| Coarse cereals(millet,buckwheat and oats)are important crops to adjust the planting structure and improve people's dietary structure in China,which are mostly planted in hilly,mountainous and plateau areas.The artificial harvesting or rice and wheat harvesting techniques are mostly adopted in the current harvest of coarse cereals due to its particularity of physical properties and the limitation of planting topography and climatic conditions.There are some problems such as low efficiency,high labor intensity and high loss,which seriously restrict the sustainable development of the coarse cereals industry.Therefore,it is important for coarse cereals to develop high efficiency,low loss and mechanized equipment to improve its industrialization level.The research on the crop properties related to mechanical harvesting is the basic theoretical content to develop the key technology and equipment of mechanized harvesting,and the research on the crop stem properties can provide support for the design and optimize of the key components used in the mechanical harvesting process,such as potting,supporting,cutting and comprehensive utilization of stem resources.In this research,the biological morphology,biomechanics and feed nutrition characteristic of coarse cereals stems were studied in order to provide reference for the development of mechanical harvesting technology and equipment for these three kinds of coarse cereals.The research was funded by the national key research and development program.The main conclusions are as follows:(1)The parameters of biological morphological characteristics of coarse cereals were determined,including spike length,spike weight,grain weight per spike,plant height,gravity height,internode length of stem,cross-sectional diameter and so on,in order to provide reference for the selection of design parameters and adjustment of working parameters of key components of coarse cereals combine harvester,such as cutting table,threshing and cleaning device.Meanwhile,the moisture content and straw-grain ratio of coarse cereals in harvest period were measured,and the straw-grain ratio was higher.As grain and feed crops,it is necessary to efficiently utilize of stem resources.(2)The conventional mechanical properties(tensile and bending)of the coarse cereals stem of were studied,and the effects of moisture content and the stem position on the mechanical properties of tensile and bending were explored.The results showed that moisture content and stem position have different effects on the mechanical indexes such as tensile strength,elastic modulus and bending modulus.A cylindrical rod-shaped material shearing test device and a quasi-static cutting test device for different cutting modes were designed according to the morphological parameters of the coarse cereals stem,and the experimental studies on the shearing and quasi-static cutting of coarse cereals stem were carried out.The shearing stress and specific cutting energy were affected by different cutting modes(oblique cutting and sliding cutting).The research results provide reference for the design and optimize of key components such as crop harvester cutter and divider,as well as basic data for the design of dynamic cutting simulation test and dynamic cutting test bench.(3)In order to find the suitable harvest time,temporal dynamics of shearing force,morphological index,and nutritional content of millet stem were investigated after grain fully matured in this study.Results showed that the shearing force,cellulose content,hemicellulose content,and lignin content increased in different stem parts with advancing maturity time.However,the linear density,moisture content and crude protein content decreased.There was negative relationship between shearing force and moisture content,and between unit diameter shearing force and linear density.In the meanwhile,the shearing force was positively related with cellulose content,hemicellulose content,and lignin content,but there was no relationship between unit diameter shearing force and crude protein content.The shearing force increased from upper part to proximal root part of plant in different sampling times,and the shearing force was positively correlated with the equivalent diameter and cross-sectional area.Further,measuring shearing force is an efficient method to evaluate morphological index and nutritional content,providing the potential for enhancement of voluntary feed intake of millet stem.It is presented that the shearing force of the part above the middle section was significantly less than that of the proximal root part of millet stem,so that above the middle part of millet stem should be selected as ruminant feed.Meanwhile,timely harvesting after grain fully matured can avoid the decrease of feed value.This study can provide a reference for improving the forage utilization of millet stem.(4)In order to analyze the deformation and failure mechanism of the coarse cereals stem under dynamic cutting conditions,the Hyper Mesh Desktop software and ANSYS/LS-DYNA solver were used to simulate the dynamic cutting of the coarse cereals stem.The failure modes of the stem were obtained intuitively under dynamic cutting,and the stress-strain distribution characteristics of the stem at different cutting stages and the stalk at different cutting speeds were obtained.The cutting force and energy of three kinds of cereals decreased with the increase of cutting speed.The cutting energy of millet epidermis was higher than that of inner layer(basic tissues and vascular bundles).This study provides support for revealing the failure mechanism of dynamic cutting stems and choosing the parameters of sensors,motors and other key components of dynamic cutting test bench.(5)The cutting test bench of crop stem was develop according to the cutting conditions of crops harvested in the field,including cutting device,stalk feeding device and testing system.The cutting device can adjust working parameters such as cutting table height,cutting inclination angle,cutting speed,blade inclination angle and cutting stroke.The ADAMS software was adopted to simulate and optimize the weight of the crank cutter mechanism to reduce the inertia force of the cutting device.The stalk feeding device can adjust the stem feeding speed and the testing system can collect the cutting force and the curve between cutting force and time.The cutting test bench has simple structure and low manufacturing cost,and it can be used for continuous dynamic cutting of the coarse cereals stem.(6)This research selected the mechanical and physical properties of the stem,the structure and motion parameters of the cutter as the experimental factors to do some some cutting tests based on the self-made crop stem cutting test bench.The single-factor experiments were conducted on the coarse cereals stem,and the results showed that the moisture content,stem position,cutter type,cutting inclination angle,blade oblique angle and average cutting speed had significant effects on the cutting stress and unit area cutting energy of stems,but the stem feeding speed had no significant effect on the cutting mechanical properties of stems.Selecting the minimum cutting stress and unit area cutting energy of millet stem as evaluation indexes,the response surface model of average cutting speed,cutting inclination angle and blade oblique angle was established.The results showed that the cutting stress of the stem can be reduced by 6.6%,and the unit area cutting energy can be reduced by 3.9% when the average cutting speed was 1.19 m/s,the blade angle was 36.4° and the cutting inclination was 7.2° compared with the standard type II moving blade.In the meanwhile,considering the validity of millet stem cutting,the average cutting speed,ratio between cutting and stem feeding speed and cutting inclination angle were optimized.When the cutting speed ratio was 1.60,the optimal cutting efficiency could reach 85.08%. |
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