The present study investigated crack visualization in metallic structures using time-domain reflectometry with a two-dimensional microstrip line. 2D inspection was enabled by covering the inspected structure surface with the microstrip conductor to compensate for the lack of information in the transverse direction. Crack visualization experiments were conducted using the proposed TDR with single ended of 2D MSL for different crack length. The experimental results demonstrated that crack propagation could be clearly visualized. However, false cracks appeared at the same position regardless of the crack position. The electromagnetic field simulation results clarified that the false cracks observed in the experiments were caused by cross talk. The problem can be eliminated by arranging the microstrip conductor appropriately.
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.
Intelligent tires, equipped with sensors for monitoring applied strain, are effective in improving reliability and control
systems such as anti-lock braking systems (ABSs). However, since a conventional foil strain gage has high stiffness, it
causes the analyzed region to behave unnaturally. The present study proposes a novel rubber-based strain sensor
fabricated using photolithography. The rubber base has the same mechanical properties as the tire surface; thereby the
sensor does not interfere with the tire deformation and can accurately monitor the behavior of the tire. We also
investigate the application of strain data for an optimized braking control and road condition warning system. Finally, we
suggested the possibility of optimized braking control and road condition warning systems. Optimized braking control
can be achieved by keeping the slip ratio constant. The road condition warning would be actuated if the recorded friction
coefficient at a certain slip ratio is lower than a 'safe' reference value.
The present paper deals with a self-deployable graphite/epoxy composite structure using a partially flexible composite
(PFC) with shape memory alloy wires. The present paper introduces the fabrication processes of the PFC. Two different
matrices are used for the PFC: epoxy resin for the normal main part, and silicone rubber for the folding line. Since the
fibers are continuous in the structure, the PFC has the same tensile strength as a normal composite. We investigate
graphite fiber breakages during the folding process by considering changes in electrical resistance. 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. The embedded SMA wire realizes compactly folded composite panel structures without loading
and Joule heating of the SMA wires enables self-deployable composite structures.
Since delamination is invisible or difficult to detect visually, the delamination causes low reliability of laminated
composites for primary structures. To improve the low reliability, smart systems of delamination identifications
in-service are desired. Recently, many researchers have employed an Electrical Resistance Change Method (ERCM)
to detect the internal damages of Carbon Fiber Reinforced Plastics (CFRP) laminates. The ERCM does not require
expensive instruments. Author's group has already experimentally investigated the applicability of the ERCM for
monitoring delamination crack and matrix cracks. In the present paper, therefore, these results performed in the previous
papers are briefly explained. These successful results enable us to monitor a lot of information of the CFRP laminates by
means of the electrical resistance changes in many applications. In these previous papers, the plate type specimens are
small. The effect of plate scale on ERCM is investigated in the present paper. 3-D FEM analyses are conducted to
calculate the electrical potential changes caused by delamination for CFRP plates of different sizes and the applicability
of ERCM to large CFRP structures is investigated.
From a traffic safety point-of-view, there is an urgent need for intelligent tires as a warning system for road conditions, for optimized braking control on poor road surfaces and as a tire fault detection system. Intelligent tires, equipped with sensors for monitoring applied strain, are effective in improving reliability and control systems such as anti-lock braking systems (ABSs). In previous studies, we developed a direct tire deformation or strain measurement system with sufficiently low stiffness and high elongation for practical use, and a wireless communication system between tires and vehicle that operates without a battery. The present study investigates the application of strain data for an optimized braking control and road condition warning system. The relationships between strain sensor outputs and tire mechanical parameters, including braking torque, effective radius and contact patch length, are calculated using finite element analysis. Finally, we suggested the possibility of optimized braking control and road condition warning systems. Optimized braking control can be achieved by keeping the slip ratio constant. The road condition warning would be actuated if the recorded friction coefficient at a certain slip ratio is lower than a 'safe' reference value.
For Unmanned aerial vehicles, a morphing wing is desired to improve the maneuverability and reduce the total weight
of structures. Our research group has developed a foldable composite structure for a morphing wing skin plate by using
Carbon Fiber Reinforced Plastics (CFRP). The material system is called Partially Flexible Composites (PFC). In the
present paper, PFC is introduced and a self-sensing system of the PFC is investigated. Since carbon fibers have
electrical conductivity, damages of the PFC can be detected by monitoring electrical resistance changes of the PFC.
This method is called Electrical Resistance Changes Method. An electrical resistance model of the PFC is built and a
relationship of ratio of fiber fractures and electrical resistance changes is obtained. Then, to investigate the
performance of the PFC, cyclic-bending tests are conducted. Damages of the PFC caused by cyclic-bending are
detected by using ERCM. As a result, the PFC with more than 10mm-long flexible part has almost no damage; the
stiffness of the structure remains unchanged. After that, a McKibben pneumatic artificial muscles actuator is made
and it is founded that this can be applied to the PFC as an actuator. This actuator consists of a silicon rubber and a
carbon fiber that are the same as the material of flexible part of the PFC. This enables us to make actuator-integrated
composite structures. In the present study, the applicability of the McKibben pneumatic artificial muscles actuator is
In-service strain monitoring of tires of automobile is quite effective for improving the reliability of tires and Anti-lock Braking System (ABS). Since conventional strain gages have high stiffness and require lead wires, the conventional strain gages are cumbersome for the strain measurements of the tires. In a previous study, the authors proposed a new wireless strain monitoring method that adopts the tire 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 tire monitoring is improved to produce a passive wireless sensor. A specimen made from a commercially available tire is connected to a tuning circuit comprising an inductance and a capacitance as a condenser. The capacitance change of tire causes change of the tuning frequency. This change of the tuned radio wave enables us to measure the applied strain of the specimen wirelessly, without any power supply from outside. This new passive wireless method is applied to a specimen and the static applied strain is measured. As a result, the method is experimentally shown to be effective as a passive wireless strain monitoring of tires.