DIGITAL TWIN FOR TANK TRACK ELASTOMERS: PREDICTING SELF-HEATING AND DURABILITY

In this work, Abrams tank track system T-158LL backer pad elastomer self-heating and fatigue behavior was characterized experimentally, and the backer pad design was digitally twinned to show how complex in-service conditions can be evaluated virtually. The material characterization included measurement of the thermal properties and dissipative characteristics of the rubber compound, as well as its fatigue crack growth rate curve and crack precursor size. The analysis included 1) a structural finite element analysis of the backer pad in operation to obtain the load history, 2) a thermal finite element analysis to obtain steady-state operating temperature distribution within the backer pad, and 3) a thermo-mechanical fatigue analysis using the Endurica CL fatigue solver to estimate the expected service life and failure mode of the backer pad. As validation, experiments were conducted on the backer pad to measure operating temperature, fatigue life, and failure mode over a matrix of loads and frequencies typical of service. Operating temperatures in a range from 125 °F to 350 °F were observed. Several failure modes occurred in backer pad tests, depending on the load and frequency. In cases where thermal runaway occurred, a thermal degradation mechanism was observed internally in the pad. Under less severe conditions, fatigue crack growth initiating near the “binocular” tubes was observed. Fatigue life was found in almost all cases to fall between 10 and 10 cycles. Thermal runaway predictions for the T-158LL backer pad were also validated against tests in cases where debonding of the rubber from the metal core occurred. The digital twin of the backer pad yielded failure modes quite similar to those observed in experiments, and gave realistic estimates of operating temperature and fatigue life. The fatigue analysis methods developed under this project have since been applied commercially, and have proven effective in a wide range of elastomer applications. Future applications of the tools will include durability improvement initiatives, light-weighting efforts, and remaining life tracking for reliability programs. Proceedings of the 2017 Ground Vehicle Systems Engineering and Technology Symposium (GVSETS) UNCLASSIFIED: Distribution Statement A. Approved for public release; distribution is unlimited. Digital twin for tank track elastomers: predicting self-heating and durability, Mars, et al. UNCLASSIFIED: Distribution Statement A. Approved for public release; distribution is unlimited. Page 2 of 10 INTRODUCTION With qualification testing costs in the range 0.75 to 1.5 million dollars per iteration for the M1 Abrams Tank Track system (Figure 1), track system elastomers require vetting prior to qualification tests. Self-heating and durability of track system elastomers (Figure 2) must therefore be ensured prior to prototype production [1-3]. In this work, track system T-158LL backer pad elastomer self-heating and fatigue behavior was characterized experimentally, and the backer pad design was digitally twinned. A digital twin is a complete virtual representation of the backer pad, matching not only the pad’s geometry, but also its mechanical, thermal and damage behavior. In this case, the digital twin is aimed at enabling vetting prospective pad designs with respect to complex in-service conditions to enable better design down-select decision making. Elastomeric Track Pad Figure 1. Abrams Tank with Elastomeric Track. MATERIAL CHARACTERIZATION Digital Twin implementation requires knowledge of the elastic, fatigue, and thermal behaviors of subject materials. These behaviors were measured via experiments on supplier-provided samples of the subject material. The characterization experiments were conducted at Axel Products, Inc. Elastic Properties Steady-state nonlinear elastic properties under finite strain cyclic loading were determined via experiments in 4 modes of deformation: simple, planar, and biaxial tension, and volumetric compression. A 2 order Ogden [4-6] hyperelastic Road wheel Ground pad Backer pad Bushing Figure 2. Track system elastomer components. energy function has been used in this work to specify stress-strain behavior, with parameters as given in Table 1. The Ogden strain energy potential W is defined in equation (1) in terms of principal stretches i  and material parameters i 