JEC COMPOSITES MAGAZINE - Issue #36 - October 2007 - 39

Application Thermoplastic composites for mass transit applications Weight and cost reduction in mass-transit buses, light rail and light/heavy trucks has a direct benefit in the form of reduced fuel consumption, less road wear, lower maintenance and increased durability. Several states in the United States have imposed stringent weight requirements on mass-transit buses and trucks. Millions of dollars are spent in maintenance and parts replacement due to corrosion and cracking. Noise and vibration reduction is even more important now, due to heightened environmental and noise pollution concerns. A number of components on existing mass transit vehicles need to be replaced or retrofitted. Reducing tooling costs by making bus parts more interchangeable and modular is also gaining more importance. DR. UDAY VAIDYA DR. SELVUM PILLAY ENGINEERING APPLICATIONS R&D CENTRE SCHOOL OF ENGINEERING UNIVERSITY OF ALABAMA AT BIRMINGHAM T he University of Alabama at Birmingham (UAB) has been working with partners National Composite Center (NCC), North American Bus Industries (NABI) and Ticona Inc. to develop advanced thermoplastic composite materials and manufacturing technologies for applications in mass transit buses, light rail and trucks. A significant amount of the developmental work has focused on thermoplastic materials that offer enhanced durability, impact resistance, damage tolerance, enhanced sound and vibration damping, low weight, and corrosion resistance. The design, analysis, process modelling, manufacturing concepts and prototypes that provide form-fit function and performance validation have now all been demonstrated for mass transit components. Innovative hot-melt impregnation technologies and process models developed by the UAB team provide the capability to combine various high-strain-energy fibres with a wide variety of tough thermoplastic polymers to produce low-cost composite products. In the hot-melt impregnation process, continuous reinforced tows are pultruded through a heated die while the individual filaments are wet out with the thermoplastic resin, e.g. polypropylene (PP), polycarbonate (PC), or polyamide (PA). This process can be used to produce impregnated rods, rovings and tapes. The rods are used to produce long-fibre thermoplastic (LFT) pellets; roving and tapes can be woven into fabrics. The thermoplastic material forms can be fabricated into continuous- and long-fibre composite structures, using low-cost fabrication techniques that include extrusion/compression moulding, thermo-stamping and vacuum thermoforming. The sound- and vibration-damping characteristics of these materials are several orders of magnitude higher than for the traditional metals used in present mass-transit systems. LFTs have high fibre-aspect ratio and can be moulded into complex geometries featuring ribs and knock-outs. They can also accommodate thickness variations and provide enhanced strength and stiffness to the part, without adding weight. Over a five-year period (2002-2007), the UAB research team developed thermoplastic composite materials and manufacturing technologies for various mass-transit bus components. These include a two-passenger bus seat, a floor segment, a side body panel and structural frame segment, a battery-box access door, and an airconditioning roof-cover door that replaces similar components in conventional steel articulated buses used in city mass transit. For these components, weight savings of about 40% and projected lifecycle cost savings of about 45-50% were demonstrated using thermoplastic composites in replacement of traditional materials such as steel, plywood, and aluminium. An integrated process product development (IPPD) approach has been taken to conduct detailed design, finite element analysis, advanced process modelling, manufacturing, and component verification steps. These applications are briefly discussed below. LFT bus seat The E-glass/polypropylene LFT two-passenger bus seat weighed only 10 kg, as opposed to 21 kg for the existing steel/sheet moulding compound shell design used on most city mass-transit systems. The seat also met all guidelines imposed by the American Public Transportation Association (APTA). The thermoplastic structure required fewer assembly points than with the metal/sheet moulding compound (SMC) design. The LFT seat was manufactured using extrusion-compression moulding in a single-step operation. Process modelling was conducted to aid in the placement of the E-glass- No36 October - November 2007 / JEC Composites Magazine

JEC COMPOSITES MAGAZINE - Issue #36 - October 2007

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #36 - October 2007