• Journal of the Korean Wood Science and Technology
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• v.42 no.2
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• pp.112-118
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• 2014

The depth effect on bending strength of Japanese larch structural lumber was investigated by using the published data of two different depth lumbers with the same length. Depth effect parameters were derived from Weibull's weakest link theory and compared to the results from other researches. Depth effect on bending strength was significant for No.1 and No.3 lumber, but not insignificant for No.2 lumber. Calculated value of the depth effect adjustment factors was 0.21, 0.11 and 0.22 by lumber grade, respectively. These results were similar to those results from previous researches and supported depth effect on bending strength of lumber. An apparent depth adjustment factor has been proposed to 0.2 in the literatures. Based on this study, depth adjustment factor was considered to 0.2 as a conservative optimum design value that should be incorporated in domestic building code (KBC) for structural lumber.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.3
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• pp.137-143
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• 2021

In this study, the fracture strength of Flexible Secondary Barrier (FSB) composites was standardized by conducting a distribution analysis of the fracture probability, considering that the fracture strength of FSB composites such as glass fiber reinforced composites is relatively large. As the mechanical performance of FSB composites varies with the fiber direction, 20 replicate uniaxial tensile tests were performed for different temperatures ranging from the ambient to cryogenic conditions, considering the actual operating environment of liquefied natural gas. For the probability statistical analysis, the Weibull distribution analysis derived from the weakest link theory was used, considering the large variance in the fracture strength and brittle fracture behavior. The results of the Weibull distribution analysis were used to calculate the standard fracture strength of the FSB composites for different fiber directions. The findings can help ensure the reliability of the FSB mechanical properties in different fiber directions in the design of the secondary barrier and structural analyses.

• Journal of Sensor Science and Technology
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• v.5 no.6
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• pp.15-24
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• 1996

In this study, as a part of the basic study for the application of optical fiber sensors to smart composite structures, the integrity of optical fiber sensors embedded within the composite structures was examined and then the laser signal transmitted through optical fiber sensors during the deformation of host structures was investigated. Firstly, it was found that bending test could be substituted for tensile test by comparing cumulative failure distribution based on weakest link theory and introducing the correction factor. Weibull parameters were obtained through the experiments and the correction factor was found to be applied to cumulative failure distribution derived from bending test. The integrity of embedded optical fiber sensors due to the thermal effect was evaluated by the comparison of the mean tensile strengths of cured and uncured optical fibers. Secondly, relationships between stress-strain curve obtained in tensile test of composite laminate and the intensity of laser signal transmitted through embedded optical fibers were examined and the possibility of the effective damage detection using optical fiber sensors was studied.

• Journal of the Korean Wood Science and Technology
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• v.46 no.5
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• pp.486-496
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• 2018

This study was conducted to confirm an effect of span length on bending properties of larch dimensional lumber in the four point bending test. The size of specimen in this study was 38 (width) ${\times}$ 89 (depth) ${\times}$ 3,600 (length) $mm^3$, and average air-dry density and moisture content of the specimens was $543.5kg/m^3$ and 10.5%, respectively. Visually graded No. 1 dimensional lumbers of 248 were divided by two groups to compare modulus of rupture (MOR) and modulus of elasticity (MOE). One group was tested in the four point bending test with span length of 1,650 mm, and other was tested with span length of 3,000 mm. While MOE was not different according to span length in 5% significance level, MOR was different in accordance with span lengths and was in inverse proportion to change of span length. Fifth percentiles of MOR in span length of 1,650 and 3,000 mm were 28.65 and 25.70 MPa, respectively. It was confirmed that the difference between MORs in each case increased as normalized rank increased. This is because of size effect in Weibull weakest link failure theory. Therefore, KS F 2150, in which there is only regulation about span to depth ratio of 15 or more, is needed to be revised to contain a method considering size effect for MOR. From the method, various results of bending test with different size of lumber could be used to determine design value of lumber.