Reseach On Stress-strain Relationship In Parallel-to-grain Direction Of Parallel Strand Bamboo

Parallel Strand Bamboo (PSB) is a new biocomposite made of raw bamboostrips with a series of industrial process. PSB, with better mechanical properties thantimber, is an ideal structural material. Study on the stress-strain relationship of PSBis the foundation of analyzing the basic members’ strength and deformation in a PSBstructure. PSB was idealized as transverse isotropic material in this dissertation, bymacromechanics experiment, the uniaxial tension and compression performance inparallel-to-grain direction of PSB was researched, as well as the uniaxialstress-strain relationship in parallel-to-grain direction. The main conclusions in thispaper are as follows:(1) Density of PSB is1.2g/cm~3, nearly1.7times than that of raw bamboo. Theaverage values of uniaxial tensile strength and MOE is, respectively,129MPa and13GPa. Meanwhile, the average values of uniaxial compressive strength and MOE is,respectively,58MPa and12GPa. Based on t-distribution, uniaxial tensilerepresentative value in parallel-to-grain direction of PSB, with a95%guarantee rate,is86.15MPa. Likewise, the representative value of MOE is10.36GPa.(2) The fracture shaps of PSB in uniaxial tensile experiment can be divided intotwo types: plane section and trap cut like letter Z. It indicated that the fracture shapis mainly affected by the distribution of bamboo filament bundle. The damage intensile experiment, which is brittle failure, manifests abruptness and non-omen, andthe relationship of stress-strain basically shows linear. Ultimate tensile strain of PSBwas analyzed, the maximum value and average value is0.0142and0.011respectively, which performs fabulous deformation ability. The design ultimatetensile strain and stress were obtained by analyses upon single line model utilized tofit the stress-strain relationship, therefore, the design ultimate tensile stress is about166.66MPa, corresponding strain is0.0089, which is about0.81times than the limittensile strain.(3) Main failure patterns of PSB in uniaxial compressive experiment revealedthree types according to the extension aspect of crack, that is, bending instabilityfailure, shear failure and adhesion failure. Study on the destruction under uniaxialcompression indicated that the failure patterns can be approximately explicated withfiber mesoscopic elastic buckling model proposed by Rose, which is associated withfiber volume content. The destruction in compressive experiment is plastic damage,with a large deformation. Moreover, stress-strain relationship is initially linear, but in a while, manifests obviously nonlinear. Experimental analysis results showed thatthe ultimate compressive strain is about0.0246; the maximum of compressive strainwithin proportional limit can reach0.0026, the homologous average value is0.0019,which is about0.077times than the ultimate compressive strain. What’s more, thecompressive stress within proportional limit is about20.71MPa. Stress-strainrelationship was fitted by utilizing piecewise function, and was in good agreementwith the experimental data after revised.(4) MOE in tensile experiment of raw bamboo and PSB are all greater than thatin compressive experiment. Besides, the deformation property appeared obviouslydecrease, and the difference between uniaxial tensile and compressive property wassignificantly reduced after the reform of raw bamboo.