A concept of a parameter U^* has been introduced by the authors to express load transfer paths in a structure. In this paper, matrix formulation of internal stiffness shows that the value of U^* expresses a degree of connection between a loading point and an internal arbitrary point. Stiffness fields, stiffness lines, and stiffness decay vectors are defined using newly introduced U^* potential lines. A concept of a load path can be expressed as a stiffness line that has a minimum stiffness decay vector. A simple model structure is calculated using FEM for an application of U^* analysis. The distribution of U^* values shows that a diagonal member between a loading point and a support point Plays an important rold for the load transfer.

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For finding the effective gettering center of cupper (Cu) impurity atom in silicon crystal, an interaction between interstitial Cu atom and substitutional dopant or carben (C) atom was studied by first principle calculations. The interaction energies of Cu and boron (B), antimony (Sb), arsenic (As), phosphorus (P) or C were estimated. It was found that only B can be an effective gettering center for Cu. This result indicates that heavily B doped P/P+epitaxial wafers will show a sufficient gettering efficiency for Cu contamination. The other calculations showed that vacancy (Vcy) -Sb, Vcy-As or Vcy-P complexes can be formed. In order to design the gettering center for Cu in nln+ epitaxial wafers, the interaction between these complexes and Cu was investigated. It was found that these complexes can be an effective gettering center for Cu. This result proposes a new Cu gettering technique in n/n+ epitaxial wafers with the formation of Vcy-Sb, Vcy-As or Vcy-P complexes.

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We invistigate the characteristic deformation behavior of rubber with carbon black filler. The deformation behaviors of plane strain rubber unit cell contained fillers under combined monotonic and cyclic straining are investigated by computational simulation with the nonaffine molecular chain network model. The results reveal the substantial enhancement of resistance to the macroscopic deformation, which is caused by the remarkable orientation hardening due to the highly localized deformation in the rubber. The disentanglement of molecular chain during the deformation of rubber results the magnification of the hysteresis of the macroscopic stress-strain relations under cyclic straining. Furthermore, we discussed an additional strengthening and hysteresis loss caused by the increase of the volume fraction of filler, the heterogeneity of the distribution of filler and the heterogeneity of initial average number of segments of modecular chains.

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The effectiveness of the Natural Strain theory for describing a large deformation is mentioned in this paper. The Natural Strain is obtained by integrating infinitesimal strain increment on an identical line element over the whole process of the deformation path. Hence, the expression of the Natural Strain is different from the strain expression of ordinary rate type, and the additive low of strain on an identical line element can be satisfied. In this paper, the finite deformation analyses of a pure elastic body concerning the three different types of deformation paths are discussed on the combined deformation of simple tension and simple shear, and we compare the Natural Strain with other strain expressions and confirm the rationality of this expression.

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In this paper, two-dimensional electro elastic analysis is performed for transversely isotropic piezoelectric materials containing arbitrary-shaped hole under the out-of-plane mechanical and in-plane electrical loads at infinity. General closed-formed solutions are provided in terms of complex functions by using the conformal mapping technique. Using the solution, several numerical examples are shown by graphical representation for various arbitrary-shaped holes. The effect of stress concentration on arbitrary-shaped holes is discussed.

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To evaluate the mechanical strength of fiber reinforced composites, it is necessary to consider singular stresses at the end of fibers because they cause crack initiation, propagation, and final failure. The singular stress field is controlled by geseralized stress intensity factor (GSIF) defined at the fiber end. In this study, periodic and zigzag arrays of cylindrical inclusions under longitudinal tension are analyzed by the application of the bady force method. The unit cell region is approximated as an axisymmetric cell ; then, the problems are solved on the superposition of two auxiliary problems under different boundary conditions. The GSIFs are systematically calculated with varying the elastic modulus ratio and spacing of fibers. The effects of volume fraction and spacing of fibers are discussed in short fiber reinforced plastics.

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Strain gage method for determining generalized stress intensity factors of V-notched plates under mixed-mode conditions is proposed. The plates with V-shaped edge notches are subjected to in-plane bending. First, a theory of determining the stress intensity factors using strain gages is presented on the basis of two dimensional elasticity theory. Two strain gages are positioned along the two lines θ₁and θ₂ extending from the bisector of the notch. The type of strain gages is a strip strain gage with five measuring grids. Second, experiments on the specimens with various notch angles are carried out to compare with the analytical results. Experimental results are consistently smaller than the analytical results, with differences within 10 percent for the specimens with various notch angles and shapes.

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To clarify the validity of evaluation of the threshold value of fracture toughness K_th on the surface layer of ceramics by sphere indentation test, sphere indentation tests with indenters of various diameters 2R were performed using Si₃N₄, specimens made by HIP-sintering and the stress intensity factor K₁ for surface crack under ball on plate contact loading was numerically obtained. The crack length c_i was estimated from experimental results using K₁, where c_i is the length of the crack leading to a ring crack and the conditions for ring crack initiation were assumed to be K₁> K_th. It was shown that the average values of ci increased with increases in 2R in the case of small 2R, but the averages of c_i gradually approached a constant value in cases with a large 2R. The constant value of ci was estimated as 8-9μm using K_th=5.3 MPa·m^1/2 and was almost equivalent to the grain size of the test material.

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The effect of microstructure on fatigue crack growth behavior under repeated two-step load sequences was investigated using compact tension specimens of Ti-6A1-4V alloy with bimodal microstructure. Fatigue crack growth rate and macroscopic crack closure were measured by means of an unloading elastic compliance method. The da/dn-ΔK_eff relationship exhibited a trilinear form in so-called Paris region corresponding to the change of growth mechanism from the intergranular fracture in the low ΔK_eff region to the transgranular one in the high ΔK_eff region. The crack opening point, Kop, was constant during one block of varying loading in the case that the crack extension during one block loading was relatively short. On the other hand, in the case that the crack grew beyond the cyclic plastic zone introduced by ΔK_H, K_op under low level loading decreased from the initial high value to the stationary low one as the crack grew. Depending on the test conditions, the fatigue crack growth rate under varying loading was found to be higher or lower than that estimated by da/dn-ΔK_eff relation under constant amplitude loading, which indicates that the load variation resulted in both crack grown acceleration and deceleration in terms of ΔK_eff. The crack growth acceleration was attributed to the change of growth mechanism due to the load variation, while the crack arrest during one block loading brought about the crack growth deceleration.

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Fatigue crack growth behavior under constant and non-stationary variable amplitude load sequences was investigated using compact tension i specimens of Ti-6Al-4V alloy with bimodal microstructure. Fatigue crack growth rate and macroscopic crack closure were measured by means of an unloading elastic compliance method. The da/dn-ΔK_eff relationship under constant amplitude exhibited a trilinear form even in so-called Paris region corresponding to the change of growth mechanism from the intergranular fracture in the low ΔK region to the transgranular one in the high ΔK region. The fatigue crack growth rate under two-step block loading was found to be higher than that estimated by da/dn-ΔK_eff relation under constant amplitude loading, indicating that the load variation resulted in the crack growth acceleration terms of ΔK_eff. The load variation induced the transgranular fracture in the low level loading where the intergranular fracture type was dominant under constant amplitude loading. It is considered that the transition of fracture type in the low level loading resulted in the acceleration. Under single over loading, however, the crack growth deceleration in terms of ΔK_eff was observed due to the blunted crack tip.

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Insulation of superconducting magnets of fusion reactors and generators is subjected to simultaneous axial and shear stresses from cryogenic to elevated temperatures. GFRPs are suitable for these insulation systems. To investigate the laminar strength of GFRP, combined compressive and shear test with parallel-and series-type fixtures and off-axis tensile test were performed. The test results showed that each test gives a characteristic failure envelope. Taking account of the friction between specimens and fixture and stress distribution at the fracture origin, a unique normalized envelope is obtained. The envelope is divided in three domains ; (i) interlaminar shear fracture under tensile and shear loadings which obeys Mohr-Coulomb or Tsai-Hill model, (ii) interlaminar shear fracture with relatively low compressive stress whose shear stress increases linearly with increasing compressive stress, (iii) translaminar shear fracture with high compressive stress whose shear stress decreases linearly with increasing compressive stress.

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The authors previously reported that the variation in volume loss rate during cavitation erosion process could be expressed by a logistic curve. In this study, the validity of this model was examined for the various materials such as pure aluminum, carbon steels, stainless steels and cobalt alloys, etc. The MDE (mean depth of erosion) d with exposure time was expressed by three parameters α, β and c in the following equation. d= (α/β) t-(1/β) ln (1+c) / (1+ce^-αt). The parameter α, β and c were derived from the relation of the incubation period and the slope of maximum rate stage in MDE curve. It was concluded that the calculation based on this model corresponds well to MDE curve due to cavitation in various materials, test conditions and test methods.

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Cavitation erosion data have been accumulated in our laboratory for about 34 years since 1970. The database was constructed as electronic data in Excel file. The data file is able to offer quick search in terms of test material, test method and test condition from among 986 data. The stainless steel data were analyzed, including various stainless steels such as ferritic, austenitic, duplex and martensitic stainless steel. The average of erosion rate under the standardized condition (ASTMG32, stationary specimen method, standoff distance 1 mm) was determined for different stainless steels. The erosion resistance was defined as a reciprocal of erosion rate, and the correlation between erosion resistance and hardness of eroded area after erosion test was better than with the other mechanical properties. The erosion resistance is equal to 2.6×10^-7× (HV×.F_max) ^2.4 (HV;Vickers hardness, F_mat; Material factor), and the correlation coefficient is Q.98. It was concluded that the erosion resistance of different stainless steels could be estimated precisely from the material hardness and material factor.

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