The Natural Strain suggested in this paper is a strain expression, which is obtained by integrating an infinitesimal strain rate on an identical line element in the body. Consequently, the shearing strain becomes pure angular strain which is obtained by removing the rigid body rotation from the rotating angle of a line element. Since the additive law of strain on an identical line element can be satisfied, this strain rate can be clearly decomposed into the elastic component and the plastic component. In this paper, the elasto-plastic decomposition of strain rates in the large pure shear is formulated on the basis of the concepts of the intermediate configuration, which is originally proposed by E.H.Lee, and the geometrical meaning of this formulation is revealed. The strain distributions of the elastic and the plastic strain component and the locus of strain on an identical line element are calculated numerically and the rationality of this formulation is verified.

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In hydraulic turbine runners, accidents due to cyclic loading often occur. In this study, cyclic tension-compression loading tests and fatigue crack growth tests using compact tension specimens under the stress ratio R-constant and repeated two-step load sequences were carried out for welding material INCONEL625, in order to clarify fatigue properties, fracture mechanisms, fatigue crack growth and closure properties. The test results are summarized as follows : (1)The volume loss rate of INCONEL625 improves 30% than that of SUS309 by using a test apparatus an ultrasonic vibratory cavitation device. (2)The S-N curve of welding material INCONEL625 used in this study has narrow scatter and the tension-compression fatigue strength was higher than the test data of the stainless cast steel SCS5 used as hydraulic turbine runner material. (3)From SEM observation of the fracture surfaces, there were two types of fracture origin ,that indicate fatigue crack initiation by slip deformation at surface and from the casting defects. (4) Fatigue crack growth rates of the specimens which are the vertical and the parallel to welded direction under the stress ratio R-constant could be correlated with the effective stress intensity factor range ΔK_eff. And ΔK_eff under varying loading was the same as that under the stress ratio R-constant. Crack propagation rate under varying loading could be predicted by fatigue crack growth data under constant amplitude loading.

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In this paper, fatigue tests were carried out under the repeated two-step and random loading condition using the spot welded joints which had the base metal categorized into 590MPa class in order to consider the effect of their loading condition on fatigue characteristics of the joints. As the results of fatigue tests under the repeated two-step loading condition, it was found that the fatigue limit of the spot welded joints was vanished. Therefore, we found that it was necessary to consider the effect of the damage caused by the loading below the fatigue limit on the fatigue damage of the spot welded joints. When the random loading fatigue tests were carried out, it was confirmed that evaluation of the cumulative damage value considered with the mean loading effect had validity though the result of them considered without it indicated the un-conservative estimation. Thus, it was necessary to estimate the mean loading effect on the cumulative damage value of the spot welded joints under the random loading condition. Moreover, for considering the local mean stress involved with the deformation of the spot welded joints, it will be achieved to make the precise cumulative damage value evaluation.

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The elasto-plastic constitutive equation based on the concept of continuum damage mechanics is extended to cover the creep behavior for the gray cast iron as used in diesel engine parts. It employs the creep strain given by Perrin and Hayhurst and the creep damage given by Dunne and Hayhurst. Lots of material parameters in the constitutive equation are determined by using the uniaxial tensile/compressive, the creep, the relaxation, and the fatigue test results at 400°C. The identified model is used to predict the creep fatigue life with 600 sec hold-time at the maximum compressive strain. The validity of the proposed model is illustrated by comparing the calculated results with the experimental results. It is expected that the developed computational modeling can be used effectively to predict the creep fatigue life of gray cast iron machine parts.

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Local compression fatigue properties of peripherally clamped HSP have been studied in consideration of usage condition as a floor panel. In this study, the effect of cell wall thickness on local compression fatigue of HSP was clarified. For that purpose, a series of fatigue test of HSP was carried out by changing the cell wall thickness, the thickness of face sheet contacted the indenter and the maximum load value. When the cell wall thickness was thin, the fracture pattern of face sheet contacted the indenter changed from the tensile type to shearing type with the increase in the thickness of face sheet contacted the indenter. In the transitional region between these two fracture types, the only dent without crack was observed on the face sheet contacted the indenter. On the other hand, when the cell wall thickness was thick, the shearing fracture around dent was observed instead of the dent type in the transitional region. This was because of the increase of buckling strength of cell wall which constrained the formation of dent. This situation resulted in the increase in the shearing stress around the dent.

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A honeycomb core sandwich panel (hereafter, HSP for brevity) is superior in impact absorption under whole surface compression, because of the buffer effect of core. However impact properties of HSP under local compression such as drop weight impact are affected by the plate as the face sheet in addition to the core layer. This research describes drop weight impact properties of double layer HSP which consists of two core layers and three plates. In order to build up the experimental database for design of double layer HSP, a series of drop weight tests was carried out by using double layer HSPs with the several ratios of the core heights. From obtained results, the follows were summarized: 1) Two or three peaks of the load appeared in the load—displacement curve. The peak loads were larger in sequence of their appearances. 2) In the load—displacement curve until the last peak of the load, there are load increase regions by deep drawing of the plates and load equilibrium regions similar to plateau region under whole surface compression. 3) When the height of the upper layer core was lower, the absorption energy was larger in total. 4) An energy absorption model has been developed and verified for design of double layer HSP.

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This study illustrates a new strategy to fabricate arbitrary cross-section honeycombs. These types of honeycombs are usually manufactured from normal flat honeycombs by curving or carving, but the proposed method enables us to construct objective shaped honeycombs directly. We first introduce the concept of the kirigami honeycomb, which is made from single flat sheets and has periodical slits resembling kirigami (Japanese art of study folding and cutting). In previous studies, honeycombs having various shapes, including tapered and aerofoil honeycombs, were made using this method, and were realized by only changing folding line diagrams (FLDs). In this study, these 3D kirigami honeycombs are generalized by numerical parameters and fabricated using a newly proposed FLD design method, which enables us to draw the FLD of arbitrary cross-section honeycombs

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When a porous solid is subjected to both gas infiltration and heat transfer, thermal stresses are generated in such a solid. This paper presents fundamental theory for a porous solid under such a complex situation. The governing equations for gas and solid phases are used to identify the gas pressure in pores and the solid temperature. The constitutive equation for a porous solid is formulated in terms of the unit cell model in which a pore exists periodically in the matrix. Using the constitutive equation, equilibrium equation of stress tensor and strain tensor obtained by differentiating displacement vector, the partial differential equation of displacement components for obtaining the deformation and stresses occurred in a porous elastic solid is introduced consequentially. As a simple example, the thermal stress problem for an infinite porous solid with a spherical cavity into which coolant gas is injected is considered.

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Ni-YSZ composites are widely used as SOFC anode materials for electrochemical devices. The mechanical properties of Ni-YSZ composites were investigated by using a Small Punch(SP) testing method under SOFC operating condition. The compositions of the Ni-YSZ composites tested in this study were 0:100 vol.%, 15:85 vol.%, 30:70 vol.%, and 50:50 vol.%. Electrical resistivity measurements suggested that the Ni particles formed a network-like structure at the Ni content greater than 30 vol.%. Experimental results obtained from the SP tests demonstrated that ductile-like deformation was induced under a reducing environment for the Ni contents of 30 and 50 vol. %. The ductile-like behavior could be attributed to the formation of Ni network. The first complete re-oxidation of NiO-YSZ composites then caused critical damage and resulted in a drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ composites under reducing environment.

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The mechanical properties of patellar tendons and anterior cruciate ligaments were in vivo evaluated in twelve male subjects. The deformation of patellar tendons was measured during isometric knee extension contractions using ultrasonography. The stiffness, cross-sectional area, and tangent modulus of the patellar tendons were positively correlated with the maximum quadriceps strength. The anterior displacement of tibiae was measured during the anterior drawer of the tibiae. There was no significant correlation between the anterior displacement and the maximum quadriceps strength. These results indicated that the stiffness, cross-sectional area, and tangent modulus of the patellar tendons were larger in the subjects with the larger quadriceps strength but the stiffness of the anterior cruciate ligaments was constant.

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The aim of this work was to examine the nucleation and development of creep voids under multiaxial stress states. Type-IV creep damage has been identified as a troublesome in-service problem in welded sections and defined as the formation of creep damage in the fine-grained/intercritical heat affected zone (HAZ). It results in the degradation of the creep strength of structural components. The stress in the fine-grained HAZ is usually under a multiaxial stress state because the HAZ is wedged between the base and the weld metals. In general it is difficult to achieve various types of multiaxial stress states in experiments. Circumferentially notched bar specimens could used to develop the multiaxial stress state around the notch root. In this study, some interrupted creep tests were performed employing the circumferentially notched bar specimen of pure aluminum to examine the relation between nucleation/development of creep voids and the multiaxial stress state. After testing, grid lines divided the metallograph into equal size areas. Subsequently the number of creep voids in each segmented metallograph was counted using a technique similar to the A-parameter method and thus the distribution of creep voids area in each area was mapped. Experimental results showed that creep voids were mainly nucleated at the notch root and subsequently developed in the direction inclined from the loading axis by about 30 to 60 degrees. Elastic-plastic creep FE analyses were also performed to calculate the triaxial factor λ inside the notch root. It was shown that distributions of the triaxial factor λ were almost the same as those of creep voids.

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