Search

Tidal turbine infrastructure is currently in the large-scale prototype and short-term demonstration phase. However, the immediate requirement is to develop materials, processes and long-term life predictive facilities for tidal turbine plant that has decades of operational lifetime requirements. Computational modelling is a key tool to interpret the experimental data, understand the relevant mechanisms and provide a predictive capability for the performance of aged components for industries. The goal of this paper is a prediction of the long-term life of marine-based glass/epoxy and carbon/epoxy composite laminates aged in artificial seawater with 3.5% salinity based on Arrhenius degradation theory and tensile strength retention over 180 days ageing at room temperature and 60°C. Three different analytical models (linear and exponential) were implemented to calculate time shift factors and corresponding life in a real marine environment. Additionally, multi-scale modelling has been implemented via a representative volume element approach for square and hexagonal cells, and two-step homogenization of textile composites in accordance with nanoindentation testing for matrix/resin cells and fibre constraint cells after 90 days of immersion in saltwater. In general, the multi-scale modelling in ABAQUS and TexGen4SC was able to approximate (with about 10% difference) the mechanical properties of dry and aged composite laminates. [ABSTRACT FROM AUTHOR]

Abstract Composites reinforced with braided textiles exhibit high structural stability and excellent damage tolerance, making them very attractive for defence, aerospace, automotive and energy industries. Considering the real-life service environment, it is crucial to study a dynamic response of a composite structure and its energy-dissipation ability, especially under repeated low-velocity impacts. So, a series of drop-weight tests were carried out followed by X-ray computed micro-tomography to characterize damage morphology of braided composite specimens. Meanwhile, a multi-scale computational approach was explored and implemented as a user-defined-material subroutine (VUMAT) for ABAQUS/Explicit to capture main damage modes of a braided textile composite, while its delamination was modelled by employing cohesive-zone elements. Load- and energy-time curves were obtained both experimentally and numerically. The predicted levels of peak forces and absorbed energy were found to agree with the experimental data. An extent of delamination and damage accumulation in the braided composite was predicted numerically and analysed; it was found that material responses to repeated impacts had two types depending on the level of normalised impact energy. The presented modelling capability could contribute to design of braided composite structures for various applications. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a test method of twin-fibre single-lap joint bonded with a micro-droplet of epoxy and subjected to tensile loading for determining fibre-matrix interfacial shear strength (IFSS). Twenty-five carbon fibre (CF)/epoxy specimens and fifty-six carbon nanotube (CNT)-grafted CF/epoxy specimens were prepared and tested. The average IFSS measured for specimens with a mean grafting density of 10.9, 25.8, 35.1 or 58.8 CNTs per μm2 can be improved by 51%, 101%, 155% and 273% (223%) respectively comparing to that without grafted CNTs. A multi-scale analytical model that relates micro-scale IFSS to nanoscale CNT grafting strength and density is developed and then used for predicting the IFSS of CNT-CF reinforced composites. There exists a good correlation between the measured and predicted IFSS of specimens with different grafting densities. [ABSTRACT FROM AUTHOR]

Advanced fibre composite materials are often used for weight-efficient thin-walled designs, making a plate-based modelling approach suitable for their structural assessment. However, as the sub-structural geometrical features of these materials govern much of their behaviour, a multi-scale approach is necessary. A related challenge, however, is that the in-plane variation of these sub-structural features may be much larger than the total thickness of the material, whereby tailored homogenisation techniques for shell elements are needed. Existing frameworks for plate- and shell-based homogenisation are typically developed using second-order homogenisation in combination with the Hill–Mandel (macro-homogeneity) condition. However, it has been reported in the literature that this approach can lead to kinematic inconsistencies in the macro- to micro-scale transition. One inconsistency that is commonly reported, is the inability to correctly account for the macro-scale transverse shear behaviour on the sub-scale level. In this contribution, we show how the method of Variationally Consistent Homogenisation (VCH) can be used to develop a homogenisation framework for Reissner-Mindlin plate elements, which guarantees kinematically consistent prolongation and homogenisation operations. The homogenisation approach is demonstrated in four numerical examples, where it is shown that the method accurately homogenise the effective sectional plate stiffnesses of homogeneous and heterogeneous sub-structures. [ABSTRACT FROM AUTHOR]

Abstract Prosthetic heart valves deployed in the left heart (aortic and mitral) are subjected to harsh hemodynamical conditions. Most of the tissue engineered heart valves have been developed for the low pressure pulmonary position because of the difficulties in fabricating a mechanically strong valve, able to withstand the systemic circulation. This necessitates the use of reinforcing scaffolds, resulting in a tissue-engineered textile reinforced tubular aortic heart valve. Therefore, to better design these implants, material behaviour of the composite, valve kinematics and its hemodynamical response need to be evaluated. Experimental assessment can be immensely time consuming and expensive, paving way for numerical studies. In this work, the material properties obtained using the previously proposed multi-scale numerical method for textile composites was evaluated for its accuracy. An in silico immersed boundary (IB) fluid structure interaction (FSI) simulation emulating the in vitro experiment was set-up to evaluate and compare the geometric orifice area and flow rate for one beat cycle. Results from the in silico FSI simulation were found to be in good coherence with the in vitro test during the systolic phase, while mean deviation of approximately 9% was observed during the diastolic phase of a beat cycle. Merits and demerits of the in silico IB-FSI method for the presented case study has been discussed with the advantages outweighing the drawbacks, indicating the potential towards an effective use of this framework in the development and analysis of heart valves. [ABSTRACT FROM AUTHOR]

Self-healing prostheses that can replace damaged native organs, like tissue-engineered valvular implants, are under development. Engineered soft tissues can greatly benefit from reinforcements to attain mechanical properties comparable with the native organs. Complex interactions at various levels between the reinforcements and engineered tissue make the selection of the most optimized reinforcing scaffold difficult and subject to an enormous amount of experimental evaluation. Hence, to reduce the extent of prototyping, it is prudent to develop a simulation based development approach. In the example of valvular prostheses which are textile-tissue composites, we test a simulation approach based on multi-scale modelling, often used for evaluating/predicting the behaviour of composites. A textile scaffold embedded in silicone is used as a replacement for the textile-tissue composite. The modelling technique provides a good correlation with the experimental results, laying the pathway to further study the complex interaction between the engineered tissue and the reinforcing scaffold. This method can further form the basis for evaluating the mechanical compatibility of scaffolds and their interaction with engineered tissues at various scales and levels. [ABSTRACT FROM AUTHOR]

The advent of new more complex classes of strongly heterogeneous materials, such as 3D woven composites, introduces new challenges for well-established finite element multiscale modelling approaches. These materials' internal architecture dominates the local stress concentrations, damage initiation and damage progression. Additionally, the material loses periodicity during manufacture and conventional homogenization approaches become inapplicable. In this paper, a multiscale modelling approach based on domain decomposition and homogenization is proposed to model the mechanical behaviour of these materials. The proposed model formulates a set of displacement and force compatibility conditions between the various subdomains. The compatibility conditions are formulated by limiting the set of kinematically admissible solutions on the smaller scales in order to satisfy the larger scale basis functions at the interfaces. The different subdomains are solved alongside the compatibility conditions in an iterative process. The proposed multiscale framework reduces the stress artefacts on the subdomains' boundaries. This feature allows the 3D woven material internal architecture represented at the smaller scales to control the structural response at the global scale. Additionally, this framework allows for selective application of nonlinear material models to the subdomains of interest through its ability to redistribute stresses across the subdomains boundaries. [ABSTRACT FROM AUTHOR]

In the paper numerical simulation of the foamed metal structures using numerical homogenization algorithm is prescribed. The first, numerical model of heterogeneous porous simplified structures of typical foamed metal, based on the FEM was built and material parameters (coefficients of elasticity matrix of the considered structure) were determined with use of numerical homogenization algorithm. In the work the different RVE models of structure were created and their properties were compared at different relative density, different numbers and the size and structure of the arrangement of voids. Finally, obtained results were used in modeling of typical elements made from foam metals structures - sandwich structures and hollow profiles filling with metal foam. Three point bending test was performed for sandwich structures. Simulation were done for different dimensions of cladding and core. Additionally, the torsion test was performed for profiles filling with metal foam. Typical behavior for torsion was observed. [ABSTRACT FROM AUTHOR]

Porosity is a major manufacturing defect which affects the matrix dominate properties of continuous fibre composites, in particular the transverse strength. The simulation of porosity allows for predictions on the reduction of strength to be made, however, there is a trade-off between accuracy and computational efficiency. The multi-scale modelling approach presented here allows for accurate 3-dimensional geometry data of voids to be used. This is accomplished by first evaluating the effect the porosity has on degrading the matrix then subsequently, by using a representative unit cell, ply level strength can be predicted. The model is validated against empirical tensile and compressive testing of unidirectional autoclave cured prepreg with strong correlation. The approach allows for a reduction in overengineered structures by predicting accurate material properties for a given porosity generation. [ABSTRACT FROM AUTHOR]

Traditional carbon-steel armour wires pose limitations ( e.g. long spans, weight reduction, corrosion and fatigue) for flexible risers to operate in demanding and deeper water environments. In this context, an alternative to carbon-steel tensile armour wires is proposed recently by the authors (Gautam et al ., 2016), comprising of hexagonally packed polymer composite rods with uni-directional fibres and an over-braided ( i.e. bi-axial braid with high performance fibres) sleeve. These hybrid composite wires offer opportunities to tailor their mechanical properties by varying the geometrical ( e.g. rod diameter, packing) and processing parameters ( e.g. material selection, braid pattern) involved. In order to understand the mechanical behaviour of these hybrid composite armour wires, this paper presents a multi-scale model developed by using a combined analytical-computational approach. The multi-scale model is developed to predict the torsional and flexural behaviour of the hybrid composite wires; and the role of over-braid structural parameters, pre-tension and internal friction are investigated. The behaviour of the multiscale model is found to be in good agreement with the experimentally observed behaviour. After validating the multi-scale model with the experimental data available for specific configurations, parametric studies are conducted on the torsional and flexural behaviour of the hybrid composite wires to study the role of internal friction between un-bonded components and the braid tow tension in the over-braided sleeves. [ABSTRACT FROM AUTHOR]

In this paper we investigate micro–macro mechanical relations in Palmetto wood, a natural composite, by means of a computational homogenisation-based multi-scale modeling approach. The homogenisation procedure is solved sequentially at multiple length scales by following a bottom-up approach. The proposed strategy consists of homogenising the three length-scales by means of representative volume elements of material. The resulting effective macroscopic properties allow us to compute the mechanical response of individual macro-fibres and bulk wood specimens by means of a standard finite element procedure. The numerical predictions are compared successfully with experimental measurements. Following the validation, a parametric study is performed to investigate the micro–macro relations in Palmetto wood. The influence of several micro-structural features present at different length scales are investigated, such as the cellulose content and its crystallinity, the microfibril angle, the cell-wall thickness of micro-fibres, and the porosity of macro-fibres and their surrounding matrix, among others. The effects of such microscopic parameters are investigated on the Young’s modulus and density of Palmetto bulk wood. These results show that the present strategy can pave the way for further studies on complex microstructure–property relationships existing in different wood species, and on the possible development of more advanced bio-inspired composite materials. [ABSTRACT FROM AUTHOR]

Predicting precisely where a crack will develop in a material under stress and exactly when in time catastrophic fracture of the component will occur is one the oldest unsolved mysteries in the design and building of large-scale engineering structures. Where human life depends upon engineering ingenuity, the burden of testing to prove a 'fracture safe design' is immense. Fitness considerations for longlife implementation of large composite structures include understanding phenomena such as impact, fatigue, creep and stress corrosion cracking that affect reliability, life expectancy and durability of structure. Structural integrity analysis treats the design, the materials used, and figures out how best components and parts can be joined, and takes service duty into account. However, there are conflicting aims in the complete design process of designing simultaneously for high efficiency and safety assurance throughout an economically viable lifetime with an acceptable level of risk. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'. [ABSTRACT FROM AUTHOR]

The problem of multi-scale modelling of damage development in a SiC ceramic fibre-reinforced SiC matrix ceramic composite tube is addressed, with the objective of demonstrating the ability of the finite-element microstructure meshfree (FEMME) model to introduce important aspects of the microstructure into a larger scale model of the component. These are particularly the location, orientation and geometry of significant porosity and the load-carrying capability and quasi-brittle failure behaviour of the fibre tows. The FEMME model uses finite-element and cellular automata layers, connected by a meshfree layer, to efficiently couple the damage in the microstructure with the strain field at the component level. Comparison is made with experimental observations of damage development in an axially loaded composite tube, studied by X-ray computed tomography and digital volume correlation. Recommendations are made for further development of the model to achieve greater fidelity to the microstructure. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'. [ABSTRACT FROM AUTHOR]

In-plane centroids of textile composites are simulated as cross-correlated random fields. Each tow position is defined as an average trend quantified from experimental data, added with zero-mean deviations produced as a stochastic field. Realisations of these fields are generated using a framework based on the Karhunen–Loève series expansion that is calibrated with experimental information from prior work. Positional deviations are obtained that are correlated along the tow and between neighbouring tows. The application is a 2/2 twill woven carbon fibre reinforced epoxy consisting of multiple unit cells. Generated in-plane deviations of the warp and weft tows resemble the experimental fluctuations with similar wavelengths. Simulation of thousand specimens demonstrates that the virtual in-plane positions possess the experimental standard deviation and correlation lengths on average. [ABSTRACT FROM AUTHOR]

Highlights: [•] The proposed M2RVE can predict stress-strain response of the balanced laminates. [•] Effect on local damage in one layer due to presence of another is captured. [•] Significant effect of matrix and interfacial properties on global response. [•] Debonding initiates at different strains for a [0/90]ns and [±45]ns laminate. [•] Model captures the amount and location of debonding at any point in the laminate. [ABSTRACT FROM AUTHOR]

Abstract: A stochastic model of an experimentally measured unit cell structure is computed using the multi-scale textile software WiseTex. The statistical characteristics of a sample, derived in prior work, are used to calibrate the recently proposed Markov Chain algorithm for textile fabrics. The generated variable tow reinforcements are transformed in the WiseTex format that is compatible with tools for micromechanical analysis and permeability simulation. The application is a seven ply polymer textile composite, with each ply consisting of a twill 2/2 woven carbon fabric in an epoxy matrix. The developed model possesses random tow centroid paths with nominal cross-sectional properties. [Copyright &y& Elsevier]

• Multi-scale micro-mechanics accurately predict the compressive strength of masonry. • Leaf interaction in multi-leaf walls is modelled by simple analytical expressions. • Unit dimensions & secondary elements strongly affect the compressive strength. Three-leaf masonry panels are typically composed of external leaves of irregularly bonded units and a rouble infill. The complexity of the response of these structures to mechanical loading arises from: a) the interaction of the leaves and b) the irregularity of the bond pattern of the outer leaves. This complexity makes analytical and computational modelling of these structures difficult and costly, respectively. This paper proposes a computational approach for the calculation of the mechanical properties of the three-leaf masonry from the properties of its constituent materials and its geometry. Using micro-mechanical analysis approaches applied in composite materials and accounting for the interaction of the leaves through a simple analytical approach, the homogenised elastic stiffness and strength of a representative volume element of three-leaf masonry can be calculated with very low computational cost. The analysis method is validated against experimental results from the literature. It is found that the proposed model provides accurate results for a relatively wide range of case studies. These results are expanded upon through a sensitivity study, highlighting the most important material and geometric parameters influencing the predicted compressive strength of three-leaf masonry walls. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper a multi-scale boundary element method for modelling damage is proposed. The constitutive behaviour of a polycrystalline macro-continuum is described by micromechanics simulations using averaging theorems. An integral non-local approach is employed to avoid the pathological localization of micro-damage at the macro-scale. At the micro-scale, multiple intergranular crack initiation and propagation under mixed mode failure conditions is considered. Moreover, a non-linear frictional contact analysis is employed for modelling the cohesive-frictional grain boundary interfaces. Both micro- and macro-scales are being modelled with the boundary element method. Additionally, a scheme for coupling the micro-BEM with a macro-FEM is also proposed. To demonstrate the accuracy of the proposed method, the mesh independency is investigated and comparisons with two macro-FEM models are made to validate the different modelling approaches. Finally, microstructural variability of the macro-continuum is considered to investigate possible applications to heterogeneous materials. [Copyright &y& Elsevier]

Numerical modelling of 3D-printed Fused Filament Fabrication (FFF) specimens with thermoplastic matrices reinforced with continuous fibres is still in its infancy. The existing numerical work is mostly related to the adhesion between printed filaments and not to the mechanical properties. However, the latter are one of the most important parameters that define the structural behaviour of the material. A numerical three-step multi-scale model is introduced in the present study, concentrating on the fundamental aspect of the elastic properties. The most encountered reinforced Nylon FFF structures with continuous fibres of glass, carbon and, Kevlar, are examined. The concept of Representative Volume Element (RVE) is utilized for the combination of matrix and fibres at the micro-scale and the addition of voids at the meso-scale. Finally, at the macro-scale, tension simulations are performed for specimens with various lay-ups. The results of the numerical model are validated using analytical models and experimental data. A new analytical micro-mechanical model is developed as an alternative to the more cumbersome Mori–Tanaka model. A series of experimental testing is performed for Kevlar-reinforced Nylon specimens to accompany the limited existing data and aid the validation process. The comparison reveals a good correlation with the analytical models for the micro- and meso-scale and to the experimental data for the macro-scale, leading to a robust conclusion for its validity and efficiency. [ABSTRACT FROM AUTHOR]

Recycled cement paste as a promising shape stabilisation support of phase change material (PCM) has been introduced to prepare cement-based phase change energy storage composite material (PCESCM) due to its advantages regarding building energy conservation and recycling construction waste. In this study, to fully consider the degrees of freedom of material design, a multi-scale framework using lattice Boltzmann method (LBM) is proposed to predict the effective thermal conductivities of hierarchical cement-based PCESCM. The representative volume elements (RVEs) of cement-based PCESCM covering nano-, micro-, and meso-scale are established capturing the complex structural characteristics. Afterwards, an LBM-based thermal conduction model is proposed to simulate the thermal conduction through the reconstructed RVEs. The results indicate that at the nano-scale the thermal conductivity of colloidal C-S-H increases with the packing density of gel particles for both saturated and dried states. At the micro-scale, the thermal conductivities of matrix and PCM composite are highly dependent on the degree of water/PCM saturation. At the meso-scale, the incorporation of PCM composites can lead to a reduction in thermal conductivity. In general, the simulated thermal conductivities of hierarchical cement-based PCESCM using the LBM-based model agree well with the measured values or the estimated results using the analytical model. Unlabelled Image • Representative volume elements of cement-based phase change energy storage composite material are successfully reconstructed. • An integrated model for simulating effective thermal conductivity of complex geometry is proposed and tested. • Thermal conductivity simulated using conduction model agrees well with results measured or estimated from analytical model. [ABSTRACT FROM AUTHOR]