The deformation behaviour of wood around moment-resisting joints was analysed using digital image correlation method (DIC) and finite element method (FEM). The joints were consisted of four drift-pins. The distribution of the strain perpendicular to grain and the shear strain parallel to the grain were examined around each drift-pin to evaluate the large deformed area and the location of initial failure. Results were as follows. Areas of large compression strain perpendicular to the grain and large shear strain were observed in the predicted loading area of each drift-pin. Large tensile strain perpendicular to the grain was observed at the area close to the loading (contacting) area of the drift-pins, and the tension area was partly overlapped with the area of large shear strain. The overlapped area coincided with the location of initial cracks propagated parallel to the grain. This coincidence suggested that the cracks occurred by mixed-mode fracture in this joints. The numerical results by finite element analysis were compared with the experimental results obtained with DIC and they gave good agreement with each other.
Mechanical properties of Sugi (Cryptomeria japonica D. Don) vary with its cultivars and provenance. The variety sometimes results in the difficulties for producing glulams stipulated in Japanese Agricultural Standard (JAS) for structural glued laminated timber. To examine the feasibility of Sugi glulams with arbitrary composition of laminations, eight kinds of full size glulams were produced in a laboratory and a glulam mill without considering the regulation of JAS. Bending tests were conducted and the results were compared with simulated data generated by a Monte-Carlo simulation model using correlated data between modulus of elasticity (MOE) and tensile strength (TS) of laminations. Modulus of rupture (MOR) of laboratory-made glulams was in a range predicted by the simulation model. However, predicted MOR of factory-made glulams did not coincide well with real testing data, because proper correlation data in the factory was not used for the simulation. The Monte-Carlo simulation model was found to be applicable to quality control for the strength of glulams. However, in order to predict the strength distribution more precisely, proper strength data of laminations at each factory should be accumulated and renewed periadically.
To investigate the relationship between moisture content and the air permeability in logs of Cryptomeria japonica, the log specimens were obtained from one standing tree and 7 trees that were felled 2-4 months beforehand, in several stages of natural drying. Each log section consisting of heartwood, white zone wood and sapwood was set in a vacuum chamber which was connected to a mercury manometer, and the changes in pressures were measured during the different stages of vacuuming. Several experiments were carried out on logs of different conditions, ranging from green to relatively dry. Furthermore, the conditions of exposing and sealing of the transverse section were changed, and the relationship between the moisture content and the ratio of volume of air space and air permeability of longitudinal and radial directions were investigated with respect to each of the points. The results obtained were as follows. 1) In heartwood, air permeation was scarcely detected regardless of the moisture contents, which ranged from 51% to 142%. 2) In white zone wood, the air permeability was remarkably high regardless of the moisture contents, which ranged from 43% to 75%. 3) In sapwood, the air permeability became remarkably higher with the decrease in moisture contents, which ranged from 70% to 191%. 4) In sapwood, an inverse relationship was detected between the ratio of volume of air space and the elapsed time from beginning of vacuuming (760mmHg (101KPa)) until the pressure of each of the points attained the value of 400mmHg (53KPa). 5) In sapwood, the air permeability of longitudinal direction became higher with the decrease in moisture content and the increase in the ratio of volume of air space. 6) The air permeability between white zone wood and sapwood in the radial direction became higher with the decrease in moisture content and the increase in the ratio of volume of air space in sapwood.
To improve mechanical properties and dimensional stabilities of low-density particleboards, a new mat forming and pressing technique was applied. An extruded mat which consists of splint-shape particles (2mm by 2mm by 50mm) was rotated by right angle and then pressed flat with the movement of all mat sides constrained. Particleboards with a density ranging 0.2-0.5g/cm3 and with isocyanate resin as binder were manufactured both in the above method (E-board) and a conventional method (C-board). E-boards showed the constructive characteristics such as more enhanced particle bond network and less particle compressive strain in the panel thickness direction than C-boards, in addition to the strong orientation to one axis on the panel plane. As a result, E-boards exhibited much smaller thickness swelling (TS) and higher residual internal bond strength after boiling than C-boards, and were given better bending properties, inter-lamina shear strength and dimensional stability (linear expansion; LE) along the axis particles oriented on the panel plane. Veneer overlaying improved bending properties and LE in the direction perpendicular to it, which provided E-boards with those basic properties equal or better than C-boards, keeping much less TS than C-boards. Furthermore, cross-lapped two-layer veneer overlaying was found to provide E-boards with better bending properties than C-boards.
A composite made from bark, named bark-block, was developed to promote utilization of the bark residue. Airdried bark of Japanese conifers (sugi and hinoki) was used as furnish. The bark-block with dimensions of 400mm by 400mm by 55mm was fabricated using urethane resin as a binder. Steam was injected during pressing through holes on the press platen. Target density of this composite was 0.4g/cm3. A small-scale production machine that can be installed in a local sawmill or a logging site was designed for this purpose. The effect of manufacturing parameters on the properties of the bark-block was investigated to obtain the optimum conditions. The experimental results showed that bending properties (MOR and MOE), compressive stiffness, and IB strength increased with increasing resin content. Mechanical properties were proved to be controlled by the amount of the resin applied. It was found that the preferable steam injecting time for resin curing was 3 minutes. Thickness swelling was from 5 to 10 percent after water immersion treatment, while the water absorption was more than 80 percent. The bark-block produced have started to be used as a paving material in a park or in an exposition.
Visual characteristics of wood which influence visual hardness of it were studied. Thirty-four photographs of H-shaped wooden backs of chairs were prepared as specimens. Questionnaires regarding visual hardness and “deluxe” image of specimens were distributed to 32 subjects using the repeated equal-division method. Color values (Y, x and y) of specimens were measured by the colorimeter. Local-area gloss G and spatial ratio of contrasts C were calculated using digital image analyses. G was the index of the local-area glossiness (highlight), and C was the index of the noticeability of wood grain figures. Calculation procedures for both indices were newly developed in this paper. The single correlation coefficient between a visual “hard” image and Y (lightness of specimen) was -0.91, and that between G was 0.83. Using visual “hardness” as a criterion variable and Y and G as predictor variables, a multiple regression analysis was performed. The multiple correlation coefficient was 0.931, the ratio of contribution was 86.7% (significant level 1%). Furthermore C was added to the regression model, above values were 0.942 and 88.8%, respectively (significant level 1%).
In order to cope with the severe solid particle erosion damage of 12%Cr steel for steam turbine nozzles, erosion tests were conducted at high temperature, by using high velocity iron oxide for solid particles. With respect to the behavior of erosion damage, the effects of impact angles and velocity of iron oxide, hardness and surface treatments of target materials were made clear. And a boronized 12%Cr steel was superior resistant to the erosion. This paper describes the characteristics of boronized layer of 12%Cr steel with excellent erosion resistance, the relationship between damage and some erosion factors and the application of boronized 12%Cr steel nozzles in actual steam turbines.
CrMoV steel has been widely used in H-LP turbine rotors. Due to their configuration, in many cases wet zones are produced in the downstream regions of such rotors. Accordingly, the possibility that stress corrosion cracking may be initiated in the rim attachments and other sections subjected to high stress during long-term use have become a concern. The specifications of CrMoV steel make it difficult to change the tempering conditions to decrease material strength in order to increase resistance to stress corrosion cracking. Accordingly, the authors studied the effect of cooling rate for quenching in particular, on susceptibility to stress corrosion cracking. The results were as follows: (1) With low cooling rates for quenching, furnace cooling, susceptibility to the initiation of stress corrosion cracking becomes high. (2) Crevices have no impact on the stress corrosion cracking of CrMoV steel in deaerated pure water. (3) There were corrosion pits at the origins of almost all of the stress corrosion cracks. (4) Since metallic inclusions became the origins of corrosion pits, improving the cleanliness of the steel through ladle furnace refining would increase the resistance to stress corrosion cracking. (5) Fracture mechanics can be applied to the initiation of stress corrosion cracking. In these tests, the threshold value of stress intensity factor exhibited at the K1SCCP was 6.1MPa·m0.5. It seems that the lowering of the cooling rate for quenching reduces this threshold value of stress intensity factor increase for the initiation of stress corrosion cracking. (6) Stress corrosion cracks of CrMoV steel in deaerated water have intergranular feature, and the grain boundary was a factor in crack propagation. When cooling rate for quenching is slow, bulky Fe3C is precipitated at the grain boundary, and this may be a factor that increases susceptibility to stress corrosion cracking.
The brittle fracture model taking into account of the interaction between pores and cracks is proposed in this paper. The model is applicable to the prediction of tensile strength of graphite materials. In the model, pores are assumed as initial cracks, and cracks are treated by the fracture mechanics method with statistical approach. From comparison between the experimental tensile strength data and the analytical results of the proposed model, it was found that the model predicts not only fairly good the mean tensile strength but also the tensile strength distribution of graphite materials, leading to the validity of the proposed model. Furthermore, it was found that the graphite with larger pore and high porosity is predicted to have a larger pore/grain interaction effect. The grain size dependence on strength is also predicted to have the same trend as the experimental results observed for ordinary ceramics.
In this paper, the theoretical solutions are shown for the cases of a two-dimensional isotropic elastic medium containing an isotropic elastic circular inclusion loaded in singular disturbances at a finite point inside and having different isotropic elastic circular inclusions, under the anti-plane loading. It is assumed that the boundary conditions among the matrix and the elastic inclusion are perfectly bonded. This analysis is based on the complex variable method using the Mebius Transformation. Using these techniques, several examples are shown by graphical representation.
This paper presents the antiplane solutions of isotropic elastic or viscoelastic medium (matrix) containing several different isotropic circular elastic or viscoelastic inclusions subject to uniform anti-plane shear stresses as well as anti-plane concentrated force or screw dislocation at a finite point. The analyses are based on the complex variable method using the Mebius transformation and the correspondence theorem of elasticity and viscoelasticity. Capital numerical examples are illustrated.
A convenient method for predicting mechanical properties of solder materials was proposed in this study.Indentation method was used to obtain mechanical properties including elastic, plastic and creep deformations.Elastic-plastic finite element method (FEM) correlated Young's modulus, E, and yield stress, σys, with unloading portion of load-displacement curve and Vickers hardness, HV, respectively. The creep properties of solders were evaluated by the Norton's law, ε=A·σn. Indentation creep and tensile creep deformations were correlated by elastic-plastic-creep FEM analysis, and the latter could be directly predicted by the former. The agreement of the prediction was confirmed for Sn-37Pb eutectic solder in the range between room temperature and 125°C. Using the proposed method, mechanical properties of lead-free solders such as Sn-3.5Ag and Sn-3Ag-0.5Cu-0-3Bi alloy systems were determined. The predicted results revealed that mechanical properties of Sn-3.5Ag and Sn-3Ag-0.5Cu alloys were sim-ilar, and that E, σys and activation energies for creep of Sn-3Ag-0.5Cu-0-3Bi lead-free solders tended to increase with increasing Bi content.
Ultrasonic attenuation in carbon fiber reinforced epoxy composites (CFRP) was studied experimentally. In this study, attenuation coefficients of longitudinal and transverse waves were measured by the spectral analysis of ultrasonic echoes obtained by aid of normal-incidence contact transducers. Measurements were carried out for epoxy resin and for unidirectional CFRP samples with different fiber volume fractions. For transverse waves, two polarization directions were examined which were parallel and perpendicular to the fiber direction. From these measurements, effects of the fiber volume fraction and the polarization direction on the ultrasonic attenuation behavior were investigated. Also, attenuation properties of CFRP laminates with different stacking sequences were measured and compared to those of unidirectional ones. Furthermore, the attenuation behavior was discussed in the light of a theoretical model for ultrasonic attenuation in unidirectional CFRP proposed by the authors.
Crack healing behavior and high temperature strength of Mullite/SiC composite ceramics have been investigated systematically, as a function of Y2O3 added (0-2.5wt%). The specimen was sintered by hot-pressing at 1650°C. Semi-elliptical surface crack of 100μm in diameter was made on the specimen. Cracked specimen was heat-treated at 1100°C for 3 hours, or at 1300°C for 1 hour in an air. Bending strength was measured by a 3-point bending test system. The bending strengths of smooth specimens were reduced to 40%-25% by the above cracking. For the case of mullite/SiC/Y2O3, the bending strength of heat-treated specimens with crack recovered completely up to that of smooth specimens. On the contrary, for the case of mullite/Y2O3 (Y2O3=0-2.5wt%), the bending strength was recovered incompletely. This strength recovery of both materials was caused by crack-healing. This crack-healing ability was increased considerably by adding SiC particle to mullite. By adding 0.5-2.0wt% Y2O3 to mullite/SiC composite ceramics, heat-resisting limit temperature of crack-healed sample was increased from about 1100°C to 1200°C.
High frequency viscoelasticity of an aqueous solution of associating polymer was directly measured. Viscoelasticity of the solution was determined at frequencies 10-1-102 rad s-1 with a conventional dynamic measurement method and at frequencies 10-2-104 rad s-1 with pulse strain method and surface loading method. The viscoelastic behavior of the solution was close to that of the Maxwell model in a range of polymer concentration 2-5wt%. Relaxation time τ and modulus G were determined by fitting data to the Maxwell model. The value of G increased with polymer concentration, while τ was independent of polymer concentration. These results were in good agreement with the prediction of Tanaka's theory.