Research On Mechanics And Failure Properties Of Moso Bamboo

In this paper, Moso bamboo is the main object. The mechanical properties and failure behavior of bamboo were researched. The variety laws of all the static mechanical properties which including compressive strength, tension strength, modulus of rupture (MOR), module of elasticity (MOE) in different developmental stages were all determined. Moreover, the static mechanical models were constructed. What's more, dynamic mechanical thermal properties of bamboo in different sites and ages were discussed. Finally, digital speckle correlation method (DSCM) was applied to researching distortion properties. A preliminary analysis on failure behavior of dynamic tension and compressive were conducted. At last,tension modulus of elasticity parallel to grain were determined by DSCM.Main results are summarized as follows:(1) Mechanical properties increases with age and stem from bottom to top, which reach maximum at 4-year-old and then decline. Age, location and height have significant effects on them. Besides, there are preferable positive correlations between the mechanical properties. In addition, there is a good relativity among mechanical properties.δt:δc:MOR:MOE=2.79:1.00:2.40:0.15.(2) Analysis on the constructing models of mechanics:a,Air-dried density:The trends of air-dried density shows:ρ6m>ρ4m>ρ2m. The air-density is affected by age, site and height significantly. It shows a decrease trend from outer to inner in the radial wall of bamboo. The decrease breadth reduces gradually when it reaches the 1/3 of walls from outer to inner. It increases a little at the inner layers.b,MFA: There is no absolute difference on microfibril angle (MFA) of bamboo, in which the difference is less than 3°. It increases firstly and then decreases from outer to inner of the walls. In addition, it increases with the height. As to the age, there were no obvious diversification laws of MFA. Though there are no obvious differences being, age, location and height has significant effects on it. The correlation between MFA and mechanical properties is low. The MFA has little effect on the variations of mechanical properties. There are good linear relationships between air-dried density and mechanical properties.(4) Storage modulus increases with temperature. Loss modulus also increases with temperature before it reaches glass transition temperature, and it reaches the peak when at the glass transition temperature, and then decreases with the rises of temperature. As to bamboo samples from different locations, the storage modulus and loss modulus increase from inner to outer in the radial of walls. The storage modulus and loss modulus increase with age. The glass transition temperatures of all the samples have some differences in the radial of the walls. It increases from inner to outer of the walls, That is to say, the outer layer is the highest, followed by the middle layer, and the inner layer is the lowest. There is no obvious difference between the samples, which from the same location but different age.(4)The patterns of dynamics tension and compressive failure parallel to grain are so complex. In the tension failure process, bamboo fibers are pulled apart between fibers, so that fibers can not give full play to the tension strength. The fibers are damaged due to the sliding between each others, so failure surfaces shows needle-like avulsion which leads to uneven fracture sections. Besides, the initial fractures that perpendicular to the fibers are on the inner side of specimens, and then the gaps increases until lognitudinal avulsions are brought. As to the dynamic compressive failure, the damages are brought at the ends of samples, for stress concentrations appeares on the contact surfaces which are between samples and loads. Moreover, as a result of the sparseness of vascular bundles, the inner layers that low carrying capacities can be crushed easily, which leads to the gross distortions takeing place at the side of the loading head.(5) Through the determination of tension modulus of elasticity by DSCM and extensometer, the relative errors between the two methods are less than 5%, which is the full proof that DSCM can be successfully applied to testing tension modulus of elasticity parallel to grainof bamboo. Besides, the variance laws of them those obtained by DSCM are the same with the results that from conventional bamboo tests. For the above study: some new and important results can be obtained by DSCM, which can be applied into conventional mechanical testing in wood science. The results will have significance in deep understanding of mechanical properties and to be the guider in processing technology. The application has significance in many practical problems. The characteristics of DSCM and the special requirements of test methods in wood-based materials determine that DSCM has abroad applications prospects.