Pozvánka na přednášku From atoms to aeroplanes: towards multiscale modelling and design of composites
03. 12. 2009
Vážení kolegové, dovolujeme si Vás pozvat na přednášku
From atoms to aeroplanes: towards multiscale modelling and design of composites,
kterou přednese Prof. Frank R Jones, PhD, CEng, CChem, CSci
(Professor of Polymers and Composites,
World Fellow of International Committee on Composites Materials,
Department of Engineering Materials,
The University of Sheffield).
Přednáška se koná ve středu 9. prosince 2009 v 10:00 hodin v kongresovém centru Fakulty strojní ČVUT v Praze, Technická 4, Praha 6 – Dejvice.
Abstract
From Atoms to Aeroplanes:
Towards Multi-scale Modelling and Design of Composites
Frank R Jones
Department of Engineering Materials
The University of Sheffield, UK
The objective of this paper is to describe how the matrix and interfacial chemistry impinge on the micromechanics and macromechanics of a fibre composite for optimising performance and reliability.
Multiscale Modelling of Composite Performance
The lecture will begin with recent work on the hierarchical modelling of
a composite material illustrating the application of group interaction modelling
(GIM) to the prediction of the thermomechanical properties of a polymer.
By introducing the predicted non-linear stress strain curve into a finite
element model for the calculation of stress concentrations near fibre-breaks,
a statistical model for the strength of a unidirectional fibre composite can
be parameterised. One aspect of this model involves introducing the elastoplasticity
of the matrix into the finite element model. The non-linear properties of the resin
can be predicted from the fundamental molecular model by including molecular
conformational change below the glass transition.
In the current work we have assumed that the interface is perfect,
however by using an ineffective length which includes the interfacial response,
the model can be extended. The ineffective length of a fibre at a fibre-break in
a composite strongly influences the ultimate strength of a unidirectional composite.
Introducing Interface and Interphases
The ineffective length of a broken fibre combines contributions from the matrix and the stress transfer capability through the interface therefore this parameter can be used to introduce the interfacial response into the model. The data from the single embedded fragmentation test can be used to measure the ineffective length as a function of the interphase and/or interfacial integrity depending on the system. In future, the GIM model will be used to model the formation of an interphase, providing the thermomechanical properties at the nanometric scale. In this way, protocols for sizing of fibres can be achieved. To do this we need to understand the chemical structure of the interphase.
The Interphase in Fibre Composite Materials
The paper will also review interphase formation in composite materials using analytical chemistry methods, Time of Flight Secondary Ion Mass Spectrometry (ToFSIMS) can be used to identify interpenetrating network formation while X-ray photoelectron spectroscopy (XPS) can be used to study the interactions at fibre surfaces. Furthermore, the fundamentals of interfacial response in a composite material can be quantified using the photoelastic method. Four-phase phase stepping photoelasticity has been used to clarify and identify the effect of transverse cracks, interfacial debonding and mixed mode failure at fibre interfaces on stress transfer efficiency. In order to marry these length scales into a multiscale model a full understanding of the performance of the composite from chemistry through to engineering is required.
Healable Composites
The understanding described above enabled us to identify techniques for healing epoxy resins used as matrices for composites. At the larger length scale, we will demonstrate how epoxy resins can be made to be self-healable and how, using the self-sensing ability of the carbon fibres, we can identify impact damage and provide a means of monitoring the healing of this damage. It has to be recognised that the healing will occur in resin cracks and cracks within the “interfacial” regions of the composite which involves molecular chemistry. The paper will demonstrate how controlling these aspects can provide a composite with a switchable healing capability.