Introduction to heat transfer

The increased usage of fiber reinforced polymer composites in load bearing applications requires a detailed understanding of the process induced residual stresses and their effect on the shape distortions. This is utmost necessary in order to have more reliable composite manufacturing since the residual stresses alter the internal stress level of the composite part during the service life and the residual shape distortions may lead to not meeting the desired geometrical tolerances. The occurrence of residual stresses during the manufacturing process inherently contains diverse interactions between the involved physical phenomena mainly related to material flow, heat transfer and polymerization or crystallization. Development of numerical process models is required for virtual design and optimization of the composite manufacturing process which avoids the expensive trial-and-error based approaches. The process models as well as applications focusing on the prediction of residual stresses and shape distortions taking place in composite manufacturing are discussed in this study. The applications on both thermoset and thermoplastic based composites are reviewed in detail.

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A Review on the Mechanical Modeling of Composite Manufacturing Processes

Spring-in and warpage of angled composite laminates

A polymer matrix composite. The composite is made from a mixture of barium titanate-based particles dispersed in a polymeric resin. The mixture includes more than one barium titanate-based component, with each component having a different composition. The different barium titanate-based components are present in the mixture in specific proportions to provide the mixture with a relatively high, temperature-stable dielectric constant. Preferably, the mixture and resulting composite meets the temperature stability requirements to satisfy X7R capacitor specifications. The polymer matrix composite may be used in a number of applications, such as printed circuit boards which include embedded capacitors.

Polymer matrix composites

Numerical modelling is increasingly supporting the analysis and optimization of manufacturing processes in the production industry. Even if being mostly applied to multistep processes, single process steps may be so complex by nature that the needed models to describe them must include multiphysics. On the other hand, processes which inherently may seem multiphysical by nature might sometimes be modelled by considerably simpler models if the problem at hand can be somehow adequately simplified. In the present article, examples of this will be presented. The cases are chosen with the aim of showing the diversity in the field of modelling of manufacturing processes as regards process, materials, generic disciplines as well as length scales: (1) modelling of tape casting for thin ceramic layers, (2) modelling the flow of polymers in extrusion, (3) modelling the deformation process of flexible stamps for nanoimprint lithography, (4) modelling manufacturing of composite parts and (5) modelling the selective la...

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Multiphysics modelling of manufacturing processes: A review

Manufacture of large composite structures presents a number o f challenges, one of the most critical o f which is prediction and control of process-induced deformation. Traditional empirical techniques for tooling and process cycle development are particularly unsuitable for large parts, especially when development costs and process variability are key issues. Thus, there is a critical need to supplement current techniques with a science-based manufacturing approach. In the present work, a two-dimensional finite element model for prediction of process-induced deformation has been developed. Integration of this model with analyses for heat transfer and resin cure and resin flow allows analysis of all major identified deformation sources. A 'virtual autoclave' concept is employed in which autoclave control algorithms and autoclave response are simulated to predict structure boundary conditions during processing. Characterization of a carbon fibre/epoxy composite is performed and models developed to describe material behaviour during processing. A n examination of autoclave heat transfer is also performed and a model developed for the observed effect of pressure on heat transfer rates. Using these data as inputs, the process model is demonstrated through application to three case studies of varying complexity. In each, model predictions are compared to experimental results and the predicted sensitivity o f processing outcomes to process parameter variation is examined. A good match between model predictions and experimental results was obtained in most cases. The developed model is expected to perform two complementary roles. First, the ability to analyse structures of practical size and complexity makes the model a potentially useful process-development tool for the industrial composites processor. Also, the integration of analyses for all major deformation sources allows examination of parameter interaction, potentially driving fundamental research into deformation mechanisms and the development of improved material behavioural models. Sommaire La fabrication de larges structures en composites comporte de nombreux defis dont l'un des plus critiques est la determination et le controle de la deformation induite durant le procede de fabrication. Dans une optique de reduction des couts de fabrication et des variations de qualite, les methodes empiriques traditionnellement utilisees pour la determination du cycle de cure et la conception de l'outillage sont particulierement inefficaces dans le cas de pieces aux dimensions importantes. Ainsi, il est necessaire de complementer les methodes actuelles par une approche scientifique aux problemes de production. Dans ce travail, un modele d'elements finis en deux dimensions calculant les deformations induites durant la fabrication a ete developpe. Ce modele permet l'analyse des principaux phenomenes contribuant aux deformations en combinant les effets du transfert de chaleur, de la polymerisation de la resine et de l'ecoulement de la resine. Un concept de "l'autoclave virtuel", dans lequel les algorythmes de controle de l'autoclave et la reponse de l'autoclave sont simules, est inclus afin de predire plus precisement les conditions frontieres de la piece durant la fabrication. Un composite fibre de carbone-epoxy est caracterise et des modeles decrivant son comportement au cours de la polymerisation sont developpes. Les caracteristiques du transfert de chaleur de l'autoclave sont determinees et un modele reliant Feffet de la pression sur le coefficient de transfert de chaleur de l'autoclave est developpe. En utilisant ces donnees, la performance du modele d'elements finis est demontree a travers trois cas ayant differents degres de complexite. Pour chacun des cas, les predictions du modele sont comparees aux resultats experimentaux. Sommaire L'effet de la variation des entrees du modele sur la stabilite des parametres du procede est egalement etudie. En general, les resultats experimentaux et numeriques concordent bien. Le modele developpe repond a deux besoins complementaires. D'une part, il est un outil pratique pour le manufacturier de pieces en composites, car il permet d'analyser des structures aux formes complexes et de grandes dimensions. D'autre part, il permet d'analyser l'interaction des parametres, car il integre les principaux mecanismes qui induisent des deformations. Ceci permettra d'encourager la progression de la recherche fondamentale sur les mecanismes causant les deformations et de developper de meilleurs modeles decrivant le comportement du materiau.

Andrew Allen Johnston

Papers

An integrated model of the development of process-induced deformation in autoclave processing of composite structures