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Highlights • Mechanical stability plays a key role in the effectiveness of external fixators. • Strength and stiffness are the main factors which contributes towards stability. • Modified configurations of linear, circular and hybrid fixators are investigated. • Light weight composite materials are gradually replacing traditional metallic alloys. • Existing research gaps in further optimizing external fixators are identified., External Fixators are a common technique used to treat a variety of issues related to bones, predominantly due to its non-intrusive nature and versatility in terms of form and materials. While it is mainly used to treat open fractures, its other uses include limb lengthening, deformity correction, bone grafting, compression of non-unions and stabilization of dislocations. Its earliest use dates as far back as 400 BCE and has undergone significant improvements, focusing on both customization and optimization. These two aspects highlight the significance of complementing the orthopaedic requirements with engineering knowledge and its applications. Hence, this review paper aims to conduct an examination of recent developments of external fixators with a special focus on its structure, the usage of materials and biomechanical investigations using experimental and numerical techniques. The paper presents the existing level of engineering knowledge with regards to these aspects and identifies research gaps, which can improve the quality of the commonly used external fixators.

ly wrinkles are commonly induced during thermal-mechanical manufacturing process of laminated composite structures or components. Fibre misalignment due to ply wrinkles compromises the structural integrity of a composite structure. The damage criticality can be assessed numerically based on non-destructive testing (NDT) results. Geometrical modelling is usually required and it is time-consuming if complex wrinkles have to be incorporated into the finite element model. This study presents an automated image-based three-dimensional geometric reconstruction method for thick laminates with complex ply wrinkles. The geometry of a thick laminate is reconstructed based on the limited inspection images from the sides of laminates. The two-dimensional geometrical reconstruction of the detected wrinkled plies is done using a multiple Gaussian functions model or linear interpolation, while the intermediate plies are defined by distance-based interpolation. Based on the reconstructed two-dimensional geometries, the three-dimensional ply wrinkles are modeled via an inverse distance weighting interpolation method. To verify the proposed method, a thick glass fibre laminate with artificially induced wrinkles is manufactured and the cross-sectional geometries of the reconstructed model are compared well with and the realistic inspection data. Progressive failure analysis of a two-dimensional and a three-dimensional reconstructed model are compared in terms of damage progression and load versus nominal strain response to highlight the relevance of modelling three-dimensional wrinkles to obtain more accurate and efficient damage criticality assessments.

Ti alloys with lattice structures are garnering more and more attention in the field of bone repair or regeneration due to their superior structural, mechanical, and biological properties. In this study, six types of composite lattice structures with different strut radius that consist of simple cubic (structure A), body-centered cubic (structure B), and edge-centered cubic (structure C) unit cells are designed. The designed structures are firstly simulated and analysed by the finite element (FE) method. Commercially pure Ti (CP–Ti) lattice structures with optimized unit cells and strut radius are then fabricated by selective laser melting (SLM), and the dimensions, microtopography, and mechanical properties are characterised. The results show that among the six types of composite lattice structures, combined BA, CA, and CB structures exhibit smaller maximum von-Mises stress, indicating that these structures have higher strength. Based on the fitting curves of stress/specific surface area versus strut radius, the optimized strut radius of BA, CA, and CB structures is 0.28, 0.23, and 0.30 mm respectively. Their corresponding compressive yield strength and compressive modulus are 42.28, 30.11, and 176.96 MPa, and 4.13, 2.16, and 7.84 GPa, respectively. The CP-Ti with CB unit structure presents a similar strength and compressive modulus to the cortical bone, which makes it a potential candidate for subchondral bone restorations., Graphical abstract Image 1, Highlights • Six types of graded lattice structures with different strut radius are designed and simulated by the FE method. • BA, CA, and CB structures exhibit smaller maximum Von-Mises stress among six type structures. • CP-Ti with CB structures exhibits similar mechanical properties to the cortical bone. • Excellent properties make CP-Ti with CB structures an attractive subchondral bone restoration material.

The thermoforming process is considered among the most promising manufacturing processes for delivering both high quality and volume of thermoplastic composite parts as it exploits all the principal advantages these materials provide. Nevertheless, a series of critical defects may be introduced during the process such as wrinkles, shear deformation of the textile, variation on the thickness as well as geometric distortions and residual stresses which are highly dependent on the material characteristics and the parameters of the process itself. In the present work presented is an analysis of these parameters and their influence on a simple semi-spherical geometry using finite element modelling. The results are also compared with actual experimental results.

Publisher Copyright: © 2022 The Authors Design of modern timber floors is often governed by the vibration serviceability requirements. One way to improve vibration serviceability is through the design of two-way floor systems. In this paper, the behaviour of two-way LVL–concrete composite plates and a plate strip is investigated experimentally, with an emphasis on the performance of proposed dovetail joint for connecting the adjacent LVL panels. The investigations consist of the experimental modal analysis and static load deformation tests, performed under multiple support conditions. The results show a significant two-way action, indicated by about 45% higher fundamental natural frequency when four edges are supported instead of two. The point load deflection in the centre of the plate was reduced of about 9%. Furthermore, a numerical model for two-way TCC plates was developed and results show a wide agreement with the experimental behaviour, except for discrepancies related to deflections on the plate edge. The results from the experimental and numerical investigations indicate that the dovetail joint can produce a stiff connection, such that the LVL layer could be regarded as continuous in the connected direction.

This work studied the interface morphology, microstructure behavior, and mechanical properties of the fabricated trilayered Cu/Al8011/Al1060 composite. In this regard, the roll-casted Cu/Al8011 bimetal was subjected to the hot-roll-bonding process with Al1060 at a thickness reduction of 47%. As a result, the hot-roll-bonding broke the produced nonuniform continuous interface within the copper and aluminum during the roll-casting process. The corresponding interface from the copper side includes Al4Cu9, AlCu, and Al2Cu, respectively. Additionally, SEM-based in-situ tensile deformation revealed that the initiated cracks at the Cu/Al8011 interface propagated into the copper layer that led to its fracture before the aluminum. Based on the FEM results, the effective stress distribution of the Cu strip is not homogeneous at the deformation zone. Moreover, the thickness reduction of the Cu and Al layers was respectively lower and slightly higher than that of the trilayered composite, indicating that plastic deformation mainly occurred at the aluminum matrix due to its large plasticity amount.

Background Transcranial direct current stimulation (tDCS) is widely investigated as a therapeutic tool to enhance cognitive function in older adults with and without neurodegenerative disease. Prior research demonstrates that electric current delivery to the brain can vary significantly across individuals. Quantification of this variability could enable person-specific optimization of tDCS outcomes. This pilot study used machine learning and MRI-derived electric field models to predict working memory improvements as a proof of concept for precision cognitive intervention. Methods Fourteen healthy older adults received 20 minutes of 2 mA tDCS stimulation (F3/F4) during a two-week cognitive training intervention. Participants performed an N-back working memory task pre-/post-intervention. MRI-derived current models were passed through a linear Support Vector Machine (SVM) learning algorithm to characterize crucial tDCS current components (intensity and direction) that induced working memory improvements in tDCS responders versus non-responders. Main results SVM models of tDCS current components had 86% overall accuracy in classifying treatment responders vs. non-responders, with current intensity producing the best overall model differentiating changes in working memory performance. Median current intensity and direction in brain regions near the electrodes were positively related to intervention responses ( r = 0.811 , p 0.001 and r = 0.774 , p = 0.001 ). Conclusions This study provides the first evidence that pattern recognition analyses of MRI-derived tDCS current models can provide individual prognostic classification of tDCS treatment response with 86% accuracy. Individual differences in current intensity and direction play important roles in determining treatment response to tDCS. These findings provide important insights into mechanisms of tDCS response as well as proof of concept for future precision dosing models of tDCS intervention.

Bagan site is one of the most remarkable heritage areas in Myanmar, belonging to the List of UNESCO World Heritage Sites. Besides its cultural importance, Bagan is located in an area with high seismic hazard and the evaluation of the seismic vulnerability is fundamental for the protection of the monuments. This work utilises Loka-Hteik-Pan temple, a typical Buddhist middle-size structure, to evaluate the seismic performance of this kind of monuments, which corresponds to more than 50 around Bagan area. Furthermore, the efficiency a strengthening proposal, composed by two kinds of steel ties, was evaluated, considering the past seismicity of the area and its current hazard defined by the Burmese code. The application of steel ties is recommended for the mitigation of the seismic vulnerability of this kind of Buddhist temple in Bagan, since it corresponds to a compatible and adequate strengthening technique., The authors wish to express gratitude to Myanmar’s Department of Archaeology, National Museum and Library (DoA), Association of Myanmar architects, Professor Mario Santana Quintero and Dr. Erik Costamagna from Carleton University (CAN) for this unique opportunity to collaborate in the preservation of the Loka-Hteik-Pan temple and the provided data, which were fundamental for the seismic analysis. Finally, the authors would like to thank to Professor Su Su and Aung Zaw Min for the supporting given during the in situ tests.

FLASH sintering is a field-assisted technique that allows the densification of ceramics in a few seconds at temperatures significantly lower than those of conventional cycles. There is still discussion among the scientific community about the mechanism behind this sintering process, that has been typically attributed to Joule heating, defect creation and movement or liquid phase assisted sintering. Computational modelling can be a powerful tool in helping to explain and predict this process. Using potassium sodium niobate (KNN) as a case study, a lead-free piezoelectric, this work explores Finite Element Modelling to evaluate the dependence of Joule heating generation and temperature distribution as a function of the cubic particle orientation.

In a tokamak fusion reactor the confinement of the plasma is guaranteed primarily by a series of Toroidal Field Coils (TFC). The TFCs generate a toroidal magnetic field, and must typically withstand large electromagnetic forces. A constant-tension theoretical approach is commonly applied to define an ideal TFC profile, equilibrating in-plane load distributions without shear and bending effects. This paper focuses on the effectiveness of reduced-order models to analyse the TFC mechanical response when also non-ideal shapes are considered. Different beam models are introduced by referring to different treatments of shear and bending effects. A bottom-up homogenisation technique is employed in order to account for the subscale arrangement of TFC components, allowing also to deduce quantitative indications on average localisation effects. The considered beam theories have been specialised to quantify the discrepancies in the macro-micro TFC mechanical response when arc-based approximations are considered instead of the ideal TFC profile. The successful comparison with numerical benchmark solutions, defined by detailed three-dimensional Finite Element models, confirm that beam-like approaches may be considered reliable in a preliminary design stage.

Rotor dynamic force coefficients of gas seals strongly depend on the machine operational conditions. These force coefficients influence the overall dynamical response and modal properties of machines, consequently defining the machine vibration levels. Accurate estimations of the rotor dynamic coefficients are required for designing machines with low vibration amplifications and well-defined stability margins throughout the operational range. Experimental methods applied to test benches are used to validate such force coefficients and they normally rely on (i) the quality of the measurements and (ii) the assumption that the mathematical model is able to capture the whole system dynamics. If relevant dynamical contributions in a system are neglected by the mathematical model, the contribution will erroneously be concluded to originate from the seal being tested. The theoretical and experimental investigation in this paper focuses on quantifying and qualifying the effect of neglected system dynamics modelling on the estimation of seals force coefficients and stability margins. The in-situ identification of seal forces shows that the direct stiffness, cross-coupling stiffness, and direct damping coefficient estimations for a gas seal with high preswirl are statistically significantly affected by the baseline model. Nevertheless, the baseline model leads to small deviations of the seal force coefficient estimations. The prediction accuracy of stability margins is found to be more influenced by the baseline model describing the system dynamics than by the deviations between the seal force coefficient estimations.

Macro-scale crack transverse to the blade length direction is one of the typical damage types observed in the trailing edge regions of wind turbine rotor blades. In this work, the mechanisms of such transverse cracks and their failure characteristics under ultimate static loading are investigated numerically by high-fidelity three-dimensional finite element modelling. Composite failure, foam crushing, and adhesive tunnelling crack are captured in the finite element model. The effects of load directions, material properties of foam cores and adhesives on the formation and development of transverse cracks, as well as longitudinal cracks along the intersection between spar cap and sandwich panels are examined in detail under ultimate static loading. We find that under static loading, the formation of macro-scale transverse cracks is a buckling-driven process. The transverse cracks occur in load directions that can result in severe buckling deformation when the trailing edge is dominated by compressive loading. The buckling resistance can be increased by replacing low stiffness foam cores in sandwich panels with high stiffness ones so that the transverse cracking process is mitigated. The effects of adhesive materials on the buckling resistance are minor and thus the formation of transverse cracks is not affected by the material properties of adhesive materials.

Práce je objasňuje, jak charakter WC-CoCr prášku, zejména velikost WC a matrice a pevnost jejich vzájemné vazby ovlivňuje kluzné třecí vlastnosti a odolnost proti cyklickému impaktnímu zatěžování povlaků deponovaných pomocí HVAF technologie. The present work aimed to clarify how the characteristics of WC-CoCr hardmetal feedstock powders, namely thegrain size of the WC carbides and of the binder and the compressive strength of the sintered aggregates, affect the dry sliding wear and impact resistance of coatings deposited by High Velocity Air-Fuel (HVAF) spraying. Ball-on-Disc tests, which mimic a sliding wear process in the presence of hard asperities as it may occur e.g. in hydraulic seal joints or papermaking components, resulted in mild wear through near-surface microscale plasticflow, the exact nature of which was significantly affected by WC size. Finite element simulations of a singleasperity sliding process indeed showed that large WC grains concentrate contact stresses, thus undergoing very localised deformation. It is experimentally seen that repeated deformation of the carbide grains resulted in their cracking and pull-out. Uniformly distributed, fine carbides allowed the matrix to take on some stress, thus undergoing more homogeneous plastic flow. Block-on-Ring tests elicited adhesive wear as it may happen e.g. in metal-to-metal contacts (e.g. petrochemical valves). This could be effectively restrained by low matrix mean free path. Cyclic impact resistance of coarse-grained coatings was better than that of fine-grained ones, because of better large-scale cohesive strength.

Structural design rules for prestressed cold-formed steel beams, considering both the prestressing and imposed vertical loading stages, are presented herein. In the proposed approach, the cold-formed steel member is designed as a beam-column using linear interaction equations in conjunction with the Direct Strength Method (DSM), while the prestressed cable is designed by ensuring that its tensile capacity is not violated during the two loading stages. In the present paper, the design approach and the failure criteria, which define the permissible design zone for the prestressed system, are first introduced. The suitability of the design recommendations is then assessed by comparing a set of parametric finite element (FE) results for several combinations of prestress levels, beam geometries and cable sizes, with the corresponding design predictions. Finally, following reliability analysis, the implementation of the design recommendations is illustrated through a practical worked example.

The correlation of blade tip timing (BTT) measurements against strain gauge (SG) measurements and finite element (FE) predictions includes a number of uncertainties. One of the main ones is the steady movement of the blades (i.e. change in their mean position and orientation). This causes the sensing positions of the probes relative to a blade tip to deviate from their intended (nominal) positions, leading to deceptive results for the BTT amplitude and the corresponding stress levels. Such movements are caused by variations in static loading conditions (thermal and pressure) associated with changes in the operating speed. A novel method is introduced for the determination of three basic types of blade tip steady movements: axial; lean; untwist. The method relies on linking the shift in the averages of the BTT data to a number of geometrical relations, depending on the type of movement. Not more than two probes (to be placed at different axial positions) are needed to measure all three types of movement. The method is validated by simulations using a novel BTT simulator, and by measurements from both a test rig and real engine tests. The validated results demonstrate the great potential of the method for practical applications.

In closed-loop geothermal systems the underground may freeze and thaw due to intensive heat extraction. Phase change alters the sediments’ mechanical and hydraulic properties and their thermal behaviour, thus affecting the thermal plume propagation and the area of potential changes. By means of a finite element model, this paper evaluates the thermal plume in a particular case study in several conditions, comparing the results obtained when considering or disregarding the freeze-thaw processes by applying a benchmarked plug-in. The model is based on experimental input data. The results show that the frost front propagates significantly faster when phase change occurs.

The local stress and strain are analyzed in a heterogeneous microstructure induced by compression of aluminium rings under nearly full sticking conditions. This analysis is based on characterization of mechanical behavior and microstructure applying three complementary techniques covering multiple length scales: microhardness, electron microscopy (electron backscatter diffraction) and finite element modelling. The findings are underpinned by applying those techniques in an analysis of a homogeneous microstructure induced by compression of hot-extruded aluminium cylinders. The local stress and strain are estimated at 14 different positions in two rings representing large variations in strain. A comparison with the stress and strain in the homogeneously compressed cylinders related to the average spacing between deformation induced low and high angle boundaries, validates the characterization techniques and supports a hypothesis that the microstructure of local regions in a heterogeneous structure evolve in accordance with universal principles and mechanisms established for the evolution of the deformation microstructure of polycrystalline metals.

Manufacturing thin metal features at miniature scale with high precision milling represents some challenges for different applications such as micro moulds, micro channels, micro gears, surgical instruments, etc. In order to enhance the cutting mechanism understanding and optimize the machining of thin features, 3D finite element modeling (FEM) is applied for the micro end-milling process of thin features. In this study, FE model was used to investigate the minimum wall thickness machinable in order to optimize the experimental machining and enhance the quality of the machined features. Wall thickness uniformity and burr formation were evaluated to achieve the finest overall feature quality. Finally, the FEM prediction results were compared against the experimental tests.

Stainless steel is widely used in construction due to its combination of excellent mechanical properties, durability and aesthetics. Towards more sustainable infrastructure, stainless steel is expected be more commonly specified and to feature in more substantial structural applications in the future; this will require larger and typically welded cross-sections. While the structural response of cold-formed stainless steel sections has been extensively studied in the literature, welded sections have received less attention to date. The stability and design of conventionally welded and laser-welded austenitic stainless steel compression members are therefore the focus of the present research. Finite element (FE) models were developed and validated against a total of 59 experiments, covering both conventionally welded and laser-welded columns, for which different residual stress patterns were applied. A subsequent parametric study was carried out, considering a range of cross-section and member geometries. The existing experimental results, together with the numerical data generated herein, were then used to assess the buckling curves given in European, North American and Chinese design standards. Following examination of the data and reliability analysis, new buckling curves were proposed, providing, for the first time, design guidance for laser-welded stainless steel members.

Offshore wind turbines (OWT) are subjected to harsh environmental conditions in addition to the variable service loads. The present study is aimed at performing a realistic fatigue life estimation of the monopile structure using operational service loads recorded by online monitoring systems. Fatigue damage analysis has been conducted at the circumferential weld joints using finite element (FE) method by considering geometrical and material property discontinuities. Global-local modelling of the OWT was performed in as-welded condition to capture the local stress range at the weld toe, which acts as the critical site where cracks are most likely to initiate and propagate. The S-N fatigue design approach and maximum stress range at the weld toe have been used to determine the fatigue crack initiation life in monopiles. The results from the proposed approach show that a realistic life assessment can be made on monopile structures by accounting for the geometrical effects at the circumferential welds.

[EN] Lattice and porous structures have attracted attention in scientific literature due to the development of 3D printers that facilitate their manufacturing. A thorough understanding of the mechanical behaviour of these structures is necessary. In this work, several lattice and porous structures are analysed using the finite element method. Eleven configurations have been studied using periodic boundary conditions, in order to numerically estimate their elastic mechanical properties (Young¿s modulus, shear modulus and Poisson¿s ratio) as a function of the structure porosity. In addition, a tensile fracture test has been modelled to analyse the predicted fracture pattern as well as the stress-strain curve for each structure. It is shown that structures based on spherical holes distributions lead to stiffer structures in tensile and shear conditions. The distribution of cavities has a strong influence on the mechanical behaviour. The square distribution improves stiffness, while the hexagonal distribution improves the shear modulus. Random distributions clearly decrease the stiffness and strength of the structure, although the damage in these structures is more progressive. Therefore, this work provides a comparative study to assess the influence of the lattice topological structure on some mechanical properties of interest in structural engineering, as a function of porosity., The authors gratefully acknowledge the funding support received from the Spanish Ministry of Economy and Competitiveness and the FEDER operation program for funding the projects DPI2017-89197-C2-1-R and DPI2017-89197-C2-2-R

State-of-the-art microelectronic devices, especially power semiconductors, are usually exposed to harsh environmental conditions on the one hand, for example large temperature hubs, and to challenging application conditions on the other hand, such as pulsed current applications. Mechanical robustness and reliability have become more and more challenging in recent years. Along with a continuous shrinkage of dimensions, thin film materials are stacked and micro-structured for optimized performance of such devices. Major risks for device reliability can result from loss of adhesion at interfaces of these stacked thin films. Therefore, it is crucial for such devices to feature perfect initial adhesion of the said thin film layers, even after exposure to thermal treatment or in presence of intrinsic stress. In order to validate device robustness, the quality of interface adhesion between isolating and metallization layers should be carefully assessed. A particular focus is set on interfaces between the following, widely employed materials: Cu, Al, WTi, BPSG, SiN etc. Robustness by design at critical interfaces has relied more and more on advanced Finite Element Modelling (FEM) methods in recent years. This includes explicit modelling of adhesion and delamination. Accurate parameters that describe interfacial adhesion - critical adhesion energies in tensile and shear mode - need to be extracted by means of suitable experiments on tailored test vehicles. FEM is able in turn to verify the existing theoretical framework about extracting adhesion energies from experiments, given that the analytical models are often phenomenological and based on simplified assumptions. Experimentally, Nanoindentation on designed multi-layer thin film stacks has proven to be a suitable method to investigate inter-layer adhesion strength on test vehicle basis. We focused on layered stacks of tungsten‑titanium (WTi) and Boron-Phosphorous-Silicate Glass (BPSG) on Silicon substrates. The WTi layer exhibits compressive stress tailored by means of deposition. When an axis-symmetric conical or spherical indenter penetrates the WTi film, buckles around the indenter imprint arise upon loading and may propagate during unloading. Buckle geometry is measured by means of focused ion beam and Scanning Electron Microscopy. Afterwards the critical adhesion energies can be determined by existing analytical models. Combining experimental and simulation methods one may follow a Physics-of-Failure approach and assess the failure mechanisms related to thin film delamination and interface fracture. With experimental results on hand, we implemented an FE model of the same multi-layer system. Initiation and propagation of delamination was modeled by means of a Cohesive Zone Model (CZM) based on a cohesive surface contact approach. The model incorporates elastic-plastic deformation as well as intrinsic stresses of all layers, including the substrate. Following an inverse FEM approach, we reproduced the size of the delaminated area and load-displacement curves of the indenter by recursively readjusting Cohesive Zone parameters. The so-obtained adhesion parameters and modelling can be used elsewhere in delamination risk assessments of industrial semiconductor applications. This approach also gives insight into the accuracy of the formulae used for calculating the total energy release rate and extracting the further relevant parameters without the need to rely on phenomenological assumptions.

Highlights • Daily delivered dose calculated and accumulated to rectal wall. • Voxel-resolution dose accumulation via finite element modelling. • Rectal subregions at risk identified for four toxicity endpoints. • Toxicity associations improved using spatial features of accumulated delivered dose., Background and Purpose Associations between dose and rectal toxicity in prostate radiotherapy are generally poorly understood. Evaluating spatial dose distributions to the rectal wall (RW) may lead to improvements in dose-toxicity modelling by incorporating geometric information, masked by dose-volume histograms. Furthermore, predictive power may be strengthened by incorporating the effects of interfraction motion into delivered dose calculations. Here we interrogate 3D dose distributions for patients with and without toxicity to identify rectal subregions at risk (SRR), and compare the discriminatory ability of planned and delivered dose. Material and Methods Daily delivered dose to the rectum was calculated using image guidance scans, and accumulated at the voxel level using biomechanical finite element modelling. SRRs were statistically determined for rectal bleeding, proctitis, faecal incontinence and stool frequency from a training set (n = 139), and tested on a validation set (n = 47). Results SRR patterns differed per endpoint. Analysing dose to SRRs improved discriminative ability with respect to the full RW for three of four endpoints. Training set AUC and OR analysis produced stronger toxicity associations from accumulated dose than planned dose. For rectal bleeding in particular, accumulated dose to the SRR (AUC 0.76) improved upon dose-toxicity associations derived from planned dose to the RW (AUC 0.63). However, validation results could not be considered significant. Conclusions Voxel-level analysis of dose to the RW revealed SRRs associated with rectal toxicity, suggesting non-homogeneous intra-organ radiosensitivity. Incorporating spatial features of accumulated delivered dose improved dose-toxicity associations. This may be an important tool for adaptive radiotherapy in the future.

In current structural design specifications, such as EN 1993-1-1 for steel and EN 1993-1-4 for stainless steel, the stability of members is typically assessed through the use of buckling curves, which consider the influence of initial geometric imperfections and residual stresses. An alternative, more direct, approach is to perform either an elastic or inelastic second-order analysis of the member or structure with imperfections. For modelling convenience, so-called ‘equivalent’ imperfections are typically utilised, which consider the combined influence of both geometric imperfections and residual stresses. Equivalent imperfections for the design of columns and beams by second-order elastic analysis, also referred to as geometrically nonlinear analysis with imperfection (GNIA), are provided in the current design specifications. For columns, equivalent imperfections for design by second-order inelastic analysis, also referred to as geometrically and materially nonlinear analysis with imperfections (GMNIA), were recently developed, but for beams that are susceptible to lateral-torsional buckling (LTB), there are currently no appropriate provisions. The aim of this study is therefore to develop equivalent imperfections for use in out-of-plane stability design of steel and stainless steel members by GMNIA. The proposals are calibrated against the results of benchmark finite element (FE) simulations performed on a large number of steel and stainless steel members with geometric imperfections and residual stresses subjected to major axis bending. Two proposals for equivalent imperfection amplitudes are developed: (1) e0,mod, for use with eigenmode-affine imperfections and (2) e0,bow, for use with sinusoidal bow imperfections. The latter is applied solely in the lateral direction and as a summation of a half-sine wave and a full-sine wave. Relative to the traditional Eurocode design calculations, employing the proposed LTB imperfections in GMNIA provides generally more accurate member resistance predictions, while remaining safe-sided relative to the benchmark FE results. The reliability of the design provisions is demonstrated through statistical analysis, where it is shown that partial safety factors of 1.0 for steel and 1.1 for stainless steel can be safely adopted.

A novel approach for creating highly detailed finite element models of wind turbine blades is presented. The approach is implemented as a software tool which handles all the different steps of the model creation process. The novel approach considers the blade to consist of a collection of parametric pre-defined blocks. This allows wind turbine blade models consisting of shell elements, solid elements or combinations to be created. By including the tools to accurately partition the outer mold layer, create the required offset surfaces and calculate accurate element-wise material orientations, a high level of detail and fidelity can be achieved.

A parametric study is presented which employs a new anisotropic constitutive law in order to study the influence of anisotropic plasticity on the deformation field of the ASymmetric Rolling (ASR) process. A version of the FACET method is presented where an analytical yield function is restricted to the subspace of the stress and strain rate space relevant for 2D FEA, but can still accurately reproduce the plastic anisotropy of an underlying Crystal Plasticity (CP) model. The influence of anisotropy on the deformation field and corresponding texture evolution is examined in terms of the changes in texture component volume fractions and formation of texture gradients. It is found that a material with the anisotropy of a sharp cold rolled aluminium alloy is more beneficial than that of a recrystallised hot rolled aluminium alloy, and this influence of anisotropy suggests that ASR may be best carried out in the latest stages of cold rolling. ispartof: Comptes Rendus Mecanique vol:346 issue:8 pages:724-742 status: published

The Sorgenfrei-Tornquist Zone (STZ) is the northwestern segment of the Tornquist Zone and extends from Bornholm across the Baltic Sea and northern Denmark into the North Sea. It represents a major lithospheric structure with a significant increase in lithosphere thickness from south to north. A series of meter-scale normal faults and soft-sediment deformation structures (SSDS) are developed in Lateglacial marine and lacustrine sediments, which are exposed along the Lønstrup Klint cliff at the North Sea coast of northern Denmark. These deformed deposits occur in the local Nørre Lyngby basin that forms part of the STZ. Most of the SSDS are postdepositional, implying major tectonic activity between the Allerød and Younger Dryas (∼14 ka to 12 ka). The occurrence of some syn- and metadepositional SSDS point to an onset of tectonic activity at around 14.5 ka. The formation of normal faults is probably the effect of neotectonic movements along the Børglum fault, which represents the northern boundary fault of the STZ in the study area. The narrow and elongated Nørre Lyngby basin can be interpreted as a strike-slip basin that developed due to right-lateral movements at the Børglum fault. As indicated by the SSDS, these movements were most likely accompanied by earthquake(s). Based on the association of SSDS these earthquake(s) had magnitudes of at least Ms ≥ 4.2 or even up to magnitude ∼ 7 as indicated by a fault with 3 m displacement. The outcrop data are supported by a topographic analysis of the terrain that points to a strong impact from the fault activity on the topography, characterized by a highly regular erosional pattern, the evolution of fault-parallel sag ponds and a potential fault scarp with a height of 1–2 m. With finite-element simulations, we test the impact of Late Pleistocene (Weichselian) glaciation-induced Coulomb stress change on the reactivation potential of the Børglum fault. The numerical simulations of deglaciation-related lithospheric stress build-up additionally support that this neotectonic activity occurred between ∼14.5 and 12 ka and was controlled by stress changes that were induced by the decay of the Scandinavian ice sheet. In the Holocene, the stress field in the study area thus changed from GIA-controlled to a stress field that is determined by plate tectonic forces. Comparable observations were described from the central STZ in the Kattegat area and the southeastern end of the STZ near Bornholm. We therefore interpret the entire STZ as a structure where glacially induced faulting very likely occurred in Lateglacial times. The fault reactivation was associated with the formation of small fault-bound basins that provided accommodation space for Lateglacial to Holocene marine and freshwater sediments. © 2018 The Authors

High speed image analysis of experimental lightning strike testing on composite specimens has demonstrated complex time-dependent arc attachment behaviour. To date simulation studies of lightning strike direct effects on composite materials have overlooked or idealised the observed arc attachment behaviour. This is significant as these preceding studies have also demonstrated joule (resistive) heating is a major contributor to composite material damage and thus the application of the current load is critically important. The objective of this paper is to quantify how arc attachment behaviour influences the prediction of composite specimen thermal loading during a simulated lightning strike test. This is achieved through a simulation study modelling experimental arc attachment behaviours referenced in the literature. The simulation results are compared with measured test specimen damage. The results quantify for the first time the significance of arc attachment behaviour, demonstrating how realistic representation of arc expansion and arc movement can alter the predicted thermal loading and generate thermal damage patterns comparable to measured experimental damage.

This paper proposes a new joining by forming process for fixing longitudinally in position two metal sheets (or plates) perpendicular to one another, at room temperature. The proposed process employs a counterbored variant of the ‘mortise-and-tenon’ joint that eliminates the protrusion of the tenon beyond the mortise after mechanical locking by plastic deformation. The presentation draws from the workability limits and material stress-strain characterization to validation by joining and destructive pull-out testing. Results demonstrate the effectiveness of the new proposed process for producing flat joint surfaces, which are advantageous over typical ‘mortise-and-tenon’ protruded surfaces in most applications.

The instability behaviour of eccentrically loaded circular masonry columns is investigated. Two approaches are considered for the analysis. One is based on a semi-analytical formulation of the relevant boundary-value problem for a no-tension material response; the other employs a plastic-damage-contact constitutive model, the CraftS model, to capture the complex microstructural behaviour of the material. The latter has been implemented in the finite element program LUSAS and has been already successfully employed to describe progressive instability in eccentrically loaded brickwork wallettes of rectangular cross section. Equilibrium paths and limit load estimates are computed for both analysis approaches for a range of column aspect ratios and load eccentricities. It is shown that the type of material response becomes less important for specimens with height-to-diameter aspect ratios greater than 7.5 and for loads applied to points in the kernel of the cross section, while for higher eccentricities the presence of a tensile strength increases considerably the limit load. The damage evolution predicted by the models is also investigated for selected cases, showing that the formulation based on the no-tension material is able to capture with good agreement the damaged zone of the column for loads with low eccentricities. For the same type of loading, a useful design formula is provided.

Glass Fibre Reinforced Polymer (GFRP) composite wrap has become an effective repair system for deteriorated structural columns. It is essential to provide an infill material in the gap between the retrofitted column and the GFRP wrap. So, the properties of the infill material can significantly influence the contribution of these wraps and thus, can affect the overall performance of the retrofitted structure. However, the research on the effect of GFRP confinement on infill materials with various properties is still limited. This study explores the effectiveness of the GFRP wrapping system and its contribution to the axial compression behaviour of concrete, grout and epoxy infill materials. A total of 18 unconfined and GFRP-wrapped cylindrical columns were cast and tested under concentric axial compression loading. A finite element (FE) modelling was implemented using ABAQUS software to analyse the compression behaviour of GFRP-wrapped infill materials. The experimental results demonstrated that the confinement effect of the GFRP wrapping system is highly influenced by the properties of the infill material. The compressive strength and modulus of elasticity significantly increased due to GFRP wrapping by 149 % and 77 %, respectively for concrete infill, and by 40 % and 72 %, respectively for grout infill whereas negligible confinement efficiency observed in wrapped epoxy infill. The FE analyses showed a good correlation with the experimental results in predicting the overall compressive behaviour of the various infill materials. This study demonstrates valuable insights on the confinement effect of GFRP wraps in the repair of columns involving infill materials which therefore could be employed to better understand the overall behaviour of columns retrofitted with GFRP wrapping systems.

The development of accurate structural modelling techniques is required to promote the use of timber as a renewable alternative to other structural materials. Due to their remarkable influence on the global behaviour of a timber structure, an accurate description of the performance of structural connections is needed. Particularly in the case of moment transmitting beam-to-column connections with dowel-type fasteners, such properties are difficult to obtain experimentally. This paper develops a finite element (FE) model that simulates the behaviour of these connections under quasi-static loading, with a focus on the estimation of rotational stiffness and load distribution among the dowels. The model is validated against short-term laboratory tests. Resulting friction between timber members due to the installation procedure must be considered, as it greatly influences the rotational response. Besides, non-linear behaviour of timber and a softened contact parameter have been implemented, and their influence on the FE model validation process is demonstrated.

With dynamic behaviour different from that of traditional discretely supported tracks, continuously supported embedded rail systems (ERSs) have been increasingly used in railway bridges, level crossings, trams, and high-speed lines. However, studies on ERSs have been limited, and none of them have addressed the wheel-rail impact-induced dynamic response, although wheel-rail impact is a main cause of ERS degradation. This paper studies, numerically and experimentally, the wheel-rail impact at an insulated rail joint (IRJ) used in the ERS. As a weak spot of the track, the IRJ results in discontinuities in the track support stiffness and wheel-rail contact geometry. This study first develops an explicit finite element model to simulate the vibration responses of the IRJ in the ERS when excited by a hammer and passing wheel loads. The simulated dynamic behaviours (represented by the hammer-excitation frequency response function) at a frequency up to 5 kHz and a wheel-rail impact vibration frequency up to 10 kHz are then validated with a field hammer test and a train pass-by measurement, respectively. Both the experimental study and numerical modelling reveals that the major frequencies of the impact vibration at the IRJ in the ERS depend mainly on geometric irregularities in the IRJ region and the train speed, rather than on the resonances of the track structure, as in the case of the discretely supported IRJ. This finding is meaningful to the engineering practice because it indicates a continuously supported IRJ in the ERS is more impact resistant, especially when the IRJ geometry is adequately maintained, e.g. by timely grinding.

Hollow-core precast concrete slabs are now being used in modular building construction to minimise the volume of concrete and to reduce their weight. However, the existence of voids in hollow-core concrete slabs makes the slab prone to premature failure. Recently, a composite reinforcing systems (CRS) has been developed to support the void in precast slabs. In this paper, the bending behaviour of a composite slab made from precast concrete with steel and CRS reinforcement was investigated. Four-point bending test was conducted for six precast slabs (solid, hollow without CRS, hollow with 2, 3 and 4 CRS, and hollow with 3 epoxy coated CRS) to comprehend the structural performance of this new precast concrete construction system. A non-linear finite element modelling was also conducted to gain an insight understanding the behaviour of the internal components of slab. The results showed that the CRS can stabilise the hollow core and act as additional reinforcement which enhances the load bearing capacity by 112% and the initial stiffness of the slabs by24%. Refereed/Peer-reviewed

This study presents a hybrid method based on artificial neural network (ANN) and micro-mechanics for the failure prediction of IM7/8552 unidirectional (UD) composite lamina under triaxial loading. The ANN is trained offline by numerical data from a high-fidelity micromechanics-based representative volume element (RVE) model using the finite element method (FEM). The RVE adopts identified constituent parameters from inverse analysis and calibrated interface strengths form uniaxial and biaxial tests. A hybrid loading strategy is proposed for the RVE under triaxial loading to obtain the failure points on sliced surfaces whilst maintaining the constant stress at different surfaces. It has been found that the ANN algorithm is robust in the failure prediction of the UD lamina when subjected to different triaxial loading conditions, with over 97.5% accuracy being achieved by the shallow ANN model , where only two hidden layers and 560 samples are used. The predicted 3D failure surface based on trained ANN model has an elliptical paraboloid shape and shows an extremely high strength in biaxial compression. The approach could be used to inform the modification of existing failure criteria and to propose ANN-based failure criteria.

The strain rate dislocation behavior in carbon nanotubes (CNTs) reinforcing aluminum is described through an explicit, analytic grain interior/grain boundary affected zone (GI/GBAZ) composite model. The model describes how the mechanical behavior of metal matrix composites, under different strain rates, depends on the different response of dislocation accommodation in GBAZ and GI which in turn origins from geometrically necessary dislocation (GNDs) and statistically stored dislocation (SSDs), respectively. An in-situ tracking of the strain rate dependent strain distribution and computational simulations were jointly employed to provide insight into the dislocation behavior. Given the different distributions of dislocations in the ultrafine grains of CNT/Al composites, mechanical response depends on how dislocations arrange in GI and GBAZ. Results from experiments and simulations, based on Crystal plasticity (CP) finite element modelling (FEM), clarified that the dominant deformation mechanism of the CNT/Al composite is strain rate dependent. The results show that the GI/GBAZ model can successfully reveal the dislocation dependency of strain rate. The results might shed some light on understanding of strain rate dependent dislocation behavior in metal matrix composites reinforced with nanocarbon structures such as CNTs.

Understanding properly electrochemical nucleation and growth phenomena is crucial for a wide range of highly active research and technological fields. In this paper, we use a Finite Element Method to solve a Time Dependent Multi-ion Transport and Reaction Model (FEM-TD-MITReM) to report on the growth of an isolated nucleus. This approach takes into account the transport driven by diffusion and migration of all species in the electrolyte together with the electrochemical reactions at the electrode boundary. The numerical results show that, a nucleus which is smaller than a critical size, even after the application of a sufficiently large overpotential, always starts to grow under kinetic control. In later stages, a transition from kinetic to mixed and to diffusion control takes place. The corresponding transition times between growth regimes have been identified and are found to be inversely proportional to the concentration of active species and to decrease exponentially with overpotential and linearly with the initial nucleus size. Both effects are more pronounced in the transition from kinetic to mixed control. Interestingly, under the conditions used for the current simulations, typical from experimental nucleation and growth studies, a few seconds are needed to achieve diffusion control. This implies that, although experiments under similar conditions are normally described by growth under diffusion control, such theory is only valid for sufficiently large active surface. As a consequence, kinetic and mixed control regimes cannot be neglected for a proper interpretation of electrochemical nucleation and growth phenomena. These findings provide a significant benchmark for correctly describing, modelling and interpreting the early stages of electrochemical growth without making assumptions on the diffusional or kinetic limitations.

Adaptive structures constituted by composites and smart materials is a remarkable engineering combination that join together the already known composites’ advantages and the possibility of actively control the mechanical response of a structure. These versatile structures are able to react and interact with their surrounding environments, continuously, to accomplish specific objectives. In this work, the main objective is to study, model and predict the mechanical behaviour of adaptive structures by programming the finite element method and optimization algorithms based on micro-bats’ echolocation capacity. An integrated symbolic-numerical-graphical package devoted to the analysis of plate/beam-type structures and its meta-heuristic optimization is implemented, with capabilities of simulating active multilayered structures, constituted by a variable number of different material models. Graded mixtures of piezoelectric particles and non-active materials are also modelled along the structures’ length direction. A set of illustrative case studies are performed, for different types of structures and materials and the results obtained are discussed and conclusions are drawn.

Highlights • A finite element model was developed to calculate micromotion of ankle implants. • Both optimally-positioned and malpositioned cases were considered. • Fixation nearer to the joint line relying on plural pegs improved implant stability. • Gaps between the implant and bone greatly increased micromotion and bone strains., Implant loosening – commonly linked with elevated initial micromotion – is the primary indication for total ankle replacement (TAR) revision. Finite element modelling has not been used to assess micromotion of TAR implants; additionally, the biomechanical consequences of TAR malpositioning – previously linked with higher failure rates – remain unexplored. The aim of this study was to estimate implant-bone micromotion and peri-implant bone strains for optimally positioned and malpositioned TAR prostheses, and thereby identify fixation features and malpositioning scenarios increasing the risk of loosening. Finite element models simulating three of the most commonly used TAR devices (BOX®, Mobility® and Salto®) implanted into the tibia/talus and subjected to physiological loads were developed. Mobility and Salto demonstrated the largest micromotion of all tibial and talar components, respectively. Any malpositioning of the implant creating a gap between it and the bone resulted in a considerable increase in micromotion and bone strains. It was concluded that better primary stability can be achieved through fixation nearer to the joint line and/or while relying on more than a single peg. Incomplete seating on the bone may result in considerably elevated implant-bone micromotion and bone strains, thereby increasing the risk for TAR failure.

The intervertebral disc (IVD) is a complex structure responsible for distributing compressive loading to adjacent vertebrae and allowing the vertebral column to bend and twist. To study the mechanical behaviour of individual components of the IVD, it is common for specimens to be dissected away from their surrounding tissues for mechanical testing. However, disrupting the continuity of the IVD to obtain material properties of each component separately may result in erroneous values. In this study, an inverse finite element (FE) modelling optimisation algorithm has been used to obtain material properties of the IVD across strain rates, therefore bypassing the need to harvest individual samples of each component. Uniaxial compression was applied to ten fresh-frozen bovine intervertebral discs at strain rates of 10-3–1/s. The experimental data were fed into the inverse FE optimisation algorithm and each experiment was simulated using the subject specific FE model of the respective specimen. A sensitivity analysis revealed that the IVD's response was most dependent upon the Young's modulus (YM) of the fibre bundles and therefore this was chosen to be the parameter to optimise. Based on the obtained YM values for each test corresponding to a different strain rate (View the MathML source), the following relationship was derived:View the MathML source. These properties can be used in finite element models of the IVD that aim to simulate spinal biomechanics across loading rates.