Search

This paper investigates whether the toughening mechanisms of a biological crossed-lamellar microstructure can be reproduced in a synthetic high-performance carbon fibre/epoxy matrix composite. The mechanics of the failure process in synthetic crossed-lamellar microstructures was investigated using the Finite Element Method. This enabled the design of a high-performance carbon-fibre reinforced polymer (CFRP) with such microstructure. Two different procedures were then developed to synthesise the first crossed-lamellar microstructures in CFRP in the literature. Test specimens were subsequently manufactured. Three-point bend tests were carried out in an SEM environment, showcasing the damage diffusion capability of the microstructure under stable conditions. The results show that the crossed-lamellar microstructure can be synthesised in CFRP with good accuracy, and that the mechanical toughening mechanisms associated with the natural crossed-lamellar microstructures can be reproduced in this synthetic material.

Composite materials are nowadays widely used in the aerospace sector both for primary and secondary structures for their high mechanical properties and the ability to model them according to project needs. Therefore, accurately predicting material behaviour when subjected to operating loads is extremely important in making the design process more efficient. For this purpose, computational approaches based on continuum damage mechanics have been largely used to study the progressive loss of material integrity due to the propagation and coalescence of microscopic defects. In this contribution, a recently developed hybrid computational technique, which combines the Virtual Element Method (VEM) with the well-known Boundary Element Method (BEM), is employed to study unidirectional fibrereinforced composite material’s transverse behaviour in the presence of inclusions with complex geometries. BEM is used to model the stiffer inclusion phase, which is considered a linear elastic material and maintains its pristine state. VEM is adopted to study the softer matrix phase, using VEM’s peculiar feature, which can simulate general nonlinear phenomena with a straightforward implementation like that of the standard FEM one. An application of the hybrid formulation mentioned above is presented to simulate damage onset and propagation in the matrix phase of the transverse section of a composite unite cell. Numerical results are discussed and compared with known results available in the relevant literature.

In this paper, a carbon-fibre/epoxy (CF) composite with nacre-inspired tiled micro-structure is designed and synthesised. The aim is to investigate the interaction between the CF discontinuous micro-structure and continuous glass-fibre/epoxy (GF) layers, which are intended to act as crack stoppers, similarly to the organic interlayers that separate layers of ceramic tiles in natural nacre. Firstly, we use a GF skin to trigger unstable failure in nacre-like mesolayers, and show how the damage mode in the latter changes from pull-out to brittle fibre fracture due to the interaction with the GF skin. Secondly, we demonstrate how continuous GF interlayers can succeed in arresting unstable crack propagation in the nacre mesolayers. Furthermore, we show that they can also change the morphology of damage in the nacre, promoting a transition from brittle tile fracture to more damage-tolerant tile pull-out.

A promising strategy to increase the tensile failure strain of carbon fibre-reinforced composites is to hybridise carbon fibres with other, higher-elongation fibres. The resulting increase in failure strain is known as the hybrid effect. In the present article, a global load-sharing model for hybrid composites is developed and used to carry out a parametric study for carbon/glass hybrids. Hybrid effects of up to 15% increase in failure strain are predicted, corresponding reasonably well to literature data. Scatter in the carbon fibre strength is shown to be crucial for the hybrid effect, while the scatter in glass fibre strength is much less important. In contrast to reports in earlier literature, the ratio of failure strains of the two fibres has only a small influence on the hybrid effect. The results provide guidelines for designing optimal hybrid composites. publisher: Elsevier articletitle: Global load-sharing model for unidirectional hybrid fibre-reinforced composites journaltitle: Journal of the Mechanics and Physics of Solids articlelink: http://dx.doi.org/10.1016/j.jmps.2015.08.009 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved. ispartof: Journal of the Mechanics and Physics of Solids vol:84 pages:380-394 status: published

The present research investigates an innovative use of fibre-reinforced composite materials (FRP) in the building industry and develops a construction system that has the potential to fuse structural, energy and architectural performances in one single shell, which is light, load bearing and efficient, with systems integrated inside it. This gives the opportunity to deal with the concept of sustainability in a broader sense, changing the approach from assessment protocols based on checklists to the idea of integration and inter-dependence of different aspects. The aforementioned concepts are applied to the design of a University students’ pavilion: its energy and daylight performances are analysed through simulations, while a 1:2 scale prototype of a pavilion portion has been fabricated to test the material characteristics. The construction system consists of a double curvature, load bearing, sandwich shell composed of two external FRP layers and a polyurethane core where systems are included. Potentialities and limitations connected to these materials are discussed, including a critical discussion of the building construction, transportation, energy consumption, environmental impact and overall efficiency and cost. The pavilion design aims to maximize daylight autonomy and solar gains in winter, while avoiding glare and minimizing cooling loads in summer. A ventilation system capable of refrigerating during the night is developed in parallel to a VRF system with heat pump, which is completely autonomous from the existing building. Operative temperature and comfort are evaluated for different periods of the year and results are displayed on maps. Software integration is a key factor in this process of extreme integration of different functions: opportunities and limitations related to the use of software are also discussed.

The translaminar fracture toughness of fibre-reinforced composites is a size-dependent property which governs the damage tolerance and failure of these materials. This paper presents the development, implementation and validation of an original analytical model to predict the tensile translaminar (fibre-dominated) toughness of composite plies and bundles, as well as the associated size effect. The model considers, as energy dissipation mechanisms, debonding and pull-out of bundles from quasi-fractal fracture surfaces; the corresponding lengths are stochastic variables predicted by the model, based on the respective bundle strength distributions and fracture mechanics. Parametric studies show that composites are toughened by stronger fibres with large strength variability, and intermediate values of interfacial toughness and friction. Predictions are validated against four different composite ply systems tested in the literature, proving the model’s ability to capture not only size effects, but also the influence of different fibres and resins.

A finite strain fibre-reinforced viscoelasto-viscoplastic model implemented in a finite element (FE) analysis is presented to study the expansive growth of plant cell walls. Three components of the deformation of growing cell wall, i.e. elasticity, viscoelasticity and viscoplasticity-like growth, are modelled within a consistent framework aiming to present an integrative growth model. The two aspects of growth—turgor-driven creep and new material deposition—and the interplay between them are considered by presenting a yield function, flow rule and hardening law. A fibre-reinforcement formulation is used to account for the role of cellulose microfibrils in the anisotropic growth. Mechanisms in in vivo growth are taken into account to represent the corresponding biologycontrolled behaviour of a cell wall. A viscoelastic formulation is proposed to capture the viscoelastic response in the cell wall. The proposed constitutive model provides a unique framework for modelling both the in vivo growth of cell wall dominated by viscoplasticity-like behaviour and in vitro deformation dominated by elastic or viscoelastic responses. A numerical scheme is devised, and FE case studies are reported and compared with experimental data.

The homogenization problem of linearly piezoelectric fibrous composites with a periodic microstructure is formulated by adopting the free- and complementary-energy minimum principles, as well as the Hashin Shtrikman principles. The auxiliary electroelastic problems involved in the Hashin-Shtrikman principles are solved by a transformation from the space domain to the Fourier domain. Approximations of those variational principles, suitable for numerical computations, are built up by adopting the Fourier-series method and the finite-element method. In this way, rigorous upper and lower bounds on the overall material moduli are obtained. An example is presented, in order to show the effectiveness of the proposed approximation techniques and to compare them.

This paper reports on the development of braided reinforced composite rods as a substitute for the steel reinforcement in concrete. The research work aims at understanding the mechanical behaviour of core-reinforced braided fabrics and braided reinforced composite rods, namely concerning the influence of the braiding angle, the type of core reinforcement fibre, and preloading and postloading conditions. The core-reinforced braided fabrics were made from polyester fibres for producing braided structures, and E-glass, carbon, HT polyethylene, and sisal fibres were used for the core reinforcement. The braided reinforced composite rods were obtained by impregnating the core-reinforced braided fabric with a vinyl ester resin. The preloading of the core-reinforced braided fabrics and the postloading of the braided reinforced composite rods were performed in three and two stages, respectively. The results of tensile tests carried out on different samples of core-reinforced braided fabrics are presented and discussed. The tensile and bending properties of the braided reinforced composite rods have been evaluated, and the results obtained are presented, discussed, and compared with those of conventional materials, such as steel.