Testing Of Inner Hole-defect In Korean Pine Square Lumber Basing On Modal Analysis

Nowdays, more and more woods are required. However, the source of wood is limited, so it is time to emphasize the effect of wood nondestructive testing to improve the utilization rate of wood. Moreover, it should improve the precision of wood nondestructive testing from the aspect of protecting wooden ancient building, high value tree, and wooden bridge.In rencent years, there are decades of testing methods used in wood testing area, including ultrasonic wave, stress wave, nuclear magnetic resonance, X-ray, impulse resistance method, microwave etc. However, these methods are almost not used widely for vairous reasons, so it needs discover new and more appropriate mothod of wood testing.Modal analysis has already been widely used to test defect in various engineering fields, including testing of concrete beam, bridge, oil derrick, offshore platforms, aerospace, railway etc. The location and degree of defect can be detected effectively by Modal analysis method. Therefore, it is necessary to introduce modal analysis method into wood testing area.ANSYS, finite element software, was used to establish the finite element models of red pine specimen and finite element models were analyzed by modal method. Firstly, three type finite element models, model not containing any defect and models containing one hole-defect in different position or different size and models containing one hole-defect in different position or different size, were established. Secondly, three modal parameters including intrinsic frequency, modal shape, and curvature mode, of finite element model were obtained. Thirdly, the modal parameter data were analyzed by statistic method and it found that modal analysis was accessible and feasible to quantitatively estimate the defect of models in theory.Doing modal experiment by experiment modal analysis (EMA) to square lumber specimens in diffent situation is an important job in this paper. There were three type square lumber specimens used in experiment. They were standard square lumber specimen, square lumber specimens with hole-defect in different position, and square lumber specimens with 3mm, 10mm, 18mm, 26mm, 35mm diameter's hole-defect. By doing experiment, the appropriate experiment method for testing square lumber's defect was found. In addition, frequency response functions (FRF) and real and imaginry frequency functions of standard square lumber specimen and square lumber specimen with hole-defect were obtained. After that, real and imaginary frequency functions were analyzed by using singal modal method.On the basis of analysis, first 4 intrinsic frequency, first 3 modal shape, and first 3 curvature mode of different specimens were obtained.Compared modal parameters of standard square lumber specimens to that of square lumber specimens with hole-defect, some conclusions are shown at following text. a) It found that intrinsic frequency of square lumber specimen with hole-defect was lower than that of standard square lumber specimens and the reduced degree of frequency would be much more when hole-defect was bigger. But there was no necessary association between the variety of frequency and hole-defect's position, because hole-defect in different position could cause the same variety of frequency.b) Displacement modal shape and curvature modal shape of hole-defect node on square lumber specimens can jump abruptly, and the variation of curvature modal is more remarkable.c) There is a significant correlation between displacement modal shape variation rate and diameter of hole, and between curvature modal variation rate and diameter of hole is also remarkable. So it can evaluate quantitatively the diameter of hole in square lumber by using displacement modal shape variation rate or curevature modal variation rate.At last, those experiment data were analyzed by using SPSS softaware. Therefore, a discrimination model used to evaluate the hole-defect in square lumber was established. The discrimination model was used to evaluate square lumber specimens with unknown hole-defect, and was verified based on testing results. By analyzing the results of experiment, it found that it can make qualitative, directional and quantitative evaluation for hole-defect in square lumber to use the discrimination model.