Ryosuke Matsuzaki

Three-dimensional printing of continuous-fiber composites by in-nozzle impregnation

We have developed a method for the three-dimensional (3D) printing of continuous fiber-reinforced thermoplastics based on fused-deposition modeling. The technique enables direct 3D fabrication without the use of molds and may become the standard next-generation composite fabrication methodology. A thermoplastic filament and continuous fibers were separately supplied to the 3D printer and the fibers were impregnated with the filament within the heated nozzle of the printer immediately before printing. Polylactic acid was used as the matrix while carbon fibers, or twisted yarns of natural jute fibers, were used as the reinforcements. The thermoplastics reinforced with unidirectional jute fibers were examples of plant-sourced composites; those reinforced with unidirectional carbon fiber showed mechanical properties superior to those of both the jute-reinforced and unreinforced thermoplastics. Continuous fiber reinforcement improved the tensile strength of the printed composites relative to the values shown by conventional 3D-printed polymer-based composites.

Wireless Monitoring of Automobile Tires for Intelligent Tires

This review discusses key technologies of intelligent tires focusing on sensors and wireless data transmission. Intelligent automobile tires, which monitor their pressure, deformation, wheel loading, friction, or tread wear, are expected to improve the reliability of tires and tire control systems. However, in installing sensors in a tire, many problems have to be considered, such as compatibility of the sensors with tire rubber, wireless transmission, and battery installments. As regards sensing, this review discusses indirect methods using existing sensors, such as that for wheel speed, and direct methods, such as surface acoustic wave sensors and piezoelectric sensors. For wireless transmission, passive wireless methods and energy harvesting are also discussed.

Passive wireless strain monitoring of tyres using capacitance and tuning frequency changes

In-service strain monitoring of tyres of automobiles is quite effective for improving the reliability of tyres and anti-lock braking systems (ABS). Conventional strain gauges have high stiffness and require lead wires. Therefore, they are cumbersome for tyre strain measurements. In a previous study, the authors proposed a new wireless strain monitoring method that adopts the tyre itself as a sensor, with an oscillating circuit. This method is very simple and useful, but it requires a battery to activate the oscillating circuit. In the present study, the previous method for wireless tyre monitoring is improved to produce a passive wireless sensor. A specimen made from a commercially available tyre is connected to a tuning circuit comprising an inductance and a capacitance as a condenser. The capacitance change of the tyre alters the tuning frequency. This change of the tuned radio wave facilitates wireless measurement of the applied strain of the specimen without any power supply. This passive wireless method is applied to a specimen and the static applied strain is measured. Experiments demonstrate that the method is effective for passive wireless strain monitoring of tyres.

Time-synchronized wireless strain and damage measurements at multiple locations in CFRP laminate using oscillating frequency changes and spectral analysis

Wireless monitoring of the health of CFRP structures reduces the cost and time of inspections and can be usefully applied for continuous monitoring. In a previous study, we presented a wireless sensor for detection of internal delamination in a CFRP laminate. The method utilizes a simple electrical resistance change in CFRP and so monitors delamination at only one location. For monitoring of large-scale structures, however, many sensors have to be distributed to cover the structure. A major problem for using many sensors is time synchronization among sensors. To overcome the problem and enable strain/damage to be monitored at multiple locations with time synchronization, we develop a simple wireless strain/damage sensor that consists of a bridge circuit, voltage-controlled oscillator and amplifiers. Since the sensor does not need A/D conversion procedures or memory storing, there is no time delay. Each sensor has an original basic frequency that changes in accordance with the electrical resistance. The frequencies from the multiple sensors are transmitted to a receiver. Using a short-time maximum entropy method, the received waves are converted to multiple electrical resistance data. The proposed method is applied to CFRP laminates and oscillating frequencies are measured in real time. The results show that the system successfully measures applied strain and detects fiber breakage at multiple locations in CFRP laminates with time synchronization.

Self-deployable Space Structure using Partially Flexible CFRP with SMA Wires

This article deals with a self-deployable composite structure using a partially flexible composite (PFC) with shape memory alloy wires and reveals the fabrication process of the PFC. Two different matrices are used in the PFC: epoxy resin for the normal part, and silicone rubber for the folding line. Since the fibers are continuous, the PFC has the same strength as a normal composite. We investigate carbon fiber breakages during the folding process by considering changes in electrical resistance, and cyclic tests are performed to confirm the availability even after long-term cyclic folding. An SMA wire is embedded in the PFC to keep the folded configuration without loading and self-deployment is achieved using Joule heating. The results confirm that a flexible part of adequate length enables foldable composite structures without causing carbon fiber breakages, while the cyclic folding tests reveal that the PFC is reliable when a long flexible part is used. The embedded SMA wire realizes compactly folded composite panel structures without loading and Joule heating of the SMA wires enables self-deployable composite structures.

Passive wireless strain monitoring of a tire using capacitance and electromagnetic induction change

Strain monitoring of tires in-service of automobiles is quite effective for improving reliability of tires and an anti-lock braking system (ABS). A previous study by the authors presented a new wireless strain monitoring method that adopts the tire itself as a sensor with an oscillator circuit. This method is simple and useful, but it requires a battery to activate the oscillator circuit. The present study proposes and investigates a new passive wireless strain measurement system using capacitance change of tires. The system consists of external antennas and strain sensor with an inductance capacitance (LC) resonant circuit. This wireless system uses electromagnetic coupling between two inductors of the antenna and the sensor. This method allows use of a part of an actual tire as a capacitor of the LC circuit. Tire deformation changes the sensors resonant frequency. This resonant frequency change is measured as a change in the phase angle of the antenna using electromagnetic induction. Tensile tests are performed and the antenna phase angles are measured during the tests. Consequently, experiments show that this method is effective for passive wireless strain monitoring of tires.

Void formation in geometry–anisotropic woven fabrics in resin transfer molding

When geometry–anisotropic fabrics, in which the thickness and width of fiber bundles differ in the warp direction and weft direction, respectively, are used for resin transfer molding (RTM), microscopic porous structures along a flow path may depend on the resin flow direction. This study investigated the influence of woven fabrics’ geometric anisotropy on inter-bundle void formation due to air entrapment at the flow front during RTM. The void content–resin flow velocity relationship was measured in warp (narrow and thick bundle) and weft (wide and thin bundle) directional impregnation. In experiments, warp directional impregnation indicated higher critical resin flow velocity of void formation and void content under a given resin flow velocity than in weft directional impregnation. Void formation was also largely affected by capillary fingering, where warp directional impregnation indicated a higher critical flow velocity of fingering formation. This may be because the gap between the fiber bundle and the mold surface is smaller in the warp direction; thus, the capillary force is higher, and fingering is facilitated compared with weft directional impregnation. Additionally, this may lead to a higher critical velocity of void formation and higher void content at a given flow velocity in warp directional impregnation.

Intelligent tires for identifying coefficient of friction of tire/road contact surfaces using three-axis accelerometer

Intelligent tires equipped with sensors as well as the monitoring of the tire/road contact conditions are in demand for improving vehicle control and safety. With the aim of identifying the coefficient of friction of tire/road contact surfaces during driving, including during cornering, we develop an identification scheme for the coefficient of friction that involves estimation of the slip angle and applied force by using a single lightweight three-axis accelerometer attached on the inner surface of the tire. To validate the developed scheme, we conduct tire-rolling tests using an accelerometer-equipped tire with various slip angles on various types of road surfaces, including dry and wet surfaces. The results of these tests confirm that the estimated slip angle and applied force are reasonable. Furthermore, the identified coefficient of friction by the developed scheme agreed with that measured by standardized tests.

In situ void content measurements during resin transfer molding

In resin transfer molding (RTM), the void content measured after resin curing does not represent the amount of voids at the point of air-trapping. To properly verify a prediction model for the void content based on the occurrence of voids due to the air-trapping mechanism, the void content must be measured immediately at the point of air-trapping. In the present study, we created an in situ method for measuring the void content during resin impregnation by combining image analysis with a technique that visualizes the resin flow and void formation during one-dimensional RTM. Using this proposed method, we measured changes in the distribution of the void content at the air-trapping site and following resin curing. As a result, an inversion phenomenon was observed, in which the void content decreased a short distance from the resin inlet due to the time that elapsed, whereas it increased at a longer distance. This phenomenon can be explained by the ease with which the void moved and by the effect of molecular diffusion. In addition, by measuring the change in void content during the time that elapsed from air-trapping until resin curing, we clarified the behavior of the void change and the factors that affect the void content following void formation.

Numerical simulation of molding-defect formation during resin transfer molding

The present study investigated a numerical simulation of molding-defect formation during resin transfer molding using boundary element method and line dynamics. The proposed method enables to simulate small molding defects by increasing the node for required position during time evolution; thereby, the method computes high-resolution flow front without being affected by the initial mesh geometry. The method was applied to the radial injection RTM with single inlet, and it was confirmed by comparison with theoretical value based on Darcy’s law that the flow advancement was computed with high accuracy. In addition, the method was also applied to the flow advancement for inclusion problem with cylinder, and four-point injection problem. The simulated flow behavior, void formation, and shrinkage agreed with the results in references. Finally, the method was compared with experiments using two-point injection problem. The computed configuration of the flow front and weld line agreed well with the experimental results.