The results of the mechanical properties of 37 poplar trees (including 13 species in Shandong) in 48 producing areas in China are shown in Table 2-18-3 and Table 2-18-4. The table shows statistics and analysis of poplar trees produced in China and Shandong.
1. Wood compressive strength
The compressive load is slowly applied along the direction of the wood (axial direction), and the maximum capacity that the wood can withstand is called the compressive strength of the wood. Wood compressive strength is one of the most important properties of wood mechanical properties. According to its strength, the allowable stress of wood can be obtained and used to design various wood compression members. It can be seen from Table 2-18-4 that the compressive strength values ​​of the 48 poplar woods are between 25.6 and 51.09 MPa, with an average of 38.13 MPa. Among them, Guizhou Tianzhu produces the largest of Populus simonii, Populus tomentosa, I-69 Yang, and Xinjiang Yangjizhi; Shandong I-214 Yang, Daguanyang and Daqingyang are the smallest.
It can be seen from Table 2-18-3 that the compressive strength value of 13 poplar woods in Shandong is between 25.6-38.5Mpa, with an average of 33.95Mpa. Among them, the south × Mao Xin Yang is the largest, and the I-214 Yang is the smallest.
2. Wood flexural strength (MOR) and flexural modulus of elasticity (MOE)
Wood bending strength, also known as static bending ultimate strength or bending strength, is the ability of wood to withstand lateral forces (loads). The flexural strength of wood is also the most important property of the mechanical properties of wood. It is mainly used for the evaluation of the strength of easily bendable members such as building beams, trusses, and floors.
The bending strength values ​​of 48 poplar woods ranged from 48.7 to 96.11 MPa with an average of 72.94 MPa. Among them, the poplar leaf produced by Tianzhu, Guizhou, the smallest one is the I-214 poplar produced in Shandong. The Populus tomentosa, I-69 poplar, and Xinjiang poplar MOR are also larger, while the Qingyang, Daguanyang, and Daqingyang, which are produced in Qinghai, are smaller.
It can be seen from Table 2-18-3 that the compressive strength value of 13 poplar woods in Shandong is between 48.7-73.0Mpa, with an average of 63.73Mpa. Among them, I-69 is the largest and I-214 is the smallest.
The flexural modulus of wood represents the elasticity or toughness of wood and is the normal stress required for a consistent positive strain of wood. That is, the ability of the beam to resist deformation and deformation within the proportional limit. When the beam is subjected to a load (load), its deformation is inversely proportional to the amount of elasticity.
It can be seen from Table 2-18-4 that the flexural modulus of the 48 poplar woods is between 6.15 and 11.89 GPa with an average of 9.29 Gpa. Among them, the poplars produced in Fengxian County of Shaanxi Province are the largest, and the smallest one is the poplar produced by the Heilongjiang Belt Ridge. Among them, Populus davidiana, Jiayang, and Populus tomentosa are the largest;
It can be seen from Table 2-18-3 that the flexural modulus of 13 poplar woods produced in Shandong is between 7.55 and 10.89 GPa, with an average of 8.93 GPa. Among them, Kappaz Yang is the largest, and I-214 is the youngest.
3. Wood shear strength
When the wood is equal in magnitude and opposite in direction, the shear stress is caused by a part of the object perpendicular to the direction of the force contact surface, which is called shear stress. The ability of wood to resist shearing is called shear strength. The more common wood used in use is the shear strength of the grain.
It can be seen from Table 2-18-4 that the shear strength of the 48 poplar wood surface is between 5.34-10.20 MPa and the average value is 9.29 MPa. Among them, Yangling produced by Yangling in Shaanxi was the largest, and the smallest was Populus euphratica produced in Heilongjiang Province. The shear strength of 48 species of poplar wood was between 6.20 and 1.28, with an average of 7.06Mpa. Among them, the large-hole white poplar produced by Yangling in Shaanxi is the largest, and the youngest is the poplar produced in Qinghai.
4, wood impact toughness
Often wood beams, sleepers, sports equipment, working stalks, wooden shuttles, paddles, parts of agricultural structures, and building components are subject to impact stress rather than static overweight loads. The impact stress is a transient load. Wood with high impact bending strength, that is, wood has good toughness, and vice versa is brittle wood. Wood impact toughness, also known as impact bending specific energy, impact energy, impact coefficient, is the energy absorbed by the wood unit area when the wood is broken by the impact load. Compared with other woods, poplar wood has the best impact toughness of wood under the same conditions of wood density, water content and other conditions. For example, Acer mono, which grows in Changbai Mountain, has a gas-dry density of 0.709 g/cm3 and an impact of 85.76 KJ/m2. It is grown in Fengxian County, Shaanxi Province, with a dry density of 0.661 g/cm3 and impact toughness. It is 24.92KJ/m2; while the dry density of Populus tomentosa grown in Haidian, Beijing is 0.525g/cm3, and the impact toughness is 78.55KJ/m2; it is grown in Qingtong, Yunnan [P.rotvndi folia Griff.var.duclouxiana (Dode) Gomb] air dry density of 0.471g / cm3, impact toughness of 72.08KJ / m2.
It can be seen from Table 2-18-4 that the impact toughness of 48 poplar woods is between 25.25-109.80 KJ/m2 with an average of 58.66 KJ/m2. Among them, the second turn of Populus euphratica produced by Yangling in Shaanxi is the largest, and the smallest one is the small black poplar produced in Beijing Shunyi.
It can be seen from Table 2-18-3 that the impact toughness of 13 poplar trees produced in Shandong is between 43-72 KJ/m2 with an average of 57 KJ/m2. Among them, Zhonglin 23 Yang is the largest, and the smallest is Zhonglin 46 Yang.
5, wood allowable stress
Wood allowable stress refers to the maximum stress that can be carried by long-term and safely under any use and load conditions. The allowable stress of wood is derived from the test value of the wood strength. The Institute of Wood Research of the Chinese Academy of Forestry collaborated with relevant research institutes and institutions of higher learning to unify the collection and test methods, extensively conducted the collection of test materials and the determination of the physical and mechanical properties of wood, and accumulated a large number of research results to provide wood structure design. The basic data. Based on these data, the allowable stress of each type of force applied to the main building materials in China is derived.
In general, poplar wood texture is straight or slightly oblique; the structure is fine to very fine and uniform; in the whole hardwood, it is soft material, light and soft; dry to medium to medium; low strength; impact toughness is medium to high .
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