Final Report Summary - SEALEDBOX (AEROSPACE HOUSING FOR EXTREME ENVIRONMENTS)
Executive Summary:
The amount of electronically controlled tasks in modern aircraft is increasing steadily and also the contribution of racks for avionics to the overall weight of an aircraft has reached a magnitude that requires an analysis to obtain mass reduction. Most of the avionics fielded today offer a monolithic architecture in form of a closed box packed with electronics and lots of connectors at the front or the back with corresponding heavy cable harness. The housing protects the electronics against the environment, ensures EMC and supports the thermal management.
Currently, housings for electronics are manufactured out of aluminium sheets. Aluminium housings tend to be quite heavy and during the machining a large amount of material is discarded, making the process not very efficient. In order to reach higher power density and lower costs, the optimisation of the housing is a must. The aluminium approach performs well, but there is still room for improvement.
SEALEDBOX project defends composite materials in electronic enclosures would provide benefits, mainly in terms of mass saving, while keeping performance. The use of composite materials in commercial airplane structures has demonstrated the technical and economic feasibility of these materials to cope with the stringent aeronautic requirements and the advantages over their metallic counterparts. Thus, it is time to transfer the composites technology and benefits to other components in order to reduce their contribution to the overall mass and improve the fuel efficiency.
Advanced fibre-reinforced composite materials have several key properties that make them especially useful in aerospace applications. Their high specific strength and stiffness, the improved fatigue behaviour and their corrosion resistance convert them in the optimum candidate materials for the design of lightweight electronic housings.
The objective of the present project was the development of an integrated solution for a hermetic sealed low weight and low cost power electronic housing for unpressurised area (DO160).
The goal is the demonstration that lightweight composite materials are a cost effective alternative for the manufacturing of hermetic sealed enclosures for housing electronic equipment to be installed in the unpressurised area of airplanes, which involves the fulfilment of vibration requirements listed in DO-160, “Environmental Conditions and Test Procedures for Airborne Equipment”.
Hermetic sealed housing has been re-engineered applying the composite approach. Specifications have been drawn and architectures, manufacturing processes and materials have been envisaged, evaluated and a traded-off.
The potential problems in the composite design have been anticipated and alternative countermeasures have been evaluated. In order to keep manufacturing costs as low as possible, a design concept having infusion as manufacturing process has been selected. Regarding the materials, standard high strength carbon fibres together with aero grade infusion epoxy resin have been selected as main materials for the production of the covers. Trials at sample level have been performed in order to explore the different material solutions identified.
Detailed analyses indicate covers are able to withstand the dynamic environment. The selected laminate fulfils both lightness and stiffness requirements. Thermal results obtained are in line with the aluminium counterpart. No problems due to CTE mismatch are foreseen.
The manufactured composite structures successfully passed the electrical bonding and sand and dust tests performed. Damage of the painting was observed during the thermal testing. It was attributed to an over thickness in the EMI layer. Additional trials performed to optimize the painting procedure showed no damage in the samples.
Compared to the current aluminium approach, significant weight reductions have been obtained: 32 % reduction with respect to the aluminium covers.
Project Context and Objectives:
The amount of electronically controlled tasks in modern aircraft is increasing steadily and also the contribution of racks for avionics to the overall weight of an aircraft. Electronics enclosures are discrete structures designed for the sole purpose of holding printed circuit boards and electrical components in place. The proper housing protects the electronics against the environment, ensures EMC and supports the thermal management. In order to reach higher power density and lower costs the optimisation of the housing is a must.
There is a tendency to replace the current aluminium electronics housings by lightweight composite housings. The advantages of high performance composites are many, including lighter weight, the ability to tailor lay-ups for optimum strength and stiffness, improved fatigue life, corrosion resistance and, with good design practice, reduced assembly costs due to fewer detail parts and fasteners. The specific strength and specific modulus of high strength fibre composites are higher than other comparable aerospace metallic alloys.
Modern structures built in composite technology are able to provide important mass savings with respect to conventional designs. The cost of composites is the number one deterrent to their broader application. However, the modularization and the manufacturing of standard components can drastically decrease the costs reducing recurring machining cost and material waste because a single reusable mould can be used to produce many near-net shape parts.
Advanced fibre-reinforced composite materials have several key properties that make them especially useful in aerospace applications. Their high specific strength and stiffness (strength/density, stiffness/density), allow obtaining structure designs that are lighter than traditional metal structures. Composite materials are lightweight and stiff. In comparison with metals, advanced composites exhibit superior fatigue performance due to their high fatigue limit and resistance to corrosion.
One of the main disadvantages of the use of composite materials in structures is their poor EMI-EMC shielding behaviour. EMI shielding requirements are based on the level and quality of continuous electrical conductivity across all housing walls, fixed joints and seams. The main objective of any type of shielding is to prevent the passage of electromagnetic waves into or out of the device. The fundamental aim is to establish a Faraday cage to provide an EMI shield. Composite materials are not as electrically conductive as traditional metal structures. Therefore, extra steps must be taken to mitigate this deficiency.
Composite components tend to be higher in cost than their metallic counterparts. Material selection has to be carried out taking into account the requirements to be fulfilled versus cost. In this specific case, materials consumption is very low, thus the raw materials cost is not driving the cost of the final component, which is much more affected by the manufacturing process and the required secondary operations. Thus, an application where a modular/standardised approach can be followed can benefit from reduced manufacturing costs.
In addition, if manufacturing of large series is required, alternative manufacturing processes as RTM could be used. The tooling costs for RTM process are much higher than the required for an infusion process because a closed two parts mould that has to withstand the high injection pressures is required. However, RTM has a clear automation potential. A specific press could be used for holding the two mould halves in order to provide the required closing force and the mould movements. Therefore, for large series, RTM process could be a more suitable process.
The objective of the present project is the development of an integrated solution for a hermetic sealed low weight and low cost power electronic housing for unpressurised area (DO160). A lightweight composite cover has to be developed for hermetic sealed housings. The aim is to reduce 40 % the weight of the covers currently made of anodized aluminium with electrically conductive bonding areas (Alodine 1200), and cost neutrality.
The innovation of the project lies on taking advantage of commercially available materials and technologies (at an affordable cost) and combining them with composite processing techniques in order to yield a multifunctional design based on CFRP laminates, with same or improved functionality (mechanical, thermal and electrical), lighter weight and reasonable initial manufacturing cost.
The project has been divided in work packages were the following activities have been carried out:
• Definition of specifications and test matrix.
• Conceptual design of the bus system housing for extreme environment.
• Identification of the critical aspects that need further study / development.
• Identification of the contingency techniques / strategies
• Development at sample level.
• Detail design of the housing
• Manufacturing of the housing
• Validation of the housing
The work has been carried out by TECNALIA.
Project Results:
This chapter summarizes the activities carried out and results achieved under SEALEDBOX Project.
A sealed housing of a Motor Control Unit (MCU) has been identified as application by LEG. The current design is based on traditional aluminium construction (machining). The box is made out of three parts: two covers +body. Covers are manufactured in 7075 T7351 aluminium alloy whereas 7050 alloy has been used for the body.
As a first step the specifications for SEALEDBOX housing have been drawn. The tests to be performed to validate the housing have been identified and specified. The validation campaign to be carried out by TECNALIA includes thermal, electrical bonding and sand and dust tests.
A conceptual design based on composite material was identified. Different architectures, manufacturing processes and materials were envisaged, evaluated and traded-off. To perform the comparison, criteria as cost, simplicity in manufacturing, simplicity in assembly and weight, among others, have been considered and weighted.
The conceptual design of the electronic housing has been defined. As a conclusion of the trade-offs performed, the following features were selected:
• Infusion manufacturing process, either liquid or film infusion
• Monolithic plate was selected for the production of the covers. The easy of manufacturing and the potential for industrialisation were the key aspects for this selection.
• Carbon fibre: low cost high strength fibre was selected based on the trade off plus the results obtained in the simplified thermal and mechanical model.
• Resin: As a first step, a fire resistant resin and some standard resins with additional materials to provide the required fire behaviour were tested. Based on the results obtained at sample level, the fire resistant resin was selected.
Additional functional layers have been added to each cover to prevent galvanic corrosion, provide electrical conductivity and protect against the harsh environment.
An extensive characterization campaign was carried out. The following trials for the points of concern have been carried out:
• Fire behaviour
Flammability: to check the non-propagation of the flame in the case that ignition would appear inside or outside of the equipment. Tests with standard resins, standard resin+intumescent veil, fire improved resin were performed. All samples passed the flammability test.
Simplified Fire Proof: flame kept for 15 minutes. Resins with and without intumescent veil and / or painting were tested. The temperature profile read in the samples is quite similar; being the lowest temperatures the ones obtained with the fire improved resin + intumescent paint. The best behaviour (less material loss) was found for the resin with improved fire behaviour coated with the intumescent paint. However, the appearance of the bare sample was just slightly The resin with improved fire behaviour was selected as the baseline project for the rest of the testing campaign.
• Fungus testing: Material with best fire performance was used. Samples without coating and samples with the coating required for EMI-EMC shielding have been tested. No growth of fungi or other effect on the surface of coated samples was observed. Growth of fungi and surface modification was observed in samples without coating.
• Fluid Susceptibility testing: Material with best fire performance was used. After putting in contact the material with the fluids, a bending test of the sample has been performed in order to see if there was a detriment in the structural performance. Although slight variations in the modulus exist, values obtained are very close to the reference material Values obtained with coating are in general very similar or better to the ones without coating. In general, there is small reduction of the strength both for the coated and uncoated specimens. The biggest reductions have been found with the Skydrol tested at 110 ºC and Aeroshell 22 when samples are without coating. The EMI coating has a beneficial effect with these fluids. The coating has had a negative effect with the Kerosene.
• Mechanical characterization of the laminates: fibre weight and volume content, tensile, in plane shear and compression testing and dry glass transition temperature measurements have been manufactured. The obtained properties are in good agreement with the properties provided in the technical datasheet. They correspond to the typical properties of an infused carbon laminate. The mean values have been used in the detailed design of the prototype.
• Thermal characterization: The glass transition temperature of the resin has been obtained using a modulated DSC analysis, with a heating ramp of 5º/min. The calculated value is 260ºC, which is in good agreement with value provided in the resin datasheet.
• EMI/EMC aspects: strategy developed in LIGHTBOX project has been implemented.
• Electrical bonding issues: The same solutions used for EMI-EMC shielding have been tested for electrical bonding. In addition, a conductive O ring has been used in the final prototype, showing a dramatic reduction of the bonding resistance and fulfilling the requirement.
• Hermeticity: Measurements in an assembly representing real housing were conducted. Standard O-ring used for the reference aluminium design has been used. A comparative study between the current approach (aluminium housing) and SEALEDBOX development (CFRP covers) was carried out. Pressure and vacuum loss before and after thermal cycling were measured. No variations are observed after 1 minute of testing. The hybrid CFRP – aluminium housing fulfils the requirements.
• Waterproofness: These tests determine whether the equipment can withstand the effects of liquid water being sprayed. This test has been performed before and after the thermal cycling. Each side of the mating area top cover- body has been subjected to 5 min of water spray. No water was detected in the inner part of the housing.
• Thermal cycling 100 cycles between the temperature range -60 ºC / 110 ºC have been carried out. No visual damage was observed.
• Galvanic corrosion: trials have been performed at sample level over materials in the final configuration (primer+EMI coating+top coat) and also in samples without primer and without top coat. Samples were kept in the chamber for 240 hours. No galvanic corrosion was found between the CFRP and the aluminium.
Based on the results obtained in the characterization campaign and on the requirements to be fulfilled detailed thermal, mechanical and thermo-mechanical analysis of the housing were carried out. From the analysis performed, it can be concluded that:
• Thermal, mechanical, thermomechanical and pressure analysis indicate the equipment is able to withstand safely the imposed load levels.
• Stresses obtained in the mechanical and pressure analyses are low and are far from the material allowable. Failure indexes encountered in the covers also indicate the housing will survive the environment.
• From the thermal point of view, temperatures similar to the current aluminium approach have been observed. Maximum temperature is observed in the electronics (129 ºC), whereas in the CFRP covers temperatures of 94 ºC were read.
• Lower margins are obtained in the thermomechanical analysis, where temperature is superposed to the mechanical restrictions. However, values obtained indicate the housing will work safely.
The validation campaign carried out indicates:
• Thermal test: A passive test considering the worst thermal conditions has been carried out. The thermal distribution on the cover was as expected. Nevertheless, after the test, some bubbles appeared in the covers, indicating an inadequate painting procedure. Additional painting trials have been performed and subjected to the thermal test. Nor bubbles nor any other degradation sight have been observed in the specimen.
• Initial electrical bonding tests carried out at unit level indicated the adopted solution based on the EMI paint was not reliable enough. Measurements were slightly below the required resistance threshold. Hence, the adopted solution was to replace the O ring gasket originally provided by LEG with the aluminium housing by conductive O ring. The bonding test conducted on the equipment with this new seal showed a dramatic reduction of the bonding resistance.
• Sand and dust: No conspicuous signs of degradation have been observed.
Hence, it can be concluded that a significant weight reduction has been achieved by SEALEDBOX CFRP prototype. A 32 % weight reduction has been obtained in the covers. This can bring about a fuel saving of 1.556 litres of fuel per year for single equipment. Considering a fuel cost of 0.5 €/l, this means a cost saving on operation costs of about 778 € per year (for one redesigned equipment).
From the manufacturing point of view, cost estimation has been conducted. The recurrent cost for a set of two covers amounts to 244 €. Considering an industrial process based on a run of 5.000 enclosures in ten years, the production cost obtained is 260 € per enclosure.
Potential Impact:
In 2012 Europe’s aeronautical sector (civil and military activities) recorded a turnover of €127,5 bn. Civil aeronautics represents nearly 64% of the European aeronautics industry in terms of turnover. It is by far the most important sector of ASD industries.
One of the impacts requested by the European Commission, is to reduce fuel consumption and hence CO2 emissions by 50% per passenger km as CO2 is a significant contributor to global warming and is directly related to fuel burn (considered in the Strategic Research Agenda). Eco-efficient aircrafts, which involve producing highly efficient aircrafts, are needed. Therefore, it is crucial to develop lightweight technologies that imply important mass savings and, as a consequence, a reduction of emissions.
Materials and systems need to be smaller, lighter, stronger, more resistant to the environment and longer lasting. According to literature, 1 kg weight reduction saves over 2900 l of fuel per year.
The current trend is to reduce weight, so lightweight composite materials have been increasingly used. Successful composite designs can provide design flexibility, lightweight parts, ease of fabrication and installation (generally fewer parts), corrosion resistance, impact resistance, high fatigue strength (compared to metal structures with the same dimensions) and product simplicity when compared to conventional fabricated metal structure. Composite materials and their manufacturing processes can be tailored specifically to given design constraints.
The main challenges restricting their use are material and processing costs, impact damage and damage tolerance, electrical properties, repair and inspection, dimensional tolerance, size effects on strength and conservatism associated with uncertainties about relatively new and sometimes variable materials.
With the lightweight and modular composite solution developed, SEALEDBOX project has achieved a mass reduction of around 32 % in the electronics housing (536 grams saved in a single housing), promoting actively the decrease of fuel consumption and, as a consequence, of detrimental gas emissions. According to the estimations obtained in literature, this can bring about a fuel saving of 1.556 litres per year and considering a fuel cost of 0.5 €/l, this means a cost saving of about 778 € per year. According to literature, this would mean 3.986 kg/year CO2, 26.414 kg/year NOx, 1,23 kg/year SO2 and 0.7 kg CO.
New technologies may open the door to high performance, environment friendly and economic aircraft operation by better exploiting available weight reduction potentials of new design philosophies without compromising the existing, high aerospace safety requirements.
Dissemination activities
General information regarding SEALEDBOX project has been provided in:
• Space Science and technology master (Basque Country University)
• JEC fair: in two different stands: TECNALIA and HUNTSMAN
A general overview of SEALEDBOX Project has been presented to the following Companies: CRISA, TAS-E, Airbus, Chomerics, Huntsman, SAFT.
Information provided does not affect knowledge protection, the partner’s and Topic Manager‘s confidentiality or their commercial interests.
Exploitation
TECNALIA
Knowledge gained in the project has strengthened TECNALIA’s position as a niche technology provider of advanced composite components. This project has enabled to extend the validation of the boxes under aeronautic standards.
Developments carried out in the area of lightweight electronics housing has allowed proving the feasibility of profitably producing an avionics box that meets the requirements in terms of functionality and at relatively low cost.
TECNALIA has reached a TRL5-6 (Component and/or breadboard validation in relevant environment, ESA definition) in the development of lightweight composite boxes. Breadboards have been qualified in the representative environment on ground. The current project has allowed increasing the applications for the lightweight housings in sealed avionics.
The project has also strengthen the collaboration between TECNALIA and LEG in the re-engineering of avionics systems by using lightweight boxes complementing the supply chain between technology provider and end user.
List of Websites:
Project Coordinator: Fundación Tecnalia Research and Innovation (Garbiñe Atxaga, garbine.atxaga@tecnalia.com)
The amount of electronically controlled tasks in modern aircraft is increasing steadily and also the contribution of racks for avionics to the overall weight of an aircraft has reached a magnitude that requires an analysis to obtain mass reduction. Most of the avionics fielded today offer a monolithic architecture in form of a closed box packed with electronics and lots of connectors at the front or the back with corresponding heavy cable harness. The housing protects the electronics against the environment, ensures EMC and supports the thermal management.
Currently, housings for electronics are manufactured out of aluminium sheets. Aluminium housings tend to be quite heavy and during the machining a large amount of material is discarded, making the process not very efficient. In order to reach higher power density and lower costs, the optimisation of the housing is a must. The aluminium approach performs well, but there is still room for improvement.
SEALEDBOX project defends composite materials in electronic enclosures would provide benefits, mainly in terms of mass saving, while keeping performance. The use of composite materials in commercial airplane structures has demonstrated the technical and economic feasibility of these materials to cope with the stringent aeronautic requirements and the advantages over their metallic counterparts. Thus, it is time to transfer the composites technology and benefits to other components in order to reduce their contribution to the overall mass and improve the fuel efficiency.
Advanced fibre-reinforced composite materials have several key properties that make them especially useful in aerospace applications. Their high specific strength and stiffness, the improved fatigue behaviour and their corrosion resistance convert them in the optimum candidate materials for the design of lightweight electronic housings.
The objective of the present project was the development of an integrated solution for a hermetic sealed low weight and low cost power electronic housing for unpressurised area (DO160).
The goal is the demonstration that lightweight composite materials are a cost effective alternative for the manufacturing of hermetic sealed enclosures for housing electronic equipment to be installed in the unpressurised area of airplanes, which involves the fulfilment of vibration requirements listed in DO-160, “Environmental Conditions and Test Procedures for Airborne Equipment”.
Hermetic sealed housing has been re-engineered applying the composite approach. Specifications have been drawn and architectures, manufacturing processes and materials have been envisaged, evaluated and a traded-off.
The potential problems in the composite design have been anticipated and alternative countermeasures have been evaluated. In order to keep manufacturing costs as low as possible, a design concept having infusion as manufacturing process has been selected. Regarding the materials, standard high strength carbon fibres together with aero grade infusion epoxy resin have been selected as main materials for the production of the covers. Trials at sample level have been performed in order to explore the different material solutions identified.
Detailed analyses indicate covers are able to withstand the dynamic environment. The selected laminate fulfils both lightness and stiffness requirements. Thermal results obtained are in line with the aluminium counterpart. No problems due to CTE mismatch are foreseen.
The manufactured composite structures successfully passed the electrical bonding and sand and dust tests performed. Damage of the painting was observed during the thermal testing. It was attributed to an over thickness in the EMI layer. Additional trials performed to optimize the painting procedure showed no damage in the samples.
Compared to the current aluminium approach, significant weight reductions have been obtained: 32 % reduction with respect to the aluminium covers.
Project Context and Objectives:
The amount of electronically controlled tasks in modern aircraft is increasing steadily and also the contribution of racks for avionics to the overall weight of an aircraft. Electronics enclosures are discrete structures designed for the sole purpose of holding printed circuit boards and electrical components in place. The proper housing protects the electronics against the environment, ensures EMC and supports the thermal management. In order to reach higher power density and lower costs the optimisation of the housing is a must.
There is a tendency to replace the current aluminium electronics housings by lightweight composite housings. The advantages of high performance composites are many, including lighter weight, the ability to tailor lay-ups for optimum strength and stiffness, improved fatigue life, corrosion resistance and, with good design practice, reduced assembly costs due to fewer detail parts and fasteners. The specific strength and specific modulus of high strength fibre composites are higher than other comparable aerospace metallic alloys.
Modern structures built in composite technology are able to provide important mass savings with respect to conventional designs. The cost of composites is the number one deterrent to their broader application. However, the modularization and the manufacturing of standard components can drastically decrease the costs reducing recurring machining cost and material waste because a single reusable mould can be used to produce many near-net shape parts.
Advanced fibre-reinforced composite materials have several key properties that make them especially useful in aerospace applications. Their high specific strength and stiffness (strength/density, stiffness/density), allow obtaining structure designs that are lighter than traditional metal structures. Composite materials are lightweight and stiff. In comparison with metals, advanced composites exhibit superior fatigue performance due to their high fatigue limit and resistance to corrosion.
One of the main disadvantages of the use of composite materials in structures is their poor EMI-EMC shielding behaviour. EMI shielding requirements are based on the level and quality of continuous electrical conductivity across all housing walls, fixed joints and seams. The main objective of any type of shielding is to prevent the passage of electromagnetic waves into or out of the device. The fundamental aim is to establish a Faraday cage to provide an EMI shield. Composite materials are not as electrically conductive as traditional metal structures. Therefore, extra steps must be taken to mitigate this deficiency.
Composite components tend to be higher in cost than their metallic counterparts. Material selection has to be carried out taking into account the requirements to be fulfilled versus cost. In this specific case, materials consumption is very low, thus the raw materials cost is not driving the cost of the final component, which is much more affected by the manufacturing process and the required secondary operations. Thus, an application where a modular/standardised approach can be followed can benefit from reduced manufacturing costs.
In addition, if manufacturing of large series is required, alternative manufacturing processes as RTM could be used. The tooling costs for RTM process are much higher than the required for an infusion process because a closed two parts mould that has to withstand the high injection pressures is required. However, RTM has a clear automation potential. A specific press could be used for holding the two mould halves in order to provide the required closing force and the mould movements. Therefore, for large series, RTM process could be a more suitable process.
The objective of the present project is the development of an integrated solution for a hermetic sealed low weight and low cost power electronic housing for unpressurised area (DO160). A lightweight composite cover has to be developed for hermetic sealed housings. The aim is to reduce 40 % the weight of the covers currently made of anodized aluminium with electrically conductive bonding areas (Alodine 1200), and cost neutrality.
The innovation of the project lies on taking advantage of commercially available materials and technologies (at an affordable cost) and combining them with composite processing techniques in order to yield a multifunctional design based on CFRP laminates, with same or improved functionality (mechanical, thermal and electrical), lighter weight and reasonable initial manufacturing cost.
The project has been divided in work packages were the following activities have been carried out:
• Definition of specifications and test matrix.
• Conceptual design of the bus system housing for extreme environment.
• Identification of the critical aspects that need further study / development.
• Identification of the contingency techniques / strategies
• Development at sample level.
• Detail design of the housing
• Manufacturing of the housing
• Validation of the housing
The work has been carried out by TECNALIA.
Project Results:
This chapter summarizes the activities carried out and results achieved under SEALEDBOX Project.
A sealed housing of a Motor Control Unit (MCU) has been identified as application by LEG. The current design is based on traditional aluminium construction (machining). The box is made out of three parts: two covers +body. Covers are manufactured in 7075 T7351 aluminium alloy whereas 7050 alloy has been used for the body.
As a first step the specifications for SEALEDBOX housing have been drawn. The tests to be performed to validate the housing have been identified and specified. The validation campaign to be carried out by TECNALIA includes thermal, electrical bonding and sand and dust tests.
A conceptual design based on composite material was identified. Different architectures, manufacturing processes and materials were envisaged, evaluated and traded-off. To perform the comparison, criteria as cost, simplicity in manufacturing, simplicity in assembly and weight, among others, have been considered and weighted.
The conceptual design of the electronic housing has been defined. As a conclusion of the trade-offs performed, the following features were selected:
• Infusion manufacturing process, either liquid or film infusion
• Monolithic plate was selected for the production of the covers. The easy of manufacturing and the potential for industrialisation were the key aspects for this selection.
• Carbon fibre: low cost high strength fibre was selected based on the trade off plus the results obtained in the simplified thermal and mechanical model.
• Resin: As a first step, a fire resistant resin and some standard resins with additional materials to provide the required fire behaviour were tested. Based on the results obtained at sample level, the fire resistant resin was selected.
Additional functional layers have been added to each cover to prevent galvanic corrosion, provide electrical conductivity and protect against the harsh environment.
An extensive characterization campaign was carried out. The following trials for the points of concern have been carried out:
• Fire behaviour
Flammability: to check the non-propagation of the flame in the case that ignition would appear inside or outside of the equipment. Tests with standard resins, standard resin+intumescent veil, fire improved resin were performed. All samples passed the flammability test.
Simplified Fire Proof: flame kept for 15 minutes. Resins with and without intumescent veil and / or painting were tested. The temperature profile read in the samples is quite similar; being the lowest temperatures the ones obtained with the fire improved resin + intumescent paint. The best behaviour (less material loss) was found for the resin with improved fire behaviour coated with the intumescent paint. However, the appearance of the bare sample was just slightly The resin with improved fire behaviour was selected as the baseline project for the rest of the testing campaign.
• Fungus testing: Material with best fire performance was used. Samples without coating and samples with the coating required for EMI-EMC shielding have been tested. No growth of fungi or other effect on the surface of coated samples was observed. Growth of fungi and surface modification was observed in samples without coating.
• Fluid Susceptibility testing: Material with best fire performance was used. After putting in contact the material with the fluids, a bending test of the sample has been performed in order to see if there was a detriment in the structural performance. Although slight variations in the modulus exist, values obtained are very close to the reference material Values obtained with coating are in general very similar or better to the ones without coating. In general, there is small reduction of the strength both for the coated and uncoated specimens. The biggest reductions have been found with the Skydrol tested at 110 ºC and Aeroshell 22 when samples are without coating. The EMI coating has a beneficial effect with these fluids. The coating has had a negative effect with the Kerosene.
• Mechanical characterization of the laminates: fibre weight and volume content, tensile, in plane shear and compression testing and dry glass transition temperature measurements have been manufactured. The obtained properties are in good agreement with the properties provided in the technical datasheet. They correspond to the typical properties of an infused carbon laminate. The mean values have been used in the detailed design of the prototype.
• Thermal characterization: The glass transition temperature of the resin has been obtained using a modulated DSC analysis, with a heating ramp of 5º/min. The calculated value is 260ºC, which is in good agreement with value provided in the resin datasheet.
• EMI/EMC aspects: strategy developed in LIGHTBOX project has been implemented.
• Electrical bonding issues: The same solutions used for EMI-EMC shielding have been tested for electrical bonding. In addition, a conductive O ring has been used in the final prototype, showing a dramatic reduction of the bonding resistance and fulfilling the requirement.
• Hermeticity: Measurements in an assembly representing real housing were conducted. Standard O-ring used for the reference aluminium design has been used. A comparative study between the current approach (aluminium housing) and SEALEDBOX development (CFRP covers) was carried out. Pressure and vacuum loss before and after thermal cycling were measured. No variations are observed after 1 minute of testing. The hybrid CFRP – aluminium housing fulfils the requirements.
• Waterproofness: These tests determine whether the equipment can withstand the effects of liquid water being sprayed. This test has been performed before and after the thermal cycling. Each side of the mating area top cover- body has been subjected to 5 min of water spray. No water was detected in the inner part of the housing.
• Thermal cycling 100 cycles between the temperature range -60 ºC / 110 ºC have been carried out. No visual damage was observed.
• Galvanic corrosion: trials have been performed at sample level over materials in the final configuration (primer+EMI coating+top coat) and also in samples without primer and without top coat. Samples were kept in the chamber for 240 hours. No galvanic corrosion was found between the CFRP and the aluminium.
Based on the results obtained in the characterization campaign and on the requirements to be fulfilled detailed thermal, mechanical and thermo-mechanical analysis of the housing were carried out. From the analysis performed, it can be concluded that:
• Thermal, mechanical, thermomechanical and pressure analysis indicate the equipment is able to withstand safely the imposed load levels.
• Stresses obtained in the mechanical and pressure analyses are low and are far from the material allowable. Failure indexes encountered in the covers also indicate the housing will survive the environment.
• From the thermal point of view, temperatures similar to the current aluminium approach have been observed. Maximum temperature is observed in the electronics (129 ºC), whereas in the CFRP covers temperatures of 94 ºC were read.
• Lower margins are obtained in the thermomechanical analysis, where temperature is superposed to the mechanical restrictions. However, values obtained indicate the housing will work safely.
The validation campaign carried out indicates:
• Thermal test: A passive test considering the worst thermal conditions has been carried out. The thermal distribution on the cover was as expected. Nevertheless, after the test, some bubbles appeared in the covers, indicating an inadequate painting procedure. Additional painting trials have been performed and subjected to the thermal test. Nor bubbles nor any other degradation sight have been observed in the specimen.
• Initial electrical bonding tests carried out at unit level indicated the adopted solution based on the EMI paint was not reliable enough. Measurements were slightly below the required resistance threshold. Hence, the adopted solution was to replace the O ring gasket originally provided by LEG with the aluminium housing by conductive O ring. The bonding test conducted on the equipment with this new seal showed a dramatic reduction of the bonding resistance.
• Sand and dust: No conspicuous signs of degradation have been observed.
Hence, it can be concluded that a significant weight reduction has been achieved by SEALEDBOX CFRP prototype. A 32 % weight reduction has been obtained in the covers. This can bring about a fuel saving of 1.556 litres of fuel per year for single equipment. Considering a fuel cost of 0.5 €/l, this means a cost saving on operation costs of about 778 € per year (for one redesigned equipment).
From the manufacturing point of view, cost estimation has been conducted. The recurrent cost for a set of two covers amounts to 244 €. Considering an industrial process based on a run of 5.000 enclosures in ten years, the production cost obtained is 260 € per enclosure.
Potential Impact:
In 2012 Europe’s aeronautical sector (civil and military activities) recorded a turnover of €127,5 bn. Civil aeronautics represents nearly 64% of the European aeronautics industry in terms of turnover. It is by far the most important sector of ASD industries.
One of the impacts requested by the European Commission, is to reduce fuel consumption and hence CO2 emissions by 50% per passenger km as CO2 is a significant contributor to global warming and is directly related to fuel burn (considered in the Strategic Research Agenda). Eco-efficient aircrafts, which involve producing highly efficient aircrafts, are needed. Therefore, it is crucial to develop lightweight technologies that imply important mass savings and, as a consequence, a reduction of emissions.
Materials and systems need to be smaller, lighter, stronger, more resistant to the environment and longer lasting. According to literature, 1 kg weight reduction saves over 2900 l of fuel per year.
The current trend is to reduce weight, so lightweight composite materials have been increasingly used. Successful composite designs can provide design flexibility, lightweight parts, ease of fabrication and installation (generally fewer parts), corrosion resistance, impact resistance, high fatigue strength (compared to metal structures with the same dimensions) and product simplicity when compared to conventional fabricated metal structure. Composite materials and their manufacturing processes can be tailored specifically to given design constraints.
The main challenges restricting their use are material and processing costs, impact damage and damage tolerance, electrical properties, repair and inspection, dimensional tolerance, size effects on strength and conservatism associated with uncertainties about relatively new and sometimes variable materials.
With the lightweight and modular composite solution developed, SEALEDBOX project has achieved a mass reduction of around 32 % in the electronics housing (536 grams saved in a single housing), promoting actively the decrease of fuel consumption and, as a consequence, of detrimental gas emissions. According to the estimations obtained in literature, this can bring about a fuel saving of 1.556 litres per year and considering a fuel cost of 0.5 €/l, this means a cost saving of about 778 € per year. According to literature, this would mean 3.986 kg/year CO2, 26.414 kg/year NOx, 1,23 kg/year SO2 and 0.7 kg CO.
New technologies may open the door to high performance, environment friendly and economic aircraft operation by better exploiting available weight reduction potentials of new design philosophies without compromising the existing, high aerospace safety requirements.
Dissemination activities
General information regarding SEALEDBOX project has been provided in:
• Space Science and technology master (Basque Country University)
• JEC fair: in two different stands: TECNALIA and HUNTSMAN
A general overview of SEALEDBOX Project has been presented to the following Companies: CRISA, TAS-E, Airbus, Chomerics, Huntsman, SAFT.
Information provided does not affect knowledge protection, the partner’s and Topic Manager‘s confidentiality or their commercial interests.
Exploitation
TECNALIA
Knowledge gained in the project has strengthened TECNALIA’s position as a niche technology provider of advanced composite components. This project has enabled to extend the validation of the boxes under aeronautic standards.
Developments carried out in the area of lightweight electronics housing has allowed proving the feasibility of profitably producing an avionics box that meets the requirements in terms of functionality and at relatively low cost.
TECNALIA has reached a TRL5-6 (Component and/or breadboard validation in relevant environment, ESA definition) in the development of lightweight composite boxes. Breadboards have been qualified in the representative environment on ground. The current project has allowed increasing the applications for the lightweight housings in sealed avionics.
The project has also strengthen the collaboration between TECNALIA and LEG in the re-engineering of avionics systems by using lightweight boxes complementing the supply chain between technology provider and end user.
List of Websites:
Project Coordinator: Fundación Tecnalia Research and Innovation (Garbiñe Atxaga, garbine.atxaga@tecnalia.com)