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Details of Grant 

EPSRC Reference: GR/T26696/01
Title: Physically-Based Mixed-Mode Failure Criteria For Delamination Growth In Composite Materials
Principal Investigator: Greenhalgh, Professor ES
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department: Aeronautics
Organisation: Imperial College London
Scheme: First Grant Scheme Pre-FEC
Starts: 01 October 2005 Ends: 31 December 2008 Value (£): 120,308
EPSRC Research Topic Classifications:
Design & Testing Technology Materials Characterisation
EPSRC Industrial Sector Classifications:
Aerospace, Defence and Marine
Related Grants:
Panel History:
Panel DatePanel NameOutcome
19 Oct 2004 Structural Prioritisation Panel (Tech) Oct 04 Deferred
Summary on Grant Application Form
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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