Adhesively bonded carbon fiber reinforced plastic (CFRP) skin-stringer structures have been widely used to build lightweight aircraft structures. However, the appearance of debonding degrades the adhesive joint. Hence, we attempted to establish a technique for monitoring the structural integrity by applying a developed ultrasonic sensing system to the debonding detection in the skin-stringer structure. In the technique, dispersion characteristics and mode conversions of Lamb waves were analyzed for providing the theoretical basis of our method. In accordance with the theoretical analysis, we used the arrival time of a mode as a damage index to successfully identify the adhesive debonding.
Acoustic emission (AE) is an elastic wave generated by the release of energy when the damage occurred in a material. In this research, we proposed a new signal processing technique by applying a neural network to analyzing the AE waveform in CFRP laminates. Through verification experiments, we demonstrated that the proposed method was able to clarify the complex relation between the AE singles with different waveform features and the damage-induced AE sources with individual mechanisms in exciting AEs. Hence, the new technique is potentially used to identify the types of damages, such as transverse crack and delamination, in CFRP laminates.
We developed a micro-scale tensile fatigue test system, which allows testing micro specimens fabricated from bulk materials. The system consists of a probe attached to a micro-manipulator, a micro-manipulator for accurate initial positioning and applying tensile stress, and a scanning electron microscope for observation. This paper reports the design of the system and the result of tensile tests and tensile fatigue tests on the specimens which are made of coarse-grained magnesium alloy, AZ31. The tensile tests suggests that the system can apply accurate tensile stress to the micro specimens and its tensile strength is much larger than that of bulk materials. In addition the tensile fatigue test indicates that the system can apply intended cyclic tensile stress.
In reproducing large-area micro shape by injection molding, one of the biggest problem is that the difference of thermal contraction between the mold material and the resin causes a residual stress in the product, and it becomes difficult to release the product from the mold. In this paper, the authors propose a new method which is called ‘directional solidification method’ for solving the problem. The method can reduce the thermal contraction of the product and the releasing resistance by letting the resin solidify sequentially from one end of the cavity toward the another end. In order to realize the method, the authors developed a mold which can make a temperature gradient, and realized the directional solidification of the resin. Using the mold, we reproduced plate-shape products which has micro shapes on their surfaces under two molding conditions such as uniform temperature and temperature gradient. The experimental results showed that the resistance under temperature gradient was 12% lower than under uniform temperature. Through this experiment, it was confirmed that the directional solidification method improved releasability of the products with micro shapes on their surfaces.
In this study, we developed the platinum iridium probe to improve the SN ratio of a low-temperature terahertz scanning near-field optical microscope. Comparing to tungsten for a conventional scanning probe, the platinum iridium is stable for oxidization and can provide a probe with high scattering performance for nearfield wave. We carried out electrolytic polishing to sharpen the platinum iridium fine wire and obtained the probe with a tip radius of approximately 50 nm. To evaluate the fabricated probe, we demonstrated detecting near-field signals on a gold film at room temperature, which showed the probe had equivalent performance with a conventional tungsten probe.
The heat-assisted dieless drawing is utilized for light metal tubes such as aluminum, magnesium and titanium alloys. The geometrical similarity law in cross section of non-circular aluminum tube is satisfied in dieless drawing process. The large reduction in area of dieless drawing can be realized for magnesium alloy with hard deformable metal. Furthermore, titanium alloy tube with 180µm can be fabricated by dieless drawing process.
Stiffness anisotropy of non-cohesive natural soils can be induced by anisotropic stress states (stress-induced anisotropy) and by fabric of soil structure (inherent anisotropy). However, the underlying mechanism of inherent anisotropy has not been fully understood. This study discusses the following questions: ①Dose the particle orientation influence anisotropy of shear wave velocities? ②What is the specific relationship between particle orientation and shear wave velocity? To answer the questions above, a cubical soil box equipped with multi-directional piezo-ceramic transducers has been developed, and cubical specimens composed of elongated rice grains have been tested to measure multi-directional shear wave velocities.
Vulnerability of geotechnical structure due to heavy rainfall, for example migration of fines from soil skeleton (suffusion), has been reported in recent years. Fine particles that contribute to the main fabric are relatively stable against seepage action; however, it is difficult to quantify the particle-scale stress transfer of soil fabric. This study investigated the relationship between soil fabric and characteristics of frequency response of gap-graded materials, mixtures of small and large particles, and found that there is a strong correlation between the stress transfer via fines and the lowpass frequency measured using elastic wave propagation simulations and laboratory experiments.
Recently, effective methods to prevent road functions from cave-in (sinkhole） problems have been discussed. To prevent catastrophic road cave-in accidents, non-destructive radar detection technique that can find shallow subsurface cavities and visualize shape of cavities has been developed and are often used in practice. However, it is still difficult to judge whether a detected subsurface cavity is stable or in risk of cave-in. This research aims to develop a discrete element modelling approach to assess stability of existing subsurface cavities. To verify simulation results, laboratory model tests were performed and compared with the numerical simulations results.
This study explored the ability of synthetic aperture radar (SAR) images for landslide detection in a tile level. Applied data are pre- and post-event ALOS-2 products captured in the affected area of 2018 Hokkaido Estern Iburi Earthquake. First, intensity information of the two applied images was extracted in SNAP software. Then the classification indicator-intensity difference absolute value was calculated using the extracted intensity information, and the analysis tiles were generated in ArcGIS software. Finally, the mean of intensity difference absolute value within each tile was calculated and employed to classify landslide and non-landslide areas. Classification results showed that 83.3% of the landslide and non-landslide tiles were distinguished in the study area.
The common practice of construction in RC framed buildings with infill masonry in urban/semi-urban areas in Nepal is to open the ground floor for commercial shutter/ parking and close the upper floor with infill masonry for residential purpose resulting vulnerable soft storey buildings. In recent 2015 Gorkha Earthquake （Mw= 7.9）, the major loss in RC frame buildings was due to this problem. There are researches recommending solution to the problem of soft storey, nevertheless there is lack of practical implementation in ground level. The authors have conducted field study comprising of questionnaire survey and interactions with different stakeholders and identified that; this problem is not a technical limitation alone but is complemented by the social condition of Nepal. Different factors to be considered while proposing retrofitting solutions for soft storey problem in Nepal are recommended through this study.
Mechanical properties of new hysteresis damping device using thin steel plates are investigated by finite element analysis (FEA) and full-scale experiments. As the result of FEA with shapes of steel plate as main parameter, steel plates with origami inspired three-dimensional resistance mechanisms show better stiffness, yield load, and more plasticized area than with flat shapes The experimental results agreed well with the FEA results by improving joints to prevent brittle fractures.
The 2016 Kumamoto earthquake caused significant geotechnical damages in the affected area. The earthquake also caused ground subsidence of 30 to 50 cm in the floodplain area along Kiyama-river. The floodplain area is located to the west of Mt. Aso and has thick volcanic soil layers, including a pumice soil. The present study examines a possibility that the pumice layer has been responsible to cause the ground subsidence in the floodplain area based on the field investigation, laboratory tests and earthquake response analysis.
Heavy rain and earthquake are major causes of slope failure. However, weathering of geomaterials is also an important factor of the slope failure. The present study investigates the effect of temperature on the weathering of geomaterial. The tested specimen is soft rock which was prepared by mixing kaolin clay with cement. The specimens were subjected to unconfined compression and creep loading under various temperature conditions to clarify the effect on the strength and deformation characteristics of the soft rock specimens.
In order to investigate the effects of immersion on creep deformation and strength characteristics of gravelly mudstones (JGS slaking index = 1, 2）, a series of direct shear tests were conducted under the different stress ratio, degree of compaction and initial water content. The specimens were immersed under creep stress conditions. After when the creep shear displacement became stable, a monotonic loading was applied. Water absorption ratio may be the threshold for the occurrence of immersion-induced deformation. The shear strength tends to decline by immersion-induced deformation. The chart figure which evaluates an increment of shear deformation or creep failure based on the initial water content and stress ratio was developed.
In this study, we investigated the validity of evaluating the maximum through pore (threshold pore) diameter from the maximum size of nanoparticles that can penetrate concrete. In the early stages of the experiments, the liquid that penetrated the specimens contained large particles that exceeded the threshold pore diameter; these particles were presumed to be hydrates that were floating in the water originally contained in the specimen. In contrast, the maximum particle size in the penetrated liquid after the initial water in the specimens was removed and nanoparticle dispersion liquid penetrated showed adequate agreement with the threshold pore diameter measured by a mercury intrusion test.