is used to demonstrate a sparse-array SHM system based on this signal processing strategy, and imaging algorithms are used to combine the information from a large number of sensor combinations, ultimately leading to the localization of defects artificially introduced in the structure.

Owing to their high surface area, excellent electrolyte permeability and ample diffusion pathways for charge transport, porous and hollow-structured electrochemically active materials attract more attention as the electrodes. In general, the process of template preparation method is used to achieve hollow structured materials over the last few decades. However, the complicated preparation process including removal of template and surface modification often results in poor uniformity, low reproducibility, and high cost of porous structure. Moreover, it incorporates functional chemicals with specific homogeneity and dispersity into the hollow porous intercrystalline structure. These problems hinder the development and application in energy storage and conversion devices of the diversified porous and hollow-structured materials. The metal-organic frameworks (MOFs), consisting of organic linkers and coordinated inorganic clusters, appear as an excellent collection of porous crystal material series with high surface areas, high porosity, and tunable structures. However, their low conductivity and electrolyte instability limit the further use of MOFs in the field of LIBs. Recently, how electrode materials for Lithium–ion batteries (LIBs) are designed and prepare using MOFs has attracted more attention. The composite materials derived from MOFs including nanostructured porous carbons and metal oxide uaing self-sacrificial template synthetic route not only solves the problem of low conductivity but also maintains the high surface area and porous structure of MOFs, providing abundant active sites for insertion/deinsertion or adsorption/desorption; Furthermore, composite materials derived from MOFs increase the complexity of nanostructures in terms of structural units and chemical components. In particular, large pore volume and open pore structure are critical to loading guest species, accommodating mechanical strains and facilitating mass transport. In this paper, we briefly examined the production of MOF-derived materials for applications in LIBs. The optimization and modification of an MOFs morphology were implemented according to the electrode material requirement for LIBs. Moreover, the preparation of MOFs-derived electrode materials with porous, hollow, or complicated construction and their effects on electrochemical performance were described. Finally, the challenge and trend in production of electrode materials derived from MOFs were analyzed.

Concrete and reinforced concrete are the main structural materials in modern construction. The area and volumes of application of these materials continues to expand. In recent years, in the practice of construction, there is a tendency to the use of structures that combine load-bearing and enclosing functions, as well as the functions of technological equipment. At the same time, their working conditions are becoming more complicated and harsh. In addition to the usual force effects (loads), structures are exposed to all kinds of environmental influences (actions) in the form of substances, energy, or a combination thereof. According to current design standards in reinforced concrete structures designed to work in aggressive environments corrosion of materials is not allowed. However, there is a large amount of structures that have received corrosion damage at the operation stage. The standards do not contain any guidelines for designing a parameters of the primary protection and repair system for reinforced concrete structures and their elements (durability forecast, repair period, determination of structural and technological parameters of the primary protection or repair systems). Thus, there are tasks of designing the protection of reinforced concrete structures both at the design stage and at the operation stage. At the design stage, it is necessary to determine the structural and technological parameters of the primary protection that ensure the service life of structures or the period between repairs. At the stage of operation, it is necessary to determine the parameters of repair systems which provide the residual service life until the next repair or liquidation of reinforced concrete structures. Our research shows the economic feasibility of designing reinforced concrete structures interacting with aggressive environment, taking into account the kinetics of concrete corrosion. The optimal design methods can be used to obtain the most economical solutions. We have developed quantitative methodology for the design of primary protection of reinforced concrete structures.

Ideas about retrieval of memories are based largely on localization of function inferred after brain damage. On the other hand, communication in the cerebral cortex occurs through an intricate network of connections, suggesting highly distributed circuits. Loss of memory after lesions thus affects not only the damaged area, but also its rich inputs and outputs. The discussion here is based on a structural model of neural communication that can help explain the process of recruiting highly distributed relevant signals for conceptual and sensory recognition and memory. Discussion of cortical communication has traditionally been sensory-centric, based on the flow of information from the periphery to primary sensory areas and beyond, or in the reverse direction. However, visual signals often do not activate areas along a sequential route as predicted by a hierarchical model, exemplified by the fact that some visual signals activate prefrontal areas earlier than some visual association areas. On the other hand, the structural model for connections is based on the fundamental principle of systematic variation in laminar architecture of the cortex and applies to all cortical systems. The structural model is relational: it predicts that laminar-specific connections in the cortex depend on the structural (laminar) relationship between linked areas. Thus, connections that link an area with simpler laminar structure originate mainly – but not exclusively – in the deep layers and terminate mainly in the upper layers of an area with more elaborate laminar structure. In the opposite direction, connections originate in the upper layers and terminate in the middle-deep layers. Because the laminar architecture across cortical areas is graded, so is the distribution of connections within layers. The structural model holds for connections in all cortical systems and diverse species. Moreover, laminar-specific connections as predicted by the structural model terminate within inhibitory microenvironments that also differ by the distribution of functionally distinct classes of inhibitory neurons that can dynamically shift activity among layers and change cortical rhythms. The relational nature of the structural model and predictions of graded patterns of connections thus suggest that distributed areas and layers are recruited dynamically to meet task demands, including recollection of concepts and events.

Biochemical markers for early detection of superficial pressure ulcers

Strengthening steel structures using carbon fiber reinforced polymer (CFRP) has attracted the attention of many researchers in recent years. Most previous research in this area has carried out on the behavior of the steel members without deficiency in bending, shear, and compression. The deficiency in steel structures may be created due to the errors caused by construction, fatigue cracking, and so on. In addition, steel structures may be located under combined loads in their lifetime. This study explored the effect of CFRP strengthening on the structural behaviors of square hollow sections (SHS) steel members having initial deficiencies under combined compressive load and torsional moment. To the author’s knowledge, there is no independent article in this area. In this study, 17 specimens were analyzed. To analyze the specimens, three dimensional (3D) modeling and nonlinear static analysis using ANSYS software were applied. The results indicated that application of CFRP sheets for the strengthening of the deficient hollow steel members under combined compressive load and torsional moment could recover the strength lost due to deficiency, significantly. The maximum recovery percentage of the compressive load and torsional moment capacity of the specimens was 256.00% and 139.96%, respectively.

Electron Beam Induced Deposition (EBID) allows deposition of three-dimensional micro- and nano-structures of conductive and insulating materials on a wide range of substrates. The process is based on the decomposition of molecules of a pre-selected precursor by a focused electron beam. In recent decades EBID of several metals, namely Au, W, Cu and Pt, from different families of precursors, has been achieved and the technique has found some application for small-scale production of laboratory devices and for repair of masks and micro-optoelectronic devices. The weak point of the technique is at present the low purity of the deposited material, caused by metal-organic precursors and by the lack of selectivity of the electron-induced decomposition process. This work is dedicated to EBID of Rh nanostructures from the precursor [RhCl(PF3)2]2. High metal content deposits are expected because the precursor does not contain C atoms and because Rh is one of the less reactive metals. [RhCl(PF3)2]2 as EBID precursor has been characterized by vapor pressure, mass spectrometry and surface residence time measurements. The vapor pressure of 7.5 Pa at room temperature reveals that the precursor is sufficiently volatile for room temperature EBID. The knowledge of the vapor pressure allows also to estimate the number of precursor molecules delivered to the reaction area per unit time. Mass spectrometry measurements allow to know the decomposition path of the precursor under electron impact in the gas phase. The measured spectrum indicates that the molecule decomposes by successive loss of PF3 groups, as confirmed by density functional theory calculations. This is compatible with a high metal content deposit. Residence time measurements show that [RhCl(PF3)2]2 does not decompose on stainless steel surfaces. The measured residence time of 2 ms allows to estimate that the activation energy for desorption of [RhCl(PF3)2]2 on stainless steel is about 0.6 eV and that precursor molecules can travel distances in the micrometer range before being desorbed. EBID structures obtained from [RhCl(PF3)2]2 have been characterized with a wide range of techniques for a better knowledge of the material properties and the deposition process. The deposit morphology has been studied by Transmisssion Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) to characterize the different steps of the deposition process. Crystallographic analysis is carried out by TEM in diffraction mode. Chemical analysis is carried out by Auger Electron Spectroscopy (AES) and Electron Energy Loss Spectroscopy (EELS). Morphological analysis of deposits carried out at different exposure times reveals that the first phase of the growth process, in close proximity to the substrate, is characterized by an increase of the deposit height and the deposit diameter. On the other hand the second phase of the growth process is characterized by increasing height and constant diameter. TEM contrast profiles of dots and Atomic Force Microscopy (AFM) sections of lines have clearly shown that the EBID rate is highest in the center of the beam and decreases in the peripheral regions. Deposition at variable distances from the precursor source allowed to obtain hollow structures, whose morphology reveals that the precursor reaches the reaction area mainly by direct gas phase transport. Structural analysis and TEM revealed that, independently of the deposition conditions, the deposited material is made up of Rh nanocrystals immersed in a lighter amorphous matrix. Chemical analysis by Auger Electron Spectroscopy revealed that, after removal of the C rich contamination layer by Ar ion sputtering, the average composition of the deposits is about: 60 at.% Rh, 20 at.% P, 5 at.% Cl, 7 at.% N, 8 at.% O. The absence of C and the presence of N and O in the deposit bulk have been confirmed by Electron Energy Loss Spectroscopy. This technique allowed also to prove that Rh is dominant also in deposits of sub-micrometer size (not analyzable with AES) and to determine the elemental distribution in the deposit with nanometer resolution. Comparison of the deposit composition and the positive ions detected by mass spectrometry revealed that EBID, compared to low pressure gas phase ionization, involves a higher number of events, i.e. multi-electron decomposition and rearrangements of partially decomposed species.

Researchers in Asia have focused on analyzing the rotational performance of traditional connections based on embedment. The Nuki through-joint has inspired work at the laboratory of wood construction (IBOIS), Ecole Polytechnique Fédérale de Lausanne, to improve the rotational behavior of the multiple tab and slot joint (MTSJ). In this work, through tenon (TT) and closed slot joints were added to initial dovetail and Nejiri arigata joints used for foldedplate structures. The bending performance of the improved MTSJ-TT joint was higher than that of screwed angular connections. Numerical monitoring of the embedded volumes under partial compression on the contact surfaces was used to characterize the directly and indirectly loaded areas. The decay coefficients for the exponential form, which defined the additional length in the indirectly loaded area, were quantified for both single (SC) and double contact (DC). The evolution of these coefficients was also monitored along the angular deformation. Finally, an analytical formulation of the embedded volumes was provided to prepare an analytical model for the MTSJ-TT joint subjected to bending.

Piezocomposites are attracting widespread interest since they can offer greater flexibility and better performances in specific applications with respect to traditional piezoelectric wafers. Design of piezocomposites requires accurate homogenisation models for the prediction of the equivalent electro-mechanical properties. In macro-scale models of structures with piezocomposite transducers, these properties are adopted in order to avoid the complexity of the piezocomposite microstructure. In the case of smart structures the accurate modelling of the actuation and the response of the structure is of primary importance. If classical structural finite elements are not sufficiently accurate, higher order or solid elements should be adopted. Thanks to adaptation or mixed-dimensional methods, it is possible to adopt computationally expensive higher order or solid elements only in some sub-domains of the structure. In this work, the modelling of smart structures equipped with thin piezoelectric transducers is considered in a multi-scale framework. Micromechanical homogenisation models are developed and employed for the prediction of the equivalent properties of piezocomposites. A micromechanical model based on the concept of inclusion is proposed to investigate the influence of the shape of the inclusions, of the constituent materials and of the polarisation on the equivalent properties. It has been found that fibre-shaped inclusions should be considered in order to obtain piezocomposites with strong piezoelectric effect and to have at the same time high direction-dependence. The equivalent properties of Macro Fiber Composites are determined via the Asymptotic Homogenisation Method (AHM) with an analytical solution and with a numerical solution via FEM which takes into account the effect of the electrodes. AHM analytical solution is adopted to investigate the effect of the material properties of the matrix on the overall piezocomposite. Results indicate that low values of the Young's modulus and of the Poisson's ratio yield high directional dependence in the piezoelectric properties. A laminated design with anisotropic layers and a piezocomposite layer is investigated via UFM. A configuration with maximum directional dependence in terms of equivalent piezoelectric strain constants is proposed, whereas maximum directional dependence in terms of piezoelectric stress constants is proved to be not achievable with such a design. Hierarchical finite elements for structural analyses based on a Unified Formulation (UF) by Carrera are developed and coupled via the Arlequin method proposed by Ben Dhia. Solid, plate and beam finite elements for mechanical and for piezoelectric problems are presented. Via UF, higher order and piezoelectric elements can be formulated straightforwardly. These elements are combined in variable kinematic solutions in the Arlequin framework. Higher-order elements are adopted locally where the stress field is three-dimensional, whereas the remaining parts of the structure are modelled with computationally cheap lower-order elements. Two electro-mechanical coupling operator for the Arlequin method in the context of piezoelectric analyses are proposed. Results are validated towards monomodel solutions and three-dimensional analytical and numerical reference solutions. Accurate solutions are obtained reducing the computational costs

Reinvigorated by algorithmic developments, faster hardware and large data sets, machine learning is pervading many aspects of chemistry. We present two examples from our recent studies, one in the area of drug discovery, the other focused on protein spectroscopy. In the first, we consider pharmaceutical lead discovery as active search in a space of labelled graphs [1]. We extend a recent data-driven adaptive Markov chain approach, and evaluate it on a focused drug design problem, where we search for an antagonist of an 훂v integrin, the target protein that belongs to a group of Arg-Gly-Asp integrin receptors. In the second example, we present a novel machine learning protocol that uses a few key structural descriptors to predict amide I IR spectra of proteins and agrees well with experiment [2]. Its transferability enabled us to distinguish protein secondary structures, probe atomic structure variations with temperature, and monitor protein folding.[1] Oglic, D., Oatley, S.A., Macdonald, S.J.F., McInally, T., Garnett, R., Hirst, J.D. & Gartner, T. Active search for computer-aided drug design. Mol. Inf., 2018, 37, 1700130. https://doi.org/10.1002/minf.201700130[2] Ye, S., Zhong, K., Zhang, J., Hu, W., Hirst, J.D., Zhang, G., Mukamel, S., Jiang, J. A transferable machine learning protocol for predicting protein amide-I infrared spectra. J. Am. Chem. Soc., 2020, 142, 19071. https://doi.org/10.1021/jacs.0c06530

NVH (Noise Vibration and Harshness) and crashworthiness are highly significant issues related to lightweighting of vehicle bodies. It is recommended to analyse vehicle NVH issues in early design phases in order to optimize vehicle design performance. The early design phase provides functional requirements and specified weight constraints to the designer for geometry optimization. Using available CAD (Computer Aided Design) data, reduced modelling of vehicle structure can be done to achieve NVH performance. The paper demonstrates and verifies an approach to reduced modelling with structural modal and FE (Finite Element) analysis. It focuses on beam selection techniques for reduced modelling and accuracy achieved in NVH performance prediction by appropriate beam cross-section selection.

Long span cross-rope suspension structure is an innovative structural system evolved from typical Cross-Rope Suspension (CRS) guyed tower, a type of supporting system with short span suspension cable supporting overhead power transmission lines. In mountainous areas, the span length of suspension cable was designed to be extended to hundreds or over one thousand meters, which is applicable for crossing deep valleys. Vortex Induced Vibration (VIV) of overhead power transmission lines was considered to be one of the major factors of its fatigue and service life. In this paper, VIV and its controlling by Stockbridge damper for long span CRS was discussed. Firstly, energy balance method and finite element method for assessing VIV of CRS were presented. An approach of establishing FE model of long span CRS structure with dampers was introduced. The effect of Stockbridge damper for overall vibration of CRS was compared in both theoretical and numerical approaches. Results indicated that vibration characteristics of conductor in long span CRS compared with traditional tower-line system. Secondly, analysis on long span CRS including Stockbridge damper showed additional dampers installed were essential for controlling maximum dynamic bending stresses of conductors at both ends. Moreover, factors, including configuration and mass of Stockbridge damper, span length of suspension cable and conductor and number of spans of conductor, were assessed for further discussion on VIV controlling of long span CRS.

Modeling of automotive Permanent Magnet Synchronous Machines (PMSM)electric drives for Noise, Vibration and Harshness (NVH)assessment involves modeling different components such as electrical machine, power electronics and controller. The usage of transistors for machine control affects the NVH performance, especially within the switching frequency range. Traditionally the method to include power electronics models is to use co-simulation to couple a circuit simulator with an electromagnetic Finite Element (FE)model. However, this approach is computationally expensive. To overcome this limitation, the electromagnetic behavior of the machine can be approximated by using reduced order models. This work compares the co-simulation approach with the system-level model in terms of high frequency NHV behavior. The comparison provides results in terms of time and accuracy.

This study was carried out on all the Etna beech distribution area and consists of a phytosociological analysis. Moreover data relating to various pysiognomical and structural aspects was collected from 12 sample areas selected on the different expositions of the volcano. From the phytosociological analysis it emerged that it is very difficult to define the Etna beech forests syntaxonomically: in most cases it can be seen that they belong to the class Querco-Fagetea, but it is not always possible to identify the association, the alliance and the order. Some communities seem to belong to the Quercetalia pubescentis rather than to the Fagetalia sylvaticae. Other communities do not even belong to the class Querco-Fagetea. These are in fact relict forests surviving in extreme life conditions. They are at the southern limit of its distribution area and are subject to unfavorable environmental conditions: a volcanic substrata, the Mediterranean climate, the high level of man’s intervention. The study of the tree and stump density, stem diameter, basal area, litter cover and litter thickness and seedling density, carried out on 12 sample areas, shows that these forests have a very variable physiognomy and structure. The forests with a more balanced physiognomy and structure are made up of forests with high trunks of different ages. The seedling density, correlated with the litter thickness and cover, was found to be significant in areas located on the east side of Etna, where there are better light conditions and greater rainfall. This study brought to light the presence of a species: Monotropa hypopytis L. not previously reported as having been found on Mt. Etna.