The Research On Multi-scale Mechanical Properties Of Dendrocalamus Farinosus

Bamboo as a natural fiber-reinforced composite with multi-layer composite structure was widely used in the architectural engineering, which integrating high strength, strong toughness, and proper stiffness, containing natural profound mechanical properties. Bamboo industrialized utilization for years developed the only mode relying on rhizome bamboos. Therefore, it was relieved the shortage of rhizome and contented the material ever-increasing demand with environment protecting in architecture by exploiting amphipodial bamboo as high value-added products, like architectural materials. The mechanical properties were the most important and most direct index in determining the processing and utilization of amphipodial bamboo. It was helpful not only for understanding bamboo’s growth mechanism from the biomechanical view, but also guiding meaning for imitated-bamboo building structural materials and it’s scientific and reasonable utilization, building the integrity testing and research system from macro to micro.In this thesis, D. farinosus were chosen as research object. The fiber longitudinal tensile properties and cell wall indenting properties were systematically studied by the microtensile and nano-indentation technology. It was revealed the influence of bamboo ages, culm height, and radial positions, respectively, on the macro, micro mechanical properties and microfibril angle (MFA). In the meanwhile, the mathematical model on the D. farinosus between macro and micro were built, which provided the theoretical basis and scientific evidence for comprehensive understanding the essential complicated mechanical behavior, and the high value-added utilization of D. farinosus bamboo. The study’s main results were summarized as follows:1. Mechanical properties almost reached maximum in4-year-old, but tended with bamboo age take different. Longitudinal compressive strength increased from2to4year, then decreased. Tensile strength, MOR, MOE and shear strength showed decrease and then increase tendency, while impact toughness was contrary. Mechanical properties except for impact toughness increased with bamboo height increasing. There was significant difference between bamboo height and MOR, MOE, compressive strength, impact toughness, but no significant difference between bamboo age and mechanical strength. 2. The results indicated that the average values of D. farinosus in tensile strength, MOE and elongation at break of single bamboo fibers respectively were1.06GPa,26.93GPa and3.84%. Besides, tensile strength and MOE both tended to increase with bamboo growing older, while elongation showed an opposite tendency. Furthermore, MOE presented decrease from base to upper position and increase from outer to inner, opposite tendencies were observed in elongation. Analysis of variance (ANVOA) indicated that bamboo age had indifference effect on mechanical properties, culm height and radial position showed significant influence on MOE, non-significant on tensile strength.3. The results indicated that among four-sampled culm ages, the fiber cell wall had average values for the elastic modulus (MOE) and hardness (HL) of18.56GPa and410.72MPa, respectively. The ages of the culm had no significant effect on the observed MOE and HL among the2-,3-,4-, and5-year-old D. farinosus test specimens, with similar results observed at three different culm heights and radial positions. Furthermore, longitudinal MOE and HL values along the thickness of the cell wall were uneven, with average values for the intercellular lamella and the edge near the cavity only20.97%to29.78%and9.22%to31.71%, respectively, of the values found in the cell wall.4. Obtained the variation of MFA with bamboo ages, culm height, and radial positions, and analyzed its effect on macro and micro mechanical properties. The mean MFA of2-,3-,4-, and5-year old D. farinosus was8.493°. There was highly significant difference for MFA in radial position, but no difference in bamboo age and longitudinal position.MFA was responsible for35%and43%of the variation found in macro longitudinal strength and MOE respectively. As well as maximum CMfs angle of the edgy of cavity, second of the middle lamella, and minimum of the secondary wall, made the elastic modulus and hardness of the edgy of cavity, the middle lamella were lower by20.97%and9.22%,29.78%and31.71%respectively, compared with those measured in the secondary wall. This implied MFA has a certain extent effect on macro and micro mechanical properties, and bamboo elastic modulus and hardness decrease with MFA increases.