Railway Track & Structures - September 2007 - (Page 22) TTCI R&D After installation into the testing fixture, a vertical load at a rate of five kips/minute was applied to the center of the half-tie specimen. The maximum vertical load applied was 20 kips, or up to tie failure. Figure 4 shows results of the rail seat bending tests. Examination of rail seat bending results showed: • Little or no effect on tie strength from temperature change. • No difference in ties with and without significant defects or inclusions as detected by the NDT process. • Test ties with the artificiallygenerated large voids were identified by NDT and failed in bending tests during preliminary testing at TieTek. strength. Performance differences due to inclusions, small voids, or discontinuities may occur in either fastener retention or long-term fatigue in the rail seat area. Differences in “new tie” performance from such defects are not known, and no test specifications are currently available that could be used to cull out ties that pass the large void test, but have inclusions or small voids. Results of the full-tie center bending test were also evaluated and full details will be available in a future TTCIissued research report. This series of tests was intended as a preliminary investigation to determine if an NDT process could locate internal voids in plastic ties, and if such voids or inclusions were detrimental to initial tie strength. Initial investigation suggests the presence of inclusions/voids, * as detected by the NDT process, may not have a direct influence on track performance. Additional evaluations using a larger number of ties and additional laboratory testing will be needed to properly calibrate the results and allow implementation as an industry recommended practice. Pending funding, the following milestones could include: • Determine what size and shape of internal defect adversely affects new tie strength • Determine if defects detected are susceptible to: –fatigue (cyclic loading) –weathering (moisturefreeze/thaw) • Evaluate effect of internal defects on fastener retention • Standardize NDT process including calibration of NDT system for different ties/fixtures. Discussion Results of rail seat bending show no significant influence of inclusions on Acknowledgement: TTCI thanks Glenn Lowrimore of TieTek for providing the NDT process. TieTek also provided time from the regular production inspection of ties to allow TTCI staff to obtain the data needed for this article. TTCI Test Engineer James Rzonca performed the laboratory tests on the tie samples in TTCI’s Component Test Laboratory. * The size and pattern of such voids have not been verified and will require subsequent destructive evaluations of the samples. 22 Railway Track & Structures September 2007 www.rtands.com http://www.aar.com http://www.bentley.com http://www.rtands.com
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