One of the major limitations of polymeric composites for structural applications was the ability of the matrix to withstand and maintain load transfer capability at high temperatures. The current project, HicTac, addressed this drawback and aimed at the development of composites capable to withstand temperatures above 360 degrees.
The technical strategy was to continue the development of polyimide (PI) based chemistries. Such development was already ongoing at one of the partners, Nexam AB – a company that develops and produces high temperature polymers and chemistries. Effort was spent on adapting and proving that such polymers can be used for manufacturing composite samples and simplified composite structures.
This development was performed at Swerea SICOMP AB - research institute devoted to development of composite material technologies. The properties of the composites material were thoroughly characterised in terms of mechanical properties under environmental loadings. The project also included development, manufacturing and testing of simplified but relevant sub-elements as well as manufacturing of a certain number of aerodynamically shaped parts.
Although ceramic and metal matrix composites can be used at several thousand degrees, there is great interest and strong incentives to use polymeric composites in high temperature applications since polymeric composites are more lightweight, have better fatigue properties and are more ductile.
The overall objective of the current project responded to this industrial need through development of a cost effective organic matrix resin with 360°C temperature capability as well as proving its feasibility in carbon fibre manufacturing. The composite system should hence exhibit both robust performance and composite processing characteristics that ultimately enabled high rate production of carbon fibre reinforced organic matrix composite components. Possible applications of this technology are the vanes at the first stage of an IP/LP Compressor or other lightweight parts of next generation aeroengines. Although not particularly addressed in the project it was foreseen that such temperature resistant and lightweight parts will be of key importance to realise next generation’s high by-pass ratios aeroengines.
Two partners, Swerea SICOMP and Nexam Chemicals, were participating in the project.
The initial part of the work was devoted to develop and define of polymer formulations, materials, manufacturing methods as well as design and planning of tests. Already early in the project it was decided to develop a new phenylethynyl terminated thermosetting polyimide formulation particularly tailored to work for so-called resin transfer moulding (RTM) processing of carbon fibre reinforced composites. A major challenge with such system was to tailor the formulation so that the temperature performance (glass transition temperature, Tg, above 360°C) could be achieved for a material with sufficiently low melt viscosity and appropriate curing characteristic. Nexam were successful in their efforts and developed a resin formulation, currently available to the market under the tradename NEXIMID® MHT-R. Development of RTM-manufacturing technologies required to manufacture these high temperature resins were successfully in parallel at the other partner in the project, Swerea SICOMP. To our knowledge, very limited efforts have been done in this aspect previous. This part of the work included tailoring of manufacturing schemes and practical procedures that enables RTM manufacturing at temperatures in the range between 250- 370°C.
The developed resins and manufacturing procedures were used to prepare laminates and coupons for mechanical and thermal characterisation. It was found and reported that the developed composites were of high general quality, they exhibited low void contents and few manufacturing induced cracks. Manufacturing induced cracks can often be an issue with polymer composites manufactured at high temperature due to high internal stresses due to thermal mismatch between fibres and matrix during cooling down from the cure temperature. Glass transition temperatures at around 370°C were achieved with the standard curing schedule used in the project. Mechanical testing was performed at various temperatures and after different environmental exposures such as thermal oxidative ageing and thermal cycling.
Eventually the material and manufacturing concepts were proven through successful development and manufacturing of demonstrators. The demonstrator component was selected and developed with input from aeroengine companies and was an about 300 mm x 150 x 30 to 3 mm large component with blade-like geometrical features. The demonstrator was manufactured using RTM.
The successful development and demonstration of durable high-temperature polymers and composites and the associated manufacturing technologies within the framework of HicTac is provides a key technology that enables wider use of lightweight technologies and polymeric composites in aero engines in general and in high by-pass ratio engines in particular.
The success of HicTac can, in the light of the above, have strong impact on aviation, the possibility to meet the visions of ACARE and more specifically to meet the targets of Clean Sky.
The measures taken by HicTac to promote and facilitate highest possible impact of the work have been to continuously work and communicate project results with the European aero engine and component producers, Rolls Royce and GKN Aerospace, involved in the program. Information about the new resin formulation, NEXIMID® MHT-R, was communicated through press releases and via the available marketing channels of the partners. In addition to this the project has communicated results through participation at scientific conferences in the area (six conference presentations). Two to three manuscript aimed at submission to scientific journals is currently under preparation.