Han-Min Park

Static bending strength performances of cross-laminated woods made with five species

Thirty types of three-ply parallel- and cross-laminated woods were prepared from five species, and their static bending strength performance were investigated. The modulus of elasticity (MOE), proportional limit stress, and modulus of rupture (MOR) perpendicular to the grain were increased by cross-laminating, and the extent of the increase increased with decreasing density of the species. The measured values of MOE parallel and perpendi-cular to the grain of parallel-laminated woods and perpendicular to the grain of face laminae of cross-laminated woods were approximately equal to those calculated from true MOEs of individual laminae. However, the MOE parallel to the grain of face laminae of cross-laminated woods was much lower than the calculated MOE owing to the effect of the deflection caused by shear force on the MOE. The percentage of deflection caused by shear force versus total deflection (Ys) showed high values, from 16.1% (buna) to 40.5% (sugi), and it decreased linearly with increasing shear modulus in the cross section of the core. In addition, there was an extremely high positive correlation between the MOR and the measured MOE parallel to the grain of face laminae of cross-laminated woods. The MOR was also highly dependent on the shear modulus in cross section of the core.

Sound Absorption Property of Heat-Treated Wood at A Low Temperature and Vacuum Conditions

ABSTRACT Heat treatment was performed to improve sound absorption properties for four tree species; Tulip tree, Korean Paulownia, Red pine and Costata birch, at temperature of 175°C and 200°C under vacuum condition. Sound absorption properties of two kinds of boards, which were in radial and tangential sec-tions, were measured under a frequency range of 100 to 3200 Hz by the two microphone transfer function method. It was found that sound absorption properties were increased by heat treatment and the efficiency was higher at 200°C than that at 175°C. Even Costata birch had a little effect on low temperature of 175°C, 200°C heat treatment for sound absorption property, the efficiencies of sound absorption were 14, 19%, respectively. The efficiencies of sound absorption ranged 22 to 120% for heat-treated Tulip tree, Korean Paulownia. Keywords: sound absorption property, heat treatment, low temperature and vacuum 1. INTRODUCTION Wood and/or wood-based materials such a laminated wood, plywood, particleboard, fiber- board etc. have been used as furniture and construction materials for a long time because they have many good properties. Recently, sound absorbing materials with advanced noises reduction are requested for construction and interiors. The glass or rock wool and foamed aluminum with closed pores are used most frequently as sound absorbing materials. In most cases, these materials have a low strength and are not environmentally-friendly and are some- times prevented from using for a good cir- cumstances. The development of sound absorbing materials with comprehensive characteristics such as being lightweight, eco-friendly and with good sound absorption property is desirable.The acoustic property of wood and/or wood- based materials was investigated by Watanabe

Bending Creep Performances of Hybrid Laminated Woods Composed of Wood-Wood Based Boards

In this study, to study an effective use and improve strength performances of woods and wood-based materials, three-ply hybrid laminated woods which are composed of spruce in the face and three kinds of wood-based boards (MDF, PB, OSB) in the core were manufactured, and the effect of constitution elements used for the core laminae on bending creep performances was investigated. The shape of creep curves showed exponential function plots which the upper right side was increased, and differed among the kinds of wood-based boards used for the core laminae of hybrid laminated wood. The creep deformation perpendicular to the grain of faces of hybrid laminated woods was in order (P) > (M) > (O) with PB, MDF and OSB in the core, respectively. It was found that the creep deformation arranged with OSB in the core had 2 times smaller than those arranged with MDF and PB in the core. By hybrid laminating, the creep deformation of spruce perpendicular to the grain was markedly decreased. On the other hand, the creep deformation parallel to the grain of the faces ( type) of hybrid laminated woods was in order (P) > (O) > (M) with PB, OSB and MDF in the core. The ratios among three hybrid laminated woods were considerably decreased, especially the difference between (P) and (O) hybrid laminated woods arranged with PB and OSB in the core was very small. These values showed 0.108~0.464 times smaller than creep deformation of three wood-based boards and it was found that creep deformation of three wood-based boards was considerably decreased by hybrid laminating. Creep anisotropy of hybrid laminated woods was greater in creep deformation than in initial deformation, whereas it was found that the values was much smaller than that of spruce parallel laminated woods.

Static Bending Strength Performance of Domestic Wood-Concrete Hybrid Laminated Materials

In this study, to develop the lattice materials with a low environmental load for restoring the destroyed forest, 7 types of wood-concrete hybrid laminated materials were manufactured with domestic four softwoods, three hardwoods and concrete, and the effects of density of wood species on static bending strength performances were investigated. Bending MOEs of wood-concrete hybrid laminated materials increased with increasing density of wood species on the whole, and the values were higher than that of concrete by hybrid-laminating woods on the concrete. It was found that the measure values of bending MOEs were slightly lower than the calculated values calculated using equivalent cross-section method from MOE of each laminae of hybrid laminated materials and the difference between them was less than 10%. Bending proportional limit stresses of hybrid laminated materials showed 1.2-1.6 times higher than that of concrete by hybrid-laminating. Bending strength (MOR) of hybrid laminated materials increased with the density of wood species. By hybrid-laminating, the MOR of concrete was considerably increased. Therefore, it is considered that wood-concrete hybrid laminated materials can be applied as a materials with a low environmental load and durability for ecological restoration.

Bending Creep Performance of Domestic Wood-Concrete Hybrid Laminated Materials

In order to develop materials with a low environmental load for restoring the destroyed forest, seven types of wood-concrete hybrid laminated materials were manufactured with four softwoods, three hardwoods and concrete, and the effect of wood density on bending creep property was investigated. The bending creep curves showed a shape to considerably increase at the upper right side, and the curves were found to show a linear behavior beyond about 30 min - 1 hour, as behaviors of solid woods and wood-based materials. The initial compliances of wood-concrete hybrid-laminated materials decreased with an increase in the wood density, and those values showed 0.9 - 1.2 times of the concrete one. The creep compliances of hybrid laminated materials showed very low values, which were 0.4 - 0.8 times of the concrete ones. The relative creep were very low with a range from 8.2% to 17.0% range, which were 0.3 - 0.7 times of the concrete ones. These results indicate that these materials can be applied for restoring the destroyed forest to reduce creep deformation of the conventional concrete materials by hybrid-laminating concrete and woods.

Effects of Heating Temperature and Time on the Mechanical Properties of Heat-Treated Woods

This study was performed to investigate the effects of heat treatment the on mechanical properties of two species of wood under different heating conditions including at 180°C for 12 h and 24 h, and at 210°C for 3 h and 6 h. Two species of wood, Pinus densiflora and Larix kaempferi, were exposed to different heat treatments to assess the effects on the volume change, bending properties in static and dynamic mode and compressive strength. The results showed heat treatment caused significant changes in mechanical properties such as the static and dynamic moduli of elasticity (MOEd and MOEs), and the modulus of rupture (MOR). The volume of the wood after heat treatment decreased as the heating temperature and time were increased. The bending strength performance of the wood after heat treatment decreased as the heating temperature and time were increased. The effect of heat treatment at a high temperature on the bending MOR was greater in both species than that for a long time. However, the compressive strengths of all the heat-treated samples were higher than the control sample. Furthermore, highly significant correlations between MOEd and MOR, and MOEs and MOR were found for all heating conditions.

Effect of Annual Ring Angles on Static Bending Strength Performances of Cross-Laminated Woods Made with Spruce

In this study, cross-laminated woods were made with spruce wood and the effects of annual ring angles of perpendic- ular direction laminae on static bending strength performance were investigated. Static bending strength performances of parallel laminated woods with all layers composed of laminae perpendicular to the grain (P⊥ type) were in the order of 90° > 0° > 45°. The MOE and MOR for the 45° annual ring angle were 0.0989 GPa and 3.25 MPa, and it showed the lowest values. By placing longitudinal-direction laminae in the core of P⊥ type, the strength performances were markedly improved. In the case of cross-laminated woods with perpendicular-direction laminae in the faces (C⊥ type), the bending strength performances were in the order of 90° > 0° > 45°, but the differences among annual ring angles were less than those of the parallel-laminated woods. In the case of cross-laminated woods with perpendicular-direction

The Effect of Finger Joint Location on Bending Strength Properties

ABSTRACT The effect of finger joint location and distance from joint to joint one another on 3 point mid-concentration bending strength properties was investigated in this experiment. Resorcinol- phenol formaldehyde (RPF) and aqueous vinyl urethane (AVU) was used to domestic Pinus densiflora Sieb. et Zucc and imported Picea sitchensis Carr. that have been cut to different width of 0.15 mm between finger tip and root width and the distance from loading point to finger joint was 0, 30, 40, 50, 60 mm. The effect was not found on the location and distance of finger joint for bending modulus of elasticity, while the efficiency of bending strength property increased proportionally as the location of finger joint from the load point and the distance between finger joint increased. No influence was shown by finger joint location and distance beyond 3 times of specimen thickness, since similar values were shown between the solid wood and no destruction occurred materials.Keywords : Finger joint, 3 point bending strength, location and distance of finger joint