Development of failure models and criteria for laminated composites

Lead Research Organisation: Imperial College London
Department Name: Dept of Aeronautics

Abstract

The potential of composite materials as structural parts is currently hindered by our lack of ability to both understand and predict failure initiation and propagation. Developments in this area can lead to faster and more economical design, as well as lighter and more efficient structures. This project will contribute to the capability of predicting failure of laminated composites consisting of unidirectional plies, by focusing on (i) experimental characterisation of each failure mode, (ii) analytical interpretation of the failure mechanisms and (iii) development of numerical simulation tools for failure propagation.The experimental investigation into each failure mode will be particularly detailed, focusing on the qualitative and quantitative description of the sequence of events leading to each failure mode and their interaction. These events take place initially at a micromechanical scale, and then progressively grow to cause structural failure. An example of this is fibre compressive kinking. The kink bands observed in failed composites are the outcome of a sequence of events which include matrix cracking, fibre-bending failure and eventually fibre micro-buckling, and are dependent on fibre misalignments and matrix nonlinear behaviour in shear. Within these events, matrix cracking for instance, is itself the result of the growth and coalescence of matrix micro-cracks. The experimental investigation aims at producing extensive, detailed, univocal information on these processes. It will require design of test rigs, and will make use of intensive instrumentation (e.g. acoustic emission, photogrammetry and strain gauges) as well as optical and scanning-electron microscopy.The experimental findings will be the basis for the development of analytical models describing the sequence of physical events leading to failure and their interaction. These analytical models will form a physical, mechanist, interpretation of each failure mode. They can be understood as a physical theory for each failure mode, translating the observed events into mathematical expressions involving material (e.g. elastic, strength, toughness) and geometric (e.g. fibre diameter, typical fibre misalignments magnitude and distribution, typical matrix micro-cracks size and distribution) properties. The outcome of these models will be a set of equations, which will be expressed as failure criteria, for direct use in design.For the accurate analysis of complex structures, numerical models have to be considered. For this reason, an advanced numerical failure model including the previous failure criteria will be developed, to be used within commercial finite elements software. In order to accurately model failure propagation and avoid spurious mesh dependency, the numerical model will be based on a to-be-developed smeared-crack methodology appropriate for the variety of issues of failure in laminated composites. These have to do with the multiple failure modes composites can exhibit and how each failure mode affects the material response. For instance, matrix cracking will result in the shear components of the traction vector on the fracture plane being reduced to zero, as well as the normal component if positive; the computational model should be able to reproduce this accurately, as well as correctly accounting for the fracture energy of the process. Finally, the numerical model will be validated against experimental data obtained for this effect during the project as well as published in the literature.

Publications

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Pimenta S (2009) A micromechanical model for kink-band formation: Part II-Analytical modelling in Composites Science and Technology

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Pinho ST (2012) On longitudinal compressive failure of carbon-fibre-reinforced polymer: from unidirectional to woven, and from virgin to recycled. in Philosophical transactions. Series A, Mathematical, physical, and engineering sciences

 
Description Better failure criteria for composites, particularly for the fibre kinking failure mode
Exploitation Route They might be used through material subroutines for FE packages.
Sectors Aerospace, Defence and Marine,Leisure Activities, including Sports, Recreation and Tourism,Manufacturing, including Industrial Biotechology,Transport

URL http://wwwf.imperial.ac.uk/aeronautics/research/pinholab/
 
Description Failure criteria have been the basis of further research by bother researchers, and have also been implemented into FE codes
First Year Of Impact 2009
Sector Aerospace, Defence and Marine,Leisure Activities, including Sports, Recreation and Tourism,Manufacturing, including Industrial Biotechology,Transport
Impact Types Economic

 
Description abc: multiscale Analysis of Bonded Composite Structures
Amount £398,243 (GBP)
Organisation Airbus Group 
Sector Academic/University
Country France
Start 09/2009 
End 09/2012
 
Description iComp: Integrated method for structural design of composite structures
Amount € 170,000 (EUR)
Organisation Airbus Group 
Sector Academic/University
Country France
Start 09/2009 
End 09/2012
 
Title Computer models for failure of composite materials 
Description This model consists of: - several new failure criteria based on physical observations of different failure modes in composites - a new smeared crack approach to model failure propagation - a new pressure-dependent constitutive law. 
Type Of Material Computer model/algorithm 
Provided To Others? No  
Impact 2nd World-Wide Failure Exercise. In this exercise, world-leading experts were asked to use their theories to provide blind predictions for a comprehensive array of benchmark cases for fail- ure of composites. The theories, and their proposers, were then ranked in two lists corresponding to 'quantitative' and 'qualitative' merit. The blind predictions of the team STP led ranked the highest in both lists. See AS Kaddour and MJ Hinton, "Maturity of 3D failure criteria for fibre- reinforced composites: Comparison between theories and experiments: Part B of WWFE-II", Journal of Composite Materials 2013 47(67) 925966, DOI: 10.1177/0021998313478710). 
 
Description AIRBUS OPERATIONS LIMITED 
Organisation Airbus Group
Country France 
Sector Academic/University 
PI Contribution STP's failure models used extensively by Airbus: "We've been collaborating with Dr Pinho over a number of years on the development of models for failure of composite structures. This is a very challenging area and these models constitute a positive contribution to our capability to predict damage in large components." (Dr Morten Ostergaard, Airbus Senior Expert in Structure Modelling and Non-Linear Finite Element Analysis, Morten.Ostergaard@Airbus.com)
Collaborator Contribution Airbus provided funding, test cases and industrial context.
Impact 1. STP's failure models used extensively by Airbus: "We've been collaborating with Dr Pinho over a number of years on the development of models for failure of composite structures. This is a very challenging area and these models constitute a positive contribution to our capability to predict damage in large components." (Dr Morten Ostergaard, Airbus Senior Expert in Structure Modelling and Non-Linear Finite Element Analysis, Morten.Ostergaard@Airbus.com) 2. Several papers are the result of funding from Airbus.
Start Year 2007
 
Description Renault F1 Team Limited 
Organisation Renault F1 Team Limited
Country United Kingdom 
Sector Private 
PI Contribution Developed failure models
Collaborator Contribution Provided funding and industrial constraints
Impact Papers
Start Year 2006