Latest advanced materials prove durability
Put under pressure at the toughest endurance motor race in the world, the latest high performance composites, adhesives and stereolithography materials help the new Courage - ORECALC70 racing car deliver an impressive performance. Harald Wiedemann reports.
Three months after the technical team at Huntsman Advanced Materials and French endurance motor racing team ORECA began working together on the development of a new prototype car for the 2008 Le Mans series, the car was on the track showing its potential podium-grabbing performance.
Drawing on many years of combined expertise in composite materials, the technicians at ORECA and Huntsman started this project by using RenShapeBM5055 epoxy tooling board to build the carbon fibre moulds for the bodywork of the Courage ORECALC70.
All the models for the bodywork components were CNC milled out of BM 5055 epoxy tooling board which was specifically developed for pre-preg tools and is widely used in automotive modelling. Its mechanical properties and heat resistance make it suitable for curing pre-pregs for high performance composite parts.
After the application of a gelcoat system (RenGelSW18/RenHY2404/RenHY5159), this tool was also used to cure several layers of carbon fibre impregnated with AralditeLY3297/Aradur3298 and RenLam113/RenHY97-1 wet lay-up system to produce void-less composite structures.
The bodywork composite parts were then bonded together using Araldite2014 two component epoxy adhesive and Araldite204 one-component foaming adhesive to fill any small gaps between the component parts. The Araldite2000 range adhesives specified by ORECA were used to bond a range of component substrates including metals, composites and thermoplastics. All offer high levels of heat and chemical resistance so are able to withstand the aggressive, very high stress environments the ORECA cars experience during both race and test conditions.
Stereolithography has played a very important role in the design development of the LC70 car and Huntsman has particular expertise in this field, marking 20 years at the forefront of stereolithography (SL) materials development in 2008.
Stereolithography produces highly durable, strong and complex components, in a very short space of time, offering great versatility to design engineers. SL materials, including the latest new generation photopolymers, RenShapeSL7800 and 7810 were used in the car's development process, particularly on the wind tunnel model.
RenShapeSL7810 is a white, ABS-like, low viscosity resin that produces tough models with good surface finish and fine detail. They also exhibit long term dimensional stability under even the hottest and most humid environmental conditions. Models can withstand up to 90 per cent humidity in the atmosphere and are stable at up to 40°C. These incredibly durable parts also have excellent high impact strength.
The latest SL technology was particularly useful for the ORECA project because the time scale for developing the aerodynamics of a race car can be very short and engineers have to be able to react quickly. Using SL technology enabled the ORECA team to test many versions of the same components incorporating very small geometry changes without undergoing the heavy manufacturing processes needed for the typical construction and development of patterns and moulds. It also delivered cost savings over the standard process for producing composite parts.
A 1:40 scale model for wind tunnel testing was designed and manufactured by ORECA with the support of the Araldite Technical Team for the production of SL components made from RenShapeSL resins and for composite tooling parts. ORECA then carried out wind tunnel testing at the ACE wind tunnel in Magny-Cours, France, formally known as the Prost Grand Prix wind tunnel.
The bodywork of the car was adapted and completely changed throughout testing, the aim of this being to gain higher performance levels and better accessibility to the suspension, engine and gearbox.
The car's aerodynamic efficiency - the ratio between the aerodynamic down-force and the drag was increased by 25 per cent over previous specifications. This development enabled ORECA to define different aero packages for different tracks.
For example Le Mans is a circuit where a low drag package is required in order to achieve high top speeds (over 330Km/h) on its many long straights.
On the other hand, at Nürburgring the need is for a high down-force configuration as the track is very twisty and the top speed is not as high. Aerodynamics were developed to achieve good results on the various tracks by changing a few of the elements.
At the same time a CFD programme (computational fluid dynamics) was also carried out in order to correlate the wind tunnel data and visualise the flows and pressures. Impact testing was not necessary as the parts were already homologated.
Using the latest SL materials, composite resin systems and high performance adhesives for bonding many critical, high stress parts, the ORECA engineers and Araldite technicians were able to produce a range of extremely tough and complex finished parts for the car. These materials also helped to accelerate the entire manufacturing process by about 20 per cent.
Overall, this combination of high performance materials and technical expertise proved an important factor during a successful season for the Courage - ORECALC70 prototype cars.
They achieved a first ever podium place for the car at the Spa circuit in Belgium - up there with the leading race teams, Audi and Peugeot - followed by an impressive 8th place in the Le Mans 24 Hour Endurance race itself in June 2008.
The knowledge gained from this project will have a direct impact on future materials technology and manufacturing methods for the general automotive industry.
If these latest composite components and adhesives can be used successfully at their very limits of performance in the toughest endurance motor race in the world, then they should certainly do the same for the family SUV.
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Harald Wiedemann is Global Marketing Director of Huntsman Advanced Materials, Basel, Switzerland. www.huntsman.com/advanced_materials
