بررسی برهم‌کنش خاک و تیغه پنجه‌غازی توسط شبیه‌سازی عددی و اعتبارسنجی نتایج با آزمون‌های انباره خاک

در این مطالعه به بررسی نیروی کششی تیغه پنجه‌غازی در دو بخش شبیه‌سازی به روش اجزای محدود با تحلیل اویلرین- لاگرانژی و آزمون‌های تجربی در محیط انباره خاک پرداخته شد. از دو تیغه با فاصله cm 35 و در سه عمق 6، 10 و 14 سانتی‌متری با سرعت 2.5 کیلومتر بر ساعت استفاده شد. نیروی کششی تیغه طی شبیه‌سازی در عمق‌های 6، 10 و 14 سانتی‌متر به‌ترتیب 0.6، 2.5 و 3 کیلونیوتن بوده و نسبت به نتایج انباره خاک دارای محدوده خطای 7.3، 5.6 و 4.16 درصد بود. بیشترین تنش ایجاد شده در خاک در سه عمق 6، 10 و 14 سانتی‌متر به‌ترتیب در حدود 20، 68 و 69 کیلوپاسکال بوده است. در عمق 6 سانتی‌متر با توجه به نرم بودن خاک، نیروی عمودی وارده بر تیغه متاثر از وزن خاک بوده است. همچنین بررسی گسترش تنش در خاک حاکی از آن بوده است که با افزایش عمق کار، مقدار به‌هم‌خوردگی سطحی خاک و همچنین انتشار تنش به سطح خاک کاهش می‌یابد. علاوه بر چگونگی تغییرات تنش، هم‌پوشانی دو تیغه مجاور نیز با افزایش عمق کار ازنظر به‌هم‌خوردگی خاک، کمتر می‌شود. با توجه به افزایش نیروی کششی تیغه در عمق‌های بالاتر، عمق کار بیشتر از 10 سانتی‌متر بر اساس نتایج مربوط به چگونگی توزیع تنش در خاک توصیه نمی‌شود. در همین رابطه، توان مصرفی هر تیغه در عمق کمتر از 10 سانتی‌متر در حدود 0.4 کیلو وات بوده است درحالی که در عمق‌های بالا در حدود 2 کیلو وات برای هر تیغه توان لازم است.

investigating the interaction between soil and cultivator blade by numerical simulation and validation of results by soil bin tests

introductionseedbed preparation, seeding, and transplanting are usually based on mechanical soil tillage. tillage by cutting, mixing, overturning, and loosening the soil can modify the physical, mechanical, and biological properties of soil. these days, because of soil protection, the use of tillage tools is less and less recommended, and some implements such as cultivators are preferred to primary tillage tools such as plows. experimental study of soil-tool interaction and field measurements of the mechanics of tillage tools are usually time-consuming and costly. on the other hand, the variety of variables and uncontrolled conditions add other dimensions to the complexity of this method. also, the experimental and analytical methods do not have a comprehensive view of stress distribution and soil deformation in the soil-tool interaction process.materials and methodsthe main purpose of this study is to validate the results of numerical simulations in two phases of experimental tests: in soil bin environment and in finite element computer simulations. experimental tests were performed in the soil bin environment of the department of mechanical engineering of biosystems, urmia university, which has a soil bin facility with dimensions of length and width of 24 and 2 m, respectively, and has clay loam soil. before experimental tests, soil preparation was performed by using some special tillage implements (harrow, leveler, and roller) which were attached to the soil bin (figure.1). for experimental tests, a mechanism set consisting of two cultivator blades with a width of 15cm, a length of 20cm, and at a spacing of 35cm from each other was prepared and constructed. the relevant mechanism is designed to have the ability to change the tillage depth. data were collected at three different soil depth levels of 6, 10, and 14cm in the soil bin with three replications. data recording was performed using a 10-channel data logger with load cell connectivity and data storage ability. also, in this study, the drucker-prager model as a finite element simulation method was used to calculate the stress during the soil-tool relationship. abaqus 6.10.1 software was used to simulate the cultivator tine. to solve the problem, the soil parameters were defined as presented in table 1, and then the interaction between the soil-tool model and the necessary constraints, including boundary conditions, were defined. in the next step, meshing was applied to the constructed model.results and discussionin the results section, first, the results related to the amount of traction force required for the tillage tine in the simulation were calculated and then compared with the soil bin experimental tests. the traction force of the finite element simulation results for three tillage depths of 6, 10, and 14 cm in three principal directions is shown in figure 4. a comparison of simulation and experimental results showed that there is a good agreement between them. in comparison, the simulation error range of the three depths of 6, 10, and 14 cm has shown 7.3, 5.6, and 4.16% at a speed of 2.5 kmh-1, respectively, as the velocity studied in this research. in the next section, the results of stress distribution contours in the soil and finally the overlap of the blade effect were discussed. figure 6 shows the status of stress contours at three depths. by increasing the depth of the tine at the three depth levels studied, the stress range is shifted from the soil surface to its depth. for this purpose, at the maximum depth studied in this study (14 cm), it shows that the stress propagation to the soil surface is less than at other depths. also, with decreasing depth, for a depth of 6 cm, the maximum stress was on the top soil surface, in other words, more deformation was seen on the soil surface.conclusioncomparing the simulation results for predicting traction force with the results of experimental tests has led to relatively acceptable results and the maximum traction force prediction error at different depths has been about 7.3%.the distribution of stress in the soil was observed due to the tine depth. the highest intensity of stress propagation was observed at the soil surface; and the highest soil surface deformation at a depth of 6 cm. with increasing depth, both parameters of stress and soil surface deformation have decreased. according to the results of the studied blades, it is better to use these types of tillage tools only at lower depths. also, in evaluating the overlap of the soil loosening zone in the side-by-side tines, it proves the superiority of the tine performance at lower depths.