Study On Relationships Between Wood Structures And Acoustic Vibration Properties

The acoustic and vibration propertics of wood, is the ability to transmit the stress wave or inspire the air medium to spread the vibration that wood shows, given an impact or mechanic vibration. The research focus on many subjects, such as acoustics, physics and material mehcanics. The acoustic and vibration propertics of wood are mostly applied in two fields, one is musical instrument, and the other field is Non-Destructive Testing Technology applied in industry and architecture materials, especially in the interior decoration, for example,wood used as an ornament material in a music hall. As a basic application research, the measurement of wood Young's moduli and loss is very important to wood utilization, wood improvement, and wood microstructures research, non-destructive testing technology. There were some researchs focus on this far from hundreds of years ago. The latest literature reported that wood acoustic and vibration properties can be controled and changed by changing its structures,which altered the dynamic mechanics properties. It is very important and useful of its application. And it is mostly the goal of this research. The study aimes at the relationships between structure and vibration and acoustic properties in 6 species, which are evidently different in structure but are widely used. The research also fucos on the acoustic and vibration properties of wood in different situation by several methods. There are many ways to measure and test wood Young's moduli and loss,which can be classified as two types by the different principles in testing: one is resonace vibration method, the other is wave velocity method. The former is a method that measure the elastic modul by testing the frequency of the specimen; while the later is a method that test the elastic modul by measuring the velocity of stress wave speading along the specimen. The 6 species are: softwood including Spruce and Masson Pine, ringporous wood including Fraxinus and Paulownia, and Poplar and Birch are porous wood. There are three dynamic experiments used in the experiment(transverse vibration, longitudinal vibration, and longitudinal wave velocity) to measure and test the vibration and acoustic characteristics, inlcuding Young's moduli Ed, specific Young's moduli E/ρ, the coefficient sound radiation resistant R, logathsm loss lnδ, loss tangent tanδ, sound resistanceω. The static bending moduli and the Young's moduli are compared and analysised , moreover, the effects of factors such as tempreture, moisture content, and the size of the specimen are also studied. The research mainly studies on the followings. Macroscopically structure characteristics were including the width of the annual ring, the latewood percentage(softwood), Anatomical characteristics were including the fiber length, cell thickness, cellwall in diameter , the ratio of vessel (hardwood)and microfiber angles, etc. Physical features were including wood density, fiberil crystalline index, which was measured by x-ray diffraction machine. The effects on vibration parameters caused by macro and micro wood structure characteristics were analyzed by statistic soft, and on the basis of above research, main copenet analysis method was used for searching the main effective factors. The acoustic and vibration method is more efficient comparing to the static bending experiment. Because of the property of the wood, which is not a pure elastic object. Therefore, there are more or less viscous stain influnce the results of the static measurement ,which cost more time. But it is very different in the Young's module, in this situation the viscous stain can be ignored. In general, the Young's moduls is more than the static bending moduls, but the difference is small, which is produced by the lag of elasticity, and the structure properties of wood. The three dynamic methods are compared to the static bending experiment, it shows that there is a high relativity between the three methods, in which the most precise and credible value results from the transverse vibration method...