Ho-Yang Kang

Optical Measurement of Deformations in Drying Lumber

None of the destructive or nondestructive testing techniques for monitoring wood behavior during drying allow continuous quantitative measurements of the deformation and strain distribution in a section undergoing nonuniform moisture content changes in a kiln drying regime. In this study, a noncontact optical measurement technique based on digital image correlation (DIC) principles was used to visualize and measure the progressive deformation of wood subjected to simulated kiln drying conditions. A test apparatus was designed to simulate kiln drying conditions in such a way that a section of the specimen was accessible for optical measurements, and a hardwood and a softwood were dried at several temperatures. Full-field maps of principal strains were developed to illustrate the progress of the deformation gradients. The principal observations are that (1) the deformation of wood starts in the beginning of drying when the average moisture contents are well above the fiber saturation point, (2) the difference between the average deformations in the tangential and radial directions is much larger than expected, and (3) the samples swell a little in the radial direction early in drying.

Radial Variation of Sound Absorption Capability in the Cross Sectional Surface of Yellow Poplar Wood

Radial variation of sound absorption capability and air permeability of yellow poplar (Liriodendron tulipifera) wood in cross sectional surface and effect of steam explosion treatment were estimated by the two microphone transfer function method and the capillary flow porometry, respectively. The sound absorption coefficients of steam explosion treated wood was higher than those of control wood and these values increased with frequency. Abundant and big vessel may behave as sound absorbing pore observed on the cross sectional surface of yellow poplar wood. The sound absorption coefficients and air permeability of sapwood were higher than those of heartwood for Liriodendron tulipifera.

Forced Air-drying of Cross-cut Disks from Small-diameter Logs of Quercus variabilis

소경 참나무 횡절목을 열처리하여 브로치 등 악세사리용 소재로 개발하였다. 그러나 국산참나무는 난건조수종으로 특히 횡절 원판을 건조결함없이 건조하기 어렵다. 소경 굴참나무(Quercus variabilis)에서 얻은 원판(섬유방향 길이 7 mm)을 여름과 가을에 강제송풍천연건조하면서 여러 조건에 따른 건조수율을 조사하였다. 같은 조건에서 가을에 건조한 시편의 최종 평균함수율이 여름에 건조한 시편의 평균함수율보다 낮았다. 두 계절 모두 큰 직경의 시편은 풍속에 따른 차이를 보이지 않았으나 작은 직경의 시편은 풍속이 높았을 때 최종 평균함수율이 약간 낮았다. 두 계절 모두 직경이 큰 시편의 할렬 발생빈도가 직경이 작은 시편보다 높았는데 가을에는 2배 정도인데 반해 여름에는 4배가 넘었다. 여름에 낮은 풍속에서 건조한 큰 직경 시편의 할렬 발생빈도가 높은 이유는 여름의 높은 습도와 낮은 풍속으로 반복적인 수분 응축과 증발이 일어났기 때문으로 설명할 수 있다. 【Cross-cut disks from small diameter oak logs were thermally modified and developed to make accessories such as a brooch. However it is known that domestic oaks are refractory and it is hard to dry their cross-cut disks without any drying defects. The cross-cut disks of Quercus variabilis (7 mm long in the longitudinal direction) were forced to dry in air at two different air velocities in summer and fall season, and their drying yields were investigated. Under the same condition, the average final moisture contents (MCs) of the specimens dried in the fall were lower than those dried in the summer. The average final MCs of the small diameter specimens dried at higher air velocity were slightly lower than those at lower air velocity while those of the large diameter specimen were not influenced by the air velocity. The number of the large diameter specimens with cross checkings was higher than that of the small diameter specimen. This discrepancy between two different diameters was twice in the fall, while it was more than four times in the summer. The large diameter specimens dried at low air velocity in Summer were cross-checked most, which was attributed to repeated water condensation and evaporation due to high humidity and low air velocity.】

Preliminary tests for the application of an optical measurement system for the development of a kiln-drying schedule

ABSTRACT The drying defects of refractory species are known to begin occurring in the early stages of kiln drying. Therefore, monitoring the strain distribution in wood at these early stages of drying is expected to be helpful for the reduction of possible defect development. In this study, the strain distribution of red oak specimens was progressively monitored on the tangential surface of the wood using an optical measurement system based on the digital image correlation (DIC) principle. The specimens were kiln-dried with three different initial conditions. The strain distribution maps obtained at various moisture contents clearly illustrated the progress of the strain development in the wood. In addition, strain velocities and strain ratios were calculated from the data extracted from the strain distribution maps. These parameters could be used for developing or modifying a kiln-drying schedule of a refractory species.

Changes of Sound Absorption Capability of Wood by Organosolv Pretreatment

Sound absorption capability and anatomical features of the organosolv pretreated Japanese larch and yellow poplar wood were estimated by stereoscopic observation and two microphone transfer function method. Sound absorption capabilities of organosolv treated wood, in the entire estimated frequency range (50~6,400 Hz), were higher than those of control specimen. Especially, the treated wood`s absorption capabilities measured in the frequency range of 2~4 kHz were about two times higher than those of control specimen. By the organosolv pretreatment (at ), the weight loss of wood occurred in less than 1% of total weight of wood and the porosity of wood increased slightly. In addition, it was presupposed that microstructural changes of wood occurred during organosolv pretreatment and this structural changes cause the increasing of the sound absorption capability of wood.

Effect of Pretreatments on Reducing Surface Cracks of Heat-treated Western Hemlock Roundwoods

ABSTRACT A large diameter roundwood is an important element of Korean traditional buildings, Hanok, and is hard to be dried without surface cracks. Four different pretreatments, such as pre-cracking, oil heating, kerf-ing-oil heating and PEG impregnation, were investigated for reducing the surface cracks of large-diameter roundwood specimens during heat treatment. The roundwood specimens of pre-cracking, oil heating and kerfing-oil heating showed surface cracks during pretreatment, but that of PEG impregnation did not. It was confirmed that kerfing reduced the total crack width. Among the four pretreatments and control only the PEG impregnation roundwood specimen had no crack on both outer and inner surfaces after heat treatment. The PEG impregnation specimen shrank only 1.6% in the tangential direction while the pre-cracking did 8.0%. Keywords : Core-hollowed roundwood, pretreatment, heat treatment, oil heating, PEG impregnation, Kerfing, Tsuga heterophylla 1. INTRODUCTION Korean traditional buildings, Hanok, are most-ly constructed with large dimension lumbers and roundwoods. They are hardly kiln-dried without severe defects, thus usually air-dried from some months to an year. It was found that heat treat-ment above 160°C made the surface cracks of large diameter roundwoods closed (Kang, 2010).A heat-treatment apparatus was recently made in Korea and was used to develop color-change technology for domestic species, such as Korean red pine, Korean pine, and Larch (Kang, 2008). It was found that the device can be used for rapid drying large dimension timbers.Heat treatment reduces the growing stress of wood, increases the crystallinity of cellulose, decreases equilibrium moisture content, and im-proves the dimensional stability (Tejada et al., 1997). It has been reported that the crystallinity of wood heat-treated at high moisture content was increased as twice as that at oven-dry con