Studying, Tailoring, and Harnessing Structural Instability for Advanced Thin-Walled and Architected Structures
Restricted (Penn State Only)
- Author:
- Doshi, Mitansh Sharad
- Graduate Program:
- Aerospace Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 25, 2023
- Committee Members:
- Namiko Yamamoto, Major Field Member
Charles Bakis, Outside Unit & Field Member
Xin Ning, Chair & Dissertation Advisor
Edward Smith, Major Field Member
Amy Pritchett, Program Head/Chair - Keywords:
- buckling
instability
aerospace
mechanical
thin-walled
composites
machine-learning
FEA
CAD
flexible structures
spherical shells
cylindrical shells
metamaterials
architected structures
soft structures - Abstract:
- Spherical and cylindrical shells are extensively used in the field of aerospace, automotive and marine engineering. Typical shell structures under external pressure (Spherical shells) or under axial compression (Cylindrical shells) exhibit a buckling behavior. This buckling behavior is often characterized as nonlinear and hinders the load-carrying capacity of the shell structures. Imperfections in shell structures further reduce the load-carrying capacity of a structure. In this thesis, the first objective is to improve the buckling load of a near-spherical (icosahedron) composite shell structure. An icosahedron structure is selected as it is less sensitive to imperfections as compared to the spherical shells. To achieve a higher buckling load, geometry and material design variables of icosahedron shells are altered. For geometry design variables, different nodes are moved on the surface of the geometry, radius to thickness (R/T) ratio is varied, strip width is changed. For the material design variables, ply angle and rotation angle are changed for the different triangular faces of the icosahedron shell. Data-driven modeling is incorporated to eliminate the computationally expensive full-scale finite element analysis (FEA). Various loading curves are created based on the design variables with the help of a data-driven model and verified using the FEA simulations. The second objective of this thesis is to improve the buckling load characteristics of conventional cylindrical shells under axial compression using the metamaterial design approach. Metamaterials are engineered materials which exhibit tunable properties such as negative stiffness, bistability, and energy absorption. In this particular study, some typical (cuboid, cuboid braced, octet truss) and some new metamaterial (House Unit Cell (HUC) variants) unit cells are analyzed. Novel metamaterial-based cylindrical shells (cylindrical meta shells) are designed and analyzed under axial compressive loading. It is shown that cylindrical meta shells have a different post-buckling behavior as compared to their conventional counterpart. Though these meta shells have a low load-carrying capacity as compared to the similar scale conventional cylindrical shell, these meta shells are appropriate for the light load-carrying members in outer space. Additionally, various metamaterials-based cylindrical shells are compared based on the mass and loading parameters (structural efficiency plot). The final objective of this work is to harness the buckling force to create 3D structures from 2D precursors. There is a growing interest in using controlled buckling to create 3D mesostructures which can be used in microelectromechanical systems, energy storage and other reconfigurable morphing devices. The idea here is to apply compressive buckling to a 2D structure and create a 3D geometry based on the loading direction. In this objective, typical 2D structures (ribbon, box, pyramid and two-floor ribbon) are analyzed. The effects of initial wrinkling (mode imperfection) and misalignment on the final 3D structure are studied. Furthermore, in the two-floor design, it is demonstrated the possibility of obtaining different 3D shapes based on the loading path. This study shows that there are some 2D structures with consistent force-strain behavior based on the initial wrinkling and misalignment imperfections.