Yasutoshi Sasaki

Near-Infrared Spectroscopic Study of the Physical and Mechanical Properties of Wood with Meso- and Micro-Scale Anatomical Observation:

Estimation of the density along with the tensile strength of wood within both the elastic and plastic deformation ranges, represented as modulus of elasticity (MOE) and ultimate tensile stress (UTS), respectively, were performed using near-infrared (NIR) spectroscopy. A partial least squares (PLS) analysis was applied to the measurements of density, MOE, and UTS, and resulted in a high accuracy of prediction, independent of wood species. The correlation coefficient between the NIR spectra and criterion variables, and the regression vector resulting from the PLS analysis, suggested that the characteristic absorption bands were strongly related to the predictability of each property. In the case of softwood, absorption bands due to intra-molecular hydrogen-bonded OH groups in the crystalline regions of cellulose, which are oriented preferentially in a direction parallel to the cellulose chain, might strongly affect the tensile strength of softwood. Hardwoods have much more complex and variable structures than softwoods; therefore, it was supposed that the key factor governing the tensile strength in hardwood would be the interaction between the three principal constituents (i.e., cellulose, hemicellulose, and lignin) of wood.

Microscopic processes of shearing fracture of old wood, examined using the acoustic emission technique

We examined the process of microscopic fracturing peculiar to old wood, based on the generation characteristics of acoustic emission (AE) events and fracture surface analysis. The shearing tests of old wood obtained from construction-derived lumber and new wood within 3 years after lumbering were performed in accordance with the Japanese Industrial Standards (JIS Z 2101-1994). The species of wood used in this study was Japanese red pine. The old wood had been used as a beam in a building for 270 years. The number of the occurrences of AEs at low load levels was larger in the old wood than in the new wood. As a result of analyzing the AE amplitude distributions, we found that the period in which AEs with small amplitudes were frequently generated was longer in the old wood than in the new wood. Also, the fracture surfaces after the final rupture under scanning electron microscope showed more uneven and complicated surfaces in the old wood. Based on the above findings, we presume that during the shearing test the old wood underwent a relatively long and stable progress of microcracking before the final fracture.

Determining Young’s modulus of timber on the basis of a strength database and stress wave propagation velocity I: an estimation method for Young’s modulus employing Monte Carlo simulation

In this article, we report on an estimation method for Young’s modulus that entails measuring only the stress wave propagation velocity of timber built into structures such as wooden buildings. Methods of estimating Young’s modulus that use the stress wave propagation velocity and characteristic frequency of timber in conjunction with timber density have long been used. In this article, we propose a method of easily and accurately estimating Young’s modulus from the stress wave propagation velocity without knowing the timber density. This method is based on a database of wood strength performance and density accumulated from a variety of research data and the method estimates Young’s modulus by a simulation method. We compared the Young’s moduli estimated by this method with those obtained by the bending test and by the measurement of the stress wave propagation velocity and density, and found similar results. This coincidence suggests that the method of estimating Young’s modulus presented in this article is valid. For example, the method is effective for convenient evaluation on site when determining whether a wooden building’s structural components should be reused or replaced when repairing or remodeling a building.

Effect of thermo-mechanical treatment on toughness of 9Cr-W ferritic-martensitic steels during aging

Abstract The precipitation behavior and toughness during aging of thermo-mechanically-treated (TMT) 9Cr-2W, 9Cr-4W and 9Cr-2No ferritic-martensitic steels were investigated. All three steels showed an increase on toughness after TMT in the as tempered condition. This was the result of a fine-grained microstructure introduced by TMT. However, in 9Cr-2Mo and 9Cr-4W steels, precipitation of M 2 3C 6 , M 6 C and the Laves phase (Fe 2 W or Fe 2 Mo) was accelerated due to TMT and the beneficial effect of fine-grained microstructure on toughness was lost by aging at 875 K for 360 ks. In the case of 9Cr-2W steel, the accelerated precipitation was slight and good structural stability and toughness were maintained after 360 ks aging. A decrease in toughness, however, was observed after 360 ks aging, when the Laves phase was finally found to precipitate.

Preparation of thermoplastic molding from steamed Japanese beech flour.

Abstract Thermoplastic molding has been prepared from beech wood flour steamed at 180°C or at higher temperatures without any additives. It exhibited a smooth and lustrous surface and had a high density of approximately 1.45 g cm-3. The internal structure of molding revealed that the flour particles were completely surrounded by black resin-like substance which was thermoplasticized by heat and pressure during the molding process. The chemical composition of the steamed flour and physical properties of molding were examined as a function of steaming temperature. Maximum bending strength and Youngs modulus of molding reached 63 MPa and 11 GPa, respectively, at 180°C of steaming, which were much higher than those of a hardboard. The water absorption of the molding was 8% or less and decreased with the steaming temperature.

Elastic properties of wood with rectangular cross section under combined static axial force and torque

It is rare for a component-member of a structure to be subjected to a simple stress state. Usually, it is subjected to a multi-axial stress state in many cases. Therefore, in order to more efficiently design a structure, it is necessary to fully understand the mechanical properties of constituent materials under such a state. In this report, the effect of combined axial force and torque loading on the elastic behavior of wood (Japanese beech and Japanese cypress) was examined. As the elastic behavior, the initial slopes of the stress-strain relationships obtained from combined loading tests are estimated. The specimen had a rectangular cross section with one of its major axes lying in the fiber (longitudinal) direction. The axial force and torque were applied in the fiber direction (along L) and about an axis lying in the L direction, respectively. Combined loading tests were performed using the proportional deformation loading method and the initial constant loading method. The results obtained were summarized as follows: (1) The effect of differences in loading methods on the relationships between shear stiffnesses and the states of combined stresses was confirmed, in particular, for Japanese cypress. (2) Differences in axial stiffness were observed between the two species under compression-shear combined stress state. While the axial stiffness of Japanese beech was not affected under the combined stress state, that of Japanese cypress tended to increase under compression-shear combined stress state. (3) The difference in shear or axial stiffness between the two planes was considered to be almost constant; however, when the axial or shear stress component of the combined stresses became dominant, the difference between the two planes tended to show a larger variation.

Theoretical estimation of the mechanical performance of traditional mortise–tenon joint involving a gap

The mortise–tenon joint, which connects columns and beams of a wooden building, often creates a gap in contact part of members. This gap is considered to affect mechanical performance of the mortise–tenon joint. This study derived a method of theoretical estimation with a gap as parameter for the mechanical performance of mortise–tenon joint. In addition, it experimentally validated the method of estimation and numerically analyzed the influence of a size of such gap on mechanical properties. As a result, the estimated relationship between moment resistance and deformation angle of column shows the agreement with the experimental results, demonstrating validity of the estimation method derived. Results of the numerical analysis quantify the influence of the size of the gap on mechanical properties of the joint. The numerically analysis clarified the large influence of the gap at joints on the mechanical properties.

Determining Young’s modulus of timber on the basis of a strength database and stress wave propagation velocity II: effect of the reference distribution database on the determination

A method of determining the Young’s modulus of timber using the stress wave propagation velocity without knowing the timber density was developed in our previous study. This method enables the estimation of Young’s modulus by Monte Carlo simulation using an existing database of the Young’s modulus versus density relationship as reference. Here, in Part II, we consider the effect of the reference distribution database on the accuracy of the estimated Young’s modulus by the developed method. Twelve different reference distribution databases were used in this study, containing Young’s modulus versus density data for more than 13 000 real-size timber specimens of ten different species. We obtained the following results: (1) the distribution of Young’s modulus estimated using an arbitrary stress wave propagation velocity depends on the reference distribution database employed, (2) the most important factor is not that the reference database has data on the same species as the timber in the test, but rather that the reference distribution database covers the foreseeable range of timber densities within the test, and (3) the estimation accuracy is higher than about 80% when the database covers many species and has wide ranges of densities and Young’s moduli. This estimation method was developed in order to measure the Young’s modulus of timber whose density cannot be measured. Considering that the quality of lumber has a large variation, such estimation accuracy will be useful for practical applications.

Fatigue of structural plywood under cyclic shear through thickness I: fatigue process and failure criterion based on strain energy

The fatigue behavior of plywood specimens under shear through thickness was examined on the basis of strain energy to obtain common empirical equations for the fatigue process and failure criterion under various loading conditions. Specimens were cut from commercial plywood panels of 9-mm thickness. Loading conditions were set as follows: a square waveform at a loading frequency of 0.5 Hz, a triangular waveform at 0.5 Hz, and a triangular waveform at 5.0 Hz. Peak stress applied was determined to be 0.5, 0.7, and 0.9 of static strength, that is, stress levels of 0.5, 0.7, and 0.9. The stress-strain relationships were measured throughout the fatigue test, and the strain energy was obtained at each loading cycle. Loading conditions apparently affected the relationship between stress level and fatigue life. On the other hand, the relationship between mean strain energy per cycle and fatigue life was found to be independent of loading conditions. Mean strain energy per cycle obtained as the fatigue limit was 5.85 kJ/m3 per cycle. Assuming that the accumulation of strain energy is a fatigue indicator, the fatigue process and failure criterion for the plywood specimens under the three loading conditions were commonly expressed by the relationship between cumulative strain energy and loading cycles.

Acoustoelastic birefringence effect in wood I: Effect of applied stresses on the velocities of ultrasonic shear waves propagating transversely to the stress direction

The velocity changes of ultrasonic shear waves propagating transversely to the applied stress direction in wood were investigated. The wave oscillation directions were parallel and normal to the uniaxially applied stress direction. The velocities of the shear waves for both oscillations decreased as the compressive load increased, and increased as the tensile load increased. The velocity of the normally oscillated shear wave showed smaller change against the stress applied than that of the parallel oscillated wave. The initial birefringence due to the orthotropy of wood was observed without any stress. Velocity changes in the two principally oscillated shear waves were proportional to the stress within the stress range tested. The acoustoelastic birefringence effect was obtained from the velocity difference between the two shear waves. The relative difference between the two velocities (called acoustic anisotropy) was given as a function of the applied stress. The acoustoelastic birefringence constants were obtained from the relationships between the acoustic anisotropy and the applied stress.