Applied Mechanics and Materials Vol. 461

Abstract: Many species of owl has ability of fly silently. To explore the mechanism of owl’s silent flight, the kinematic character of the silent flight owl have been studied preliminarily on 3D motion capture technology. The paper has compared the flight motion between the long eared owl(Asio otus) and sparrow hawk(Accipiter nisus). According to the kinematic data, the flight trajectory, flapping frequency, flapping cycle, wrist angle, upstroke and downstroke percentage of cycle were computed and analyzed. The results show that wing tip, wrist and primary feather P10 of long eared owl and the eagle owl have obvious trajectory in flapping flight. Especially the wing tip trajectory in upstroke shows double“8”type. However, the wing tip trajectory in upstroke of sparrow hawk shows single“8”type. The wrist angle of silent owl keeps in downstroke and decreases in upstroke. But the wrist angle of sparrow hawk has increased first and then kept in downstroke, and the angle has begun decrease in upstroke. The above results show the difference of wing kinematics between silent owl and sparrow hawk, and will be useful for bionic design and silent fly technology.

Abstract: Biomaterials have an integrated, hierarchical structure with outstanding mechanical properties which are far beyond those achieved by using the same synthetic materials. nanoindentation techniques have recently been adapted for studying the biological materials. In this paper, the surface texture and nanomechanical properties of claw material in beetle Dorcus titanus were investigated. It is founded that the claw possesses of an optimized shape as well as the non-smooth surface texture with many stripes like as the fullows close to the arc inside. The results of nanoindentation tests indicate that the modulus value of the claw cuticle near the tip (11.25±0.57 GPa) is over three times larger than that near the claw root (3.61±0.22 GPa) and there is an incremental hardness and modulus values from the claw root to the tip. Quantitive measurements on the nanomechanical properties of claw material could help to develop biomimetic materials suitable for industrial products.

Abstract: Fish can swim swiftly in complicated flow environments, which conceives inspirations for man-made underwater vehicles. This paper concentrates on observation and modeling of fish adaptive behaviors in unsteady flows. A good representative of bony fish, crucian, is taken as the experimental specimen for investigating biological adaptation with response to alteration of surrounding flow patterns. Difference of swimming parameters is confirmed by recorded samples within several flow patterns. Furthermore, a bio-inspired gait model is constructed to stimulate fish adaptive behaviors, since the traditional model is hardly suitable. The model is inspired and supported by biological neural oscillators. By using the developed neural oscillator model, not only certain rhythmic motions under a steady flow pattern can be generated, but also behavioral transitions between multiple different patterns within unsteady flows come true. Experimental results validate the effectiveness of the developed neural model in continuously and smoothly regulating fish propulsive patterns within unsteady flows.

Abstract: Ionic polymer metal composite actuators (IPMCs), a new kind of smart material, have taken much attention as suitable candidates for the next generation actuators, micro-electromechanical systems, medical devices and micro air vehicles. In this paper, a new kind of IPMCs was developed by incorporating sulfonated poly (styrene-co-maleic anhydride) (SSMA) into the Nafion structure to overcome some of the major drawbacks of traditional electro-active polymers. The results show that the ion exchange capacity and water uptake ratio of the SSMA-Nation membrane increased dramatically. Compared with general IPMCs, the maximum bending displacement and the maximum blocking force of the SSMA-reinforced IPMCs improved greatly: the 1 wt.% SSMA-IPMC exhibited the maximum bending displacement of 11 mm up to 1.4 times, while the 5 wt.% SSMA-IPMC exhibited the maximum blocking force of 26 mN up to 1.2 times.

Abstract: An unconventional inchworm stepping actuator based on bionics is presented, which consists of driving unit (PZT stack pump), fluid control unit (ER fluids valve), actuating mechanism (precision hydraulic cylinder). As a new type of precision force/ displacement driving and positioning system, it inherits the advantages of conventional inchworm actuators, and also has its own remarkable characteristics, such as that stepping displacement can be adjusted precisely through varying the working voltage and frequency, etc. The driving unit is actuated jointly by double PZT stacks; Multi-channel parallel cylindrical ER fluids valve is designed as the control valve. In the lab, the inchworm bionic stepping actuator based on PZT/ ER hybrid dive and control is designed and manufactured, and the related performances are testedsystematically. The maximum driving force reaches 49N, and the step size and driving speed VS the working voltage shows a good linear relationship under three different signal waveforms. At the same time, in the frequency range less than 40Hz, the driving speed VS the frequency approximately shows a linear relationship. When working voltage is 100V and rectangle wave signal inputs, the step size reaches 12.6μm. When the working voltage and frequency is 100V, 40Hz, respectively, the driving speed reaches 420μm/s. The maximum drive speed of test prototype reaches 1051 μm/s, when working in frequency 75 Hz. The systematic test shows that the method using PZT and ER hybrid drive and control technology to develop a new type of inchworm bionic stepping actuator is feasible, which provides a reference for the future development of new type of actuator.

Abstract: In order to improve the IPMC artificial muscle output force, research the forming process of the Nafion membrane, prepare the different thickness of the Nafion membrane, select the Nafion membrane of 1 mm and 2 mm for preparation IPMC, test the output force of IPMC samples end. The results show that, with the thickness of base film increasing, IPMC tip output force increases. Based on the characteristics of low drive voltage of IPMC material and high response deformation, design a kind of imitation raie propulsion system. The power supply voltage of the device is 1 ~ 3 v, through controlling the change of driving voltage amplitude which load on the IPMC material and the change of frequency to control the speed of imitation raie propulsion system. From the underwater actual testing, the highest travelling speed is 1 cm/s. Through the experiment effectively proves the feasibility of IPMC material as an actuator.

Abstract: As a new intelligent material, IPMC (Ionic polymer-metal composite) can be driven under low voltage with large deformation, and has been widely used in biomedical and robotic systems. Traditional IPMC testing system is bulky, high cost, and inconvenient to use. In order to achieve the portability and convenience of the IPMC testing system, a small and low-cost IPMC tester was designed. The power supply and control system of the tester were integrated into an IPMC electrode clamp. The main research work included control system circuit design, electrode clamp and overall exterior design. The displacement measurement results showed that the design for the IPMC tester was correct and feasible.

Abstract: Dielectric Electroactive Polymers (EAPs) are closest to natural muscles in terms of strain, energy density, efficiency and speed. A 2-DOF (Degree of Freedom) rotary manipulator driven by soft dielectric EAP is designed based on the biological agonist–antagonist configuration. Compact rolled actuators are chosen and implemented to drive the manipulator. To avoid the complicated solving of nonlinear differential equations, electromechanical characteristics of actuators are obtained by measuring their force behavior under different voltages and lengths. A CMAC (Cerebellar model articulation controller) neural network-based closed loop controller is developed to implement the position control of the manipulator and is evaluated by tracking a circle. According to the force analysis of the manipulator, forces of antagonistic actuators are determined by force decomposition to produce the desired force output, and then the voltages for actuators at certain lengths can be calculated through measured electromechanical characteristics. Experiment shows the measured force agrees well with the desired force. Due to the advantages of dielectric EAP, the manipulator has application prospects in areas of rehabilitation, force feedback or flexible manipulation without damage.

Abstract: Ionic polymer-metal composite (IPMC) is a new kind of electroactive polymer with the advantages of low driving voltage and large bend, which has shown great potential for practical applications. In this paper, IPMC was fabricated by casting and electroless plating. Using the as-fabricated IPMC, a linear actuator was designed to transform bending motion of a cantilever IPMC into straight line motion. The linear actuator's output displacement and blocking force were investigated on a test apparatus. The results showed that the mechanism design for the linear actuator was feasible.

Abstract: Wear has been the primary failure mode affecting the long-term performance of orthopaedic implants. The tribological evaluation of orthopaedic biomaterials in vitro is regarded as an essential material characterization before implantation. In this paper, a new biotribometer of pin-on-disk type, the Ortho-POD, was designed and built for the biotribological tests of orthopaedic biomaterials. The primary goal of developing this Ortho-POD is to simulate and predict the wear properties of orthopaedic biomaterials in clinical application, especially in the form of hip, knee and spine prostheses. This 6-station Ortho-POD, including a pin guiding module, a motion module, a framework module and a loading module, provides multidirectional slide track shapes and variable load via a computer-controlled programmer. A frequency controller and heating system were assembled in the Ortho-POD so as to offer a wide range of testing conditions. Keywords-biotribology; wear; orthopaedic biomaterial; pin on disk; wear testing