Analyzing and Testing Bimetallic Additively Manufactured Structures for Tailored Thermal Expansion
Discipline: Technology and Engineering
Subcategory: Aerospace Engineering
Session: 2
Room: L'efant Plaza
Uchechukwu Agwu - Carnegie Mellon University
Co-Author(s): Kenji Shimada
Introduction: Support structures for optical instruments must be designed to withstand the thermal extremes of space. The supports for these instruments must have minimal thermal expansion displacements to maintain specific stability and pointing accuracy to operate correctly. Typically, the supports are made of materials with a low coefficient of thermal expansion (CTE), such as Invar. These materials can be expensive and operate within a narrow temperature range. Therefore, researchers have developed multi-material geometric designs with less expensive metals that have a substantial CTE difference between them. This CTE mismatch creates dissimilar thermal expansion allowing for the structures to have controllable effective CTEs, ranging from low/near-zero, zero, and even negative CTEs. Generally, adhesives, snap-fit joints, or welds are used to combine different metals. However, there has been limited work in trying to design these geometries with additive manufacturing (AM). AM provides a unique opportunity to design these multi-material structures without external/additional connections. Objective: This work explores the feasibility of using muti-material AM to develop controllable effective CTE triangular structures. Methods: The primary materials examined are IN625 and SS316L due to their established compatibility in bonding. Nevertheless, additional material combinations were explored as well. Numerical and analytical models are developed for the IN625 and SS316L combination, along with the other material combinations. To validate the numerical models for the IN625 and SS316L combination, thermal expansion testing was performed on three different bimetallic triangles with varying strut lengths that were printed using directed energy deposition.Results: It was shown that by adjusting the strut length ratio of the triangles and having a large difference in CTE between materials, the effective vertical expansion of the bimetallic triangles could be minimized and tailored. The thermal expansion test agreed well with the numerical models as the thermal expansion and effective CTEs of the structure ranged from a difference of 0.02% to 14%. Design Application: Finally, after confidence was established in the numerical and experimental work, these concepts were applied towards designing a mounting structure for an optical instrument on a spacecraft. It requires minimum thermal expansion for optical functionality as it undergoes the thermal extremes of space. By using the principles of these bimetallic structures, it was found that a tailorable CTE structure could be developed to meet these constraints. Overall, this work is meant to aid in developing a foundation for how bimetallic AM can be utilized to develop tailorable CTE structures for spacecraft applications.
Funder Acknowledgement(s): The Aerospace Corporation
Faculty Advisor: Kenji Shimada, shimada@cmu.edu
Role: I performed all of the design aspects for the project, I performed all the analytical and numerical analyses, and I reviewed the CTE test data that were performed at a testing facility. I then compared this data to my numerical results. I will also be writing the paper for this work and creating the poster.