Study On Property Of Longitudinal Tension And Compression Of Fast-growing Poplar At The Condition Of Hydrothermal Treatment

The thesis is supported by the Jiangsu science and technology program"Poplar wood pretreated with high strength and high fixed size used for outdoor structure material". The paper adopts fast-growing poplar I-69 with two very different densities grown in the north of Jiangsu province commonly as the research object. The hydrothermal treatment method is adopted to pre-treat poplar, this thesis studies the influence of the different hydrothermal conditions and cooling time on the property of longitudinal tension and compression and finds out the best technology. And based on this, the study also works over the bend of poplar and recovery condition of compressed poplar. The paper also summarizes the relationship of all major mechanics properties at the condition of different hyrothermal pretreatments, to supply a theory basis for the use of poplar.Adopt the hot water to soften wood that can be realized easily on the industry, review the influence of changing technology conditions on the property of longitudinal tension and compression. The experiment design takes the water temperature, heat preserving time and cooling time as the influence factors, and discusses how these factors effect the the property of longitudinal tension and compression. Adopt the optimizing design to find out the best result, and use the regression to set up the relationship of compression properties and softening conditions. Finally, base on these, the thesis studies the bend and recovery of poplar after compressed. The results of whole thesis are as follows:1. Along with the water temperature increasing, the compression strength, tension strength, bend strength and elastic of modulus all present the descending trend, the maximum compression strain, maximum tension strain and maximum bend deflection all present increasing trend, at this condition, the plastic of poplar is enhanced, but the the yield strain decreases slightly. Along with the heat preserving time prolongation, the strength of poplar decreases first, when it reaches to a lowest value, then it is kept as a constant, the strain of poplar first increases first, when the heat preserving time reaches to one hour, the strain is the maximum, then the strain decreases, the yield strains are the same at all kinds of conditions. At the condition of water temperature 100℃and heat preserving time 1h, the plastic property of poplar is the best, the wood can be deformed easily.2. Along with the prolongation of cooling time, the strength increases a little, when cooled to a certain of time, the strength does not increase any more, which is a constant. The cooling time does not effect the plastic strain obviously, which only effects the strain under the maximum load.3. Along with the compression ratio and pressure keeping time increasing, the size of compressed wood is more stable, the recovery ratio is smaller. After unloaded, the samples recover soon, the recovery ratio reaches to 76%, with the time of one minute, the recovery ratio increases to 80% soon, then the recovery ratio nearly keeps a constant.4. All kinds of strengths of the poplar with density 0.525g/cm3 are all bigger than the density of 0.430g/cm3, but the strains are opposite.5. The bending property h/r of the poplar with the density 0.525g/cm3 can reaches to 0.2, the bending property h/r of the poplar with the density 0.525g/cm3 can reaches to 0.31, the bended samples after fixed and recovery, h/r is between 1/5 and 1/10, which can meet the requirement of production.6. When the poplar softened by hot water comes back to the air condition, all kinds of properties of which are the same as poplar without any treatment.