Yoshihiko Hirashima

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.

Influence of finger-joint geometry and end pressure on tensile properties of three finger-jointed Tropical African Hardwoods

SYNOPSIS Three tropical African hardwoods, Obeche (Triplochiton scleroxylon), Makore (Tieghemella heckelii) and Moabi (Baillonella toxisperma), were finger-jointed using three different finger profile geometries, three different end pressures, and resorcinol formaldehyde adhesive, with a view to assessing the effect of these factors on the tensile properties of the joint. Finger profile geometry was found to significantly affect ultimate tensile strength, but not tension modulus of elasticity (MOE) of finger-joints from the three species. The finger profile geometry having 18 mm finger length exhibited significantly the strongest and the most efficient finger-joint compared with finger profile geometry having 10 mm and 20 mm finger lengths. End pressure significantly increased ultimate tensile strength of finger-joints only when it seemed to have resulted in an increase in the tightness of the fit of the fingers in the joint. Finger-joints of high strength and efficiency were produced when the profile having 18mm finger length was combined with the end pressure of 12 MPa for Makore and Moabi, and end pressure of 8 MPa for Obeche. Among the three species, finger-joints from the low density Obeche exhibited the highest joint efficiency with a high percentage wood failure, followed by the medium density Makore and the high density Moabi. Tropical African hardwoods of low- to medium-densities are recommended for the production of finger-joints of high joint efficiency and high wood failure, using resorcinol formaldehyde glue.

Monitoring Acoustic Emissions from Finger-Joints from Tropical African Hardwoods for Predicting Ultimate Tensile Strength

Summary The patterns of acoustic emissions generated during tension test of finger-joints from three tropical African hardwoods, Obeche (Triplochiton scleroxylon), Makore (Tieghemella heckelii) and Moabi (Baillonella toxisperma) were evaluated to assess their potential usefulness for non-destructively predicting ultimate tensile strength. The acoustic emission patterns generated were observed to differ depending on the type of finger profile and the wood species. Regression coefficients from cumulative acoustic emission count versus applied stress squared functions also varied with the profile and species type. When ultimate tensile strength was correlated with these regression coefficients, for stresses applied up to 50% of mean ultimate strength, the logarithmic regression model developed could predict finger-joint strength accurate to ±12%, ±13% and ±18% for Obeche, Makore and Moabi, respectively. The model was also sensitive to the type of finger profile used for all three tropical African hardwoods. The results indicate that this acoustic emission monitoring procedure could be useful for non-destructively predicting ultimate tensile strength of finger-joints from the three tropical African hardwoods.

Predicting ultimate tensile and bending strengths of three finger-jointed tropical African hardwoods using acoustic emissions.

SYNOPSIS The acoustic emissions behaviour of finger-joints from three tropical African hardwoods, Obeche (Triplochiton scleroxylon), Makore (Tieghemella heckelii) and Moabi (Baillonella toxisperma) were examined with a view to establishing their potential usefulness for non-destructively predicting ultimate tensile and bending strengths. Stress at first acoustic emission event-count as well as the cumulative event-count at 80 percent of mean failure stress and the cumulative event-count at 80 percent of mean proportional limit stress for all specimens were separately correlated to finger-joint strengths. The correlation suggested that all three acoustic emission properties could be used to non-destructively predict the ultimate tensile and bending strengths of finger-joints from the three hardwoods. Correlation coefficients obtained for the prediction models developed were, generally, good and statistically significant (a = 0.05). Stress at first event-count seemed best correlated to ultimate tensile strength of finger-joints from the three species, whilst cumulative event-count at 80 percent of mean failure stress was best correlated to modulus of rupture. A logarithmic regression function seemed to fit the regression of acoustic emission event-counts on ultimate tensile strength and modulus of rupture better than a linear function. The acoustic emission technique seems applicable as a non-destructive testing method for predicting the tensile and bending strengths of finger-joints from the three tropical African hardwoods.