This proposal designed and manufactured an innovative shield to protect critical components of an aircraft against high velocity shrapnel from an engine burst.
The concept of the shield design was based on in house modelling capabilities of Imperial consultant to use different fibres acting as membranes through the thickness of the ballistic structure. In addition to this, these fibre layers are interlaced by foam to provide optimum performance. This use of almost dry layers within foam sub-laminates was investigated at the modeling stage. The specific polymer used heavily depended on the temperature requirements as well as other aircraft integration constraints and hence subjected to more detailed discussions. The manufacturing was provisionally done by press with matrix film layers. The specific matrix used was again subject to the temperature requirements.
The proposal had come from a close collaboration between the Imperial College Consultants and Swerea SICOMP. It was therefore the result of the combined skills in manufacturing structural composites for the defence and aeronautical industry as well as specific ballistic design skills. Both institutes have the necessary skills, experience and equipment to design and manufacture a successful shield. As both these institutes are non profit research establishments actively working to advance composite technology, the materials and techniques have been chosen based on the type of treat and the aircraft integration constraints and there is no constrain to use any one particular material supplier. Publishing and dissemination of the results was also not a problem if so desired.
Advisory Council for Aeronautical Research in Europe (ACARE) have set out a goal of reducing fuel consumption per passenger by 50% from the levels in 2000 by 2020. In the clean sky partnership program fuel saving and thus weight savings are a central issue towards achieving these ACARE goals. One accepted approach to achieving these goals is widespread use of composite materials in aircraft. Another approach is the use of uncontained engines mounted close to the fuselage, as suggested in the Clean Sky Smart Fixed Wing Aircraft (SFWA) initiative. Failure of rotating aircraft engine components may result in fragments thrown outwards at high velocity and may easily damage the fuselage or other primary structure. To prevent this damage occurring, impact shielding has to be integrated with the fuselage and other structures at risk. The main objective of this project was to design and manufacture three innovative shielding design concepts to protect critical components of an aircraft against high velocity shrapnel from an engine burst. In order to meet the requirement for low weight in aircraft applications, making the shielding from high performance fibres was an obvious solution. The concepts proposed therefore used well-established high-performance fibres and manufacturing methods to fit the requirements of medium to high maturity level and low manufacturing costs stated in the call.
From the negotiations in 2012, the decision was made to divide the IMPSHIELD project into three projects (A, B and C). Then, since SICOMP coordinated the three projects and as the approach and structure were the same for the three projects, the consortium and project partners agreed to handle IMPSHIELD A, B and C as a single project from a management and reporting point of view. From a financial point of view, the summarized time spent on each project over the three reporting periods reflects the work done respectively in the projects.
The kick-off meeting was held together with the IMPTEST project in April 2013 since the IMPSHIELD project was so closely connected to the IMPTEST project. It was agreed about having the project meetings together in the future. A lot of valuable time was spent on getting access to the projects as a coordinator for the three projects; it was finally solved in December 2014 one and a half years after the project started.
Most of the design work for the three shields was performed by subcontractor ICON (Imperial College Consultants) in WP2 of each project. The differences in size and weight between the three projectiles led to changes in the design along the way for the three shields.
The corrugated design for shield A was abandoned since the impact simulations showed that the waves should be too small for the smallest and lightest projectile, i.e. almost flat. The shields were built up from a number of flat 2mm S2-glass laminates depending of projectile, all in all 155 2mm laminates were manufactured for the phase one delivery of 15 A-shields.
For the B shield the idea with folded loops was abandoned when the simulations showed that the folded loops will not unfold as wanted for these projectiles as they do for example on bird impact. A UHMWPE prepreg was used for the B-shields.
The design calculations for shield C showed that an air gap (foam core) between the laminates in the shield did not improve the performance of the shields for these projectiles. The consortium decided to go for a pure aramid laminate solution built up from several 5mm laminates without an air gap, for phase one delivery 50 5mm laminates were manufactured.
After initial compaction-, bleed- and process tests for the A and C shields, the manufacturing (WP3) of the panels for phase one started at SICOMP according to the design agreed. Both shields were hot-pressed, but the application of the resin differed. For shield A the resin was applied using a spray-gun since the resin was a thermoset powder and for the C-shield the resin was an epoxy film. Shield B was manufactured according to the design specification with chosen high performance fibre, (UHMWPE) according to the prepreg solution, and hot-pressed, by Honeywell since they would not let the project buy just the material. The panels were delivered to SICOMP for control and making mounting holes to fit the test rig. Honeywell could not share all of the data with the project due to a mixture of the data being ITAR controlled or Honeywell proprietary. Analysis was performed at SICOMP to get at least some of the data needed for the evaluation of the B-panels.
Problems getting the material needed and the IMPTEST-project not being able to fire their gas-gun as scheduled, due to safety regulations, to test the phase one panels led in November to an amendment for the project to be extended to July 2015. At the delayed “mid-term” review in January 2015 it was decided, from the phase one testing results in IMPTEST, that the project was to continue with the B- and C-panels for phase two and ageing. Most of the manufactured panels were delivered to Imperial College in London for phase two testing in IMPTEST, but five of each was kept for ageing at SICOMP. A literature review on the effects of environment of the materials was done (WP4) and led to the ageing conditions. The panels were aged in an environmental chamber for almost two months, monitoring the weight gain approximately ever 100th hour. After the ageing process, the panels were delivered to London for testing in IMPTEST.
Some of the work and lessons learned in the IMPSHIELD projects will be included in the dissemination of the IMPTEST project.