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Summary We report an energy harvesting damper composed of a composite of piezoelectric polyvinylidene fluoride film and silicone rubber for applications in offshore structures. We describe the generation efficiency of sandwiched and coiled sheet geometries. Piezoelectricity was generated by cyclic compressive loading with frequency of 2 Hz and a displacement of 3 mm using a fatigue-testing machine, and the voltage and power were measured. We used digital image correlation and finite element method modeling to investigate the deformation of the silicone matrix. The coiled sheet specimen exhibited higher power with larger and more uniform deformation; however the sandwiched geometry exhibited better durability. The lower power of the sandwiched geometry was attributed to localized deformation because of friction at the interface between specimen and fixture, and the performance of this design was improved via the use of a lubricant. Copyright © 2015 John Wiley & Sons, Ltd.

For vacuum-assisted resin transfer molding (VARTM), we propose adding a cover mold, inserted between the distribution medium and the peel ply, to achieve a higher fiber volume fraction in the final product. As the conventional VARTM process does not use a cover mold, improved processes using different rigid covers were explored. A three-dimensional digital image correlation system was developed to monitor the thickness evolution of the vacuum package during the infusion stage. This system was validated as a full-field displacement test. The results demonstrate that there are three advantages to using a cover mold. First, in the filling stage, a rigid cover mold can prevent shrinkage of the part at the resin flow front, and even cause slight expansion of the unsaturated part. This improves the resin flow and shortens the time required for complete infusion. Second, a cover mold can limit the amount of excess resin needed to infuse the saturated part. Third, in the postfilling stage, the cover mold can be used to accelerate extrusion of the excess resin in the package. The overall effect is to increase the fiber volume fraction in the final product. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers

Study on displacement and deformation behaviors of periodontium under dental occlusion, in general, was concluded only from two information, which are a single-point displacement value from a strain gauge, applied force from a load cell, etc. Direct visualization of these behaviors has been actively conducted by various research groups in the world. However, these studies have relied on dried periodontia or photoelastic materials such as resin to simulate living tissue. Thus, their results may differ significantly from the displacement and deformation behaviors that occur under the dental occlusion of fresh periodontium. In this study, the visualization of displacement and deformation behaviors of fresh periodontium was attempted by using the skull of a pig killed in several days earlier for rendering to obtain fresh periodontia as close as possible to live tissues. The dental occlusion was simulated by applying a forced displacement using a material tester. In addition to the dental occlusion process, we observed the displacement behavior of the fresh and dried periodontium in the process of restoration. To clarify difference in these behaviors between both periodontia, similar experiments were also conducted to compare their displacement distributions. A digital image correlation method was applied to the analysis.

Vacuum-assisted resin transfer molding (VARTM) is a manufacturing process that is used to make large and complex composite structures. While promising, VARTM still suffers from relatively low fiber volume fractions and high void content in the final products. The infusion step of VARTM is very important, because the quality of the final product is usually decided by this process. Consequently, a comprehensive understanding of the infusion process is essential. In this study, a three-dimensional digital image correlation (3D-DIC) testing system was set up to research the entire infusion process through the monitor of the thickness change of the laminates in this process. Two distinct VARTM processes, with and without a rigid cover mold, were designed to be studied. The 3D-DIC technique proved to be a valid method that not only can monitor the thickness evolution of isolated points but also can give a full-field distribution of the thickness change of the laminate. The results showed that, without the use of a rigid cover mold, the stack of reinforcements initially shrank and then expanded as the resin filled the cavities before closing the inlet, while when using a rigid cover mold there was an additional expansion period before the shrinkage occurred. Such an expansion stage could promote the flow of the resin, shortening the infusion time.

Inclined-mirror Hugoniot measurements were performed on pure AlN polycrystals in the pressure range up to 150 GPa to study the yield properties, phase transition, and equation of state. The Hugoniot-elastic limit (HEL) stress was approximately 9.4 GPa. Above the HEL, the Hugoniot data converged to a static compression curve despite the high thermal conductivity, which indicated that the thermal property is not an important factor in determining the shock yield property. The phase transformation from wurtzite-type (B4) to rock salt-type (B1) structure took place at approximately 19.4 GPa, and was completed by about 75 GPa. The corrected transition pressure at 298 K was 19.2 GPa. Shock velocity (Us) versus particle velocity (Up) relation of the final phase was given by Us=3.27+1.81Up km/s. The Birch–Murnaghan fitting curve of the calculated isothermal compression curve of the B1-type phase roughly coincided with the recent static x-ray diffraction data up to over 100 GPa. The Gruneisen parameter, bulk moduli (K0), and the pressure derivative (K0′) at zero pressure of the B1-type phase were estimated to be 1.51±0.03, 304±4 GPa, and 3.9±0.2 (K0″=−0.02), respectively.

Shock and static compression experiments were performed on zinc sulfide (ZnS) polycrystal in the pressure range up to 135 GPa to investigate the phase transition and equation of state (EOS). Hugoniot data were measured by means of the inclined-mirror method combined with a powder gun and two-stage light gas guns, and the static X-ray diffraction experiment was conducted using a diamond-anvil cell. This material behaved as an elasto-isotropic solid which lost its shear strength above the Hugoniot-elastic limit (less than 4.4 GPa). The phase transition from zinc blende-type (B3) to rock salt-type (B1) took place at approximately 15.7 GPa under shock compression, and finished up to about 37 GPa. The corrected phase transition pressure at 298 K was 15.5 GPa. It was confirmed by the static X-ray diffraction experiment that the B1-type phase was stable at the pressure range up to 80 GPa. The unstable inclined-mirror images over 75 GPa, double inclined-mirror images over 99 GPa, and a discontinuous decrease in free-surface velocity between 87 and 99 GPa were observed. The melting and decomposition were discussed in relation to these peculiar free-surface motion behaviors. The density, Gruneisen parameter, bulk moduli ( K 0 ) and the pressure derivative ( K 0 ′) of the B1-type phase were estimated to be 4.91±0.03 g/cm 3 , 0.96±0.03, 105±6 GPa and K 0 ′=3.8±0.1 ( K 0 ″=− 0.05 GPa −1 ), respectively.

A long‐pulsed neodymium‐doped yttrium aluminum garnet (Nd:YAG) frequency‐doubled laser with no Q‐switch was constructed for optical measurements of high‐velocity phenomena. The laser consists of a doubled‐elliptical pump cavity with a Nd:YAG rod and two xenon flash lamps, an intracavity potassium titanyl phosphate crystal, and a high‐voltage electrical‐pulse source. A narrow‐band‐stimulated emission at the frequency‐doubled 532‐nm wavelength was confirmed by a spectrometer. The delay time from a trigger signal and the effective pulse duration were approximately 40 and 65 μs, respectively. The laser average output power was measured to be larger than 6 kW by a pyroelectric joulemeter. This laser may be used as a flash monowavelength light source, and also as a long‐pulsed single‐mode laser in the visible wavelength region using for example, an intracavity etalon and/or a brewster plate.

A porcine mandible was separated to prepare thin periodontium specimens consisting of a molar, periodontal ligament (PDL), and alveolar bone. Occlusion was simulated by applying a forced compressive displacement using a table-top material tester. We photographed images of the displacing periodontium specimen and simultaneously obtained the load–displacement curve during the test. The displacement and deformation distributions were examined using digital image correlation analysis. Then, we correlated the distribution with the load–displacement curve, which was characterized by biphasic behavior, as noted in many previous studies. We found that the displacement and deformation distributions of actual periodontium correlated with the load–displacement curve during dental occlusion. Regarding the biphasic characteristics of the load–displacement curve, we showed experimentally that the first phase indicated deformation of the PDL and the second indicated deformation of the alveolar bone and tooth.

We produced a long-pulsed dye laser with no Q-switch for the shock-wave measurement or time-resolved spectroscopy under shock compression of solids. The average output power of this laser was larger than 13 kW (effective pulse duration ; ∼50 μs). This laser has been used as a light source for the Hugoniot measurement of solids by the inclined-mirror method combined with a rotating-mirror type streak camera. It was confirmed that the time resolution of Hugoniot measurement increased to higher than 1 ns.

Observations of the free-surface behavior under shock compression by the gapped-flat mirror method were performed on B4C and Si3N4 ceramics to study their shock-yielding properties. Jagged profiles of the moving free-surface in the plastic region, with a special scale of about one mm and a maximum local displacement of a few 10s of μm, were observed for B4C polycrystals. Similar profiles for Si3N4 polycrystals were smooth. Such profiles for B4C polycrystals were also observed in the elastic region. It is suggested that these observations reflect the heterogeneous nature of shock compression in solids, and further indicate that a macroscopic slip system plays an important role in the elastoplastic transition of B4C material under shock compression and decompression.

The entire infusion step in a vacuum-assisted resin transfer molding (VARTM) process was measured by a three-dimensional digital image correlation (DIC) testing system. The results showed that a stack of fibre reinforcements initially shrank and then expanded as the resin filled the cavities before closing the inlet. The full-field thickness change distribution calculated from 3D DIC revealed zones that were unsaturated, partly saturated, and fully saturated with resin.

Shock-compression behavior of LiF under shock compression in the pressure region between several and several 10s of GPa had not been studied, while the elastoplastic transition in the very low stress region had been well investigated. We had measured the anisotropic Hugoniot-compression curves on LiF single crystal within the region of a few 10s of GPa by the inclined-mirror method. In this study, the shock-wave structures for 〈100〉 and 〈110〉 axis orientations were measured by the VISAR (Velocity Interferometer System for Any Reflector). Three-waves structure shock waves were observed for both axis orientations, but the cause of the diffused step structure following the elastic precursor remained unknown. The final-wave Hugoniot data also showed a crystallographic anisotropy in the low pressure region.

The high-time-resolution streak photographic system equipped with a powder gun and a two-stage light gas gun has been constructed for the Hugoniot measurement of solids at pressures up to >300 GPa. For this system, a compact rotating-mirror-type streak camera and a long-pulsed dye laser with no Q-switch were produced. A time resolution higher than 1 ns was achieved by using a 2-µm-wide slit of the camera formed using the laser. The shock velocity and particle velocity of steady shock waves of the materials with a shock velocity of ~6 km/s can be measured by the inclined-mirror method with the basic errors of 0.2 and 0.1–0.2%, and 0.2 and 0.35–0.45% for symmetrical and asymmetrical impact, respectively, depending on shock velocity and impact velocity.

Hugoniot measurements on the highly dense, pure B4C polycrystal were performed by the inclined-mirror method to study the elastoplastic transition and to search phase transition. In inclined-mirror streak photographs, the smoothly jagged structure was observed at the free-surface shape in the plastic region. The Hugoniot-elastic limit (HEL) has been determined to be approximately 19.5GPa. In the plastic region, a kink was observed at a particle velocity of around 1.26km∕s. The shock velocity (US)–particle velocity (UP) Hugoniot relations in the plastic region were given by US=3.7+5.4UPkm∕s in the Up range of 0.54–1.26km∕s and US=9.61+0.73UPkm∕s in the Up range of 1.26–4.3km∕s. The S value (0.73) in US=C0+SUP above UP=1.26km∕s is significantly small compared with the result of Vogler et al. [J. Appl. Phys. 95, 4173 (2004)], and was much smaller than those of many oxides and nitrides. This material behaved as an elastoisotropic solid above the HEL and showed a large and linear change in the pressure-density...