Analysis Of Active Morphing Skin Structures Based On Pneumatic Muscle Fibers

A major aim of any engineering discipline is to improve the efficiency of existing systems or to design new systems with greater efficiency than their predecessors. In aerospace engineering, this means optimising the aerodynamic, thermodynamic and structural layout of an air vehicle. One way of achieving this is by using the concept of morphing. Morphology, as a science, is defined as the study or classification of a shape, form, external structure or arrangement. In the field of engineering the word morphing is used when referring to continuous shape change i.e. no discrete parts are moved relative to each other but one entity deforms upon actuation. For example, on an aircraft wing this could mean that a hinged aileron and/or flap would be replaced by a structure that could transform its surface area and camber without opening gaps in and between itself and the main wing or lead to sudden changes in cross-section which result in significant aerodynamic losses, excessive noise and vibration in the airframe.A morphing skin can be envisaged as an aerodynamic fairing to cover an underlying morphing structure. A requirement for use in an aerospace application is that it must be able to change shape in at least one of two ways: change in surface area(e.g. flaps, slats on an aircraft wing) and changes in camber(e.g. aileron, flaps, slats, winglet on an aircraft wing or variable pitch propeller). This shape change can be instigated either by external or integrated actuators which would make the skin self-actuating or active and potentially ’smart’. An active structure can be defined as possessing an ability to change shape whilst maintaining a continuous form, whereas a passive structure, such as a hinged aileron, has discrete components which move relative to each other. A smart structure is able to sense external stimuli(pressure, velocity, density or temperature change), process the information and respond in a controlled manner, in realtime. Overall, sensing, actuation and control are embedded in a single multifunctional ‘smart’ structure. Smart materials encompass a broad range of components that can respond mechanically(e.g. shorten, elongate, flex) to a variety of stimuli including electromagnetic fields, pressure, temperature and/or light. Note that it is often not obvious how to differentiate between the material and structural levels of any given system due to the hierarchical nature and multi-functionality of the components involved.In this thesis a bio-inspried active morphing skins has been designed, fabricated and investigated. A kind of improved pneumatic muscle fiber is proposed from the bionics perspective. Three kinds of commercial latex tubes of different specifications are selected for pneumatic muscle fiber. Since it is the commercial material the properties of pneumatic muscle fiber are determined through the experimental test. The output force and contraction of pneumatic muscle fiber are tested with internal air pressure varying from 0 to 0.35 MPa. The experiment results show that a kind of proper latex tube could be chosen from three kinds of different latex tubes, so as to get larger contraction and relatively greater output force. For analyzing the properties of pneumatic muscle fibers the independent output force and contraction ratio of pneumatic muscle fibers are compared. Then the most suitable pneumatic muscle fiber can be chosen for further study. It could be realized that morphing skin, especially variable stiffness skins would employ this kind of improved pneumatic muscle fiber to accomplish the morphing target.Then the stiffness behaviors of pressurized PMFs and a variable stiffness structures are investigated. The pressurized PMF can be seen not only as artificial muscle actuator which obtains contraction deformation capability but also as a spring system with variable stiffness characteristic. A non-linear quasi-static model adopted for investigating the relationship between the generative force and displacement of pressurized PMF, which is known as the spring stiffness. Experiments are conducted to validate the model, and the test results show good agreement with the model predictions. By taking advantage of the designed PMFs which are conducted by the non-linear quasi-static model and the pressurizing air, significant changes in the spring stiffness of elasticity can be achieved by simply controlling the air pressure levels. A case study is presented to explore the potential behavior of a structure with circular permutation PMFs. The structure used in this case consists of sixteen PMFs which are circular uniform arrangement and a circular supporter with sixteen slide way runners. The stiffness of presented structure can vary flexibly in wide range through controlling the air pressure levels and slide deformation respectively.Further, PMFs were embedded into elastomer to form one kind of shape-adaptive panels. The shape-adaptive panel can be seen not only as a panel which obtains contraction and bending deformation capability but also as artificial muscle actuator primally. A model was adopted for investigating the relationship between the generative force and contraction of the shape-adaptive panel while being similar to the used method for PAM. Four panels with embedded 1, 2, 4 and 16 PMFs were designed, fabricated, and tested respectively. The model was accurate enough and valid for predicting the generative force of the panels through comparing with the tested results. The panels with embedded 1, 2 and 4 PMFs were designed for the single-layer structures. The panel with embedded 16 PMFs was designed for the four-layer structures respectively. The PMFs in the designed panels was spaced 0.82 initial diameter of PMF apart. The experimental results showed that the single-layer panels were intended to exhibit in-plane deformation including contraction and slide through pressurizing selected PMFs. The four-layer panel was intended to exhibit 9 degrees of freedom(DOF) through pressurizing selected PMFs at least.Finally, one kind of developed morphing skin embedded with pneumatic muscle fibers was manufactured and was employed for camber morphing structures. Due to these properties, this active morphing skin could be easily used for the morphing structures. Then the proper airfoil profile was chosen to manufacture the adaptive airfoil. The chord-wise bending airfoil structure was achieved by employing this kind of active morphing skin. The deformed shapes of this chord-wise bending airfoil structure were obtained by 3-dimensions scanning measurement. Meanwhile the camber morphing structures were analyzed through the finite element method(FEM) and the deformed shapes of the upper surface skins were obtained. The experimental result and FEM analysis result of deformed shapes of the upper surface skins were compared in this paper.