جستجوی مقالات مرتبط با کلیدواژه « ارتعاش خمشی » در نشریات گروه « صنایع چوب و کاغذ »

In this investigation, the potential of flexural vibration method as nondestructive tool was studied in order to evaluate the acoustical and the mechanical properties of bagasse composites. For this purpose, more than 40 cubic samples (36×4×1.6 cm3) were taken from the given materials. The results showed that the acoustical behavior of particle board were better than that measured for medium density fiber board. In MDF samples, the resonance frequency, the sound velocity, the quality factor as well as the acoustic coefficients were significantly lower than those measured in PB samples. In contrast, the internal friction measured in MDF was greater than values of PB. But no significant difference was observed of ACE in both MDF and PB samples. The young's modulus of MDF and PB were obtained by conducting a flexural vibration method under the free- free condition based on Timoshenko's vibration theory. The results were also compared with the modulus of elasticity and rupture calculated by 3 point bending test. The modulus of elasticity values, measured by dynamic method were 15% and 6% higher than those achieved by static bending method for MDF and PB respectively. It was also illustrated that the modulus of elasticity and the sound velocity were significantly positively related to the density of MDF and PB while the other acoustical properties had negative relations with density. As good correlations were found between dynamic and static modulus of elasticity (0.71) and also static modulus of rupture and dynamic modulus of elasticity (0.44), it can be drawn that the flexural vibration is valuable tool in order to evaluate mechanical properties of MDF made by bagasse while the same results were not observed in PB composites.

The effect of lamination and adhesive coverage rate in layered products made from Poplar wood was studied The effect of lamination and adhesive coverage rate in layered products made from Poplar wood was studied by non-destructive free vibration test. 120 samples with nominal dimensions of 2. 5×2. 5×45 cm without any obvious deficiencies were selected and free flexural vibration in free-free bars were performed for testing them. Samples were longitudinal cut in three thinner tangential layers and jointed together again using Poly Vinyl Acetate glue. The specimens were divided into four groups according to adhesive coverage rates، which one group was fully glued and 3 groups were carrying some glue deficiencies in different rates. Manipulated samples were tried again in above mentioned test. Results indicated that shear moduli compare to modulus of elasticity is a more sensitive parameter to evaluate glue efficiency in laminated beams but concerns remained due to blind points in flexural vibration nondestructive method.

The objective of this study was to investigate the influence of hydrothermal treatment of walnut (Juglans regia) and caucasian elm (Zelkova Carpinifolia) wood species on their acoustic properties in radial and tangential directions. For this purpose، specimens were prepared with dimensions of 360 (L) ×20 (R) ×20 (T) mm. Heat treatments in water medium were performed at 150ºC for 5 hours. Acoustic properties of specimens (specific modulus of elasticity، damping، acoustical coefficient، acoustical conversion efficiency and wave velocity) measured by free flexural vibration on a free-free bar method. Properties of treated specimens compared with control specimens. Result showed that hydrothermal treatment improved all acoustic properties of specimens. Acoustic properties of radial and tangential surfaces of walnut wood did not show significant difference; while in caucasian elm significant differences obtained between radial and tangential surface properties. Generally، better acoustic properties achieved in tangential direction of heat-treated Caucasian elm species. So، it is recommended as a suitable specimen to be used in making the sound-boards of musical instruments such as Iranian Santour and Xylophones and also resonator boxes.

Detection, detect of damage in scarf joint and finger joint using the various in dynamic shear modulus values and correlation coefficient factor of the beech wood specimens were investigated. Forty two Samples were selected in accordance with international standard No. 3129. The Scarf and finger joints created with three different glue coverage rates in samples and then free-free flexural vibration test were performed. The results showed that defects changed the dynamic shear modulus values in both joints; however it is not possible to realize the amount of defects from these variations, whereas, the changes in correlation coefficient factor were useful to detect the amount of defects in both joints.