The increasing demand for polymer matrix composites (PMCs) from the airframe industry raises the issues of productivity, cost and reproducibility of manufactured PMC components. Performance reproducibility is closely related to the manufacturing technique. Resin transfer moulding (RTM) offers the advantage of flexible manufacturing of net-shape PMC components with superior repeatability starting from ready-to-impregnate dry reinforcements. An RTM apparatus was developed for manufacturing PMC plates and demonstrator components representative of actual, PMC components and PMC moulds made and used in the airframe industry. The RTM process developed in this work involved making net-shape dry carbon fibre preforms and impregnating them an epoxy resin, targeting mould applications. Thermal repeatability of different net-shape PMC components manufactured using the RTM apparatus developed in-house was investigated. Effects of bonding an outer copper plate onto the PMC material, targeting mould applications known as integrally heated copper tooling (IHCT), were explored. Heat conduction through the PMC components was studied using simulation models validated by experimental data obtained primarily by thermography. Manufactured PMC components showed good repeatability, particularly in terms of thermal behaviour. The IHCT technique was found to be well suited for mould applications. Expected advantages of thermography were materialised. Finally, the simulation models developed were in good agreement with experimental data.

The increasing demand for polymer matrix composites (PMCs) from the airframe industry raises the issues of productivity, cost and reproducibility of manufactured PMC components. Performance reproducibility is closely related to the manufacturing technique. Resin transfer moulding (RTM) offers the advantage of flexible manufacturing of net-shape PMC components with superior repeatability starting from ready-to-impregnate dry reinforcements. An RTM apparatus was developed for manufacturing PMC plates and demonstrator components representative of actual, PMC components and PMC moulds made and used in the airframe industry. The RTM process developed in this work involved making net-shape dry carbon fibre preforms and impregnating them an epoxy resin, targeting mould applications. Thermal repeatability of different net-shape PMC components manufactured using the RTM apparatus developed in-house was investigated. Effects of bonding an outer copper plate onto the PMC material, targeting mould applications known as integrally heated copper tooling (IHCT), were explored. Heat conduction through the PMC components was studied using simulation models validated by experimental data obtained primarily by thermography. Manufactured PMC components showed good repeatability, particularly in terms of thermal behaviour. The IHCT technique was found to be well suited for mould applications. Expected advantages of thermography were materialised. Finally, the simulation models developed were in good agreement with experimental data.

L’influence des propriétés microscopiques de l’interphase entre la matrice et les fibres sur le comportement mécanique macroscopique n’est pas suffisamment connue dans le domaine des polymères renforcés par fibres courtes. Dans le cadre de cette thèse, une étude systématique des propriétés géométriques et mécaniques de l’interphase est réalisée concernant la description des effets sur la réponse viscoélastique linéaire du composite. Dans ce contexte, les résultats présentés mettent l’accent sur l’interaction entre la modélisation micromécanique et la caractérisation expérimentale. D’une part, un nouveau modèle micromécanique en deux étapes est développé pour la description d’un composite anisotrope à trois phases avec interphases. D’autre part, les paramètres du matériau utilisés pour la modélisation micromécanique sont identifiés avec des méthodes expérimentales aux échelles micro- et macroscopiques. En comparaison des résultats expérimentaux avec les propriétés effectives calculées de matériau composite, une inférence peut être faite sur les propriétés mécaniques du composite à partir de celles de l’interphase. Par conséquent, une méthode inverse est proposée offrant un accès aux propriétés inconnues de l’interphase. Enfin, la combinaison de la modélisation micromécanique et des résultats expérimentaux permet une meilleure compréhension des propriétés mécaniques de l’interphase, qui n’étaient auparavant pas accessibles au moyen de seules approches expérimentales / In order to improve the mechanical properties of short fiber composites, the fiber-matrix adhesion is decisive and depends strongly on the intersection region between the fiber and the matrix material. However, no perspicuous information about the influence or mechanical properties of the fiber-matrix interphase in short fiber reinforced thermoplastic composites is available. Thus, the present thesis aims for a systematic identification of the geometrical and mechanical impacts of an interphase on the linear-viscoelastic behavior in short glass fiber reinforced thermoplastics. Thereby, the performed investigations are focused on the interaction between micromechanical material modeling and experimental testing. On the one hand, a two-step modeling approach is developed for the realistic description of an entire three phase composite with interphase including anisotropic and linear-viscoelastic effects. On the other hand, the input of this model is provided by different experimental testing methods ranging from the micro- to the macroscale characterization of the composite and matrix material. By comparing these experimental results with the linear-viscoelastic modeling output, the impact of the interphase on the mechanical properties of the composite is accessible. Thus, it is shown that a realistic material modeling and experimental investigations are closely interlinked

abstract: Composite materials are now beginning to provide uses hitherto reserved for metals in structural systems such as airframes and engine containment systems, wraps for repair and rehabilitation, and ballistic/blast mitigation systems. These structural systems are often subjected to impact loads and there is a pressing need for accurate prediction of deformation, damage and failure. There are numerous material models that have been developed to analyze the dynamic impact response of polymer matrix composites. However, there are key features that are missing in those models that prevent them from providing accurate predictive capabilities. In this dissertation, a general purpose orthotropic elasto-plastic computational constitutive material model has been developed to predict the response of composites subjected to high velocity impacts. The constitutive model is divided into three components – deformation model, damage model and failure model, with failure to be added at a later date. The deformation model generalizes the Tsai-Wu failure criteria and extends it using a strain-hardening-based orthotropic yield function with a non-associative flow rule. A strain equivalent formulation is utilized in the damage model that permits plastic and damage calculations to be uncoupled and capture the nonlinear unloading and local softening of the stress-strain response. A diagonal damage tensor is defined to account for the directionally dependent variation of damage. However, in composites it has been found that loading in one direction can lead to damage in multiple coordinate directions. To account for this phenomena, the terms in the damage matrix are semi-coupled such that the damage in a particular coordinate direction is a function of the stresses and plastic strains in all of the coordinate directions. The overall framework is driven by experimental tabulated temperature and rate-dependent stress-strain data as well as data that characterizes the damage matrix and failure. The developed theory has been implemented in a commercial explicit finite element analysis code, LS-DYNA®, as MAT213. Several verification and validation tests using a commonly available carbon-fiber composite, Toyobo’s T800/F3900, have been carried and the results show that the theory and implementation are efficient, robust and accurate. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2016

No description available.

The increasing demand for polymer matrix composites (PMCs) from the airframe industry raises the issues of productivity, cost and reproducibility of manufactured PMC components. Performance reproducibility is closely related to the manufacturing technique. Resin transfer moulding (RTM) offers the advantage of flexible manufacturing of net-shape PMC components with superior repeatability starting from ready-to-impregnate dry reinforcements. An RTM apparatus was developed for manufacturing PMC plates and demonstrator components representative of actual, PMC components and PMC moulds made and used in the airframe industry. The RTM process developed in this work involved making net-shape dry carbon fibre preforms and impregnating them an epoxy resin, targeting mould applications. Thermal repeatability of different net-shape PMC components manufactured using the RTM apparatus developed in-house was investigated. Effects of bonding an outer copper plate onto the PMC material, targeting mould applications known as integrally heated copper tooling (IHCT), were explored. Heat conduction through the PMC components was studied using simulation models validated by experimental data obtained primarily by thermography. Manufactured PMC components showed good repeatability, particularly in terms of thermal behaviour. The IHCT technique was found to be well suited for mould applications. Expected advantages of thermography were materialised. Finally, the simulation models developed were in good agreement with experimental data.

No description available.

No description available.

<p dir="ltr">Single screw extrusion is widely used in injection molding, extrusion additive manufacturing, and material pre-compounding. A single screw extruder has three stages – the solid conveying zone, the melt-transition or compression zone, and the melt-conveying zone. As the pellets are processed, pellet rupture and fiber breakage occur in the transition and melt-conveying stages of extrusion. Existing literature focuses on modeling fiber breakage in fully molten stage, and there is a lack of understanding of fiber breakage during the partially molten – transition zone. Moreover, existing theoretical melting models apply to continuous solid melting and cannot be applied to study melting of individual pellets. As fiber length influences the thermo-mechanical properties of the manufactured composites, it is crucial to understand why and how fibers break. The goal of this thesis is to identify the mechanisms of pellet melting and fiber breakage by tracking the motion and heat transfer of an individual pellet. In the first part of this thesis, flow of long discontinuous fiber pellets through a single screw extruder is modeled using discrete element method. Results indicate a translational-conveying motion in the first half of the screw and rotational-conveying motion in the second half. In the second part, a sequentially coupled heat transfer model is developed to capture the melting of a single pellet, occurring mainly through the thermal contacts with the heated screw and barrel surfaces. Partial melting, partial crystallization, and re-melting are captured using melting and crystallization kinetics of semi-crystalline polymers. Heat transfer results indicate that the pellets melt from the outside-in, with a molten shell and a solid core. Based on the average pellet degree of melting, the region of interest for ‘melting zone’ is identified. Finally, some common modes of pellet deformation are identified for closer study.</p><p dir="ltr">Once the common pellet deformation modes are identified, analytical models based on three-point bending loading condition are developed to model pellet deformation. For a partially molten pellet with molten shell and a softer core, temperature dependent properties are used to estimate pellet deflection. The surface fibers are studied closely to identify a fiber separation mechanism. For the separated fibers, a Weibull based strength distribution is used to develop a fiber attrition algorithm for varying end loads. Results indicate that fiber attrition starts as soon as the outer layer of the pellet melts and then continues until the end of the screw. Recommendations for validation experiments and future work are provided in the end.</p>

Yes / Composites have clinical application for their ability to mimic the hierarchical structure of human tissues. In tissue engineering applications the use of degradable biopolymer matrices reinforced by bioactive ceramics is seen as a viable process to increase osteoconductivity and accelerate tissue regeneration, and technologies such as additive manufacturing provide the design freedom needed to create patient-specific implants with complex shapes and controlled porous structures. In this study a medical grade poly(l-lactide) (PLLA) was used as matrix while apatite-wollastonite (AW) was used as reinforcement (5 wt% loading). Premade rods of composite were pelletized and processed to create a filament with an average diameter of 1.6 mm, using a twin-screw extruder. The resultant filament was 3D printed into three types of porous woodpile samples: PLLA, PLLA reinforced with AW particles, and PLLA with short AW fibres. None of the samples degraded in phosphate buffered solution over a period of 8 weeks, and an average effective modulus of 0.8 GPa, 1 GPa and 1.5 GPa was obtained for the polymer, particle and fibre composites, respectively. Composite samples immersed in simulated body fluid exhibited bioactivity, producing a surface apatite layer. Furthermore, cell viability and differentiation were demonstrated for human mesenchymal stromal cells for all sample types, with mineralisation detected solely for biocomposites. It is concluded that both composites have potential for use in critical size bone defects, with the AW fibre composite showing greater levels of ion release, stimulating more rapid cell proliferation and greater levels of mineralisation. / The research was funded in part by the UK EPSRC Centre for Doctoral Training in Additive Manufacturing and 3D Printing (EP/L01534X/1), the UK EPSRC Centre for Innovative Manufacture in Medical Devices (EP/K029592/1), and Glass Technology Services Ltd., Sheffield, UK.