Projects: Projects for Investigator
Reference Number GR/T26696/01
Title Physically-Based Mixed-Mode Failure Criteria For Delamination Growth In Composite Materials
Status Completed
Energy Categories Renewable Energy Sources(Wind Energy) 10%;
Not Energy Related 90%;
Research Types Basic and strategic applied research 100%
Science and Technology Fields PHYSICAL SCIENCES AND MATHEMATICS (Metallurgy and Materials) 50%;
ENGINEERING AND TECHNOLOGY (Mechanical, Aeronautical and Manufacturing Engineering) 50%;
UKERC Cross Cutting Characterisation Not Cross-cutting 100%
Principal Investigator Dr ES Greenhalgh
No email address given
Imperial College London
Award Type Standard
Funding Source EPSRC
Start Date 01 October 2005
End Date 31 December 2008
Duration 39 months
Total Grant Value £120,308
Industrial Sectors Aerospace; Defence and Marine
Region London
Programme Materials, Mechanical and Medical Eng, Physical Sciences
Investigators Principal Investigator Dr ES Greenhalgh , Aeronautics, Imperial College London (100.000%)
Web Site
Abstract Although delamination has long been recognised as the 'Achilles Heel' of laminar composites, reliable prediction of delamination growth is still proving to be problematic, leading to the use of large safety factors and reticence in using composites in safety-critical applications. This has led to composite structures being perceived as expensive to fabricate and needing frequent inspection and repair, significantly impacting upon ownership costs. The recognised approach to studying delamination has been to characterise fracture toughness (G); the change in strain energy for an increment of crack growth. When the applied strain energy exceeds a critical material property (Gc), crack growth will occur. G is usually split into mode I (peel) and mode 11 (shear) components because Gc is dependant upon the relative proportions of these components (mode mixity). By conducting experimental tests under controlled mixed-mode combinations, a delamination failure locus is produced; a graph of GI against Gil. Such a locus can be described by a mathematical expression (failure criterion) which can be implemented within a finite element model of a damaged composite structure.However, in practice, this approach has proved to be problematic and can be unreliable. Although a range of failure criteria have been developed, most of them are purely empirical (i.e. no physical basis). In particular, there is little or no relationship between the physical mechanisms for delamination growth, and the parameters used in failure criteria. Clearly, if engineers are to have confidence in designing composite structures against delamination, developing criteria with physical basis is vital. The principle aims of this proposal are to develop failure criteria which are based on the physics of delamination fracture in composites. These criteria will include parameters that relate to the influence of loading, material and environmental factors. These aims will be achieved through both experimental investigation (fracture toughness testing) and predictive (analytical and numerical) models, linking these approaches through detailed fractographic analysis. This approach will provide an insight into the dominant failure mechanisms that control delamination toughness, model their contributions, leading to formulation of a physically based failure criterion. The research will focus on carbon-fibre composites (modified epoxy and thermoplastic), but the findings will be generic, being applicable to a range of platforms such as aerospace, marine, civil infrastructure and transport structures. The research will entail a Studentship at the Composites Centre at Imperial College London and will extend over three years, costing a total of 115K
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Final Report (none)
Added to Database 23/03/12