【作者】 李宁；

【导师】 俞国胜；

【作者基本信息】 北京林业大学 ， 机械设计及理论， 2010， 博士

【摘要】 灌木是我国重要的森林资源,对我国西北部防风固沙起着重要的作用。随着大面积人工灌木林的成熟以及工业化生产的需要,为满足其平茬复壮的要求,研制出高效的收割设备。沙生灌木平茬技术的研究是十一五科技支撑项目之一,本课题是其中的一项任务,即对灌木活立木的切割性能和灌木收割机刀具进行研究,为设计高效率的切割器提供理论依据。灌木每3-4年需要收割（平茬）一次以保证其生长速度不会减慢。通过实地调查研究和统计分析适值收割的柠条等几种常见灌木的距地50 mm左右处的直径一般不超过15 mm,适宜收割期间（深秋和冬季）柠条含水率为55%左右,荆条含水率为55%左右,四倍体刺槐含水率为61%左右,扁担木含水率为50%左右。通过冲击和顺纹压缩实验测定了柠条、荆条、扁担木和四倍体刺槐的活立木冲击韧性和顺纹抗压强度及顺纹抗压弹性模量。柠条的冲击强度为6.07J/cm²,顺纹抗压强度为23.67MPa,顺纹抗压弹性模量为1787.98MPa;荆条的冲击强度为11.78J/cm²,顺纹抗压强度为48.06 MPa,顺纹抗压弹性模量为3544.36MPa;四倍体刺槐冲击强度为10.09 J/cm²,顺纹抗压强度为40.78 MPa,顺纹抗压弹性模量为2304.87 MPa;扁担木的冲击强度为8.47J/cm²,顺纹抗压强度为65.88MPa,顺纹抗压弹性模量为2523.88 MPa。四种灌木的冲击强度在国产木材范围之内（冲击强度数值为1.60-18.22 J/cm²）,顺纹抗压强度和抗压弹性模量与常见的木材相比偏小。建立了单根灌木活立木切割的力学模型,设计一套实验装置,实验测定不同楔角的刀具（30°,40°,45°,50°,60°,70°）剪切不同直径灌木的剪断力。结果表明,树种、灌木直径和刀具楔角对剪断力都有显著性影响,直径与楔角角度的交互作用对剪断力的影响较小（用50°刀剪切四倍体刺槐时例外）。按照树种剪断力F与直径d、刀具楔角β之间有二次线性关系,因此在设计切割器时需要调查灌木的种类和待切断处的直径范围。当用前角较大的刀具剪切直径较大的灌木时,断口处产生了严重的挤压,导致灌木萌发率降低。对北京林业大学研制的步进手扶式割灌机圆锯片进行模态分析,3种圆锯片采用不同的夹持直径（100mm,70mm,57mm）,采用Br（?）el＆Kjae系统进行了对3种圆锯片（装卡在机体上）进行实验研究发现前两阶频率值比ANSYS计算值大,其中一阶频率比较接近,大部分相比ANSYS计算值提高了8%左右,二阶频率提高较大,幅度达到了20%～55%,结果表明在安装在机体上圆锯片的稳定性有所提高。对圆锯片的临界转速进行分析,提出圆锯片的工作转速的合理区间,实际工作转速ω应大于临界切断速度ω_l而小于最大输出转速ω_max且不在临界转速区间[ω_p]内,从而为北京林业大学研制的步进手扶式割灌机圆锯片的合理选用和传动机构的优化设计提供了理论依据。更多还原

【Abstract】 Shrub is an important kind of forest resource with great effect on breaking wind and stabilizing sand in northwest China. Reach on high efficiency equipment for rejuvenation of shrubs is the key with the maturity of large-scale forest plantation and the demand of industrialized production. Sandy-shrub harvesting technology is one of the programs of Science Research for the 11th Five-year Plan. As a task of the program, this study researched into mechanical properties of shrubs and cutting tools, and the results provide theory basis for the design of high-efficiency cutters.In order to keep growth, shrubs need be reaped every 3 to 4 years. The investigation results show that the shrubs diameter apart from root 50 mm mostly shall not exceed 15mm, such as Caragana Korshinskii Kom, Vitex, Fourfold Acacia, and Grewia biloba var.parviflora. The moisture content of the above shrubs is about 55%, 55%, 61% and 50% separately in late autumn and winter when they are reaped.Impact toughness, compressive strength and compression elastic modulus parallel to grain of these shrubs were researched by experiments. According to the order, the data of Caragana Korshinskii Kom is about 6.07 J/cm², 23.67 MPa, and 1787.98 MPa separately, and the data of Vitex is about 11.78 J/cm², 48.06 MPa and 3544.36 MPa separately. Additionally, the data of Fourfold Acacia is about 10.09 J/cm², 40.78 MPa and 2304.87 MPa , whereas the data of Grewia biloba var.parviflora is about 8.47 J/cm², 65.88MPa and 2523.88MPa respectively. The impact toughness four shrubs is in the bound of the data of wood in China, but the compressive strength and compression elastic modulus parallel to grain are some small than those of ordinary wood.Shearing mechanical model of single standing shrub was upbuilt, and a suit of experiment equipment was designed. The shearing forces of shrubs with different diameters by different cutters with variant front angles （30°, 40°, 45°, 50°, 60°, 70°） were tested. The results show that the species, diameter, and angle of the cutter have remarkable influence on shearing force, but the effect of interaction of diameter and angle is not very prominent （however, Fourfold Acacia is irregular occasionally）. According to species, shearing force "F", diameter "d" and wedge angle of "β" is quadratic linear relationship. So the species and diameter of the shrub should be investigated before the design of reciprocating cutters. The shrub will be extruded when sheared by cutters with big wedge angles and the aftereffect is a lower germination rate.Modal analysis for a single circular saw with different clamp diameter （100mm, 70mm and 57mm） was carried out by ANSYS and Brüel & Kj（?）r system. The results show that the value of natural frequency by experiment is some higher than that by ANSYS. The values of fundamental natural frequency are mostly increased by 8%, and the values of second-order frequency have an increase range about 20%-55%. The comparison shows that the stability circular saws are improved when they are fixed on the Pedestrian Controlled Circular Saw Shrub-cutter designed by Beijing Forestry University. The proper range of working rotate speed of circular saws was ascertained after the analysis of criticalspeed. The relation working rotate speed "ω", critical cut-off speed "ω_l", the max output speedω_max and critical speed range [ω_p] isω_l <ω<ω_max , at the same time,ω（?） [ω_p]. So the researchprovided theory basis for appropriate use and optimum design of drive mechanism of the Circular Saw Shrub-cutter.更多还原