|In their efforts to render cars and trains more economical, manufacturers are trying to find lighter materials to replace those currently used. But there is a problem: Lighter materials tend not to be as tough as steel or aluminum. Manufacturers need to decide which components can really afford to have weight shaved off and how to integrate them into the overall systems.
A glass reinforced polyurethane sandwich material for use in reducing weight of train components has been developed by Fraunhofer Institute for Chemical Technology (ICT). A new material capable of withstanding even extreme stresses has now been developed. It is suitable for a variety of applications, like diesel engine housings on trains � and it makes these components over 35% lighter than their steel and aluminum counterparts. Working with Bombardier GmbH, KraussMaffei Kunststofftechnik GmbH, Bayer MaterialScience AG, DECS GmbH, the DLR�s Institute for Vehicle Concepts, the University of Stuttgart and the Karlsruhe Institute for Technology, researchers at Franhofer ICT has now developed a polyurethane-based sandwich material that is extremely resilient and was used in the manufacture of diesel engine housing. This housing is located beneath the passenger compartment, i.e. between the car and the tracks. Not only does it shield the engine against flying stones and protect the environment from any oil that might escape, but in the event of a fire, it also stops the flames from spreading, thus meeting the flame retardant and fire safety standards for railway vehicles. The researchers opted for a sandwich construction to ensure component stability: Glass fiber reinforced polyurethane layers form the outer facings, while the core is made of paper honeycomb. Polyurethane is a bulk plastic combining two substances. Since it can be adapted to fulfill various requirements, it is referred to as a �customizable material�. In foamed form it is soft, and can be used for example as a material for mattresses; in compact form it is strong and hard. The researchers began by incorporating various additives into their polyurethane, altering it in such a way as to ensure it would meet fire safety standards. Then, the partners optimized the standard manufacturing process, fiber spraying, by developing a mixing chamber which allows even more complex structures to be produced in any required size. The diesel engine housing they made is approximately 4.5 meters long and more than 2 meters wide. A problem encountered with fiber spraying was that it was impossible to determine the precise thickness of the polyurethane top layers. But now the researchers have found a way to do this, using computer tomography to inspect the manufactured layers and then applying a specially-adapted evaluation routine to establish their exact thickness. This information helps to simulate the strength of the component, as well as its ability to withstand stresses.
PUR composites are produced with rigid thermoset resins, and have superior tensile strength, impact resistance, and abrasion resistance compared with composites based on unsaturated polyester and vinyl ester resins. Tensile modulus is around 430,000 psi, tensile strength of about 12,500 psi, and elongation to failure of over 7.5%. The super toughness of PUR composites aids secondary operations such as drilling, machining, and assembly. PUR composites are also said to be attractive for their processing advantages. Cure times are much faster than for polyester spray-up. PUR spray processes are also much less labor-intensive than polyester spray-up, which requires rolling out the glass to remove air and ensure complete wet-out.
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