Composite Materials

A.T. Di Benedetto, L. Nicolais, R. Watanabe

• Publisher: North Holland
• Year: 1992
• Print ISBN: 9780444893567
• eBook ISBN: 9780444600790
• Topic: Tecnología e ingeniería
• Subtopic: Ingeniería química y bioquímica

The contributions in this volume bring together the experience of specialists on the highly complex technology required for manufacturing composite structural parts, presenting fundamental descriptions of the processing and properties of these advanced materials.The 34 papers give a thorough overview on recent advances in this field. The contributions have been collected in two general categories: composites based on organic matrices; and composites based on inorganic matrices. In each group properties and manufacturing technologies are analyzed together with long term durability and the special applications for such advanced materials.

Part I

Composites with Organic Matrices

Modelling of Processing Technologies for Polymer Matrix Composites

Jose M. Kenny Department of Materials and Production Engineering, University of Naples, P. Tecchio, 80125, Naples, ITALY

Abstract

A general model for the description of the thermo-chemo-rheological changes of the matrix during the processing of polymer based composites, has been developed in recent years. The master model includes, specific submodels dedicated to the different physico-chemical aspects of composite processing: reaction kinetics, heat transfer, viscosity, fluid flow and void formation during processing. The main objective of this work is to highlight the contribution of the understanding of the matrix behaviour to the right choice of processing conditions.

MODELLING PRINCIPLES FOR COMPOSITES PROCESSING

In the last decade several studies of the fundamental aspects of the processing of high performance composites have been reported [1–6]. In those research works a common scientific approach based on the understanding of the fundamental chemical and physical phenomena governing the behaviour of the composite matrix and allowing a better choice and control of processing conditions has been developed.

The final objective of those activities was the construction of a general processing model that could be adapted to different specific technologies. In order to develop such general model several submodels are needed as shown in Fig. 1. The first submodel describes the kinetics of the matrix chemical transformations, responsible of the final structure of the composite. The thermokinetic model predicts the exothermal heat of reaction and the degree of cure as a function of process time and temperature. The rheological model describes the viscosity evolution as function of time, temperature and degree of cure. Therefore, the rheological model is combined with the thermokinetic model forming the chemorheologicał model including also the gel point. For non-isothermal conditions also a heat transfer model is needed. If the heat transfer model is combined with the chemorheologicał and cure kinetic models, the degree of cure, temperature and viscosity, as a function of time and position in the composite, can be predicted. The flow model predicts resin content distribution and final composite thickness. Finally, the void model predicts the conditions needed to avoid the formation of voids.

Figure 1 Modeling philosophy of the processing of composite materials

A more detailed examination of the modelling of composite processing technologies will be given in the following sections where each of the submodels mentioned in this section, integrated into a general master model, will be discussed.

THERMOKINETIC MODEL

The thermokinetic model is the first step in the construction of the master model being a prerequisite for all the other submodels. It describes the rate at which heat is given off during the reaction, and the degree of cure, α, as a function of temperature and time. For curing reactions, the rate of heat flow dH/dt, can be conveniently measured by differential scanning calorimetry (DSC) [7]. It has been assumed for these processes that the quantity dH/dt is directly proportional to the rate of disappearance of reactive groups during curing, dα/dt. Empirical thermokinetic models for non-autocatalytic reactions have usually the following form:

$\mathrm{d}\mathrm{\alpha }/\mathrm{d}\mathrm{t}=\mathrm{K}{\left(1-\mathrm{\alpha }\right)}^{\mathrm{n}}$

(1)

Integration of this equation can be used to predict α, dα/dt and dH/dt as a function of time and temperature. The rate constant K depends on temperature and generally is given by:

$\mathrm{K}={\mathrm{K}}_{\mathrm{O}}exp\left(–\mathrm{E}/\mathrm{R}\mathrm{T}\right)$

(2)

K_O is a preexponencial factor (frequency factor), E is the activation energy, R is me gas constant and T the absolute temperature. A much better description of the thermoset behavior has recently been reported [8]:

$\mathrm{d}\mathrm{\alpha }/\mathrm{d}\mathrm{t}=\mathrm{A}exp\left(–\mathrm{E}/\mathrm{R}\mathrm{T}\right){\left({\mathrm{\alpha }}_{\mathrm{m}}–\mathrm{\alpha }\right)}^{\mathrm{n}}$

(3)

where α_m is the maximum degree of reaction obtained at a given temperature in an isothermal test. For reactions with autocatalytic behavior the following rate equation has been ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Preface
• Symposium Information
• Part I: Composites with Organic Matrices
• Part II: Composites with Inorganic Matrices
• Author Index