• Journal of the Korean Wood Science and Technology
• /
• v.12 no.2
• /
• pp.3-9
• /
• 1984

This study was carried out to examine the practicality of DAP[$(NH_4)_2HPO_4$] as fire retardant for plywood by static bending test the redried plywoods which had been soaked in 20% $(NH_4)_2HPO_4$ solution. Being hot/cold soaked in the solution for 3/3, 6/3, 9/3 and 12/3 hours and redried by cyclic press-drying method at the platen temp. of 130, 145, 100 and $175^{\circ}C$, the treated plywoods were tested to offer the mechanical data, that is, $S_{pl}$(stress at proportional limit), MOE(modulus of elasticity), MOR(modulus of rupture) and $W_{pl}$(work per unit volume to proportional limit ) in flexure. The results obtained were summarized as follows. 1. $S_{pl}$ of fire retardant treated plywoods ("FRP" would be used hereinafter) decreased as the platen temperature increased, but it was superior to that of non-treated plywoods(Control) at $160^{\circ}C$ or higher. 2. MOE of FRP decreased roughly with the increase of temperature, hut this tendency was not constant. And the value of FRP was higher than that of Control even at $175^{\circ}C$. 3. MOR of FRP showed same temperature-dependent tendency as MOE, but it was influenced more sensitively at the higher temperature. 4. $W_{pl}$ of FRP also decreased gradually with the increase of platen temperature and the value in DAP 9/3 treatment was Jess than 70% of control plywoods. 5. In view of redrying time and mechanical properties, the most reasonable platen temperature for DAP treated FRP was $160^{\circ}C$ in this study.

• Journal of the Korean Wood Science and Technology
• /
• v.43 no.1
• /
• pp.36-42
• /
• 2015

This study examined true modulus of elasticity (MOE) and modulus of rigidity (G) for domestic woods with different slenderness ratios (L/D) using the static bending and stress wave tests. Bending properties of small clear wood specimen of three domestic wood species were determined at 12% moisture content. The results of this study indicated that both MOR and MOE of domestic woods were affected by the slenderness ratio. As the slenderness ratio increased, MOR and MOE increased. G and true MOE of domestic timber beams were obtained at different slenderness ratios by flexure test and stress wave test. The values reported here can be useful if these species woods are used for structural purposes. However, the reported values are only indicative and do not represent the true average of wood species due to the limited number of specimens tested.

• Journal of the Korean Wood Science and Technology
• /
• v.39 no.6
• /
• pp.538-547
• /
• 2011

In this study, eco-friendly hybrid composite boards were manufactured from green tea and wood fibers for application as interior materials with various functionalities of green tea and strong strength properties of wood fibers. In this relation, the effect of green tea content on dynamic MOEs (modulus of elasticity) of these green tea and wood fibers composite boards were investigated. The dynamic MOEs of hybrid composite boards were lower than those of control boards without green tea, and the values decreased with the increase of green tea content. Also, the dynamic MOEs appeared to be somewhat different by resin type used for board manufacture. The hybrid composite boards manufactured from $E_1$ grade urea resin, which has higher molar ratio of formaldehyde to urea than that of $E_0$ grade one, were 1.06~1.54 times higher than that manufactured from $E_0$ grade. And, the differences between hybrid composite boards manufactured from both adhesive increased with the increase of green tea content. On the other hand, high correlations were found between dynamic MOE and static bending strength performances, it was concluded that static bending strength performances could be estimated from the dynamic MOE, except for a few hybrid board types with large variations.

• Journal of the Korean Wood Science and Technology
• /
• v.39 no.5
• /
• pp.398-405
• /
• 2011

Nondestructive evaluation (NDE) technique method using a resonance frequency mode was carried out for woodceramics made by different phenol resin impregnation ratios (40, 50, 60, 70%) for Broussonetia Kazinoki Sieb. Dynamic modulus of elasticity increased with increasing resin impregnation ratios. There was a close relationship between dynamic modulus of elasticity and static bending modulus of elasticity and between dynamic modulus of elasticity and MOR and between static bending modulus of elasticity and MOR. Therefore, the dynamic modulus of elasticity using resonance frequency mode is useful as a nondestructive evaluation method for predicting the MOR of woodceramics made by different impregnation ratios.

• Journal of the Korean Wood Science and Technology
• /
• v.23 no.2
• /
• pp.32-36
• /
• 1995

A study was conducted to evaluate the dynamic mechanical properties (modulus of elasticity, resonant frequency and interanal friction) of compression wood in Pinus densiflora. Vibration method was used for estimation of dynamic modulus of elasticity and the values were compared to those of static bending modulus of elasticity. The results obtained are as follows: 1. The dynamic modulus of elasticity of compression wood decreased, whereas that of normal wood increased, with increasing specific gravity. 2. The resonant frequency of compression wood decreased, whereas that of normal wood increased, with increasing specific gravity. 3. The internal friction of compression wood increased with increasing specific gravity. 4. The correlation coefficients between dynamic and static moduli of elasticity in compression and normal woods were high.

• Journal of Korea Foresty Energy
• /
• v.25 no.2
• /
• pp.49-54
• /
• 2006

This study was carried out to provide basic data for using domestic structural softwood lumber efficiently and ensuring structural safety of timber structures. The ratios (k-factor) between static and dynamic MOE measured by ultrasonic device for $2{\times}6$ domestic softwood structural lumber are 1.0602 for Korean red pine, 1.0013 for Korean white pine and 1.2320 for Japanese larch. In machine grade using nondestructive method, 76% of Korean red pine was classified into higher than E9 grade, 85% of Korean white pine was sorted into higher than E7 grade and 68% of Japanese larch was classified into higher than E11 grade. Correlation between MOE and MOR by static bending with k-factor from nondestructive method provide a possibility to predict bending strength and allowable stress of domestic softwood structural lumber.

• Steel and Composite Structures
• /
• v.29 no.3
• /
• pp.301-308
• /
• 2018

Properties of AFS vary with the changes in the face-sheet materials. Hence, the performance of AFS can be optimized by selecting face-sheet materials. In this work, three types of face-sheet materials representing elastic-perfectly plastic, elastic-plastic strain hardening and purely elastic materials were employed to study their effects on the flexural behavior and failure mechanism of AFS systematically. Result showed face-sheet materials affected the failure mechanism and energy absorption ability of AFS significantly. When the foam cores were sandwiched by aluminum alloy 6061, the AFS failed by face-sheet yielding and crack without collapse of the foam core, there was no clear plastic platform in the Load-Displacement curve. When the foam cores were sandwiched by stainless steel 304 and carbon fiber fabric, there were no face-sheet crack and the sandwich structure failed by core shear and collapse, plastic platform appeared. Energy absorption abilities of steel and carbon fiber reinforced AFS were much higher than aluminum alloy reinforced one. Carbon fiber was suggested as the best choice for AFS for its light weight and high performance. The versus strength ratio of face sheet to core was suggested to be a significant value for AFS structure design which may determine the failure mechanism of a certain AFS structure.

• Journal of the Korean Wood Science and Technology
• /
• v.41 no.5
• /
• pp.466-473
• /
• 2013

Nondestructive evaluation (NDE) technique method using a resonance frequency mode was carried out for heat-treated wood under different conditions. The effect of heat treatment on the bending strength and NDE technique using the resonance frequency by impact hammer and force transducer mode for Korean paulownia, Pinus densiflora, Lidiodendron tulipifera and Betula costata were measured. The heat treatment temperature has been investigated at $175^{\circ}C$ and $200^{\circ}C$, respectively. There were a close relationship of dynamic modulus of elasticity and static bending modulus of elasticity to MOR. In all conditions, It was found that there were a high correlation at 1% level between dynamic modulus of elasticity and MOR, and static modulus of elasticity and MOR. However, the result indicated that correlation coefficient is higher in dynamic modulus of elasticity to MOR than that in static modulus of elasticity to MOR. Therefore, the dynamic modulus of elasticity using resonance frequency by impact hammer mode is more useful as a nondestructive evaluation method for predicting the MOR of heat-treated wood under different temperature and species conditions.

• Journal of the Korean Wood Science and Technology
• /
• v.48 no.5
• /
• pp.696-709
• /
• 2020

A board was manufactured for each resin and sawdust addition using the chaff made by carbonizing the chaff charcoal, an agricultural by-product that emerge during the rice pounding process, and sawdust. And effects of the additions of resin and sawdust on coefficients of dynamic and static modulus of elasticity, modulus of rupture, as well as the relationship between the dynamic modulus of elasticity, statis modulus of elasticity, and modulus of rupture were investigated. As phenol resin addition of chaff charcoal-sawdust compound board increases to 10~25%, the bending performance has increased. This suggests that resin addition largely effects the bending performance. Although the bending performance was gradually increased with the increase in sawdust addition, since the coefficients of determination (R²) between the sawdust addition with the coefficients of dynamic, static modulus of elasticity, and modulus of rupture were 0.4012, 0.0809, and 0.1971, respectively. Thus, it showed a relatively lower correlation, and the effect of sawdust on bending performance was small. Since a high correlation was confirmed between dynamic and static modulus of elasticity, and modulus of rupture of chaff charcoal-sawdust compound board, it was confirmed that prediction of static modulus of elasticity and modulus of rupture can be made in a nondestructive way from the dynamic modulus of elasticity.

• Journal of Korea Foresty Energy
• /
• v.25 no.2
• /
• pp.34-41
• /
• 2006

In this study, new engineered woods, which can be used as structural members, are developed using three different mechanical jointing methods with large elements produced from logs in a high yield. Flitches of relatively large cross-section are produced from small or medium diameter logs, and are joined with steel bolts, wood dowesl and steel lag bolts. Static bending tests are performed for these three types of built-up beams. Built-up beams joined with steel bolts show $514kgf/cm^2$ for MOR and $129,000kgf/cm^2$ for MOE, which are close to those of typical structural glulams. In case that wood dowels and steel lag bolts are used, elements are isolated as load increases and resists the applied load individually. Therefore, built-up beams joined with wood dowels or steel lag bolts show almost half of steel bolts for both MOE and MOR. From the results of this study, it was indicated that bending properties of engineered woods manufactured using mechanical jointing methods with large elements are influenced mainly by jointing performance between each elements.