اثر ناهمگني مصنوعي دانسيته بر مدول‌برشي ديناميك چوب بلوط بلند مازو (Quercus castaneifolia)

Effect of artificial inhomogeneity of density on dynamic shear modulus of Oak wood (Quercus castaneifolia)

در اﯾﻦ ﺗﺤﻘﯿﻖ ﺑﻪ ﺑﺮرﺳﯽ ﺗﺎأﺛﯿﺮ اﯾﺠﺎد ﻧﺎﻫﻤﮕﻨﯽ ﻣﺼﻨﻮﻋﯽ داﻧﺴﯿﺘﻪ در ﻧﺎﺣﯿﻪ اﺑﺘﺪاﯾﯽ و ﻣﯿﺎﻧﯽ ﺗﯿﺮﻫﺎي ﺑﻠﻮط ﺑﻠﻨﺪ ﻣﺎزو )Quercus castaneifolia( ﺑﺎ ﺑﺮرﺳﯽ ﺗﻐﯿﯿﺮات ﺣﺎﺻﻞ در ﻣﺪولﺑﺮﺷﯽ دﯾﻨﺎﻣﯿﮏ ﺣﺎﺻﻞ از روش ارﺗﻌﺎش ﺧﻤﺸﯽ آزاد در ﺗﯿﺮ دو ﺳﺮ آزاد ﭘﺮداﺧﺘﻪ ﺷﺪه اﺳﺖ. ﺑﺪﯾﻦ ﻣﻨﻈﻮر ﺗﻌﺪاد 10 آزﻣﻮﻧﻪ از ﮔﻮﻧﻪ ﺑﻠﻮط ﺑﺎ اﺑﻌﺎد 20 ×40 ×720 ﻣﯿﻠﯽﻣﺘﺮ )ﻃﻮﻟﯽ، ﺷﻌﺎﻋﯽ و ﻣﻤﺎﺳﯽ( ﺟﻬﺖ ﺗﻌﯿﯿﻦ ﻣﺪولﺑﺮﺷﯽ در ﺗﯿﺮﻫﺎي اوﻟﯿﻪ ﻣﻮرد آزﻣﻮن ارﺗﻌﺎش ﺧﻤﺸﯽ آزاد در ﺗﯿﺮ دو ﺳﺮ آزاد ﻗﺮار ﮔﺮﻓﺘﻨﺪ. ﭘﺲ از آن آزﻣﻮﻧﻪﻫﺎ ﺑﻪ دو ﮔﺮوه ﺗﻘﺴﯿﻢ ﺷﺪه و از ﮔﺮوه اول ﺑﻠﻮكﻫﺎﯾﯽ ﺑﻪ اﺑﻌﺎد 20×40×40 ﻣﯿﻠﯽﻣﺘﺮ از ﻗﺴﻤﺖ اﺑﺘﺪاﯾﯽ و از ﮔﺮوه دوم ﺑﻠﻮكﻫﺎﯾﯽ ﺑﺎ اﺑﻌﺎد ذﮐﺮﺷﺪه از ﻗﺴﻤﺖ ﻣﯿﺎﻧﯽ اﺳﺘﺨﺮاج ﺷﺪه و ﺗﻮﺳﻂ ﭼﺴﺐ ﭘﻠﯽوﯾﻨﯿﻞاﺳﺘﺎت ﺑﻪ ﯾﮑﺪﯾﮕﺮ ﻣﺘﺼﻞ ﺷﺪه و ﭘﺲ از ﺑﺮﻗﺮاري اﺗﺼﺎل آزﻣﻮن ارﺗﻌﺎش ﺧﻤﺸﯽ آزاد ﻣﺠﺪدا ﺑﺮ روي آزﻣﻮﻧﻪﻫﺎ ﺻﻮرت ﭘﺬﯾﺮﻓﺖ. ﭘﺲ از آن ﺑﻠﻮكﻫﺎي ﺑﻠﻮط از ﻣﺤﻞ اﺗﺼﺎل ﺧﺎرج ﺷﺪه و در دو ﻣﺮﺣﻠﻪ ﺑﻠﻮكﻫﺎﯾﯽ از دو ﮔﻮﻧﻪ ﺻﻨﻮﺑﺮ )Populus nigra( و اﻧﺠﯿﻠﯽ )Parrotia persica( در آﻧﻬﺎ ﺟﺎﯾﮕﺰاري ﺷﺪه و ﺑﻪﻣﻨﻈﻮر ﺗﺎﺛﯿﺮ ﻧﺎﻫﻤﮕﻨﯽ اﯾﺠﺎد ﺷﺪه ﺗﻮﺳﻂ ﻫﺮ ﯾﮏ از ﺑﻠﻮكﻫﺎي ﺟﺎﯾﮕﺰﯾﻦ ﺷﺪه ﺑﺮ ﻣﻘﺎدﯾﺮ ﻣﺪولﺑﺮﺷﯽ، آزﻣﻮن ارﺗﻌﺎش ﺧﻤﺸﯽ ﺑﺮ روي آﻧﻬﺎ ﺻﻮرت ﭘﺬﯾﺮﻓﺖ. ﻧﺘﺎﯾﺞ ﺣﺎﮐﯽ از آن ﺑﻮد ﮐﻪ اﯾﺠﺎد ﻧﺎﻫﻤﮕﻨﯽ ﻣﺼﻨﻮﻋﯽ داﻧﺴﯿﺘﻪ در ﻧﺎﺣﯿﻪ اﺑﺘﺪاﯾﯽ ﺗﯿﺮ ﺗﻮﺳﻂ ﻫﺮ ﺳﻪ ﮔﻮﻧﻪ ﺑﻠﻮط، ﺻﻨﻮﺑﺮ و اﻧﺠﯿﻠﯽ ﺗﺎﺛﯿﺮ ﻣﻌﻨﯽداري ﺑﺮ ﻣﻘﺎدﯾﺮ ﻣﺪولﺑﺮﺷﯽ دﯾﻨﺎﻣﯿﮏ ﻧﺪارد، درﺣﺎﻟﯽﮐﻪ اﯾﺠﺎد ﻧﺎﻫﻤﮕﻨﯽ در ﻗﺴﻤﺖ ﻣﯿﺎﻧﯽ ﺗﯿﺮ ﺑﺎﻋﺚ اﻓﺖ ﻣﻌﻨﯽدار ﻣﻘﺎدﯾﺮ ﺣﺎﺻﻞ از اﯾﻦ ﻓﺎﮐﺘﻮر ﺷﺪه اﺳﺖ. ﺗﯿﺮﻫﺎي ﻧﺎﻫﻤﮕﻦ ﺷﺪه ﺗﻮﺳﻂ ﮔﻮﻧﻪ اﻧﺠﯿﻠﯽ ﺑﯿﺸﺘﺮﯾﻦ، و ﺗﯿﺮﻫﺎي ﻧﺎﻫﻤﮕﻦ ﺷﺪه ﺗﻮﺳﻂ ﮔﻮﻧﻪ ﺑﻠﻮط ﺑﺎ ﮐﻤﺘﺮﯾﻦ درﺻﺪ اﻓﺖ در ﻣﻘﺎدﯾﺮ ﻣﺪولﺑﺮﺷﯽ دﯾﻨﺎﻣﯿﮏ ﻣﻮاﺟﻪ ﺷﺪﻧﺪ.

In this study, the effect of artificial inhomogeneity of density in the initial and middle of Oak wood beams (Quercus castaneifolia) by the changes in the dynamic shear modulus values obtained from the free vibration in free-free beam method have been investigated. For this purpose, 10 specimens of Oak wood species with a dimension of 720×40×20 mm (longitudinal, radial, and tangential) were tested by the free flexural vibration method to determine the shear modulus in the solid wood beams. After that, the samples were divided into two groups and from the first group, the blocks with a dimension of 40×40×20 mm from the initial part, and from the second group, the blocks with the mentioned dimension were extracted from the middle part of the solid beams, and jointed to each other by polyvinyl acetate adhesive. After the jointing, the free bending vibration test was performed on both groups again. Afterward, the Oak blocks were removed from the junction and in two stages, blocks of two species of Poplar wood (Populus nigra) and Iron wood (Parrotia persica) were replaced and in order to the effect of artificial inhomogeneity created by each of the replaced blocks on the values of the shear modulus, the flexural vibration test was performed on them. The results showed that the development of artificial inhomogeneity of density in the initial area of the beam by all three species of Oak, Poplar, and Iron wood did not have a significant effect on the values of dynamic shear modulus, while creating inhomogeneity in the middle of the beam has caused a significant drop in the values of this factor. Heterogeneous beams by Iron wood species had the highest, and heterogeneous beams by Oak wood species had the lowest percentage decrease in dynamic shear modulus values.