The Study On High-performance Bamboo-wood Composite Material For Wind Turbine Blades

On the basic study of physical and mechanical properties and surface wettability of bamboo strips and birch veneer, the paper analyzed heat-conduction of bamboo-wood composite LVL during hot-pressing process; the preparation process was confirmed by orthogonal test; the bong performance and aging resistant performance were researched; and the effect of hot-pressing temperature and pressure on the micro structure and mechanical properties was analyzed; finally using the classical lamination theory predicted the tensile elastic modulus of bamboo-wood composite LVL. The main results showed:1. The longitudinal tensile strength (elastic modulus) of testing bamboo strips and birch veneer were reached to 234.22MPa (28.93GPa) and 68.38MPa (16.92GPa); using different sizing methods the veneer's mechanical properties were enhanced to varying degrees and the enhancement of dipped veneer was better than the glued veneer's.The testing birch veneer's surface roughness (Ra) was greater than the testing bamboo strips and the surface wettability was changed with the surface roughness of material; measured by three different liquors the wetting angle of the material were less than 90°illustrating that the birch veneer and bamboo strips can be wet by phenolic resins.2. Resin content, hot-pressing temperature, sizing methods and board density affected heat-conduction of mat central layer during hot-pressing process significantly. The veneer's dipping time in the atmospheric conditions impacted heat-conduction of mat central layer during hot-pressing process indistinctively.3. Glued resin content affected longitudinal tensile strength significantly and the impacting of board density to all mechanical properties reached to a significant level. In the testing range other factors and levels affected the board properties indistinctively. Taking all factors into consideration the better production process of bamboo-wood composite LVL was that using dipped veneer and three bamboo curtains placed in the upper, the lower and the core of the mat, the hot-pressing pressure being 4MPa and the board density being in the range from 0.9g/cm3 to 1.0g/cm3. The board's longitudinal tensile strength, compressive strength and longitudinal tensile elastic modulus reached to 241.92MPa,167.03Mpa and 25.27GPa.4. Hot-pressing pressure, resin content, surface roughness and veneer's sizing methods influenced the bonding strength significantly; microscopic examination revealed that the substrates of bamboo-wood composite LVL and the adhesive had a good curing reaction because a stable cross-linked network was formed between them.5. Hot-pressing pressure, hot-pressing temperature and board density had a significant impact on microstructure of bamboo-wood composite LVL especially on the veneer's micro structure; with increased levels of each factor the cell of board's substrate showed different degrees of deformation and slip, and even crush injury.6. The mechanical properties of bamboo-wood composite LVL, bamboo laminated timber and bamboo scrimber were carried out varying degrees of reduction with accelerated aging process; the mechanical properties had a high retention rate (above 75%) after accelerated aging process; regression analysis of mechanical properties found that logarithmic regression trend line was well fitted for the bamboo-wood composite LVL and bamboo laminated timber fitted with exponential regression trend line was better.7. Based on classical laminated plate theory the elastic modulus prediction model of bamboo-wood composite LVL was built in this paper, and it was verified well by the comparison of measured tensile elastic modulus and predicted values; the mean, value of relative error between model predictions and experimental values was less than 15%.8. The longitudinal tensile strength and elastic modulus of bamboo-wood composite LVL can reach to 241.92MPa and 25.27GPa; its longitudinal compressive strength was up to 167.03MPa; its vertical and horizontal shear strength reached to 14.54MPa and 17.47MPa; the tensile specific strength (elastic modulus) was up to 249.48MPa (26GPa) and the compressive specific strength reached to 172.16MPa.