Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 150288

150288 - Buckling of Deployable Propeller Blades 

The wings of beetles can quickly switch configurations between resting and flying, gaining advanced agility to explore broad terrains and evade predators. This rapid wing unfolding is achieved by releasing the elastic strain energy and thus requires no actuation. Inspired by such biosystems, deployable structures based on instability have been explored. This type of deployable structure usually has an open, curved thin-shell geometry. However, most existing deployable thin shells are uniform curved and symmetric, such as tape spring. They are not suitable for aviation applications, for example propeller blades which has airfoil shape and twisting. By introducing a small gap at the leading and the trailing edges, the instability on an airfoil thin shell is invoked. Then, a stiffening spar is attached inside the hollow deployable blades. This stiffened deployable propeller blade can collapse and fold or roll up during storage and launching and self-deploy for flight. Sufficient pre-buckling stiffness to resist aerodynamic loads but compliant behavior after buckling is necessary. Consequently, predicting and characterizing the bending stiffness and propagation moment is important for structural design.

A deployable propeller blade consists of NACA-4412 airfoil skin and an omega-shaped stiffening spar is studied by experimental and numerical method for the pre-buckling stiffness, buckling load, and buckle propagation moment. A rotation-controlled bending apparatus is employed to probe the instability response of deployable propeller blades under pure bending. Multi-axial forces and moments resulted from the asymmetric geometry are measured. The dominant bending moment increases linearly in the pre-buckling regime, followed by a snap-through buckling. At this process, a completed flattened cross-section is formed with the moment decreased to the lowest point. Two coupled moment components, in-plane moment My and twisting moment Mz, are also captured under this pure bending process. They come from the asymmetrical geometry and twisting of this aerodynamic surface. In the post-buckling regime, three moment components remain low stiffness. The flattened cross-section slightly spread in the longitudinal direction until the fully folded configuration. The deployment process has similar path during post-buckling and pre-buckling state. A small inconsistency during the snap position was observed. It provides the locking ability during the aerodynamic performance.

A physics-based bending and deployment simulation is completed in finite element analysis, including composites material characterization, construction of the testing sample, and finite element model. Due to highly nonlinear relationships existing in the folding and deploying processes, the quasi-static algorithm is applied. From the energy change curve, the accuracy of the simulation is first calculated and evaluated. Then, the snap-through buckling for three moment components are concluded based on the strain energy variation. A stable post-buckling regime is accurately predicted. All moment-rotation relationships in simulation match closely with the experimental results. A quantitative translation comparison between simulation and experiment indicates that the global deformation and the buckling behavior results are accurate and reliable.

Presenting Author: Bowen Li Purdue university

Presenting Author Biography: Ph.D student at Purdue University

Authors:

Bowen Li Purdue university
Kawai Kwok Purdue University