Railway Track & Structures - September 2007 - (Page 20) TTCI R&D Non-destructive testing of plastic and composite ties TTCI researchers apply a wellestablished testing technique to new materials. T he use of plastic and composite ties by major freight railroads has increased in recent years for a variety of reasons. Plastic ties are less susceptible to decay and rot than wood ties and have been shown to provide adequate performance in areas of poor support where concrete ties may fail. Plastic and composites ties manufactured by a wide range of suppliers have been installed and are under evaluation by a number of railroads. While testing and screening methodologies for conventional materials (wood and concrete) are well established, the use of plastic and composites has brought new challenges to both users and suppliers. Unlike concrete ties, which are homogeneous, plastic ties often contain discontinuities or voids that may or may not impact performance. To ensure a quality product is being installed, one 20 Railway Track & Structures supplier, TieTek LLC, has developed a nondestructive testing process that inspects the internal integrity of plastic ties at the end of the manufacturing process. This process prevents ties containing large voids or undesirable discontinuities from being installed in track. With funding provided by the Association of American Railroads, a number of ties from different suppliers were evaluated using the NDT process. This was a preliminary effort to determine the range of voids and/or internal defects that might be detectable by this method and to determine the effect voids may have on tie strength. To ensure that proprietary information was not disclosed, ties from a variety of sources were identified by codes to control inventory during the process. Some of the selected ties came from rejected stock that was known to have excessive voids. To determine the sensitivity of the inspection process, large voids were manually created in a number of selected ties. Evaluation results in screening new plastic/composite ties using the NDT process suggest that a range of voids Figure 1, left, shows an intentional hole dug into the bottom of a tie. Figure 2 shows a sample of and X-ray printout of a tie with a large hole drilled near the center of it. and/or internal defects can be identified. Additional efforts are needed to optimize the process for all plastic ties from all vendors, as the NDT equipment used for this demonstration was calibrated for only TieTek’s material. Other materials or tie compositions may require that the NDT system be tuned or adjusted for a particular tie formulation. While the NDT results are encouraging, additional evaluations are needed to bring the process into industry-wide acceptance and more universal application. For example, does the size or location of the defect affect track performance or adversely affect new tie strength? Results of conducting a limited number of laboratory strength tests suggest that most defects located by the NDT process do not adversely affect the strength of new by Richard Reiff, principal investigator, TTCI, Richard Joy, principal investigator, TTCI, and Dr. Henry Sullivan, senior scientist, TieTek. www.rtands.com September 2007 http://www.aar.com http://www.rtands.com
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.