Retardation of fatigue crack propagation due to a single tensile overload and crack closure behavior were investigated on a high tensile strength steel, HT-80 and an aluminum alloy, A5083-O by using the unloading elastic compliance method. Although the delayed retardation was observed at the specimen surface where the plane stress condition dominated, retardation of fatigue crack propagation was found to occur immediately after a peak overload at the interior of the specimen where the plane strain condition was developed. In the latter case, the crack tip blunting due to an overload, which might be the reason of the nodelayed retardation, was confirmed by fractography and also by the load-displacement hysteresis curve. Moreover, it was found that the retardation behavior of fatigue cracks which initiated and propagated from the root of the blunted crack could not be explained only by the change of the macroscopically measured crack tip opening level.
Observations on the tissues in the trunk of Cunninghamia lanceolata have been carried out by scanning electron microscope and optical microscope. C. lanceolata was mostly composed of tracheid and ray, and almost no axial parenchyma were observed. Starch was observed in the ray parenchyma. It was found that the ratio of ray was higher than that of Cryptomeria japonica and Chamaecyparis obtusa. The results of the measurement of cell length revealed that the length and width of ray of C. lanceolata is longer and wider than those of C. japonica and C. obtusa. These indicate that conductive tissues of C. lanceolata is more developed compared to those of C. japonica and C. obtusa, which presumably contributes to the fast growing of C. lanceolata.
The Wang-Brown or Dong methods were incorporated into the multiaxial high cycle constant-amplitude fatigue life prediction method proposed by the authors in the previous papers, so as to predict multiaxial high cycle irregular variable amplitude fatigue life. Multiaxial high cycle fatigue tests were performed using SNCM439 steel for verification. The stress amplitude, mean stress, and principal stress direction change in the stress waveform of the tests. The fatigue lives predicted by the Wang-Brown method were about three times longer than the experimental values. By contrast, the Dong method predicted fatigue lives that were about one-third shorter than experiments. This is thought to be because the stress range of each path is calculated to be smaller by the Wang-Brown method and larger by the Dong method in the stress waveform converted into Euclidean coordinates.
To establish the creep life assessment method for wrought precipitation strengthened Ni-based alloys, the factors which influence the hardness after creep damage were studied. Hardness measurements and microstructure quantification were done for crept specimen of γ’-Ni3Al precipitation strengthened alloy, TOS1X-2. Hardness increased with EBSD KAM and GAM value of measured location, suggesting the hardening by creep induced strains. Grain boundary and twin boundary were found to suppress the plastic deformation by hardness indent. Grains oriented <001> to the stress axis showed high hardness, while grains oriented <101> showed relatively low. This indicated the possible existence of orientation dependence of strain hardening, which might be explained by the number of slip systems likely to operate and the interactions of dislocation movement. The hardness seemed to be influenced by the γ’ phase precipitation strengthening, plastic deformation resistance by grain boundary and strain hardening for each grain orientations.
Two-rail shear method is popularly adopted in Japan as in-plane shear test for wood-based structural panels. We studied analytically and experimentally on the stress concentration and the distribution of strain when two-rail shear method was verificated. Parameters were materials (MDF and plywood), thickness (9, 15, 24mm) and shape of the specimen. Two kinds of the shape were conducted. One was conformed to ASTM standard (N type), and the other was the specimen which had fillets at the corner in order to suppress failure caused by the stress concentration (F type). In FEM analysis, stress concentrations at the corner were observed. We classified the stress concentration areas into the two types. One was named as T area, which was loaded the tear force from the rails, and the other was named as C area, which was loaded compressive stress at the diagonal cut area. Furthermore, in order to study the effect by the yield and the failure of T and C area, the FEM model containing slits in these areas was analyzed. As a result, the strain in the y axis, positive strain was increased by the yield of C area and negative one was increased by the yield of T area. It suggested that strain in the y axis could be utilized as a barometer of the local yield and failure. In the experimental result, N and F type of MDF were different in the failure area and in the apparent shear strength. On the other hand, no difference was observed about plywood. The load-strain curves in the y axis measured experimentally were observed in various types. These curves were classified based on their shape. As a result, curves convex into positive were observed about N type of MDF and the reverse was about F type of MDF. It suggested the validity of fillets. On the other hand, no trend was observed on the plywood. It suggested that the failure areas of plywood would be different by specimens and that the stress concentration rarely affected on the plywood under the ultimate condition.
It is very important to notice clay minerals, for resource development, stability evaluation of underground utilization and others. However, few quantitative data on the effects of clay-mineral type on the swelling characteristics and permeability of clays and clay minerals have been reported to date. This study was conducted to investigate the effects of clay-mineral type on the swelling characteristics and permeability of compacted clays using one-dimensional swelling-pressure and constant-pressure permeability tests. Comparative tests revealed that the difference of clay-mineral type in the clays influences the swelling-pressure and hydraulic conductivity. The swelling-pressure and hydraulic conductivity were closely associated with the specific surface area of clays. Furthermore, hydraulic conductivity was almost consistent that measured with the Kozeny-Carman equation. This result suggests that hydraulic conductivity can be estimated based on a specific surface area and void ratio of compacted clays.