JUL 2018


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JULY 2018 54 CompositesWorld FOCUS ON DESIGN High-speed trains create significant air pressure as they enter a tunnel. But even more significantly, "when they exit, they create a vacuum that, along with other forces, will try to pull the panels out of their fixtures," Bansal explains. A specially designed nut- and-bolt anchorage system developed by CELO-APOLO Construc- tion Systems (Castellar del Vallès, Spain) helps keep the panels in place, while the panels themselves are designed to handle the kinds of loads created both by the speeding trains and by the ongoing water seepage. Bansal's team also had to find a way to address the seemingly conflicting needs of panel manufacture versus panel installation. On the one hand, flat panels are much easier, faster and more cost-efficient to manufacture than curved panels. On the other hand, the panels need to conform and be secured effectively to the curved tunnel struc- ture. Addressing both sets of needs, the answer was to manufacture flat panels with a consider- able proportion of the reinforcement in the longitudinal direction, so that they could be flexed into their final shape as they were installed. Because of the panels' flexibility, their final shape met design requirements and did not compromise laminate integrity, Bansal reports. e flex- ibility also enabled relatively easy adaptation to irregular tunnel features. To create the mix of physical and mechanical properties needed in the panels, the ACCIONA team incorporated three types of glass fiber reinforcement: unidirectional and bidirectional continuous rovings as well as continuous filament mat. e unidirectional product was developed, manufactured and supplied by Owens Corning (Toledo, OH, US). ACCIONA also collaborated with resin manufacturer Scott Bader Co. Ltd. (Northamptonshire, UK) to formulate a workable resin system. is was especially difficult because the resin formulation had to meet stringent subterranean flammability standards, yet also maintain the pre-cure fluid char- acteristics necessary for manufacturability. Mass production With more than two decades of experience in the fabrication of composite components, Bansal nevertheless faced new manu- facturing challenges with this project— starting with its sheer magnitude and very tight production schedule. To line more than 200,000m 2 of tunnel wall — a stretch of about 10 km — ACCIONA produced more than 15,000 panels, each 9.2m by 1.5m. "We chose pultrusion from the beginning because we needed an automated process," Bansal explains. Its relatively low labor requirements and high manufacturing consistency also made pultrusion the fabrica- tion method of choice. ACCIONA employed a pultrusion machine built by LYT Composite Equipment Manufacturer (Nanjing, China). But working with the specially designed resin system added a layer of complexity to the engineering of the pultrusion process. ACCIONA started with Scott Bader Crestapol 1212 pultrusion resin, a rapid-cure methacrylate-based thermosetting resin. Additives needed to meet performance requirements — in particular, a high filler level of 170 phr (per hundred resin) alumina trihydrate (ATH) to meet the flammability standard — changed the resin system's composition significantly enough to demand a change in Read this article online | Production speed and repeatability This pultrusion line, with a specially designed infusion system that ensured complete fiber wetout, completed each of the more than 15,000 9.2 by 1.5m composite panels in 34 minutes. Source | ACCIONA Design for practicality and manufacturability The basic panel's design minimized potentially troublesome horizontal seams (there is only one, at the curvature's peak) and enabled both flat-panel manufacture and delivery via standard trucking equipment. Source | ACCIONA

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