Strain rate dependent material model for polymer composites

We propose a micromechanical model that is able to predict the nonlinear behaviour and failure of unidirectional fibre reinforced polymer composites subjected to dynamic loading conditions. This novel material model is heterogeneous on the micro level and homogeneous on the ply level.The fibres are assumed to be hyperelastic transversely isotropic and the matrix obeys a hypoelastic viscoelastic/plastic constitutive model enhanced by a continuum damage model. To model the matrix, a Zener rheological model for the viscoelastic behaviour combined with a Bingham model for the viscoplastic behaviour is assumed.The proposed model is formulated in a framework that separates the fibre and the matrix contributions. Typical applications are unidirectional composites manufactured, for example, from unidirectional fibres embedded in a polymer matrix. Generally, the quasi-brittle compressive failure behaviour of composites happens during fairly large strains in the matrix. Therefore, a geometrically nonlinear descriptionhas been developed.Finally, using this model, we characterize the shear induced post-failure behaviour in compression of the composite material. Finite element simulations are conducted to predict the rate dependent properties of unidirectional polymer composites. The predictions of the finite element simulations are compared to published experimental results of an IM7/8552 material system under compression loading at different strain rates. The results are in a reasonably good agreement with the experiments

A cooperative mobile robot and manipulator system (Co-MRMS) for transport and lay-up of fibre plies in modern composite material manufacture

Composite materials are widely used in industry due to their light weight and specific performance. Currently, composite manufacturing mainly relies on manual labour and individual skills, especially in transport and lay-up processes, which are time consuming and prone to errors. As part of a preliminary investigation into the feasibility of deploying autonomous robotics for composite manufacturing, this paper presents a case study that investigates a cooperative mobile robot and manipulator system (Co-MRMS) for material transport and composite lay-up, which mainly comprises a mobile robot, a fixed-base manipulator and a machine vision sub-system. In the proposed system, marker-based and Fourier transform-based machine vision approaches are used to achieve high accuracy capability in localisation and fibre orientation detection respectively. Moreover, a particle-based approach is adopted to model material deformation during manipulation within robotic simulations. As a case study, a vacuum suction-based end-effector model is developed to deal with sagging effects and to quickly evaluate different gripper designs, comprising of an array of multiple suction cups. Comprehensive simulations and physical experiments, conducted with a 6-DOF serial manipulator and a two-wheeled differential drive mobile robot, demonstrate the efficient interaction and high performance of the Co-MRMS for autonomous material transportation, material localisation, fibre orientation detection and grasping of deformable material. Additionally, the experimental results verify that the presented machine vision approach achieves high accuracy in localisation (the root mean square error is 4.04 mm) and fibre orientation detection (the root mean square error is 1.84 18) and enables dealing with uncertainties such as the shape and size of fibre plies

Gallic Acid as a Potential Substitution for Phenol in Phenol-Formaldehyde Resin for Biocomposite Matrices

This project explores the production of new resins using gallic acid (GA) as a substitute for phenol in phenol-formaldehyde (PF) resin. A special curing schedule was made tailored to the limitations of the equipment used. Phenol was substituted with GA at various contents until the optimum ratio has been reached, which in this present study is 31% of gallic acid. The effects of co-reaction of GA and phenol with formaldehyde on mechanical, thermal, chemical and morphological properties were investigated. Test specimens were prepared by synthesising the pre-polymer at certain processing conditions and curing it in the autoclave. From the flexural test, addition of GA showed improvement in the flexural modulus and strength. The thermal properties of PF resin and GA resin were investigated by Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and Thermogravimetry Analysis (TGA). From the DSC result, no residual exotherm can be seen below 150 ℃ which indicates that the resin is suitable for use in natural fibre composites. Glass transition temperature (Tg) from DMA suggest that substitution of phenol with GA in production of resol resin has increased the glass transition temperature while TGA results showed that increasing GA substitution level in the compound resulted in increasing weight loss at lower temperature, and hence lower thermal stability. Based on Scanning Electron Microscopy (SEM) analysis, the flexural fracture surfaces for PF and GA resin displays no bubbles and voids present in the resin. It shows that the cure cycle proved to be successful in producing bubble-free specimens. In this study, Group Interaction Modelling (GIM) was also used to predict the Tg of the resin, which compares very well with the experimental work. Following the successful production of resin, nettle fibre was added as a reinforcing agent in producing the biocomposites. It shows that up to certain amount of nettle fibres, which is in this study 15 wt% of nettle fibres, the mechanical properties of the resin improved substantially. However, in composite systems, we can see particles and holes where fibres have pulled out upon fracture are clearly visible in the SEM images, which indicates poor interaction between fibre-matrix

Mechanical properties and sustainability aspects of coconut fiber modified concrete: Propiedades mecánicas y aspectos de sostenibilidad de concreto modificado con fibras de coco

Coir fiber has been examined for their suitability as reinforcement of concrete. Mechanical properties and sustainability aspects of concrete composites were estimated after 7. 14, and 28 days of curing. Natural reinforcement of 0.46 and 0.62% by weight of coir fiber was added. Fibers were analyzed by means of scanning electron microscope (SEM). Besides, an Eco-audit tool has been used to estimate energy and carbon emission of material, manufacturing, transportation, and disposal phases. It was found that fibers additions lowered the compressive strength compared to plain concrete. However, failures of the composites exhibited good post-cracking behavior. The use of vegetable fibers affects positively the life cycle of the material. Eco-audit results indicate that there is a potential to reduce between 9.15% and 13.35% of embodied energy and between 9.61% and 13.94% of CO2 during the material production phase. These suggest that coir fibers could be useful from the environmental view, although more studies regarding their durability are needed.Fibras de coco han sido examinadas por su sostenibilidad como refuerzo de concreto. Propiedades mecánicas y aspectos sostenibles de compuestos de concreto fueron estimadas luego de 7. 14, y 28 días de curado. Se adicionaron refuerzos naturales de 0.46 y 0.62% en peso de fibra de coco. Las fibras fueron analizadas mediante microscopía electrónica de barrido (SEM). Además, una herramienta de Eco-Auditoría se utilizó para estimar la energía y emisiones de carbono en las fases de material, manufactura, transporte y disposición. Se encontró que las adiciones de fibra disminuía la resistencia a la compresión comparado con el concreto normal. Sin embargo, las fallas de los compuestos exhibieron un buen comportamiento post-agrietamiento.  El uso de fibras vegetales afecta positivamente el ciclo de vida del material. Los resultados de la Eco-auditoría indican que hay un potencial para reducir la energía incorporada entre 9.15% y 13.35% y el CO2 entre 9.61% y 13.94% durante la fase de producción del material. Esto sugiere que las fibras de coco pueden ser útiles desde el punto de vista ambiental aunque son necesarios más estudios con relación a su durabilidad. &nbsp

Mechanical properties and sustainability aspects of coconut fiber modified concrete: Propiedades mecánicas y aspectos de sostenibilidad de concreto modificado con fibras de coco

Coir fiber has been examined for their suitability as reinforcement of concrete. Mechanical properties and sustainability aspects of concrete composites were estimated after 7. 14, and 28 days of curing. Natural reinforcement of 0.46 and 0.62% by weight of coir fiber was added. Fibers were analyzed by means of scanning electron microscope (SEM). Besides, an Eco-audit tool has been used to estimate energy and carbon emission of material, manufacturing, transportation, and disposal phases. It was found that fibers additions lowered the compressive strength compared to plain concrete. However, failures of the composites exhibited good post-cracking behavior. The use of vegetable fibers affects positively the life cycle of the material. Eco-audit results indicate that there is a potential to reduce between 9.15% and 13.35% of embodied energy and between 9.61% and 13.94% of CO2 during the material production phase. These suggest that coir fibers could be useful from the environmental view, although more studies regarding their durability are needed.Fibras de coco han sido examinadas por su sostenibilidad como refuerzo de concreto. Propiedades mecánicas y aspectos sostenibles de compuestos de concreto fueron estimadas luego de 7. 14, y 28 días de curado. Se adicionaron refuerzos naturales de 0.46 y 0.62% en peso de fibra de coco. Las fibras fueron analizadas mediante microscopía electrónica de barrido (SEM). Además, una herramienta de Eco-Auditoría se utilizó para estimar la energía y emisiones de carbono en las fases de material, manufactura, transporte y disposición. Se encontró que las adiciones de fibra disminuía la resistencia a la compresión comparado con el concreto normal. Sin embargo, las fallas de los compuestos exhibieron un buen comportamiento post-agrietamiento.  El uso de fibras vegetales afecta positivamente el ciclo de vida del material. Los resultados de la Eco-auditoría indican que hay un potencial para reducir la energía incorporada entre 9.15% y 13.35% y el CO2 entre 9.61% y 13.94% durante la fase de producción del material. Esto sugiere que las fibras de coco pueden ser útiles desde el punto de vista ambiental aunque son necesarios más estudios con relación a su durabilidad. &nbsp

Insight into microstructure and flexural strength of ultra-high temperature ceramics enriched SICARBON™ composite

Research efforts on Ceramic Matrix Composites (CMCs) are aimed to increase the operating temperature in oxidizing environments by adding Ultra-High Temperature Ceramic (UHTC) phases to the matrix. The structural performances of UHTC-enriched CMCs are generally investigated through bending test because it requires simple fixture and specimen geometry with small quantity of plate material. However, there are hardly any scientific studies which bring out what bending test conditions are required to determine reliable flexural strength of these composites. In this study, the effect of span length and specimen orientation on the flexural strength of UHTC-enriched SICARBON™ material, produced by Airbus, was comprehensively evaluated and reported. Transition of the failure mode was obtained by tilting the specimens with horizontal build direction instead of lay-up configuration (vertical build direction). The tilted configuration allowed to get a valid flexural strength of 370 MPa even with small specimens of about 30 mm. To assess failure mode in different test configurations, virtual microstructure was generated on the base of cumulative distribution functions of observed microstructural features. Tsai-Wu failure criterion was extended in order to evaluate direction dependent failure indices for different lay-up configurations

Virtual cardiac monolayers for electrical wave propagation

The complex structure of cardiac tissue is considered to be one of the main determinants of an arrhythmogenic substrate. This study is aimed at developing the first mathematical model to describe the formation of cardiac tissue, using a joint in silico-in vitro approach. First, we performed experiments under various conditions to carefully characterise the morphology of cardiac tissue in a culture of neonatal rat ventricular cells. We considered two cell types, namely, cardiomyocytes and fibroblasts. Next, we proposed a mathematical model, based on the Glazier-Graner-Hogeweg model, which is widely used in tissue growth studies. The resultant tissue morphology was coupled to the detailed electrophysiological Korhonen-Majumder model for neonatal rat ventricular cardiomyocytes, in order to study wave propagation. The simulated waves had the same anisotropy ratio and wavefront complexity as those in the experiment. Thus, we conclude that our approach allows us to reproduce the morphological and physiological properties of cardiac tissue