Search

In the present paper changes of validity in Euler-Bernoulli's elementary theory of flexural vibration for homogeneous materials were tested with respect to changing severity and position of a single defect in wood. As an orthotropic material, wood has different material properties or strengths in different orthogonal directions. A set of absolutely clear specimens of oriental beech was chosen and hand drilled in different diameters (severities) at different relative distances from an end oriented in the R direction. A clear specimen showed a steady decrease in evaluated moduli of elasticity related to increasing mode numbers. After creating the defects, this steady decrease line showed some breakages. The slope breakages of modally evaluated elastic moduli in LT and LR vibrations are suggested as potential finger-prints of single hole defects in the specimen by considering the shape and rate of breakages in the decreasing lines. The recognition scenarios of slope breakages for defect severity and position are summarized. [ABSTRACT FROM AUTHOR]

Considerable errors caused by shear deflection and rotary inertia in both-ends clamped flexural vibration make the modulus of elasticity hardly obtainable in flexurally excited beams with similar ending conditions. As both-ends clamped beams and columns are necessarily quality controlled in situ within the building structures, this study has attempted to identify some initial requirements for the dynamic responses of a sound both-ends clamped beam under flexural vibration. Accordingly, the dynamic responses of the both-ends clamped wooden beams in radial and tangential flexural vibration were compared to beams in a free-free condition while stepwise increasing axial compressions were applied to the beams. Both-ends clamped beams had the potential to be subjected to in situ longitudinal Young's modulus evaluations. The strong correlations among both-ends clamped and free-free beams in terms of evaluated moduli verified the possibility. [ABSTRACT FROM AUTHOR]

An inexpensive methodology is proposed to identify and locate a single defect within a wooden beam using free flexural vibration technique. A similar approach has been introduced in the literature based on free longitudinal vibration, which was selected to be a leading frontier for the present research. The flexural vibration technique was tested for five groups of the absolutely clear specimens while holding a manually drilled hole at 0.1, 0.2, 0.3, 0.4, and 0.5 of their total span. The beams were tested in free flexural vibration with both ends in a free condition before and after drilling, and relative shifts of modal frequencies due to the presence of the defects were measured and compared to their mathematically calculated values in a sinusoidal equation. Using the method of least squares, a coincidence factor was developed based on the differences of the measured and calculated shifts of the four initial resonance frequencies where the minimum district of the coincidence factor curves successfully indicated the defected area. Though the longitudinal vibration approach was promising enough to estimate the position of the defect, its combination with the flexural vibration might increase the degree of confidence in the identifications. [ABSTRACT FROM AUTHOR]

In this study, researchers attempted to investigate the effects of drilling and hole widening on the dynamic response of wood using nondestructive methods. Clear and sound rectangular (2 × 2 × 36 cm R × T × L) bars were prepared from Beech timber (Fagus orientalis) and drilled in four steps with 3, 5, 8 and 10-mm diameters at central points in length on the tangential (LT) surface in the radial (LR) direction. To evaluate the longitudinal modulus of elasticity, the free-free bars before and after drilling procedure were brought to free flexural vibration test. To study the effects of stepwise hole widening, the dynamic evaluations were compared with two flexural vibrations parallel to LR and LT surfaces. The holes decreased the longitudinal modulus of elasticity values when the bars were vibrated in LR, while the values in LT remained significantly constant throughout the stepwise drilling. The differences due to longitudinal modulus of elasticity values comparing LR and LT free flexural vibrations were proposed as defect indicators. [ABSTRACT FROM AUTHOR]