Ngoc San Ha

Anisotropy and non-homogeneity of an Allomyrina Dichotoma beetle hind wing membrane

Biomimetics is one of the most important paradigms as researchers seek to invent better engineering designs over human history. However, the observation of insect flight is a relatively recent work. Several researchers have tried to address the aerodynamic performance of flapping creatures and other natural properties of insects, although there are still many unsolved questions. In this study, we try to answer the questions related to the mechanical properties of a beetles hind wing, which consists of a stiff vein structure and a flexible membrane. The membrane of a beetles hind wing is small and flexible to the point that conventional methods cannot adequately quantify the material properties. The digital image correlation method, a non-contact displacement measurement method, is used along with a specially designed mini-tensile testing system. To reduce the end effects, we developed an experimental method that can deal with specimens with as high an aspect ratio as possible. Youngs modulus varies over the area in the wing and ranges from 2.97 to 4.5 GPa in the chordwise direction and from 1.63 to 2.24 GPa in the spanwise direction. Furthermore, Poissons ratio in the chordwise direction is 0.63-0.73 and approximately twice as large as that in the spanwise direction (0.33-0.39). From these results, we can conclude that the membrane of a beetles hind wing is an anisotropic and non-homogeneous material. Our results will provide a better understanding of the flapping mechanism through the formulation of a fluid-structure interaction analysis or aero-elasticity analysis and meritorious data for biomaterial properties database as well as a creative design concept for a micro aerial flapper that mimics an insect.

Propulsion Modeling and Analysis of a Biomimetic Swimmer

We have studied a biomimetic swimmer based on the motion of bacteria such as Escherichia coli (E. coli) theoretically and experimentally. The swimmer has an ellipsoidal cell body propelled by a helical filament. The performance of this swimmer was estimated by modeling the dynamics of a swimmer in viscous fluid. We applied the Resistive Force Theory (RFT) on this model to calculate the linear swimming speed and the efficiency of the model. A parametric study on linear velocity and efficiency to optimize the design of this swimmer was demonstrated. In order to validate the theoretical results, a biomimetic swimmer was fabricated and an experiment setup was prepared to measure the swimming speed and thrust force in silicone oil. The experimental results agree well with the theoretical values predicted by RFT. In addition, we studied the flow patterns surrounding the filament with a finite element simulation with different Reynolds number (Re) to understand the mechanism of propulsion. The simulation results provide information on the nature of flow patterns generated by swimming filament. Furthermore, the thrust forces from the simulation were compared with the thrust forces from theory. The simulation results are in good agreement with the theoretical results.

Biomechanical Properties of Insect Wings: The Stress Stiffening Effects on the Asymmetric Bending of the Allomyrina dichotoma Beetle's Hind Wing

Although the asymmetry in the upward and downward bending of insect wings is well known, the structural origin of this asymmetry is not yet clearly understood. Some researchers have suggested that based on experimental results, the bending asymmetry of insect wings appears to be a consequence of the camber inherent in the wings. Although an experimental approach can reveal this phenomenon, another method is required to reveal the underlying theory behind the experimental results. The finite element method (FEM) is a powerful tool for evaluating experimental measurements and is useful for studying the bending asymmetry of insect wings. Therefore, in this study, the asymmetric bending of the Allomyrina dichotoma beetles hind wing was investigated through FEM analyses rather than through an experimental approach. The results demonstrated that both the stressed stiffening of the membrane and the camber of the wing affect the bending asymmetry of insect wings. In particular, the chordwise camber increased the rigidity of the wing when a load was applied to the ventral side, while the spanwise camber increased the rigidity of the wing when a load was applied to the dorsal side. These results provide an appropriate explanation of the mechanical behavior of cambered insect wings, including the bending asymmetry behavior, and suggest an appropriate approach for analyzing the structural behavior of insect wings.

Structural Characteristics of Allomyrina Dichotoma Beetle’s Hind Wings for Flapping Wing Micro Air Vehicle

In this study, we present a complete structural analysis of Allomyrina dichotoma beetle’s hind wings by investigating their static and dynamic characteristics. The wing was subjected to the static loading to determine its overall flexural stiffness. Dynamic characteristics such as natural frequency, mode shape, and damping ratio of vibration modes in the operating frequency range were determined using a Bruel & Kjaer fast Fourier transform analyzer along with a laser sensor. The static and dynamic characteristics of natural Allomyrina dichotoma beetle’s hind wings were compared to those of a fabricated artificial wing. The results indicate that natural frequencies of the natural wing were significantly correlated to the wing surface area density that was defined as the wing mass divided by the hind wing surface area. Moreover, the bending behaviors of the natural wing and artificial wing were similar to that of a cantilever beam. Furthermore, the flexural stiffness of the artificial wing was a little higher than that of the natural one whereas the natural frequency of the natural wing was close to that of the artificial wing. These results provide important information for the biomimetic design of insect-scale artificial wings, with which highly maneuverable and efficient micro air vehicles can be designed.

Performance of piezo-stacks for a piezoelectric hybrid actuator by experiments

Piezoelectric-hydraulic actuator is a hybrid device that consists of a hydraulic pump driven by piezoelectric stacks coupled with a conventional hydraulic cylinder and a set of fast-acting valves. Nowadays, such hybrid actuators are being researched and developed actively in many developed countries by requirement of high performance and compact flight system. In this research, operation principle and performance testing of the hybrid actuator were introduced. Two types of piezo-stacks are selected for experimental performance testing to identify the factors of piezo-stack which affect the performance of the hybrid actuator. The performance of piezo-stacks due to electrical power supply and self-heating was considered. Output no-load velocities and blocked force were measured on performance testing. The results showed that the maximum blocked force was 346 N and no-load velocity was 101 mm/s, resulting in maximum output power of 8.74 W at 1000 V applied voltage and 250 Hz pumping frequency.

Experimental Study on the Performance of a Bidirectional Hybrid Piezoelectric-Hydraulic Actuator

The piezoelectric-hydraulic actuator is a hybrid device that consists of a hydraulic pump driven by a piezo-stack coupled to a conventional hydraulic cylinder. The actuator is of compact size, but can produce a moderate energy output. Such hybrid actuators are currently being researched and developed in many industrialized countries due to the requirement for high performance and compact flight systems. In a previous study, we designed and manufactured a unidirectional hybrid actuator. However, the blocking force was not as high as expected. Therefore, in this study, we redesigned the pump chamber and hydraulic cylinder and also improved the system by removing the air bubbles. Two different types of piezo-stacks were used. In order to achieve bidirectional capabilities in the actuator, commercial solenoid valves were used to control the direction of the output cylinder. Experimental testing of the actuator in unidirectional and bidirectional modes was performed to examine performance issues related to driving frequency, bias pressure, reed valve thickness, etc. The results showed that the maximum blocking force was measured as 970.2N when the frequency was 185Hz.

Dynamic Characteristic of an Artificial Wing Mimicking a Beetle Hind Wing

Biomimetics is one of the most important paradigms as researchers seek to invent better engineering designs over human history. However, the observation of insect flight is a relatively recent work. Several researchers have tried to address the aerodynamic performance of flapping creatures and other natural properties of insects, although there are still many unsolved questions. In this study, we have attempted to investigate the structural dynamic characteristic of an artificial wing that mimicked the wing shape and main venation structure of a beetle hind wing using a non contact measurement method. The structural dynamic characteristic of the artificial wing was measured and compared to the real beetle hind wing by determining the natural frequencies and damping factor. The artificial wing was glued with the cyanoacrylate adhesive at the wing base onto the acrylic stand which was attached to the base of a shaker. The shaker produces the translation motion in the lateral direction of the wing plane. A non-contact laser sensor was used to measure the displacement history of the painted spots on the hind wing. A Bruel & Kjaer FFT analyzer was adopted to calculate the frequency response functions where the natural frequencies of the wing structure can be extracted. The fundamental natural frequency of artificial wing is 51.3 Hz while the natural frequency of the beetle hind wing is 48.8 Hz. In addition, the wing structures were lightly damped with damping factor around 3.1% that is close to the one of beetle hind wing. We found that, in terms of the wing elasticity, the plastic wing frame of artificial wing was suitable for beetle-like flight.Copyright

Design, fabrication, and bending test of shape memory polymer composite hinges for space deployable structures:

Shape memory polymers are smart materials characterized by a recoverability memory effect and a large strain, but their mechanical properties such as low stiffness need to be improved for mechanical applications with large recovering force. Researchers have reported that the characteristics of shape memory polymers can be significantly improved when the shape memory polymers are used with fiber–reinforced composite material. In this study, a carbon fiber fabric-reinforced shape memory polymer composite hinge was designed, fabricated, and characterized for space deployable structure applications. The main idea is that the carbon–epoxy composite itself and the shape memory polymer are combined, which means both epoxy resin and shape memory polymer resin are used together and the epoxy resin remains in a B-stage after curing. As such, the stiffness and shape recovery ratio are increased. The shape memory polymer composite hinge specimens with four plies of carbon fiber fabric and a shape memory polymer were prepared for the experiment. The glass transition temperature, which was 70.9°C, was determined using dynamic mechanical analyzer. The effect of temperature on shape recovery capability was investigated. We investigated the reasons of damage evolution to shape memory polymer composite tapes occurring in the folding and deploying process. To do that, damage to the hinge was observed with a USB digital microscope and a scanning electron microscopy and then explained with ABAQUS analysis. The results confirm that the shape memory polymer composite hinge is a good candidate for an antenna in spacecraft in space.

Development of a biomimetic swimmer and the flow pattern surrounding the filament

We have studied a biomimetic swimmer inspired by the motility mechanisms of bacteria such as E. coli theoretically and experimentally. Even though E. coli uses one or several rotating helical filaments to swim, a single rotating helical filament swimmer is considered in this work. The performance of this swimmer was estimated by modeling the dynamics of a swimmer in viscous fluid. The model has an ellipsoidal cell body propelled by a helical filament. We applied the resistive force theory on this model to calculate the linear swimming speed and the efficiency of the model. A parametric study on the swimming velocity was performed. To validate the theoretical results, a biomimetic swimmer was fabricated and an experiment setup was prepared to measure the swimming speed in silicone oil. In addition, we have studied the flow patterns surrounding the filament with a finite element simulation to understand the mechanism of propulsion.

Thermal Protective Properties of the Allomyrina dichotoma Beetle Forewing for Thermal Protection Systems

ABSTRACT This paper studies the heat-shielding performance of a beetle forewing to explore how it has excellent thermal protective properties. With an experimental setup of a self-developed heating environment, the heat transfer characteristics of the beetle forewing were tested at 50°C under steady state conditions. Two types of the forewings are considered: cut wing and live wing. The heat transfer results show that the live forewing provides a good heat-shielding performance with the heat-shielding index stabilizing at around 22.1%, which is 60% higher than that of the cut wing. Based on scanning electron microscope images of the microstructure of the cross section of the beetle forewing, a simplified finite element analysis is performed to numerically calculate the heat transfer properties of the forewing. The numerical simulations reveal that the proposed structure of the forewing is good for the design of an effective thermal protection system. In addition, the uncertainty analysis is performed to evaluate the quality of experimental data. These results provide a foundational understanding of the heat transfer characteristics of beetle forewing, which will inspire a promising candidate for an actively cooled thermal protection systems.