Railway Track & Structures - September 2007 - (Page 21) TTCI R&D Figure 3, top left, shows a rail seat bending test configuration. Table 1, bottom left, shows the ties evaluated for the rail seat bending test. Figure 4, top right, is the rail seat bending test results at -30 F and room temperature by tie number from Table 1, shown in pounds/in. of deflection. Several ties were modified by drilling a large hole near the bottom center of the tie to represent a major production defect visible from the outside (Figure 1). The ties were then inspected with the defect facing down — not visible to the operator. Figure 2 shows NDT results from testing one of the ties. The picture in Figure 2 is foreshortened, allowing the entire tie to be displayed on screen; therefore, the dimensions are not to scale. When visually inspected, no obvious flaws were detected on several of the modified ties. But, after going through the NDT process, they were rejected and failed during subsequent rail seat bending tests run at TieTek. Summary of NDT inspections ties. However, more testing is needed to determine if defects detected are detrimental to long-term life of a tie in use, such as through fatigue (cyclic loading) or weathering (moisture freeze/thaw). Also, the effect of internal defects on fastener retention has not been evaluated at this time. For industry-wide implementation of the NDT process, the method must be standardized, including the specification of system calibration for different ties/fixtures. All ties inspected exhibited a range of voids and/or light density. Due to calibration and optimization of the NDT system to TieTek products, the clarity of the results for ties donated by TieTek was better than for the other ties inspected. Future work could include optimization of the NDT process for ties from other manufacturers. Laboratory strength test results Upon completion of NDT, inspection ties were shipped back to the Transportation Technology Center, Inc., in Pueblo, Colo., for further evaluation. Approximately 17 tie (or 1/2 tie) samples that indicated voids or other inclusions were evaluated using standard bending tests specified by AREMA. The laboratory tests were conducted to determine the effect, if any, on the strength/stiffness of the ties identified with voids present. NDT process TieTek has developed an x-ray inspection process by which all ties are inspected before leaving the plant. As the ties pass through the machine, multiple x-ray images are generated simultaneously. Results are digitally integrated with internal software and immediately displayed on screen. While the location and size of defects may be estimated by looking at the image on the screen, an internal software process determines the size, location and type of discontinuity or void, allowing users to determine if the tie should be rejected, while providing information to adjust the manufacturing processes. Additional proprietary software determines whether the tie meets specifications established by the supplier and railroad customer. A calibration tie with known defects is run through the machine at the beginning of each shift in order to ensure that defects can be detected and the appropriate standards are met. It should be emphasized that the current process has been optimized for TieTek’s product. Results for ties of different dimensions and densities may vary. www.rtands.com Procedures/ties selected Laboratory evaluations conducted at TTCI followed standard AREMA recommendations for center bending and rail seat bending. Table 1 lists the ties and NDT inspection observations for the ties selected for rail seat bending tests. Note that the two halves of the same tie are designated by the tie number followed by letter a or b (e.g., 104-b and 104-a). Ties selected for rail seat tests had defects located at or near the area where tie plates would be attached to the tie. Rail seat bending results Figure 3 shows the rail seat bending configuration. Railway Track & Structures September 2007 21 http://www.aar.com http://www.rtands.com
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