Study On Harvest Cutting Property And Cutter Parameters Of Standing Shrubs

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.