Multi-functional Polymer and Polymer Composite Structures
H.A. Bruck, S.K. Gupta, W. Babcock, C. Lopatin
This project is sponsored by NSF and ONR.
Embedded Electronics, Thermal Management, Micro-air Vehicles, energy-absorbing structures
The development of advanced polymer and polymer composite structures for applications such as flapping wing micro-air vehicles and energy-absorbing structures require the manufacture of structures using materials with enhanced properties (e.g., heat dissipation, impact resistance, corrosion resistance). Moreover, by varying materials in different portions of a structure, we can perform multiple functions (e.g., carry load and transfer motion). Hence, multifunctional structures have emerged as a very useful concept for realizing high performance solutions in highly demanding environments with many different requirements. Cost-effective and high-throughput manufacturing of these multifunctional structures remains a challenge. Traditional macroscale assembly-based approaches impose restrictions on the size and geometric complexity of multi-material interfaces, which leads to highly suboptimal solutions (e.g., assembling components with miniature features require expensive robotic systems or time-consuming manual assembly under a microscope). On the other hand, more complex geometries can be realized through self assembly, but is not cost-effective for the size scales that go beyond the microscale. Hence, we are developing new multi-functional polymer and polymer composite structures using advanced molding techniques and materials that are addressing the following challenges:
• Formulating high-performance materials that have multiple enhanced properties (e.g., thermal, electrical, and mechanical)
• Integrating materials and components with different functionality that do not break apart and can be cost-effectively manufactured
We believe that addressing these challenges will lead to new design models and manufacturing techniques for creating multi-functional polymer and polymer-composite structures.
The objectives of this project are:
1. Embed electronic components to minimize weight and enhance mechanical performance of multifunctional structures. This will enable electronic components to be integrated into a structure in order to bear load instead of requiring parasitic packaging. Thus, multifunctional structures can be created that are lighter than conventional structures.
2. Add nanoscale ingredients to enhance electrical and mechanical behavior of energy-absorbing structures. Nanoscale ingredients, such as carbon nanotubes, hold the potential to enhance multifunctional properties, such as electrical conductivity, strength, and stiffness, of polymers and polymer composites at very low concentrations to absorb more energy while having integrated damage sensing mechanisms.
3. Integrate energy harvesting technologies into flapping wing micro-air vehicles. Micro-air vehicles require more energy and less weight to improve performance. Integrating energy harvesting technologies, such as solar cells, into compliant wings for flapping wing micro-air vehicles will optimize energy while minimizing mass.
Overview of Approach
Embed electronics: We can now embed electronics into polymer and polymer composite structures using new in-mold assembly processes. Currently, we do not fully understand the impact of various parameters governing the new in-mold assembly process on the residual strain distributions in and around embedded components. For example, thermal loading experienced by a sensor during the processing step might change its performance by accelerating thermal or mechanical fatigue. There are ways to control the thermal and thermomechanical stress distribution by changing the molding materials, component geometry, or processing conditions. However, models must be developed that relate these processing parameters to the thermal and thermomechanical stress distributions. Also, fully embedded structures lead to interfaces in the material that are multi-scale in size. For example, we encounter interfaces that have microscopic features due to surface conditions of the molds. In addition the interface may contain engineered mesoscopic geometric features to increase interlocking. Finally, it may contain macroscopic features that conform to the shape and arrangement of embedded components. We need to fully understand how such multi-scale features will affect the performance of the embedded components. In order to address these issues, we are designing and executing experiments to measure the strains involved and the manner in which these strains develop. An in situ open mold experiment is employed using the full-field deformation technique of Digital Image Correlation (DIC) to characterize the displacement and corresponding strain fields that evolve near embedded electronic elements as the polymer shrinks from the molten to the solid state during processes and during break-in of the electronic component. We are also investigating the displacement and strain fields of multi-material modules with embedded electronic components to characterize the effects of internal heat generation during break-in.
Add nanoscale ingredients: By adding nanoscale ingredients to polymers and polymer composites, it is possible to create hierarchical microstructures. Both conventional and multifunctional composite structures can be created using hierarchically-structured polymer and polymer composite materials, along with embedded electronic components for power and sensing. In the development of these structures, it is necessary to understand how the hierarchically-structured polymer composites affect dynamic failure in the composite structures. The proposed research addresses this problem by creating hierarchically-structured polymer composites using VARTM processing. Dynamic mechanical experiments can then be conducted to characterize the dynamic damage mechanisms. Both Split Hopkinson Pressure Bar tests providing dynamic constitutive response and three-point bend impact tests providing dynamic interfacial failure will be conducted. Details of the dynamic damage mechanisms are being obtained using the full-field deformation measurement technique of Digital Image Correlation (DIC). From the experimental data, multi-scale models of the dynamic damage mechanisms can be developed using a combination of analytical formulas, dynamic FEA, and micromechanical analysis based on High Fidelity Generalized Method of Cells. Model multifunctional structures can then be created by embedding electronic components in the hierarchically-structured polymer composite. The effect of the embedded component on the dynamic damage of the hierarchically-structured polymer composite and the subsequent multifunctional performance can then be characterized.
Integrate Energy Harvesting Technologies: The development of autonomous robots, such as flapping wing micro-air vehicles requires a new class of composite structures which are compliant and multifunctional. To develop fundamental principles for the development of compliant multifunctional composite structures for autonomous robots, we are investigating the integration of flexible solar cells into a compliant wing design for a flapping wing micro-air vehicle (MAV). This involves identifying an appropriate compliant wing design and flexible solar cell technology for integration. It is also necessary to develop an approach for integrating different configurations of flexible solar cells into the compliant wing to create a compliant multifunctional composite structure. It is then possible to characterize and model the effect of different solar cell configurations on the compliance of the wing and its aerodynamic performance. The performance of the solar cell and its degradation with cyclic loading also must be characterized in order to develop a model for a multifunctional performance index. Ultimately, it may be possible to fabricate and directly transfer a thin film solar cell onto compliant wings. We are using a novel test stand for flapping wing MAVs we have developed for characterizing the lift and thrust forces generated by the multifunctional wings. We are currently investigating mechanical and performance characterization of the multifunctional wings with different solar cell configurations, and the model development for mechanical behavior, aerodynamic performance, and multifunctional performance index.
Dr. Hugh A. Bruck
Department of Mechanical Engineering
2153 Martin Hall
University of Maryland
College Park, MD-20742
Project Website: http://terpconnect.umd.edu/~bruck/WAM-pub/