With looming environmental problems and the global energy crisis, fully green composites of natural fibers and biodegradable resin have increasingly attracted research interest because of their advantages of low cost, renewable resource usage, and biodegradability. Recent studies and developments are reviewed in this article, including short fiber green composites, unidirectional green composites, textile and cross-ply green composites, and technologies for improvement of natural fibers and these composites. Fabrication methods, molding conditions, and mechanical properties of the composites are discussed in detail. A key approach of natural fiber toughness improvement by chemical treatment along with its effect on the composites is reported as an excellent example. Finally, future development trends related to fully green composites are predicted.

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This study presents an associated structural design to continuous material topology optimization and a particular case of shape optimization using node-wise densities as design parameters. The generation of optimal shapes and topologies represented in this study is based on a three-dimensional density function bilinearly interpolated by element shape functions and nodal densities. The material interface between void and solid regions is described by a specific 0.5 cut-off level of continuous and smooth iso-lines of the nodal density function on a fixed mesh. This approach allows us to perform a simultaneous node-wise topology and shape optimization, which can be easily implemented by existing gradient-based optimization codes. Contrary to those of conventional material topology optimization methods, these optimal solutions are similar to ideal optimal solutions from analytical optimization techniques. Numerical examples for structural reinforced modeling of Michell-type concrete deep beams are used to demonstrate the efficiency and superiority of the resolutions of the present method.

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By processing triangle or square pyramid shaped indents on a flat sheet, panels with periodical indents in regular plane tiling patterns are manufactured. Highly rigid core panels are newly developed by setting this panel (as top panel) on a reversed one (as bottom panel), and gluing/welding them at the apexes of pyramids to the vertexes of the tiling patterns in the bottom panel. The basic model named Dia-Core is a panel created in the form of Octet-Truss developed by Fuller which corresponds to the space filling model consisting of a combination of two tetrahedra and one octahedron. By varying the geometric patterns that appear on the panel surfaces, all possible patterns based on geometrical considerations are devised, systematically creating various modified models with larger welding portions.

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It has been well realized that anatase TiO₂ transforms to a more thermodynamically stable rutile phase by heat treatment at moderately high temperature, typically higher than 600 °C. However, by using suitable synthesis condition the anatast-to-rutitle phase transformation can occur at much lower temperature. In this present work, phase transformation during aging of TiO₂ sol at room temperature was investigated. The sol was prepared based on hydrolysis and condensation of tetrabutyl orthotitanate precursor in the presence of small amount of water and hydrochloric acid. During aging time span of 50 days, the sol was sampled every 10 days for crystal structure and size analysis. It was found that aging time had a pronounced effect on anatase-to-rutile phase transformation accompanied by crystallite growth. Complete phase transformation was observed within 40 days of aging.

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In this paper, an analysis of one-dimensional wave propagation is carried out in which combined dynamic axial force and torsional moment are loaded on a thin-walled tube by using the incompressible elastic-plastic-viscoplastic constitutive equation. In this analysis, theoretical equations are derived for propagation speeds of elastic-plastic-viscoplastic stress waves. Moreover, the derived theoretical equations of propagation speeds are shown to be strain, strain rate, stress and stress rate dependent, and to include those of strain rate independent theory. Last, calculated examples are shown.

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The possibility of detecting laser-generated ultrasound using slight temperature increases with piezoelectric sensors was investigated. The ultrasound noise generated by nanosecond laser irradiation with a theoretically 1 K temperature-rise was detected clearly by the piezoelectric AE sensors using a built-in head amplifier. The amplitude of the first arrival peaks obtained using the side and front sensors decreased monotonically with the source-sensor separation. The amplitude of ultrasound generated by femtosecond laser irradiation was greater than that by nanosecond laser irradiation with same pulse energy, but no great difference existed in the frequency spectrum of the ultrasonic waveforms.

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In this paper, an analytical solution for an infinite strip having an eccentrically located circular hole is given when the strip is subjected to internal pressure around the hole. The solution is based on an approach involving Papcovich-Neuber displacement potentials and deduced using the simple forms of Cartesian and cylindrical harmonics. The boundary conditions on both sides of the strip and around the hole are completely satisfied with the aid of the relations between the Cartesian and cylindrical harmonics. The solution is shown in graphs and the effect of the eccentric hole on the stress distribution is clarified.

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Polycrystalline piezoelectric ceramics have a large possibility to exhibit higher performance in a macroscopic scale by design of crystal morphology in a microscopic scale. In this paper, a multi-scale finite element method by using crystallographic homogenization theory has been applied to a typical piezoelectric ceramics, barium titanate (BaTiO₃) in order to estimate macroscopic properties considering microscopic crystal morphology. Then, microscopic crystal orientation distribution has been optimized by steepest decent method to maximize macroscopic piezoelectric strain constant d₃₃₃. Computational results indicated that BaTiO₃ polycrystal consisting of three layers with different crystal orientations has the highest piezoelectric performance d₃₃₃=258 pC/N, that is beyond single crystal because of mechanical effect in microscopic inhomogeneous structure.

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Lysine triisocyanate (LTI) was used to blends of poly(lactide) (PLA) with poly(ε-caprolactone) (PCL) to improve the immiscibility of the two different kinds of biodegradable polymers. Fracture properties such as the J-integral at initiation, J_in, and the total fracture energy, J_f, of PLA/PCL and PLA/PCL/LTI were evaluated, and compared the results to assess the effectiveness of LTI additive on improvement of the fracture properties. Fracture surfaces were also examined using a scanning electron microscope (SEM) to characterize fracture mechanism. The results of the SEM observation exhibited that the size of PCL spherulites became smaller by adding LTI, and therefore void formation was inhibited, resulting in improvement of the fracture properties.

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The mechanism of enhancement of the nucleation and growth of oxide precipitates (SiO₂) in heavily boron (B)-doped Czochralski (CZ) silicon (Si) crystals was analyzed by first principles calculation. At the initial stage of oxygen precipitation including a small number n of interstitial oxygen (O) atoms with and without one substitutional B atom, i.e., B-O_n complex and O_n complex, reduction of the total energy of stable B-O_n complex formation was greater than that of stable O_n complex formation from isolated B and O atoms. Other calculations showed that the O atom in B-doped Si diffused as O²⁺ charge state with a diffusion barrier of about 2.0 eV, which was lower than the barrier of about 2.5 eV for the O⁰ charge state in intrinsic Si. This reduction of the diffusion barrier should be the mechanism responsible for the enhanced oxygen diffusion and enhanced precipitate growth in heavily B-doped CZ Si crystals.

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The effects of p-type (B) or n-type (P or As) dopant concentration on the formation energy E_F of point defects in silicon (Si) crystals during the cooling process of the Czochralski (CZ) method were studied by first principles analysis. E_F of several charge states of vacancy (V) and interstitial Si (I) was calculated as a function of the Fermi level. E_F of the most stable state of V and I in Si crystals was estimated by considering the dependence of the Fermi level on crystal temperature. The V concentration was found to decrease in p-type but to increase in n-type Si crystals when dopant concentration was higher than about 1×10¹⁹ atoms/cm³. This explains the reported experimental results for void formation behavior in Si crystals, i.e., void formation is suppressed by an increase in p-type dopant concentration above about 1×10¹⁹ atoms/cm³, but is enhanced by an increase in n-type dopant concentration to about 3×10¹⁹ atoms/cm³. Other calculations showed that, at the initial stage of void formation, the reduction of the total energy of stable P-V_n or As-V_n complex formation was greater than that of stable V_n complex formation from isolated P or As atoms and vacancies.

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