• Journal of the Korean Wood Science and Technology
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• 제34권2호
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• pp.46-57
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• 2006

To estimate nondestructively strength performances of laminated woods, 3-ply parallel- and cross-laminated wood specimens exposed under atmosphere conditions after bending creep test were prepared for this study. The effects of density of species, arrangement of laminae and lamination types on dynamic MOE obtained by flexural vibration were investigated, and regression analyses were conducted in order to estimate static bending strength and bending creep performances. Dynamic MOE of parallel-laminated woods showed 1.0~1.2 times higher values than static bending MOE, and those of cross-laminated woods showed 1.0~1.4 times higher values than static bending MOE. The degree of anisotropy of dynamic MOE perpendicular to the grain of face laminae versus that parallel to the grain of face laminae was markedly decreased by cross-laminating. There were strong correlations between dynamic MOE by flexural vibration and static bending MOE (correlation coefficient r = 0.919~0.972) or bending MOR (correlation coefficient r = 0.811~0.947) of 3-ply laminated woods, and the correlation coefficient were higher in parallel-laminated woods than in cross-laminated woods. It indicated that static bending strength performances were able to be estimated from dynamic MOE by flexural vibration. Also, close correlations between the reciprocal of dynamic MOE by flexural vibration and initial compliance at 0.008 h of 3-ply laminated woods were found (correlation coefficient r = 0.873~0.991). However, the correlation coefficient between the reciprocal of dynamic MOE and creep compliance at 168 h of 3-ply laminated woods was considerably lower than those between dynamic MOE and initial compliance, and it was hard to estimate creep compliance with a high accuracy from dynamic MOE due to the variation of creep deformation.

• Journal of the Korean Wood Science and Technology
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• 제33권5호통권133호
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• pp.13-20
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• 2005

This paper deals with flexural vibration techniques as a means of predicting bending strength properties for quarter-sawn and flat-sawn planes of red pine containing knots. Dynamic modulus of elasticity $(MOE_d)$ was calculated from resonance frequency obtained from the flexural vibration induced by a magnetic driver in quarter-sawn and flat-sawn planes of red pine containing knots. The dynamic MOE were well correlated to bending strength properties. Their correlation coefficients ranged from 0.866 to 0.800 for the regression between dynamic MOE and static bending MOE or MOR. The difference of the values between quarter-sawn and flat-sawn was very small. These values were higher than correlation between percentage of total knot diameter to total width of red pine specimen $(K_T(%))$ as well as $K_O(%)$ base upon ASTM D 3737 and static bending strength properties (correlation coefficient r = 0.448~0.704), and were similar to those between static bending MOE and bending MOR (r = 0.850). These results indicate that dynamic MOE obtained from resonance frequency induced by flexural vibration of magnetic driver is able to effectively use for predicting of static bending strength of red pine containing knots as well as static MOE.

• Journal of the Korean Wood Science and Technology
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• 제32권3호
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• pp.8-14
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• 2004

Nondestructive evaluation (NDE) technique method using a resonance frequency mode was carried out for woodceramics produced at different carbonizing temperatures (600℃, 800℃, 1000℃, 1200℃, 1500℃) at the phenol resin impregnation rate of 70%, for three kinds of species (Pinus densifora, Pinus koraiensis, Larix leptolepis), respectively. There was a poor relationship between density and static bending MOR. However, close correlations were found between dynamic MOE_d and static bending MOR, and between static MOEs and MOR. Especially, the correlation coefficient was highest between MOE_d and static bending MOR. Therefore, the MOE_d using the resonance frequency mode is useful as a NDE method for predicting the MOR of woodceramics produced at different carbonizing temperatures.

• Journal of the Korean Wood Science and Technology
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• 제26권3호
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• pp.9-15
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• 1998

The strength and stiffness of structures would be weakened by thermal degradation of wood members which are exposed to a variety of heat including a fire. For this reason, thermal degraded wood members can't pertinently support the load. However, it is easy to repair or rehabilitate wood structures. So, the degraded wood members which can't support the load can be replaced with new members. For the sake of this advantage, there is a need for nondestructive evaluation(NDE) technique, which is very effective to assess wood members in service. In this paper, it was considered whether the stress wave method is adequate to estimate static bending MOE of thermal degraded wood. As the result, the relationship between static bending MOE and MOEsw in elevated temperature was found out significant. Therefore, the application of stress wave method for estimating static bending MOE of thermal degraded zzwood would be possible. However, it is thought that further research for the effects of exposure temperature, time, and thermal degradation on the relationship between static bending MOEb and MOEsw would be needed.

• Journal of the Korean Wood Science and Technology
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• 제49권5호
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• pp.504-513
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• 2021

In this study, cross-laminated wood panels were manufactured with four softwoods and three hardwoods with the goal of efficiently predicting the static strength performance using dynamic modulus of elasticity (MOE) and simultaneously revealing the dynamic performance of cross-laminated wood panels. The effect of the density of the species on the dynamic MOE of the laminated wood panels was investigated. Moreover, the static bending strength performance was predicted nondestructively through the correlation regression between the dynamic MOE and static bending strength performance. For the dynamic MOE, the parallel- and cross-laminated wood panels composed of oriental oak showed the highest value, whereas the laminated wood panels composed of Japanese cedar showed the lowest value. In all types of parallel- and cross-laminated wood panels, the density dependence was confirmed, and the extent of the density dependence was found to be greater in the P_⊥ and C_⊥ types with perpendicular-direction laminae in the faces than in the P_∥ and C_∥ types with longitudinal-direction laminae in the faces. Our findings confirmed that a high correlation exists at a significance level of 1% between the dynamic modulus and static bending modulus or bending strength in all types of laminated wood panels, and that the static bending strength performance can be predicted through the dynamic MOE.

• 임산에너지
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• 제22권1호
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• pp.8-16
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• 2003

경남 진주시 가좌동에 위치한 남부임업시험장내의 생육이 양호한 1년산, 2년산, 3년산의 맹종죽을 이용하여 2001년 6월부터 다음해인 2002년 5월까지 실험을 실시하여 죽령과 벌채시기(달별)에 따른 물리적ㆍ기계적 성질에 대한 실험 결과는 다음과 같다. 생장부위에 따라서는 상부위에서 밀도, MOEs, MOE/sub d/의 값이 가장 높게 나타났으며, 또한 전체 밀도와 3년생의 MOEs와 MOE/sub d/는 벌채시기가 늦어질수록 점차적으로 그 값이 증가하였다. 그러나 함수율과 1, 2년산의 맹종죽재에서는 뚜렷한 차이점을 보이지 않아 죽령과 벌채시기에 따라서는 아무런 경향을 나타내지 않았다. MOEs와 MOE/sub d/의 상관관계에 있어서 r값은 생재가 0.88, 기건재가 0.92로 나타났으며, MOE/sub d/가 MOEs의 값보다 생재가 18.5%, 기건재가 7%정도 높게 나타났다. 또한 죽령과 벌채시기에 따른 MOEs와 MOE/sub d/가 거의 동일한 경향으로 매우 잘 대응하여 맹종죽재의 탄성적 성질을 평가하는데 있어서 공진주파수를 이용한 비파괴 측정법이 일반 소재와 마찬가지로 맹종죽재의 경우에도 이용 가능하였다.

• Journal of the Korean Wood Science and Technology
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• 제25권1호
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• pp.8-14
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• 1997

Stress wave velocity, wave impedance, and stress wave elasticity of small, clear bending specimens of five domestic softwoods (Pinus densiflora, Pinus koraiensis, Chamaecyparis obtusa, Cryptomeria japonica, and Larix leptolepis) and four tropical hardwoods(Kempas, Malas, Taun, and Terminalia) were correlated with static bending modulus of elasticity(MOE) and modulus of rupture(MOR). The degree of correlation between stress wave parameters and static bending properties was dependent on wood species tested. Stress wave elasticity and wave impedance were better predictors for static bending properties than stress wave velocity for each species individually and for softwood or hardwood species taken as a group, even though elasticity and impedance were nearly equally correlated with static bending properties apparently. Based upon the correlation coefficient between stress wave parameters and static properties, stress wave elasticity and wave impedance were found as stress wave parameters which can be used for the purpose of the reliable and successful prediction of bending properties. The degree of correlation between static MOE and MOR was also different according to wood species tested. Static MOE was nearly as well correlated with MOR as was stress wave elasticity. The results of this research are encouraging and can be considered as a basis for further work using full-size lumber. From the results of this study, it was concluded that stress wave measurements could provide useful predictions of static bending properties and was a feasible method for machine stress grading of domestic softwoods and tropical hardwoods tested in this study.

• Journal of the Korean Wood Science and Technology
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• 제46권1호
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• pp.93-99
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• 2018

국내산 낙엽송 소경각재의 휨 강도 성능을 예측하기 위하여 비파괴적인 지표의 검토가 필요하다. 본 연구에서는 낙엽송 소경각재(단면 $89{\times}120mm$)를 초음파법, 종진동법, 소하중법의 비파괴 방법으로 탄성계수를 측정하였다. 실측 탄성계수와 유의성이 높은 비파괴 측정 방법을 결정 후 휨 파괴계수 예측 지표로 적용하였다. 종진동법으로 측정된 탄성계수가 실측 탄성계수와 가장 높은 유의성을 나타냈다. 휨 파괴계수와 실측 탄성계수의 유의성도 매우 밀접하게 측정되었으므로 종진동법에 의한 비파괴 탄성계수로 소경각재의 휨 파괴계수를 예측하였다.

• Journal of the Korean Wood Science and Technology
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• 제24권3호
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• pp.12-17
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• 1996

This study was carried out to investigate some mechanical properties for wood rational utilization of heartwood and sapwood in radiata pine according to basic density, ring width and proportion of latewood which were grown in New Zealand. This result were summarized as follow: Heartwood showed 35.78(MPa) of the compression strength parallel to the grain while sapwood showed 42.08(MPa). The modulus of rupture in static bending was higher in sapwood showing 86.12(MPa) than in heartwood 72.99(MPa) Heartwood had 7.38(GPa) for the modulus of elasticity in static bending and sapwood 8.17(GPa). As the basic density and proportion of latewood increased: compression strength parallel to the grain, MOR and MOE in static bending had a tendency to increase. As ring width increased, the mechanical properties decreased.

• Journal of the Korean Wood Science and Technology
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• 제42권3호
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• pp.275-281
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• 2014

본 연구에서는 전통 목조 건축물의 주재료인 목재를 인공 촉진 열화 시킨 후 초음파 전달 속도 측정을 통하여 탄성계수를 측정하였다. 촉진 열화 시간은 0시간에서 500, 1000, 1500, 2000시간이며, 자외선 조사와 주기적인 인공 강우를 통해 열화를 진행시켰다. 초음파 전달 속도 측정을 통하여 동적 탄성 계수를 평가하고 이를 3점 휨 시험을 통하여 측정한 정적 탄성계수와 비교분석하였다. 초음파 전달 속도, 정적 탄성계수, 동적 탄성계수는 열화 시간이 증가함에 따라 동일한 경향을 나타내었는데, 열화 1000시간까지는 탄성계수가 감소하다가 1500시간 이후 다시 회복되는 경향을 보였다. 이러한 결과는 비파괴 검사법을 통하여 전통 목조 건축물의 구조 부재의 열화 평가는 물론 구조 안전성 평가의 기초 자료로 활용될 수 있음을 알려준다.