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A Methodology of Design for Fatigue Using an Accelerated Life Testing Approach with Saddlepoint Approximation

US Army TARDEC-Monica Majcher
Oakland University-Zissimos Mourelatos
Published 2019-04-02 by SAE International in United States
We present an Accelerated Life Testing (ALT) methodology along with a design for fatigue approach, using Gaussian or non-Gaussian excitations. The accuracy of fatigue life prediction at nominal loading conditions is affected by model and material uncertainty. This uncertainty is reduced by performing tests at a higher loading level, resulting in a reduction in test duration. Based on the data obtained from experiments, we formulate an optimization problem to calculate the Maximum Likelihood Estimator (MLE) values of the uncertain model parameters. In our proposed ALT method, we lift all the assumptions on the type of life distribution or the stress-life relationship and we use Saddlepoint Approximation (SPA) method to calculate the fatigue life Probability Density Functions (PDFs). Finally, a design for fatigue is performed where a Reliability-Based Design Optimization (RBDO) process is developed to optimize the system’s characteristics (model parameters, fatigue and/or material properties) which are subject to probabilistic constraints. This optimization problem determines optimal values of system parameters to achieve a fatigue reliability target. We will demonstrate all developments using a representative example.
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An Innovative Electric Motor Cooling System for Hybrid Vehicles - Model and Test

US Army TARDEC-Denise Rizzo, Katherine Sebeck, Scott Shurin
Clemson University-Shervin Shoai Naini, Junkui (Allen) Huang, Richard Miller, John R. Wagner
Published 2019-04-02 by SAE International in United States
Enhanced electric motor performance in transportation vehicles can improve system reliability and durability over rigorous operating cycles. The design of innovative heat rejection strategies in electric motors can minimize cooling power consumption and associated noise generation while offering configuration flexibility. This study investigates an innovative electric motor cooling strategy through bench top thermal testing on an emulated electric motor. The system design includes passive (e.g., heat pipes) cooling as the primary heat rejection pathway with supplemental conventional cooling using a variable speed coolant pump and radiator fan(s). The integrated thermal structure, “cradle”, transfers heat from the motor shell towards an end plate for heat dissipation to the ambient surroundings or transmission to an external thermal bus to remote heat exchanger. A complete lumped parameter numerical modelling was implemented to estimate the thermal behavior of the corresponding electric motor cooling system. Experimental and numerical results compare the temperature, heat flux, and cooling power measurements. For 250VA thermal load applied, the hybrid heat rejection strategy could save up to 33% of the power consumption while the operating…
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A Software Tool for Injury Analysis of Blast and Crash Data

US Army TARDEC-Darryl Bryk, Craig Foster
Published 2019-04-02 by SAE International in United States
In recent years the U.S. Army Tank-Automotive Research, Development, and Engineering Center (TARDEC) has been investigating the survivability and injury mechanisms of underbody blast and crash, and their effects on personnel, with the use of Anthropomorphic Test Devices (ATD), or crash test dummies. Injury Assessment Reference Values (IARV) for crash have been researched for decades, and the US Army Research Laboratory (ARL), some years ago, also developed IARVs for underbody blast for the Hybrid III 50th percentile ATD. More recently, TARDEC extended these IARVs for the 5th and 95th percentile. With the advent of TARDEC’s Occupant Protection Laboratory large amounts of data were accumulated, which brought an interest in automating the analysis, and so a software tool was developed. The interactive in-house written software, called ICalc, allows the user to open test data files acquired from blast testing, drop tower testing, and crash testing. Data can be automatically bias corrected (zeroed), filtered, and graphed with pertinent IARV functions automatically applied. Data from multiple sensor channels and multiple files may be graphed together for comparison and…
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Surface Contamination Simulation for a Military Ground Vehicle

US Army TARDEC-In-ho Lee, Yeefeng Ruan, Vamshi Korivi
Published 2019-04-02 by SAE International in United States
Vehicle surface contamination can degrade not only soldier vision but also the effectiveness of camera and sensor systems mounted externally on the vehicle for autonomy and situational awareness. In order to control vehicle surface contamination, a better understanding of dust particle generation, transport and accumulation is necessary. The focus of the present work is simulation of vehicle surface contamination on the rear part of the vehicle due to the interaction of the combat vehicle track with the ground and dust in the surrounding ambient atmosphere. A notional tracked military vehicle is used for the Computational fluid dynamics (CFD) simulation. A CFD methodology with one-way-coupled Lagrangian particle modeling is used. The simulation is initially run with only air flow to solve the air pressure, velocity, and turbulence quantities in a steady state condition. The steady state solution values are used to initialize particle advection analysis for the dust particles to transport in the atmosphere and accumulate on the exterior surface of the vehicle. The findings from study done to date using the aforementioned method for engineering…
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A Hybrid Thermal Bus for Ground Vehicles Featuring Parallel Heat Transfer Pathways

SAE International Journal of Commercial Vehicles

US Army TARDEC-Denise Rizzo, Katherine Sebeck, Scott Shurin
Clemson Unversity-Shervin Shoai Naini, Junkui (Allen) Huang, Richard Miller, John R. Wagner
  • Journal Article
  • 2018-01-1111
Published 2018-04-03 by SAE International in United States
Improved propulsion system cooling remains an important challenge in the transportation industry as heat generating components, embedded in ground vehicles, trend toward higher heat fluxes and power requirements. The further minimization of the thermal management system power consumption necessitates the integration of parallel heat rejection strategies to maintain prescribed temperature limits. When properly designed, the cooling solution will offer lower noise, weight, and total volume while improving system durability, reliability, and power efficiency. This study investigates the integration of high thermal conductivity (HTC) materials, carbon fibers, and heat pipes with conventional liquid cooling to create a hybrid “thermal bus” to move the thermal energy from the heat source(s) to the ambient surroundings. The innovative design can transfer heat between the separated heat source(s) and heat sink(s) without sensitivity to gravity. A case study examines the thermal stability, heat dissipation capabilities, power requirements, and system weights for several driving cycles. Representative numerical results show that the HTC materials and carbon fibers offer moderate cooling while loop heat pipes provide significant improvements for passive cooling.
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Diminishment of Cuts in Durability Test Time Reduction Methods

US Army TARDEC-Mark Brudnak, James Walsh, Bryan LaRose
Agency for Defense Development-Ho Jung Lee
Published 2018-04-03 by SAE International in United States
In this study, we extend and improve on the methods introduced by Brudnak et al. [1] by adding a second objective to the reduction of test time. This second objective under consideration is to diminish or reduce the number of cuts or deletions to the time histories during an editing process. As discussed in [1], segment-based methods consider each segment for retention or deletion based on its own localized severity, not considering the segments around it. As a result, retained segments can be widely scattered in the time domain depending on signal characteristics and therefore a large number of cuts can be induced unintentionally. Regardless of the joining method, such cuts and joins require artificial signal processing and should therefore be minimized. In this paper we present techniques to minimize these cuts while at the same time maintaining our original goals of time reduction and severity retention. The methods presented here use the same segment ordering methods presented in [1], but they additionally add heuristics which prefer minimum retained region sizes and minimum deletion region…
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A Fast Running Loading Methodology for Ground Vehicle Underbody Blast Events

US Army TARDEC-Jaisankar Ramalingam, Ravi Thyagarajan
Published 2018-04-03 by SAE International in United States
A full-system, end-to-end blast modeling and simulation of vehicle underbody buried blast events typically includes detailed modeling of soil, high explosive (HE) charge and air. The complex computations involved in these simulations take days to just capture the initial 50-millisecond blast-off phase, and in some cases, even weeks. The single most intricate step in the buried blast event simulation is in the modeling of the explosive loading on the underbody structure from the blast products; it is also one of the most computationally expensive steps of the simulation. Therefore, there is significant interest in the modeling and simulation community to develop various methodologies for fast running tools to run full simulation events in quicker turnarounds of time. This paper discusses investigation of a fast running blast loading methodology wherein the effects of the soil can be adequately captured without having to employ a highly detailed and computationally intensive soil/explosive model, and the interactions thereof (with each other and with the vehicle), in the simulation. The paper will also present a basis of such methodology utilizing…
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An Integrated Cooling System for Hybrid Electric Vehicle Motors: Design and Simulation

SAE International Journal of Commercial Vehicles

US Army TARDEC-Denise Rizzo, Katherine Sebeck, Scott Shurin
Clemson University-Junkui (Allen) Huang, Shervin Shoai Naini, Richard miller, John R. Wagner
  • Journal Article
  • 2018-01-1108
Published 2018-04-03 by SAE International in United States
Hybrid electric vehicles offer the advantages of reduced emissions and greater travel range in comparison to conventional and electric ground vehicles. Regardless of propulsion strategy, efficient cooling of electric motors remains an open challenge due to the operating cycles and ambient conditions. The onboard thermal management system must remove the generated heat so that the motors and other vehicle components operate within their designed temperature ranges. In this article, an integrated thermal structure, or cradle, is designed to efficiently transfer heat within the motor housing to the end plates for transmission to an external heat exchanger. A radial array of heat pipes function as an efficient thermal connector between the motor and heat connector, or thermal bus, depending on the configuration. Cooling performance has been evaluated for various driving cycles. Numerical results show that 1.3 kW of peak heat wattage can be accommodated with free convection while 3.2 kW is obtained by adding forced convection using 13.7 W of electric power. The internal motor temperature is maintained within the prescribed limits of 75°C and 55°C…
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Optimizing Occupant Restraint Systems for Tactical Vehicles in Frontal Crashes

US Army TARDEC-Rebekah Gruber, David Clark, Risa Scherer
Emory University-Jonathan Rupp
Published 2018-04-03 by SAE International in United States
The objective of this study was to optimize the occupant restraint systems for a light tactical vehicle in frontal crashes. A combination of sled testing and computational modeling were performed to find the optimal seatbelt and airbag designs for protecting occupants represented by three size of ATDs and two military gear configurations. This study started with 20 sled frontal crash tests to setup the baseline performance of existing seatbelts, which have been presented previously; followed by parametric computational simulations to find the best combinations of seatbelt and airbag designs for different sizes of ATDs and military gear configurations involving both driver and passengers. Then 12 sled tests were conducted with the simulation-recommended restraint designs. The test results were further used to validate the models. Another series of computational simulations and 4 sled tests were performed to fine-tune the optimal restraint design solutions. The sled tests with the optimized seatbelt and airbag designs provided significant improvement of occupant protection from the baseline tests in terms of the head, neck, chest, and lower extremity injury measures. Using…
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Cooling Parasitic Considerations for Optimal Sizing and Power Split Strategy for Military Robot Powered by Hydrogen Fuel Cells

US Army TARDEC-Denise Rizzo
University of Michigan-Jason B. Siegel, Anna G. Stefanopoulou, Niket Prakash
Published 2018-04-03 by SAE International in United States
Military vehicles are typically armored, hence the open surface area for heat rejection is limited. Hence, the cooling parasitic load for a given heat rejection can be considerably higher and important to consider upfront in the system design. Since PEMFCs operate at low temp, the required cooling flow is larger to account for the smaller delta temperature to the air. This research aims to address the combined problem of optimal sizing of the lithium ion battery and PEM Fuel Cell stack along with development of the scalable power split strategy for small a PackBot robot. We will apply scalable physics-based models of the fuel cell stack and balance of plant that includes a realistic and scalable parasitic load from cooling integrated with existing scalable models of the lithium ion battery. This model allows the combined optimization that captures the dominant trends relevant to component sizing and system performance. The baseline optimal performance is assessed using dynamic programming for a reduced order model, by assuming a static cooling load required to maintain the stack at the…
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