混合组坯对杨木单板层积材弹性常数及力学性能的影响
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摘要
单板层积材具有结构均匀、强度高等优点,材料、结构、制造工艺等差异对其性能影响显著。以13层22 mm厚全顺纹、2层及3层横纹其余顺纹混合组坯的杨木单板层积材为对象,通过电测法、三点弯曲及拉伸实验,对其主要弹性常数及力学性能参数进行测试,得出以下结论:1)随着横纹层数的增加,顺纹方向的弹性模量下降,横纹方向的弹性模量增加,层积方向的弹性模量先减小后增加,单板层积材的各向异性降低;2)随着横纹层数的增加,静曲强度减小,变异性逐渐增大,进行结构设计时需更多考虑材料的性能稳定性;3)组坯方式对LVL抗拉强度的影响不大,适当增加横纹层板可提高抗拉强度;4)组坯方式对泊松比的影响较大,随着横纹层数的增加,泊松比总体降低,采用纵横混合式组坯可能有利于抵抗由拉、压载荷所造成的材料变形。
Laminated veneer lumber has the advantages of uniform structure and high strength, and material, structure and manufacturing process have significant influences on its properties. The poplar veneer lumber was selected as the test object, and three kinds of assemble patterns were adopted as follows: 1) single boards were all assembled in the direction of the grain direction; 2) fourth and tenth layer were horizontal stripes, and the rest are in the direction of the grain direction; 3) third, seventh, and eleventh layers were assembled in the direction of horizontal stripes, and the rest layers were assembled along the direction of the grain. The veneer thickness was 2 mm and the total number of layer was 13 layers. After completion, the thickness of the poplar veneer was 22 mm. By electrometric method,three point bending and tensile test, the main elastic constants and mechanical properties of poplar veneer lumber were tested. The findings are as follows. 1) With the increase of transverse layer number, the modulus of elasticity along the grain direction decreased, the elastic modulus of transverse direction increased, and the elastic modulus of laminated direction decreased first and then increased, and the anisotropy of LVL decreased; 2) With the increase of the number of transverse lines, the strength of the static curvature decreased and the variability increased, and more consideration should be given to the performance stability of the material when the structure was designed; 3) The effect of the assemble pattern on the tensile strength of LVL was little, and the proper increase of the transverse laminate may improve the tensile strength; 4) the assemble pattern had a greater impact on Poisson's ratio. With the increase of the number of transverse layers, Poisson's ratio decreased. The use of longitudinal and transverse mixed slabs may be beneficial to resist material deformation caused by tensile and compressive loads.
Laminated veneer lumber has the advantages of uniform structure and high strength, and material, structure and manufacturing process have significant influences on its properties. The poplar veneer lumber was selected as the test object, and three kinds of assemble patterns were adopted as follows: 1) single boards were all assembled in the direction of the grain direction; 2) fourth and tenth layer were horizontal stripes, and the rest are in the direction of the grain direction; 3) third, seventh, and eleventh layers were assembled in the direction of horizontal stripes, and the rest layers were assembled along the direction of the grain. The veneer thickness was 2 mm and the total number of layer was 13 layers. After completion, the thickness of the poplar veneer was 22 mm. By electrometric method,three point bending and tensile test, the main elastic constants and mechanical properties of poplar veneer lumber were tested. The findings are as follows. 1) With the increase of transverse layer number, the modulus of elasticity along the grain direction decreased, the elastic modulus of transverse direction increased, and the elastic modulus of laminated direction decreased first and then increased, and the anisotropy of LVL decreased; 2) With the increase of the number of transverse lines, the strength of the static curvature decreased and the variability increased, and more consideration should be given to the performance stability of the material when the structure was designed; 3) The effect of the assemble pattern on the tensile strength of LVL was little, and the proper increase of the transverse laminate may improve the tensile strength; 4) the assemble pattern had a greater impact on Poisson's ratio. With the increase of the number of transverse layers, Poisson's ratio decreased. The use of longitudinal and transverse mixed slabs may be beneficial to resist material deformation caused by tensile and compressive loads.
引文
[1]董国庆.单板层积材(LVL)受弯构件的结构性能研究[D].南京:南京工业大学,2005.
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[5]卫佩行,王泉中,周定国.分离刚度法测试杨木单板层积材木梁剪切模量的试验研究[J].土木建筑与环境工程,2012(增刊2):177-180.
[6]BAO F,FU F,CHOONG E T,et al.Contribution factor of wood properties of three poplar clones to strength of laminated veneer lumber[J].Wood and Fiber Science,2007,33(3):345-352.
[7]马良.应变电测与传感技术[M].北京:中国计量出版社,1993.
[8]王丽宇,鹿振友,申世杰.白桦材12个弹性常数的研究[J].北京林业大学学报,2003,25(6):64-67.
[9]徐有明.木材学[M].北京:中国林业出版社,2006.
[10]OH S C.Determining shear modulus of 3-ply laminated veneer lumber by uniaxial tension test[J].Journal of the Korean Wood Science and Technology,2013,41(5):425-431.
[11]GON?ALVES R,TRINCA A J,CERRI D G P.Comparison of elastic constants of wood determined by ultrasonic wave propagation and static compression testing[J].Wood and fiber science,2011,43(1):64-75.
[12]孙焕纯,柴山,王跃方.离散变量结构优化设计的发展、现状及展望[J].力学与实践,1997,19(4):7-11.
[13]?Z?IF?I A,YAPICI F.Effects of machining method and grain orientation on the bonding strength of some wood species[J].Journal of materials processing technology,2008,202(1-3):353-358.
[14]陈国宁,孙正军,陈桂华,等.组坯方式对竹木复合层积材胶合性能的影响[J].中南林业科技大学学报,2013,33(12):166-169.
[15]王志强,付红梅,陈银慧.锯材/单板层积材混合正交胶合木力学性能研究[J].中南林业科技大学学报,2016,36(8):121-124.
[2]ROBBINS E H.Laminated veneer lumber(LVL):U.S.Patent4,844,763[P].1989-7-4.
[3]GILBERT B P,BAILLERES H,ZHANG H,et al.Strength modelling of Laminated Veneer Lumber(LVL)beams[J].Construction and Building Materials,2017,149(15):763-77.
[4]韩雪山,何渊井,陈志强.单板层积材在机电产品包装上的应用前景[J].中国包装工业,2012(11):40-41.
[5]卫佩行,王泉中,周定国.分离刚度法测试杨木单板层积材木梁剪切模量的试验研究[J].土木建筑与环境工程,2012(增刊2):177-180.
[6]BAO F,FU F,CHOONG E T,et al.Contribution factor of wood properties of three poplar clones to strength of laminated veneer lumber[J].Wood and Fiber Science,2007,33(3):345-352.
[7]马良.应变电测与传感技术[M].北京:中国计量出版社,1993.
[8]王丽宇,鹿振友,申世杰.白桦材12个弹性常数的研究[J].北京林业大学学报,2003,25(6):64-67.
[9]徐有明.木材学[M].北京:中国林业出版社,2006.
[10]OH S C.Determining shear modulus of 3-ply laminated veneer lumber by uniaxial tension test[J].Journal of the Korean Wood Science and Technology,2013,41(5):425-431.
[11]GON?ALVES R,TRINCA A J,CERRI D G P.Comparison of elastic constants of wood determined by ultrasonic wave propagation and static compression testing[J].Wood and fiber science,2011,43(1):64-75.
[12]孙焕纯,柴山,王跃方.离散变量结构优化设计的发展、现状及展望[J].力学与实践,1997,19(4):7-11.
[13]?Z?IF?I A,YAPICI F.Effects of machining method and grain orientation on the bonding strength of some wood species[J].Journal of materials processing technology,2008,202(1-3):353-358.
[14]陈国宁,孙正军,陈桂华,等.组坯方式对竹木复合层积材胶合性能的影响[J].中南林业科技大学学报,2013,33(12):166-169.
[15]王志强,付红梅,陈银慧.锯材/单板层积材混合正交胶合木力学性能研究[J].中南林业科技大学学报,2016,36(8):121-124.