MxV Rail R&D, Railway Age January 2025 Issue: Recently, the Association of American Railroads (AAR) Coupling Systems and Truck Castings Committee asked MxV Rail to evaluate how warp restraint systems might be evaluated for performance and durability in service. MxV Rail performed this evaluation under the AAR Strategic Research Initiatives Program.
Truck warp is a serious performance concern for three-piece trucks. Premium trucks of various types and designs, all of which address the warp problem in one way or another, have entered the market over the years. Some truck designs address warp by using wider wedges, split-type wedges, or additional components and hardware designed to keep the bolster square with the side frames. Transoms (also called spring planks) and cross braces are the most common components or hardware used to address truck warp. While transoms and cross braces have been in service providing proven superior performance for decades (Ref. 1), the problems associated with them, including transom plate fractures and cross brace breaks, have been around for almost as long. The current assessment demonstrated that using hydraulic actuators in a load frame to attempt to warp a truck appears to be a feasible way to apply relevant stresses to truck warp restraint hardware.
Truck warp occurs when the connections between the sideframes and bolster and both wheelsets take a parallelogram shape instead of the normal square shape. Truck warp results in elevated angles of attack (AoA) on both wheelsets and, therefore, high lateral (gage spreading) forces on both rails (2-4). Optimal performance is achieved when the truck remains as square as possible. Warp restraint hardware can add significant beneficial warp stiffness without relying solely on the use of wedges. Figure 1 shows relevant geometry, forces, and moments.
MxV Rail developed a test program to measure warp angles and warp-induced strains in the components of two cross-braced trucks operating in MxV Rail’s Facility for Accelerated Service Testing (FAST®) train. After collecting data while negotiating track curves as tight as six degrees during two weeks of FAST train operations, both trucks were removed and set up, in turn, in a laboratory environment per the “standard warp test” (5, 6). The laboratory warp test measurements were not intended to duplicate FAST measurements. Instead, these measurements were intended to be complementary; providing a means to assess the warp moment observed with strains in the brace rods and warp angles of the truck. This assessment included measuring the warp behavior both with and without wedges installed.
This work shows the viability of laboratory testing of warp restraint hardware, such as sideframe cross braces. In general, this study produced the following
key findings:
Attempting to warp a truck using hydraulic actuators in a load frame appears to be a feasible method to stress-test warp restraint hardware.
Laboratory warp testing produced warp moments and angles and warp stiffnesses consistent with previous tests. Frame brace rod strains that were generally greater than the strains produced during FAST testing.
The load frame could be optimized in a way that focuses the warp energy on the warp restraint hardware. The top three aspects of optimization are 1) a unitized vertical load frame that controls the vertical and pitch motions of the sideframes; 2) A unitized warp load frame that accepts warp actuator reactions; and 3) support at the bearing pedestals that does not rely on specialized wheelsets with independently rotating wheels.
References
- 1. Rownd, K and R. Walker. 1999. “Improving the Economy of Bulk-Commodity Service Through Improved Suspensions.” Technology Digest TD99-027. Association of American Railroads/Transportation Technology Center, Inc., Pueblo, Colo.
- 2. Mace, S.E. 1993. “Evaluation of Rail Rollover Derailment Study.” DOT/FRA/ORD-93/12, Washington D.C.
- 3. Hannafious, J.S. and S.E. Mace. 1995. “Effects of Profile Grinding and Lubrication on Gage Spreading.” Technology Digest TD95-006, AAR/TTCI, Pueblo, Colo.
- 4. Read, D.M. and S. Kalay. 1996. “Initial Results of FAST/HAL Phase III Testing.” Technology Digest TD96-025. AAR/TTCI. Pueblo, Colo.
- 5. Tournay, H., H. Wu, and N.G. Wilson. 2008. “Investigation into the Root Causes for Loaded Car Hunting.” AAR Research Report R-995, AAR/TTCI. Pueblo, Colo.
- 6. Tunna, J. and R. Walker. 2004. “Characteristics of Long Service, Warp Stiffened Trucks.” Technology Digest TD04-023. AAR/TTCI. Pueblo, Colo.
