Impact resistance and energy absorbing capability are of great interest in the design of sandwich structures. Thispaper experimentally studies damage, failure, and energy absorption properties of polyurethane (PUR) and polystyrene (PS)foam core sandwich panels with aluminum and glass fiber reinforced (GFR) composite face sheets subjected to low velocityimpact. Tests are performed using an Instron Ceast 9340 drop tower impact system at different impact velocities. Drop weighttests were conducted on sandwich panels with different types of foam and face sheet. Two commercial foams were used ascore for the sandwich panels: polyurethane Necuron 100 of 100 kg/m³ density and extruded polystyrene of 32 kg/m³ density.The experimental results were compared in terms of force-displacement response and damage status. It was found that theaddition of short glass fibers to the composite face sheets increased the maximum impact force and reduced the debonding ofthe bottom face sheets for both foam grades. The use of lower density polystyrene foam increased the flexibility of the panelsand improved the ultimate failure response of the composite sandwich panels. The energy absorbing capabilities of aluminumand composite face sheet sandwich panels with PUR and PS foam cores are evaluated by means of absorbed energy-timehistories and by specific parameters as normalized absorbed energy, specific energy absorption, and crush force efficiency.Stiffer panels behave better at lower impact velocities, while more ductile ones perform better if impact energy is increased.

In this study, we developed a simultaneous measurement system for measuring the concentration fluctuations of three species by the light absorption spectrometric method using pulsed laser diodes. The conventional method utilizes halogen lamps or continuous laser diodes as light sources for concentration measurements. These light sources require multi-monochromators or dichroic mirrors, which makes these methods rather expensive. However, pulsed laser diodes as the light sources eliminate the need for additional multi-monochromators and dichroic mirrors. A diffusion field consisting of three dye species in an axisymmetric turbulent jet was measured using the developed concentration measurement system. To ascertain the validity of our concentration measurements, we compared the present measurement results with those of a single dye species and previous studies. It was observed that the concentrations of the three dye species were measured accurately by the present measuring system. Therefore, such low-cost concentration measurement systems can be developed and applied in various simultaneous measurements of concentration fluctuations of multiple species such as in turbulent reactive flows.

Several researchers have investigated the flow characteristics that plants have acquired through evolution, such as seeds that can be transferred far by the wind. However, there are only a few discussions of the hydrodynamic characteristics of flowers after they fall on the ground. This study focused on the unique phenomenon of light azaleas that remain on the ground without being blown away by the wind. It experimentally evaluated the hydrodynamic forces on the azaleas (Rhododendron pulchrum and Rhododendron indicum) and three-dimensional printed flower models. Observations on the symphonic flowers of azalea revealed that these 5-cm-big flowers lie in different directions after they fall. However, they all turn in an upside down posture at once when the wind blows. Force measurement test results show that the drag characteristics of the azalea shaped flowers are significantly different from those of other flower models. The survival strategy implications of the flowers that are not blown away are beyond the scope of this paper; however, this unique behavior has potential applications in the engineering field.

The influence of the phase difference between a pitching foil and a periodic flow on maneuverability in the lift direction is investigated experimentally at a low Reynolds number of 4.1×10³, where the periodic flow is the time-varying freestream in the streamwise direction. A strain gauge force balance is used to measure the thrust and lift forces, and it is found that the phase difference offers control of the lift coefficient without affecting the thrust coefficient. Also, the velocity field in the vicinity of the foil is measured using particle image velocimetry (PIV). From the velocity data, a leading-edge vortex (LEV) is observed only on the upper surface at zero phase difference. A numerical simulation is conducted to reveal how this LEV affects the surface pressure, and it is found that the asymmetry of the LEV formation between the upper and lower surfaces enhances the lift coefficient.

Laser cutting is expected to reduce the volume of radioactive substances based on their radioactive levels. The laser has the advantage of being able to access remotely (non-contact) substances in high-level radiation environments. The scattering of radioactive dust, such as fumes and spatter, generated throughout the laser cutting process, is a major issue faced when cutting highly radioactive substances. One driving force of the spatter could be collapse of the cavitation bubble which is caused by rapid thermal loading due to laser irradiation. To elucidate the spattering mechanism, a spark discharge in water was used to generate cavitation bubble. The growth and collapse behaviors influenced by the interaction between a free surface and bubble resulting in the spattering phenomena are observed by using an ultra-high-speed video camera. Numerical simulations also were performed. The spatter height increased as the distance between the bubble and the free surface decreased and the qualitative trend observed was described numerically using simulations.

This paper proposes a method to measure the in-plane displacement and strain distributions inside a rubber sample using X-ray imaging and 2D digital image correlation. To obtain images with random pattern inside the opaque rubber specimen, metal particles are blended into the inner layer of the specimen. The images before and after deformation are then recorded through an X-ray imaging system. With the above procedure, a random pattern of metal particles can be observed and the 2D digital image correlation is successfully applied to the images under a sliding contact. The results show that the in-plane displacements and strains inside the rubber sample are obtained using the proposed method. The results also show that the content of silica greatly affects the deformation behavior of rubber under sliding contact. Since the proposed method can be used to evaluate the deformation behavior of rubber test pieces, further investigation of the rubber deformation behavior at various filler contents is expected.

We developed an impact-micro-indentation testing machine and measurement system on the basis of electromagnetic phenomena to measure histories of the impact load and indentation depth as well as the impact load-indentation depth curve for evaluating surface fractures. Four indenters consisting of tungsten-carbide cylindrical cones with different tip shapes and neodymium magnets were prepared. The total masses of the indenters ranged from 1 to 2 g. We conducted impact-microindentation tests on soda-lime glass plates by freely dropping an indenter onto a plate. We evaluated the effectiveness of the developed machine and measurement system based on the fact that the maximum measured indentation depths by the machine and system agreed with the maximum indentation depths on the glass plates observed after the tests when the sharp-tipped indenter collided with little fragmentation in the vicinity of the impact point. Comparing the results of the indenters with the same tip curvature, the indentation work-indentation depth curves were approximately the same up to an initial indentation stage. However, the curve slope was found to be affected by the tip angle of the indenter. These results indicate that the developed machine and measurement system are effective for evaluating surface fractures.

Metastable β-titanium alloys exhibit good cold formability due to a body-centered cubic crystal structure. However, since the primary plastic deformation mechanism also changes with the amount of β-stabilizing element, their mechanical properties have not been fully understood especially under biaxial loading conditions. In this study, the uniaxial and the biaxial compression tests were conducted on binary metastable titanium-molybdenum (Ti-Mo) alloys with Mo content from 10 to 18 mass% and the effect of Mo content on compressive plastic deformation behavior was investigated. The clear β-stabilizer content dependency was found on the stress-strain relations. The electron microscopy revealed that the {332} twin was activated on Ti-10~16Mo alloys. Meanwhile, Ti-18Mo alloy exhibited higher yield stress and lower strain hardening rate. It was also found that the area fraction of twins in biaxial compression was lower than that in uniaxial compression. Based on those results, the mechanism that induced changes of plastic deformation behavior with Mo contents in uniaxial and biaxial compressions was discussed with relation to the activation of deformation twinning.

In order to use diamond-like carbon (DLC) as a protective film, adhesion to the substrate is crucial. However, an effective nondestructive testing method for evaluation has not been established yet. Therefore, this study proposes reflective laser photoelasticity to measure the residual stress in DLC films. Through this method, the principal stress and its direction in DLC films can be measured nondestructively from the optical retardation, and the adhesion of DLC films can be evaluated indirectly from the stress states. The effectiveness of the reflective measurements is examined by comparison with the transmissive measurements of the same specimen. The value obtained by reflective measurements was 3.42 % smaller than that obtained by transmissive measurements. This error is partly caused by the reflection of laser light from the specimen surface, and a practical correction method is presented to show that the error is not a major problem. The results of this study will facilitate the non-destructive and non-contact measurement of residual stress in DLC, which can be used to determine the optimal deposition conditions with low residual stress and high adhesion.

We developed a system that can measure the cross-sectional area of a deformed rotating tire by the sampling moiré method. The cross-sectional area is an essential factor in tire cavity resonance theory. Fringe patterns on the tire surface are projected by a projector and recorded by a camera, and patterns on two flat planes are recorded as reference patterns at different known positions along the depth direction to calibrate the deformation. The shape of the deformed rotating tire is obtained from the phase differences between the planes and the tire surface. Also, the noise is suppressed by using an image averaged from multiple fringe images. This measurement method is the basis of a method for checking the degree of deformation caused by roller jacks and determining the cross-sectional area of the whole tire. Finally, the ratio of the cross-sectional area of the loaded tire to that of unloaded tire is obtained, and the ratio at the contact surface is as good as that obtained using a three-dimensional laser scanner.

With an increase in the relative grain size to the macrostructure, the collective behavior of the crystal grains will affect the macroscopic deformation field. Experimental quantification and theoretical modeling of the development of such a micro- to macroscopic non-uniform deformation are important to optimize the manufacturing process of the miniaturized metal parts in various small-sized devices. To investigate the relative size effect on the mechanical behavior of the polycrystalline material, the interaction between the microstructure-induced non-uniform deformation and the macroscopic boundary condition-induced non-uniform deformation of polycrystalline copper was evaluated. The development of the strain distribution was measured by the digital image correlation (DIC) method. A non-uniform deformation depending on the macroscopic boundary condition was observed in the specimen with smaller grains, whereas the microscopic non-uniform deformation affected the macroscopic non-uniform deformation in the specimen with larger grains.

Hydrogel contains a large amount of solvent such as water inside a three-dimensional molecular chain network structure. The content of the solvent changes during the swelling and drying processes of the hydrogel. The mechanical properties of the gel significantly change depending on the solvent content. In this study, the effects of the cross-link density and swelling ratio on the nonlinear mechanical responses of hydrogel were investigated by the cyclic tensile test. To evaluate the irreversible deformation of the hydrogel, we performed the one-time and stepwise loading-unloading tests. The stress-strain curves for the loading and unloading process obtained from the crosshead displacement were different owing to the sliding between chuck and specimen. In contrast, they were consistent for all the experimental conditions when the strain was evaluated by the digital image correlation method. Therefore, the hydrogel showed the less-rate-dependent reversible deformation from small to large strain range. Furthermore, obtained results were compared with the theoretical model based on the molecular chain network model with swelling effect. Although the model could represent the nonlinear increase in the stress during the tensile test and the decrease in the stiffness owing to the swelling, the model results were not consistent with the experimental results. Experimental and numerical results indicate that the improvement of the mechanical model is necessary based on the less-rate-dependent reversible deformation mechanisms of the hydrogel.

The acoustic emission (AE) method was applied to analyze the fracture mechanism of woven fabrics and evaluate the fracture mechanism of fabrics degraded by ultraviolet (UV) rays. The fracture mechanism of the woven poly-paraphenylene terephthalamide fabric was first estimated by monitoring its tensile strength using the AE method. Two different AE waveforms were detected during the tensile tests. Next, an experimental simulation was conducted. The two types of waveforms were found to be caused by fiber breakage in one case and friction in the other. Then, the fracture mechanism of woven fabric with UV degradation was investigated. The fracture strength and Young's modulus of the UV-exposed specimens decreased. This decrease in strength is assumed to be caused by the fiber strength of the UV-irradiated surface of the woven fabric, which breaks down and becomes brittle owing to hardening, as well as the increase of microcrack initiation by fiber friction resulting from the unevenness that occurs because of UV irradiation. Furthermore, during the tensile test, the UV-degraded fabrics were monitored using the AE method. It was found that the longer the UV exposure, the earlier the fiber breakage in the UV-degraded woven fabric, and the more the friction and pull-out between yarns.

Pulsed Nd:YAG laser was irradiated to two glasses with the different lead content and a lead-free glass for the radidamatagioe no sf hthiee ldleading.-free Irradiglatass ionwas damviasugeally andco mnfirmechanied calin prthe opelasertri eisr oradf eiaaticohn g cloansds iwtioenre o ifn tvheiss tsigtuadteyd, .t hAel tihrroaudgiaht nioon i draramdaigate ioin n the lead glasses could be recognized and the lead glass with the high lead content tends to cause the higher irradiation damage. Microhardness, elastic modulus, fracture toughness, and thermal shock fracture toughness were evaluated by indentation technique with a Vickers indenter. These values of the lead glasses were 82 - 75 %, 90 – 80 %, 71 – 65 %and 73 – 61 % of the lead-free glass, respectively. The microhardness obtained using the conical indenter in black irradiated area was 10 % smaller than that in unirradiated area of the lead glass with the lead content of 55 wt%.

A Ni-Al sacrificial-core method is a powder metallurgical process to directly produce a microchannel and a Ni-Al intermetallic alloy layer lining the microchannel wall in a nickel body. Aluminum wire was used for the sacrificial-core metal which gave the shape of the microchannel. Influence of the initial porosity of the nickel powder compact on the formation of cracks and their self-healing behavior near the lining layer has been investigated. When the initial porosity Ε0 was 28.7%, both clacks and healed regions, in which molten aluminum infiltrated and filled the cracks, were observed. When the initial porosity was lower (Ε₀ = 23.3%), a continuous, large-sized healed region was observed and there were no clacks. In the case of higher porosity (Ε₀ = 36.2%), only the healed regions had extended in a circumferential direction of the microchannel.

With the advancement of civilization, mankind has designed various mechanical devices, several of which incorporate mechanical elements such as gears. However, to keep up with the constantly evolving modern technology and for the future development of mechanical devices, it is important to develop gears with smaller transmission errors compared to those of conventional gears. In this study, two plastic spur gears were aligned with different pitch phases and glued together to produce spur gears with pitch phase shift. The spur gears with pitch phase shift were designed to have a better meshing ratio and reduced transmission error. The transmission error was measured in four different patterns: normal spur gears, spur gears with pitch phase shift, spur gears with pitch phase shift and varying pitch displacements, and spur gears with pitch phase shift and varying torque. Using spur gears with pitch phase shift, we successfully reduced the transmission error to less than half that of a normal gear. As a result, the greatest reduction in transmission error was achieved when the gear was shifted by exactly half a pitch.

We propose a broadband frequency-tunable dynamic vibration absorber to mitigate vibrations along the horizontal and vertical directions of a vibrating object. The absorber is based on the primary design principle of mass dampers. A magnetorheological elastomer that changes its relative stiffness according to an external magnetic field controls the natural frequency of the movable mass in the absorber. A coil generates the magnetic field and also serves as the movable mass to decrease the total absorber weight while generating a closed-loop magnetic force. Furthermore, an elliptical magneto-rheological elastomer performs two-directional damping. Experimental results show that the natural frequency of the coil can be adjusted by the electric current applied to the coil along both the horizontal and vertical directions. Moreover, vibrations along the horizontal and vertical directions of the upper torque rod in a commercial vehicle can be mitigated by applying an appropriate current to the coil.

Due to the increase in wheel diameter and improvement in braking force recently, the tonal noise generated around the wheel at extremely low speed owing to the frictional vibration generated in the brake disc has become one of the problems. Research on the noise generation from the disk brake system of the vehicle have been carried out by many researchers but there are few researches focused on the noise generation by the resonation of the wheel. In this study, we used a commercial vehicle and measured the tonal noise generated around the wheel when the vehicle was moving low speed and the braking force was slightly working. Further, we simultaneously measured the vibrational acceleration on the wheel surface and performed modal analysis and operational transfer path analysis to investigate the mechanism of the noise generation. Results showed that the generated noise had the tonal peak at the harmonic frequency of 250 Hz. The vibration that contributed to the generation of the fundamental frequency of 250Hz noise was generated by the wheel near the ground and that contributed to the generation of the third harmonic noise was generated at the spoke of the wheel based on the natural frequency of the wheel.

We propose a theoretical method to predict the vertical and horizontal frequencies of a rotating tire cavity resonance by using two complementary theoretical models and measured tire geometry. The first model predicts the frequencies of the rotating tire from those of a non-rotating tire obtained by modal testing. The second model predicts the frequencies of a non rotating tire using two tire geometries. We predict the frequencies of the rotating tire by substituting those of non-rotating tire by the second model into the first model. We compare the theoretical prediction with numerical simulation to verify the proposed two complementary models in the speed range from 0 km/h to 120 km/h. The horizontal and vertical frequencies of the theoretical prediction agree well with numerical results, within errors of 0.33 Hz and 0.49 Hz, respectively. We also compare its predictions with temperature change to experimental results and are consistent with the results at the speeds of 40 km/h, 50 km./h, and 60 km/h. Therefore, the proposed approach gives the resonance frequencies of a rotating tire by using two complementary models under these conditions.

A new recycling method for high water content sludge called the “Fiber-cement-stabilized soil method” was developed in Japan by using paper debris and cement. However, recently, the cost of paper debris is increasing which leads the recycling cost to be also increased. Therefore, a new material with a low cost to replace paper debris is desired. By the way, perlite by-products are industrial wastes discharged from the production of perlite and are currently being disposed in the final disposal site with a high cost. On the other hand, their porous bodies have a high ability for absorbing water. Therefore, if they can improve the high-water sludge as a water-absorbing material, the reduction of the additive amounts of paper debris and the recycling cost will be possible. In this study, unconfined compression test and the cyclic test for drying and wetting are carried out to obtain the compressive properties and durability of Fiber-cement-stabilized soil with perlite by-products. The experimental results show that the failure strength increases with the increase of the additive amounts of perlite by-product. It was indicated that perlite by-products work as a replacement for paper debris and additive amounts of paper can be reduced.

To understand the effect of deterioration on the load-carrying capacity and deformation performance of reinforced concrete members, multiple model beams with various types of artificial deterioration were developed, such as removal of the concrete cover and stirrup rebar. Then, static-loading tests were performed on the model beams to investigate their mechanical behavior in terms of the load–deflection relationship. The result revealed that the moderately deteriorated model beams whose concrete covers were removed exhibited similar load–deflection-related patterns before their yield deflection values compared with the sound model beam. On the other hand, the load-carrying capacity and deformation performance of the model beams with moderate deteriorations after the yield deflection values were found to be proportional to the removal intervals of the concrete cover. For the model beams with severe deterioration whose concrete cover and stirrup rebar were removed, the loadcarrying capacity and deformation performance were weaker than the other model beams. The damage to the concrete cover became noticeable after their yielding. However, damage to the rebars was suggested to affect the bending strength and rigidity of structures and members even before they yielded.

For establishing reasonable tsunami-resistant design and reinforcement methods for cylindrical oil storage tanks at oil storage bases in coastal areas, it is necessary to investigate the tsunami-induced loads and damage modes of these tanks. However, there are few studies conducted on these subjects. Even for isolated tanks, only a few studies have been conducted. Therefore, it is important to properly evaluate the tsunami forces acting on isolated and grouped tanks using hydraulic experiments. First, a series of hydraulic experiments with scale models were conducted on isolated and grouped tanks. Next, the characteristics of the tsunami forces acting on the isolated and grouped tanks were investigated based on the experimental results. Finally, the tsunami resistant performance of the tanks is discussed based on the predicted damage modes. The results indicated that overturning and/or sliding of tanks would occur, even when the tanks are full of oil, depending on the arrangement of tanks.

A wind tunnel experiment was carried out in a turbulent boundary layer wind tunnel to measure the vertical wind profile near the ground using a hot-wire anemometer. According to the Building Standard Law or AIJ Recommendation for Loads on Buildings, the wind speed near the ground surface at a height below Z_b is specified as a constant value. In the practical case, however, as the height approaches the ground surface, the wind speed decreases owing to the friction of the ground surface. In the present study, the focus was on the vertical wind profiles of the mean and maximum wind speeds and turbulence intensity near the ground with roughness blocks. The relationship between the mean and maximum wind speeds was investigated based on the results of the wind tunnel experiment. Finally, an equation that can estimate the maximum wind speed from the mean wind speed was proposed and compared with the equation proposed in a previous study.

The computation of holographic reconstruction in digital holography has been accelerated by graphics processing units (GPUs). CUDA is an extension of the C/C++ language for GPU programming and is widely used for its performance and accessibility. However, CUDA is difficult to implement for beginners due to its memory management, hardware execution unit declarations, and kernel definitions. In this study, we used CuPy, a GPU computation library for Python, to reimplement the holographic reconstruction algorithm in Python and to compare it with the CUDA implementation. The Python implementation was only 70 lines, less than a third of the CUDA implementation. In addition, holographic reconstruction on a GPU in Python was approximately 20 times faster than a CPU implemented in C++, but approximately 2.5 times slower than the execution on the GPU implemented in CUDA. Our results demonstrate the usefulness of Python with CuPy for implementing and executing image measurement processes on GPUs.