
NSF Org: |
CMMI Division of Civil, Mechanical, and Manufacturing Innovation |
Recipient: |
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Initial Amendment Date: | March 26, 2015 |
Latest Amendment Date: | March 26, 2015 |
Award Number: | 1462870 |
Award Instrument: | Standard Grant |
Program Manager: |
Irina Dolinskaya
idolinsk@nsf.gov (703)292-7078 CMMI Division of Civil, Mechanical, and Manufacturing Innovation ENG Directorate for Engineering |
Start Date: | April 1, 2015 |
End Date: | March 31, 2018 (Estimated) |
Total Intended Award Amount: | $251,597.00 |
Total Awarded Amount to Date: | $251,597.00 |
Funds Obligated to Date: |
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History of Investigator: |
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Recipient Sponsored Research Office: |
21 N PARK ST STE 6301 MADISON WI US 53715-1218 (608)262-3822 |
Sponsor Congressional District: |
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Primary Place of Performance: |
1513 University Avenue Madison WI US 53706-1539 |
Primary Place of
Performance Congressional District: |
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Unique Entity Identifier (UEI): |
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Parent UEI: |
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NSF Program(s): | Dynamics, Control and System D |
Primary Program Source: |
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Program Reference Code(s): |
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Program Element Code(s): |
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Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.041 |
ABSTRACT
Interface damping is a primary source of energy losses in built-up structures such as weapon systems, space vehicles, aircrafts, ships, automobiles, buildings, bridges, and turbine engines. Accurate prediction and control of interface damping is critical for safety, reliability and energy efficiency of built-up structures operating in dynamic conditions. Interface damping results mainly from frictional energy losses over contacting surfaces. Variability, nonlinearity and uncertainty in contact interactions limit the ability to accurately predict and model interface damping. This research project aims at identifying the main mechanisms that govern interface damping, its magnitude and its nonlinear characteristics. The project will investigate and outline effective methods to adjust such characteristics to desired values. Results from this award will enable designs of structural interfaces with desired interface damping. The expected outcome is the improvement of safety, reliability and energy efficiency of built-up structures. The results from the research will be shared with the community and K 12, undergraduate and graduate students through design projects involving vibrations and acoustics of simple built-up structures.
Time and load dependent stochastic interfacial events introduce nonlinearity to interface damping, and deter predictability of dynamical response. The current state-of-the-art in estimating interface damping is through phenomenological models, which cannot ensure predictive results for untested conditions. Physics-based models cannot account for all possible events and changes occurring at the interfaces. This research offers an effective alternative to complicated modeling whereby the mismatch of elastic properties across interfaces are adjusted, and loading conditions are identified to reduce and if possible eliminate nonlinearities and variability in interface damping. Additional benefit of this alternative approach is the ability to tune interface damping over several orders of magnitude based on operational needs. The research approach is a concerted effort in modeling and experimentation that bridges two distinct disciplines such as tribology and structural dynamics. The PI will systematically study interfacial mechanics, geometry, friction, material properties and loading conditions to identify the major contributors to interfacial energy dissipation. Built-up structures containing interfaces with controlled material properties, preloads and geometries will be designed and constructed. Finally, forced and free vibrations tests will be performed on the built-up structures to explore tunable interface damping in dynamic response. An education and outreach program will also be conducted to disseminate the research results to a broader audience, and introduce important concepts of damping and friction to the students at various stages of their education process.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Interface damping is a primary source of energy losses in built-up structures such as weapon systems, space vehicles, aircrafts, ships, automobiles, buildings, bridges, and turbine engines. Accurate prediction and control of interface damping is critical for safety, reliability and energy efficiency of built-up structures operating in dynamic conditions. Interface damping results mainly from frictional energy losses over contacting surfaces. Variability, nonlinearity and uncertainty in contact interactions limit the ability to accurately predict and model interface damping. This research project aims at identifying the main mechanisms that govern interface damping, its magnitude and nonlinear characteristics.
Throughout the project duration, various numerical and experimental studies have been completed for:
- systematic investigation of interfacial mechanics, geometry, friction, material properties and loading conditions, and their contributions to interfacial energy dissipation;
- developing simple assemblies containing interfaces with material properties, preloads and geometries tailored for contrasting interface damping properties, and
- Demonstrating through forced and free vibrations experiments on the assembled structures a prototype of tunable interfacial dissipation.
Influence of loading conditions:
In the literature, simultaneous exposure of interfaces to normal and tangential vibrations was suggested as a tuning parameter for frictional damping. However, experimental validation was lacking. The PI’s group conducted experiments on polyimide surfaces under varying normal and tangential vibrations, and showed that nearly 90 degree phase difference between normal and tangential vibrations increases interfacial dissipation substantially. Degree of nonlinearity, however, was found independent of phase. This is in contrast with the previously published literature including the PI’s numerical analyses. One major factor contributing to this discrepancy is internal (material) damping, which is constant under small to moderate stress conditions.
Influence of material properties and surface geometry:
After noticing this, the PI’s group designed simple assemblies consisting of flat plate made of three different materials; namely, Al6061, 304 Steel and high density polyethylene (HDPE). Those materials span an order of magnitude in internal damping values as documented in the literature. Therefore, forced and free vibration experiments on those materials would show the influence of material properties and internal damping on the interfacial damping measured. While preparing the plates, surface waviness was controlled, and roughness was varied from mirror-polished (smooth) to as-machined (rough) to identify if roughness contributed to the interfacial damping. Preliminary results on these forced dynamic response, and measured interfacial damping lead to the following conclusions:
1) Long wavelength surface features (waviness) can be varied to tune the interfacial energy dissipation 10-fold.
2) Out-of-phase normal and tangential vibrations acting on a frictional interface results in more dissipation when compared to in-phase counterparts.
3) At small to moderate shear stresses, internal damping in the contacting materials dominate the mechanical dissipation, whereas frictional effects dominate at larger stresses.
4) Since internal damping is found influential, the degree of nonlinearity in the interfacial damping is found to depend heavily on vibration-amplitude (shear stress). For small vibrations, the damping is constant, and thus linear system models can represent the dynamics of the assemblies. For large vibrations, frictional slip contributes significantly in the dissipation. Therefore, degree of nonlinearities in damping increases.
5) Roughness is found to have very limited influence on the interfacial damping (dissipation increases very little with roughness). By the same token, plasticity acting at roughness scale found to have negligible influence after running-in period.
In the presence of those experimental observations, the PI’s group developed simple numerical models to incorporate both the frictional and internal damping effects on a rough plate contact. Those numerical models adopt two different but converging approaches of statistical mechanics and fractal representations of the surface roughness. Those models promises to deliver physics-based predictive models for interfacial damping in assembled structures, and alter the state-of-the-art in structural dynamics modeling.
Key findings of this research were presented at three prestigious conferences, and documented in four journal articles (three published and one in preparation). Also, the PI’s group demonstrated frictional slip at an exhibition stand at the Engineering Exposition 2018 held in the University of Wisconsin-Madison. In this public exhibition, attendees tried to slip their fingers across various surfaces made of different materials with different corrugated patterns. With this, the attendees learned the importance of materials and surface geometry on the slipperiness feeling in their touch. Also, the PI presented some of the key findings of this project in his graduate-level course on friction, wear and lubrication in Spring 2018 semester.
Last Modified: 07/01/2018
Modified by: Melih Eriten
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