ARC PROJECT REPORT. Meta-material design for tank track pads. Project Start Date: 17 January 2013 Quad Members:

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1 Meta-material design for tank track pads Project Start Date: 17 January 2013 Quad Members: ARC PROJECT REPORT Name Position, Affiliation Contact Dr.Georges Fadel Professor, Clemson University Dr. Gang Li Associate Professor, Clemson University Dr. Nicole Coutris Research Scientist (unfunded) Samuel Franklin Graduate Student, Clemson University Qing Mao Post doc, Clemson University Christopher Cardine General Dynamics Land Systems Dr. Matt Castanier Engineer, US Army TARDEC Matthew.p. David Ostberg Engineer, US Army TARDEC Bill Bradford R&D Scientist, US Army TARDEC Motivation, Background and Objectives: Fig. 1 Tank track temperatures under exercise Tank track elastomeric pads have been under investigation for many years because of their high rate of failure. Improving this component design would increase military vehicle reliability, reduce maintenance costs and time. From recent work focusing on understanding damage mechanisms, it was observed that the temperature wheel and pad elastomer increases upto o F. In addition to harsh working environment and abrasivon due to soil debris and sand, the high temperature increase maybe attributed to the hysteretic property of elastomeric material. The dynamic cyclic loading during vehicle motion results in substantial energy dissipation inside the elastomer and consequent temperature rise. 1

2 The ideal design solution would require replacing the elastomeric material with low loss coefficient and high compliance substitute. This tradeoff can be achieved by tailoring Meta-materials to target these properties. The challenge is defining the optimal meta-material structure that achieves the desired properties. Approach: The proposed method originated in topology optimization. It involved a two level optimization process for the design of the track pad. The goal of the top level (system-level) optimization accomplished three years ago was to determine the design variables characterizing the pad and to identify the target properties that have to be achieved by the meta-material. The custom formulated, carbon black filled Styrene-Butadiene Rubber currently used has been used in the simulation and the targets were obtained. Note that the analysis was only two dimensional as the emphasis was on the inside pads in contact with the road wheels, and these pads mostly experience 2D effects. Three curves obtained were stress strain curves that matched the tangent elastic constants at various strain levels for the cases of Uniaxial Tension (UT), Pure Shear (PT) and Equi-Biaxial Tension (ET). From the results of the system optimization, the meta-material topology optimization was attempted. For this purpose, multiscale methods such as asymptotic homogenization and volume averaging were investigated. [5] [6] [7]. Unfortunately, we were not able to reproduce the non-linear curves using elastic materials since the curves that were obtained had to be matched at various loads and displacement levels. We therefore considered the non-linear compression of the pad, which is the main loading applied to its boundary, and attempted to generate a structure that would deform similarly to the rubber pad. We showed that we were able to obtain similar behavior to that of the rubber; however, the stresses were initially excessive. We considered several materials, and achieved numerically two feasible solutions that met our stress criteria and should survive fatigue loading. The methodology to design the metamaterials was established. We called it the Unit cell Synthesis method. Our numerical study enabled us to design a titanium pad that is designed to have the same behavior in compression as the elastomeric pad. Figure 2 shows the design obtained and its predicted compressive deformation behavior compared to that of the original elastomeric pad. Fig, 2. Ti pad designed by Clemson This pad and the process to design it were presented at the 2016 ARC review meeting. What was left was to test the pad to see whether it performed as predicted. Previous Year(s) Accomplishments: 2013 Completed FE Abaqus model setup for conducting sensitivity analysis and consequently determining material properties which need to be targeted to design optimal meta-material structure. Stress and strain characteristics of the tank track pad under both dynamic and static conditions were obtained. 2

3 2013 Partially Accomplished: Topology optimization code adapted for the Tank pad geometry Tangent elasticity tensors were extracted from the Ogden model for the rubber material of the tank track pad Target stress strain curves for three load cases were established using the tangent elasticity tensors. These provide constraints for the topology optimization at various strain levels Q1 Proposed work: Generate topology optimization solutions that target rubber stress-strain behavior for single-criteria loading condition. Issue is large deformation, non linearity and multiple load cases (uniaxial, bi-axial compression and pure shear) Using additive manufacturing techniques to build segments of pad prototypes for single-criteria loading condition and conduct testing Q1 Accomplishments: Topology optimization continued and shown not to work with non-linear material and deformation targets. Additive manufacturing not performed since solutions not acceptable Q2 Proposed: Investigate and implement methods for combining topology solutions via multicriteria and multi-scenario optimization techniques Q2 Accomplishments: Heuristic approach applied to generate possible meta-material structures at the cell level considering compression load on the boundary. Multiple load cases (multi-scenarios) considered instead of multi-objective approaches. Positive results were obtained, however stress levels were too high using steel as base material and the initial geometries investigated 2015 Optimization approaches applied to the geometries to reduce stress levels. Currently, two metamaterial solutions in a Titanium alloy show very promising results Q3 Proposed: Investigate and implement methods for combining topology solutions via multicriteria and multi-scenario optimization techniques. Use additive manufacturing techniques to build pad prototypes for solutions optimized for multi-criteria and conduct testing. Q3 Accomplishments: We have generated acceptable geometries using heuristic approaches and using alternative materials (Titanium). Stress levels seem acceptable, but we do not know how this will perform in fatigue conditions. Presented the solutions to the Army and to GDLS. They are encouraged by the results, and we discussed continuation and testing approaches Q4 Proposed: write report. We will be continuing to explore additional geometries, and initiate rolling wheel topologies. And conduct testing. Discussions with the Army resulted in a slight redirection of the work to focus on the system as a whole, road wheel and pad. We will start looking at that after testing is accomplished Q1 Proposed: Generate topology optimization solutions that target rubber stress-strain behavior for two-criteria performance: (1) required deformation behavior and (2) acceptable maximum stress level under wheel loading conditions. Using additive manufacturing techniques to build segments of pad prototypes for two-criteria performance and conduct testing in house Initiate roadwheel metamaterial simulation work 3

4 Q1 Accomplishments: Continued analysis and optimization, and refined the two structures that are promising. We mainly addressed the Army concerns that sharp edges would be detrimental to fatigue. Champfers were added where needed Q2 Proposed: Investigate and implement methods for improving topology solutions for multicriteria performance: (1) required deformation behavior, (2) acceptable maximum stress level under wheel loading conditions, (3) required fatigure performance, (4) given manufacturing restrictions, and (5) given assembly restrictions. Continue roadwheel metamaterial work and couple with pad Q1 Accomplishments: We are still working on the pad as the results obtained are promising. The pad geometry was sent to a service bureau using additive manufacturing, and three pads were built. They were delivered just before the ARC program review Q3 Proposed: Investigate and implement methods for improving topology solutions for multicriteria performance (continued). Study functionally gradient issues of Ti to Steel and generate solutions. Simulate roadweel and pad system and compare energy dissipation if possible Q3 Accomplishments: We initiated static testing on the pad. The pad behaved non-linearly as designed, but the curve is significantly different from analysis results. We performed various sensitivity tests to identify the reason for the discrepencies. The wheel track model was developed for the dynamic testing of the pad. It needs to be also modified to have a metamaterial around the wheel. We decided to delay the system approach and propose it for next year Q4 Proposed: Continue testing and write report and papers Q4 Accomplishments: We conducted a Design of Experiments and identified three major factors for the different results. These are the uncertainty in material properties of the additively manufactured titanium pad versus the published material properties. Second, the accuracy of the additive manufacturing wall thicknesses is less than what was assumed for the analytical model. We reran the model with slightly modified thicknesses and material properties and can match the experimental curve. This result will be presented at the ARC review meeting Simultaneously, we analytically studied the fatigue behavior of the pads, and have been working on experimentally assessing its life. External Review Board Recommendations and Researcher Feedback (2015) 21 st Automotive Research Center Annual Program Review Project # and Title: 3.9 Meta-Material Design for Tank Track Pads PI: Fadel 4

5 Excellent Relevance to ARC Mission 10. Technical Quality 9.5 Comments/Suggestions Nice approach of using metamaterial design approach to improve material design in tire rubber peel design. Poor The project team made reasonable simplification to identify the optimal solution to match with desired property. The project team is encouraged to further explore the solution using topology optimization and refine their design objectives to match with the failure modes and analysis. Gathering test results would be helpful too. PI Response: Thank you for the review and the support. We have continued as you asked to validate the model and compare with experimental results. 5

6 22 ND AUTOMOTIVE RESEARCH CENTER ANNUAL PROGRAM REVIEW Project # and Title: 3.9 Meta-Material Design for Tank Track Pads PI: Fadel (Clemson) Excellent Poor 1. Relevance to ARC Mission 2. Technical Quality 3. Comments/Suggestions PI Response: This is presented as a case study. PI's have done excellent job in presenting this material. Project is presented as a complete effort including using 3-D additive manufacturing to showcase the concept. case study concept clearly helped this project. Different computational approaches can be used to address objectives proposed in this project. PI's explained why they chose this approach compared to other approach. May be a clear vision or goal for this engineering research project will help to define objectives including multi-physics approaches and/or specific experiments needed for this proposed work. May be this may help to show case the need to move to 3-D form periodic 2-D problem. We have continued to work on explaining the difference in results using a DOE and conducting fatigue analysis and experiments. We are not yet at the point where we can consider 3D approach. However, since this project is finishing, we will instead move to the system of the wheel and track as recommended by the army and proposed in our 2017 proposal. Major Milestones and Deliverables since Project Start: Year/Month 2013/04 Completed FE model of tank track pad in existing configuration 2013/06 Completed FE model using Ogden hyperelastic model with static and dynamic loading conditions. 2013/09 Validated friction formulations, contacts, boundary conditions and loads in static and dynamic 2D FE models 2014/01 Completed formulation and implementation of computing the tangent elasticity tensors for the hyperelastic tank track pad material with arbitrary stains. 2014/03 Submitted abstract and received acceptance for presentation for EngOpt th International Conference on Engineering Optimization, Lisboa Portugal 2014/05 Completed and presented thesis defense titled Identifying target properties for the design of meta-material tank track pads 2014/09 Attempted topology optimization using the homogenization approach to design the metamaterial. Difficulties matching the multiple load cases. 2014/12 Attempted topology optimization using the volume averaging method. Still same difficulties matching the multiple load cases. 2015/05 Decided to approach the problem differently and implement a method inspired from 6

7 our knowledge of mechanics and deformation of known structures such as a cantilever beam, a fixed fixed beam or a cantilevered oval. 2015/12 Approach developed was turned into a synthesis method for metamaterial we called the unit cell synthesis method. It allowed us to design a structure that had characteristically the behavior sought. Mr. Zachary Satterfield graduated with an MS, describing the method. 2016/6 Mr. Kulkarni further developed the designs using other shapes, and achieved a much better match with the desired properties. He also conducted dynamic simulations. The Pad was built using titanium in additive manufacturing. Three samples were built. The obtained geometry was presented at the ARC review meeting, and Mr. Kulkarni won best poster award. 2016/9 A new student, Mr. Franklin took over the project. The task was to perform physical tests and confirm that the part behaves as expected. Static tests showed a large deviation from the Rubber curve, although the non-linear behavior was visible. Thus, before performing fatigue, we had to attempt to understand why the results did not match. 2017/5 We performed a design of experiment to see the effects of variations in any of our dimensions or material properties. The DOE identify three potential issues, and we could alter numerically these values and match the experiment. Fatigue analysis and testing was initiated. We are currently in the process of completing the fatigue analysis, and we started work on the new project which consists in considering the complete system of road wheel and pad. ARC/TARDEC/Industry Benefits: Investigations are being done on tank track pad elastomers since a long time by TARDEC. It is mainly due to their high rate of failure. Component testing methods were devised to predict durability of elastomeric components in M1 Abrams T-158LL track systems. FE models have been used to predict the performance of the track pad and damage accumulation due to cyclic loading. This research work is based on the idea to develop a meta-materials design methodology to solve the problem. Linear elastic meta-material would be designed based on topoplogy optimization. A linear elastic material would not be affected by hysteresis which is inherent in elastomeric materials. This would result in a redesigned track pad component which is more reliable and has reduced maintenance costs and time. Leveraged Funding: Publications, Presentations, Copyrights, Patents or other Tech Transfer: Presentations Presented the research work at the 2 nd Annual Poster and Conference Session organized by the Mechanical Engineering Graduate School Council at Clemson University. Presented research poster at the ARC 19 th Annual Program Review at University of Michigan, Ann Arbor. Presented the research progress at the ARC Collobarative Research Seminar Series in November Presented at the ARC review meeting in May

8 Dangeti, S.V, Satterfield, Z., Fadel, G.M., Li, G., Coutris, N., Castanier, M. and Ostberg, D. Identifying target properties for the design of meta-material tank track pads, ASME IDETC2015. Presented at the ARC review meeting in May 2015 Performed case study for the ARC review meeting in May Collaborated with the University of Iowa and with TARDEC to prepare the case study. The poster of Mr. Kulkarni won first place in the poster competition. Satterfield, Z., Kulkarni, N., Coutris, N., Li, G., Fadel, G.M., Castanier, M, Unit cell synthesis method to design meta-materials with targeted nonlinear deformation response paper submitted to the J. Mech. Des, 2016 Education and Training: Sampath V. Dangeti, graduated in May Currently working in Boston Nitheesha Cheenadi, graduated in August Zachary Satterfield, started working on the project in May 2014, graduated with a BS and then continued with his MS. He graduated in December 2015 and joined Corvid technologies in Charlotte. Neehar Kulkarni picked up the project in August 2015, overlapped with Zach Satterfield, built up on his results and defended in May He is currently employed at Gamma Technologies in Chicago. Hayden Wilson did one semester undergraduate research in the spring of He helped test the pad we received in April and graduated in May He joined the Army. Samual Franklin is a current MS student on the project. He has performed the DOE and was able to reproduce the results of Mr. Kulkarni. He has set up the fatigue testing apparatus and started collecting data. Qing Mao completed her Ph.D. in additive manufacturing in December She is now a postdoc, performing fatigue analysis and helping Mr. Franklin with the physical experiments. Honors, Awards, Keynote/Plenary and Named Lectures, Special Memberships: Duke-Owens award for Best Research Poster, ARC best poster award Case study at ARC 2016 with Dr. KK Choi from the University of Iowa. Eastman award for Best Research Poster, Presentation at TARDEC, October