Material gains

This year’s Antec – or Annual Technical Conference – organised by the Society of Plastics Engineers (SPE) in the US – was the usual welter of technical papers. More than 500 were presented in a hectic five-day schedule in Cincinnati, Ohio in early May. Dow Automotive showcased its blow moulded plastic rear seatback, which promises weight savings of up to 25%, gives greater scope for including additional design features, and also meets US and European automotive safety regulations. Unlike conventional designs, Dow Automotive’s seatback does not need steel reinforcements to pass safety requirements. Steel is traditionally used for automotive seating applications to meet stiffness and loading requirements – with use of plastics limited due to its comparative lack of stiffness and strength. The first commercial vehicle to use Dow Automotive’s technology – the Audi TT Coupe, introduced in Europe in 2006 – is already on the road. The plastic rear seatback resulted in mass savings of 1.2 kg over a traditional steel reinforced design, according to the company. The finished seatback is made up of the single blow-moulded part, two hinges with one release, and a top tether attachment. Dow Automotive says high stiffness was achieved through closed sections in the double shell blow moulded structure. A PC/ABS resin – Pulse 2200BG PC/ABS, an unfilled engineering thermoplastic – was chosen to absorb and dissipate energy during impact and to meet deflection requirements. Padraig Naughton, from Dow Automotive’s application development team, told Eureka: “The material was chosen for its impact properties at low temperature and the stable behaviour up to high temperatures which may be experienced by the seats. It has a relatively high yield strength and high strain to failure, which translates to high levels of energy absorption in impact. This particular grade was tuned to fit the blow-moulding process. This was chosen as the optimum material for this set of requirements.” He said that the blow moulding process and the Pulse material made it possible to design the seat shape according to the force impacting the part – and to achieve the front and back side in one moulding step. “And this is with a low weight solution,” he said. “This seatback is a fully plastic structure which withstands the luggage retention requirements over a wide range of temperatures.” Naughton says the light weight and complex finished shape of the blow moulded part – with a design which withstands the impacting force – produced in one process step, could not have been produced if the seat had steel reinforcements. “Blow moulding enables a closed profile structure which is very effective in obtaining stiffness and the finished shape in one shot,” he said. Other process options could be used, such as injection moulding. “But the solution will take another form and will be dependent on the requirements of the car, costs and weight,” he said. Further advantages of blow moulding include reduced development time and tooling costs when compared to steel designs. Using plastic also allows integration of features including the headrest and map pockets into the seatback’s design, says Dow. The company’s research was not limited to the Audi TT Coupe. It has prototyped several seatback configurations, including designs that could be used in sedans, hatchbacks, SUVs and mini-vans. Dow Automotive says that seatbacks developed for the sedans and hatchbacks were 1.8-2.3 kg lighter than traditional steel designs, equivalent to a 20-25 % saving. There are plans to integrate the seat backs into other cars, but the company could not reveal makes and models. Smarter plastics Another hot topic at Antec was plastics of the future – incorporating smart materials into conventional polymers to create smarter systems. Smart or intelligent systems require sensing, processing, actuation, self-diagnosing and self-recovery. The term smart materials currently includes those that perform the first three functions – that is, a change of behaviour when stimulated by light, pressure, thermal, electrical or magnetic fields. The paper Smarter materials systems designs for the future discussed how polymer technology could be advanced by using smart material systems in application design. Creative Polymer’s Clive Bosnyak, one of the joint authors of the paper, told Eureka: “Today, we are primarily dealing with market applications such as sensors which are estimated as being $8 billion annually and growing at 8% per annum. Piezoelectric materials account for 50% of the market.” In principle, he says, all markets currently enjoyed by commercial polymers could be expanded by new and improved applications if one can obtain the increased performance functionality possible with smart materials incorporation at the right price. “These new opportunities are most likely to arise from redesigning applications with an integrated smart materials systems approach, rather than retrofitting smart materials into existing applications,” he said. “Smart materials systems are now emerging in the textile and sports and remedial physical therapy industries where higher prices are not a deterrent.” The paper highlights several markets where polymers could be combined with smart materials for potential applications. The first is smart fibres, where there are already several emerging businesses and applications. US technology firms Eeonyx and Nanosonic have both developed inherently conductive polymer coatings for fabrics. UK company Eleksen and US firm International Fashion Machines are making pressure-sensitive textiles and control electronics such as capacitive textile switches, while US-based Textronics is developing textiles that contain inherently conductive polymers so that heart rates can be monitored during sports events. Finally US company Konarka is developing nanometre scale coatings on fabric and thin films substrates to act as photovoltaic cells. Other market areas include smart buildings, with applications such as smart floors which count people, or incorporate light management through windows that lighten when someone approaches. Smarter material systems, could also lead to smarter product design and extend the use of polymers in various applications. Bosnyak said: “Probably the biggest challenge to designers today with polymers is to provide the intended function for the lifetime of the application at lowest cost. The higher the penalty for failure of the part, the more the tendency to overdesign.” The ability for a system to become smarter will allow feedback on impending failure, or even take some corrective actions to minimise harm, he said. “This could expand polymeric material usage further in airplanes, automobiles and commercial buildings.” The systems could also reduce part complexity – often arising from the need to bring together several polymers to achieve a balance of functionality or properties. “A specific functionality may only be needed under a special circumstance,” said Bosnyak. “Examples include non-slip on water or ice, and insulation when cold – not hot. Incorporation of smart materials could bring that specific function on demand.” Next steps for developing smart materials include improving the materials’ durability, consistency, characterisation, fabrication and cost, according to Bosnyak. He also believes it is crucial that industry and universities provide an environment where a multidisciplinary approach – bringing together, for instance, biology, physics and chemistry smart materials systems research – can be adopted to develop the materials. As for smart polymeric material systems in the near future, Bosnyak says: “My intuition says that a focus on high value applications such as with human health – physical therapy, sports, drug delivery, and water and air purity – will continue to expand first, followed by energy conservation applications such as photovoltaics, smart insulation and portable power.” Interest in failure The new SPE special interest group, the European failure analysis and prevention special interest group (FAPSIG), is creating a database containing details of failed products. SIG members will share the database and contribute their own failure investigations – the idea being that designers will review failure cases to prevent them from making mistakes others have already made. The two main groups included are failure causes and failure mechanisms. Failure causes is subdivided into stress concentrations, low mass or mould temperature, highly stressed weld lines, faulty ribbing, too high stiffness of construction elements, incorrect joining, and incorrect material selection. Failure mechanisms include creep and stress relaxation, wear, fatigue, UV degradation, chemical attack, environmental stress cracking. (www.4spe.org/communities/sig/sig002e.php)