Photovoltaic power generation systems using solar cells are attracting much attention as a clean, new energy system to reduce environmental problems. This paper reviews advances in crytalline silicon solar cells. First, ingot growth and cell processing technologies developed to obtain low-cost high-efficiency crystalline silicon solar cells are introduced. Recent results include the demonstration of 245% cell efficiency for a small-area single-crystalline cell and 17% for a large-area polycrystalline cell. Second, module technologies concerning structure and durability are discussed. Finally, the progress in performance and cost reduction are reviewed.

View full abstract

We carried out a repeating internal pressure test on a thin-wall cylinder of austempered ductile iron (ADI) which has been noted for its good combination of high static strength and elongation. We examined the effect of the austempering and surface hardening treatments by means of roller burnishing, which affects fatigue strength. For the lathe turned specimen (not roller burnished), the fatigue life of ADI was longer than that of the as-cast sample at a high pressure. But this difference of fatigue life became less clear with decreasing pressure. At the lowest pressure, most of the specimens were unfractured at 1 X 10⁷ cycles; the fatigue life of the ADI sample was shorter than that of the as-cast specimen. On the other hand, for a roller burnished specimen, the fatigue life of ADI was longer than that of the as-cast specimen at all pressures. After the scanning electron microscopic (SEM) observation of the fracture surface, it was clarified that most of the fracture origins were 0.1∼0.15 mm casting defects.

View full abstract

Region 3 crack propagation under static loading is independent of the environment. This mechanical crack propagation curve can be expressed by the four-parameter Weibull function. On the other hand, Region 1 crack propagation is very sensitive to the humidity in the environment. This effect can be well explained by introducing the environmental fracture toughness, K_ie, into the Weibull function. From the numerical integration of the equations of these static crack growth curves, the cyclic fatigue cracking behavior can be predicted. The data for a lower range of the stress intensity factor, ΔK, show the acceleration of cracking by cyclic loading. The rough specimen surface and the partially fractured grain boundary near crack path, appearing only in cyclic fatigue fracture, may explain this acceleration.

View full abstract

The finite element method was applied to generation phase analyses for stable crack growth in inhomogeneous materials. Experimental data on stable crack growth in bimaterial CT specimens, which were composed of a base metal and a weld metal, were numerically simulated using the node-release technique, and the variations of the fracture mechanics parameters such as the J-integral, T^*-integral, j-integral and CTOA were calculated. The effects of the fusion line and the weld material on the near-crack fracture mechanics parameters were discussed.

View full abstract

In this paper, we consider the dynamic singular stresses in G-10CR glass-epoxy laminates with a crack at low temperatures. Laplace and Fourier transforms are used to reduce the transient problem to the solution of a pair of dual integral equations in the Laplace transform plane. The solution of the dual integral equations is then expressed in terms of a Fredholm integral equation of the second kind. A numerical Laplace inversion routine is used to recover the time dependence of the solution. Numerical results on the dynamic stress intensity factor at low temperatures are obtained and presented in a graphic form.

View full abstract

A closed-form solution is presented for calculating the strains produced by temperature changes in semiconductor chip bonding structures ; it is based on beam theory and elasto-perfect plastic bonding layer assumptions. This solution agrees well with three-dimensional FEM and experimental results. The parameters that govern the strains produced in bonding structures are derived from this solution. These parameters are charted in order to obtain the maximum shearing strains of bonding layers and the maximum normal stresses of chips.

View full abstract

The elastic-plastic problem of a bimaterial plate subjected to a prescribed uniform axial displacement along the upper boundary is studied by means of the finite element method. The materials above and below the interface are assumed to be different from each other in terms of Young's modulus and/or yield stress. Numerical results show that development of the plasic region is affected by the difference in elastic moduli as well as yield stresses. Concentration of the tensile stress at the bonding edge disappears as the yield region is extended, while the shear stress is concentrated at the edge under general yielding and is represented by |τ| = K_r^-λ. For a wide range of deformation stages, A takes a constant value which depends on the ratio of the yield stresses as well as the ratio of Young's moduli when the ratio of the yield stresses is small.

View full abstract

By using the body force method, in which stress field in a composite of multiphases is treated as if it exists in an infinite plate of homogeneous phase, the Dundurs parameters a and β are extended to multiphases. When a composite contains n-phases, the stress field induced by prescribed tractions depends only on 2( n - 1) parameters ap and βp (P=1, …, n-1), provided that the vector sums of tractions on holes are zero for every individual hole.

View full abstract

The stress-strain-temperature relationship associated with the R-phase transformation in TiNi shape memory alloy is investigated experimentally and theoretically. The main results are summarized as follows. (1) The R-phase transformation showing a clear yielding stage in the stress-strain-temperature relationship appears at a certain shape memory processing temperature. (2) The R-phase transformation strip and the reverse transformation strip on the stress-temperature plane, which specify the characteristics due to the R-phase transformation are almost overlapping. Both transformation strips are narrow at high shape memory processing temperature. (3) The constitutive equation considering the volume fraction of the R-phase well describes the deformation behavior, such as the shape memory effect, pseudoelasticity and partial pseudoelasticity.

View full abstract

In this paper, we propose an approach for design optimization aiming at reduction of mechanical vibration under complicated conditions. Machine structures in operation generally require reduced vibrational response, which must be evaluated at many response and excitation points. Moreover, multiple vibrational natural modes of the machines must also be taken into account. The design optimization problem is first formulated on the basis of a multiobjective optimization method. Then, the weighted mini-max method with the Tchebychev norm is presented to solve the optimization problem. This approach is then demonstrated for a motorcycle frame design in which the frame is subjected to engine excitation with many directional components and the vibrational response is evaluated at three points : the handlebar end, the front footrest and the rear footrest.

View full abstract

This paper concerns a strategy for using boundary element shape optimization as a post-process of the finite element solver. In this strategy, first, from the finite element solution of the initial assumed problem, the subregion to be optimized is determined and separated from the remaining region. The boundary element mesh of the subregion is automatically generated from the initial finite element mesh, and is employed as the initial data of the shape optimization. The present method is applied to the local shape optimization of a two-dimensional elastic problem in order to examine its validity.

View full abstract

A hypothetical regulation mechanism of adaptive bone remodeling is proposed. In this hypothesis, the growth factors and bone cells are involved in the mechanim as follows : first osteoclasts activate the growth factors contained in the bone matrix and release them into bone fluid, then the growth factors are transported to the bone surface with fluid flow induced by the mechanical loads applied to the bone, and finally the growth factors transported regulate the activities of osteoblasts which are responsible for bone formation. It is shown that many curious features which have been reported for adaptive bone remodeling are explained by the proposed hypothesis. Furthermore, a simple analytical model is constructed based on the hypothesis, which can simulate some typical adaptation processes such as the adaptation to applied repetitive moments and the correction of abnormal curvature after misaligned fracture.

View full abstract