Fumio Nogata

Enhancement of mechanical strength by shape memory effect in TiNi fiber-reinforced composites

Abstract Since there are strong demands for materials that have the high mechanical properties, the authors developed the new design concept that improve the material strength. It uses SMA to actively control the material strength. Using the TiNi shape memory fiber-reinforced epoxy matrix composite as the test specimen, the experiment was conducted to analyze the effectiveness of the new design concept. The test was conducted by the photoelastic method. The photoelastic fringe patterns and the behavior of K -value at the crack tip clearly support the effectiveness of the new design concept. Then, an analytical model based on Eshelby’s model is developed in order to compute the average matrix compressive stress. The experimental trend that |Δ K 1 | increases with prestrain ϵ T was in good agreement with the predictions based on the present model.

Influence of metal plating treatment on the electric response of Nafion

A potentially promising material as a high performance electroactive polymer gel actuator, Nafion, is known for its fast and large bending upon an applied voltage. Not long ago, it was reported that copper plating on Nafion enhances the degree of its bending. We performed the combinational metal plating treatment on Nafion surfaces with silver, copper and nickel, and the performances of metal plated Nafions—bending curvature and generated force—upon an applied voltage were quantitatively evaluated. From the obtained results, it was speculated that the hydrated mobile ions play substantial roles for the large bending of Nafion as has been widely believed and for the enhancement of its generated force. In addition to them, nickel plating on Nafion surfaces was found to enable Nafion to exhibit a large force without a significant force decay owing to the low-elastic property of nickel layers.

Mechanical characteristics of ionic polymer-metal composite in the process of self-bending

An ionic polymer-metal composite (IPMC) consisting of a thin Nafion sheet sandwiched between two thin metallic plates like platinum, silver, and copper ones exhibits a large self-bending motion in its transversal direction upon such a small voltage as 1 V. Estimating Young’s moduli and generated force, which are time dependent and difficult to measure by standard methods, is fundamental for understanding their mechanical properties. We propose a simple method to estimate the time-dependent nominal Young’s moduli and generated force in experiments. We use cantilever beams of IPMCs and obtain their Young’s moduli and generated force (bending moments) from their shapes and vertical force at the tips by neglecting their inertia and viscosity property. The validity of the method is demonstrated by numerical simulation results. For an IPMC consisting of a Nafion sheet and two thin silver plates we give experimental results, which are considerably consistent with ones previously reported. Moreover, we see that i...

Bending curvature and generated force by Nafion actuator

It was revealed that Cu-plated Nafion exhibits an extremely large bending upon applied voltage recently. Although this phenomenon has been thought to be owing to the continuous transport of hydrated Cu/sup 2+/ through the ionization of Cu layer on Nafion surface, we reached the conclusion that it is primarily owing to the shift of a large amount of hydrated Cu/sup 2+/ en masse, which were originally contained in Nafion body. Formation of another Ni metal layers on Nafion surfaces drastically improves the force Nafion generates. This is owing to the reinforcement of Nafion matrix. The force of Ni plated Nafion continues to increase with time upon applied voltage, although it decays without nickel plating layers. Furthermore, it was found that Nafion bending curvature was sensitive to the applied load on it. It demands a detail investigation on Nafion for the purpose of achievement a practical Nafion actuator.

Estimation of carotid diameter with heartbeat on longitudinal B-mode ultrasonic images

Arteriosclerosis, i.e. degrading arterial elasticity, causes cerebral infarction and myocardial infarction. Premonition of arteriosclerosis is important because arteriosclerosis is never cured completely. We therefore propose a method to track the carotid diameter to evaluate the initial carotid elasticity accompanied with a persons heartbeat using the longitudinal B-mode ultrasonic images. If the diameter of carotid artery can be accurately estimated, it is possible to implies for initial inference of the presence of arteriosclerosis. In future studies, it has to be assessed with comparisons to anaother established method.

Estimation of Carotid Stiffness Using Ultrasonic Dynamic Images for Evaluating the Degree of Arteriosclerosis

Some methods for evaluating the degree of arteriosclerosis utilizing the magnitude of systaltic movement of carotid artery have been proposed. The magnitude of carotid movement depends on the stiffness of surrounding tissues around carotid artery as well as the stiffness of carotid artery itself. Therefore, accurate criterion for the degree of arteriosclerosis cannot be obtained only by observing the magnitude of carotid movement. This study proposes an estimation method of the “self-”stiffness of carotid artery by excluding influence of the stiffness of surrounding tissues. In the proposed method, the systaltic movement of surrounding tissues as well as carotid artery is tracked by an optical flow method using ultrasonic B-mode images drawing the cross section of carotid artery.

Propagation Route Estimation of Heart Sound through Simultaneous Multi-site Recording on the Chest Wall

While vibration source of the heart sound has been well-studied, the propagation route of the heart sound on the chest wall has not been clarified. In this study, we first measured the heat sound simultaneously at 64 positions on the chest wall of healthy subjects using 64 small accelerometers. We next calculated the delay times in the vibration propagation between all possible pair of neighboring positions. We proposed the estimation method for the propagation route of heart sound vibration on the chest wall by solving the shortest path problem in the graph-network theory only using such neighboring delay times. Applying to the recorded heart sound signals, we can obtain the estimated propagation route originated at the cardiac apex for the first heart sound, and that originated at aortic valve for the second heart sound.

Ultrasound image-based estimation system for arteriosclerosis of in vivo blood vessels

With aging, the mechanical properties of a blood vessel degrade; its strength and elongation decreases. However, its stiffness (stress/strain) increases. Also the rate of hardening of the vessel depends on the individual. It is an urgent task to establish an inspection technique for strength parameters as hardening progresses. This report presents such a technique for estimating sclerosis of in vivo blood vessel with ultrasound B-mode image. The method is based on in vivo stiffness (Eth) calculated from variations in vessel diameter with changes in systolic and diastolic blood pressures. In addition, we obtained a correlation between Eth and strength (σu) from the results of tensile and internal pressure tests using some animal model and human artery specimens. Therefore, we can estimate in vivo Eth and σu of an artery using B-mode image and an associated correlation curve. To simplify the measurement of changes in diameter, prototype software was developed. To examine the validity of this technique, clinical data was collected at some hospitals. The results indicated that Eth and σu are useful symptom indices for arteriosclerosis, particularly for identifying the beginning of sclerosis in patients in their early twenties.

Evaluation of dermal segment on viscoelasticity measurement of skin by rheometer

The engineering of human tissue represents a major technique in clinical medicine. Material evaluation of skin is important as preventive medicine. Decubitus originates in pressure and the rub. However, shearing in the skin has exerted the influences on the sore pressures most. This paper examines one demand of crucial importance, namely the real time in vivo monitoring of the shearing characteristics skin tissue. Rheometer is a technology developed to measure viscoelasticity of solid and liquid. To measure viscoelasticity of the skin in the noninvasive with this device, we remodeled it. It is ideal for the continuous monitoring of tissues in vivo.

Effect of Crack Closure in Shape Memory Alloy TiNi Fiber Reinforced/CFRP Composite

We develop the TiNi fiber reinforced / CFRP (Carbon Fiber Reinforced Plastic) composites. Various levels of prestrain ε = 0, 1, 3, and 5% are applied to the embedded TiNi fiber. We coat the thin layer of photoelastic material on the surface of the specimen. Then we process a pre-crack on one side the specimens. We engage tensile tests under constant load. We investigate the stress concentration reduction, enhancement of mechanical properties and resistance of deformation of the TiNi fiber reinforced / CFRP composites. To do this, we observe the crack closure behavior by using the reflection photoelasticity method. We calculate Stress intensity factor K value from reflection photoelasticity. We find our proposed TiNi fiber reinforced / CFRP improves the crack closure effect greatly. We confirm that the crack closure effect is due to the compressive stress field in the matrix by shrinkage of the TiNi fibers above austenitic finishing temperature (Af). Introduction Research and development for improving the mechanical property of composite materials, reducing material degradation of machines and making long life structures become important as the safety design requirement for an industrial application. Thus, the development of the material systems with the artificial defense such as intelligent materials is indispensable. There are several researches about the intelligent composite system that actively control the damage fracture. For example, Rogers et al. reported the possibility of controlling the stress intensity factor at the crack tip by using the current-carrying shrinkage phenomenon of shape memory alloy (SMA) TiNi wire that was implanted in the bottom of a notch. However, a systematic research for this proposal has not been performed yet [1]. We previously proposed the composite design concept that used the high temperature side reinforcement. By embedding the shape memory TiNi fiber in the matrix, we use its high temperature side reverse transformation to generate the compressive stress in the matrix [2-6]. (Refer to figure 1.) In this study, we examined the stress reducing effect above the reverse transformation temperature (Af). We used the TiNi fiber reinforced / CFRP composite that we developed as the specimen. We calculated KI value (fracture toughness) at the notch tip vicinity by the reflection photoelasticity. Shape Memory Effect Fiber Shrinkage Temperature Heating above A Prestrain Heat Treatment Shape Memory