Babii A. Durability calculation methods and improvement of agricultural sprayers broadcast booms design

Completely new experimental and theoretical approaches to the durability calculation methods of the broadcast booms of agricultural spraying machines taking into account operational and physical-chemical factors have been obtained in the thesis under discussion. Some mechanisms of metal corrosion failure of the sprayer boom section frame in the saturated insecticide Nurelle D solutions and liquid complex fertilizer UN-32 media have been determined. The most intensive corrosion of the steel Ст3пс has been found to occur in the demineralized water. During the first 24 hours the velocity in the saturated solutions of insecticide Nurelle D and also liquid complex fertilizer UN-32 is approximately 23 and 53% lower respectively. The similar tendencies have been observed under long-term exposition conditions as well: the highest speed of steel corrosion was observed in the demineralized water, lower speed was observed in insecticide Nurelle D, and the lowest – in the liquid complex fertilizer UN-32 medium whose composition includes an inhibitor (compounds of ammonia phosphate). The necessary studies have been carried out and the influence of these media on both the fatigue and corrosion-fatigue durability of steel Ст3пс of the boom section frame and on the characteristics of its crack resistance under cyclic loading conditions as well has been estimated. It has been found that corrosion-fatigue resistance of steel Ст3пс in the corrosion media of demineralized water and in the saturated solutions of insecticide Nurelle D and liquid complex fertilizer UN-32 is being decreased in comparison with the air: the conventional border of corrosion fatigue was 1,4 times lower in the demineralized water, and in the saturated solutions of insecticide Nurelle D and liquid complex fertilizer UN-32 was 1,8 and 6,4 times lower respectively. The calculation model to determine the service life of sprayer booms components under cyclic operational load conditions has been constructed. It was found that the service life was mainly determined by the period of fatigue crack initiation which was more than twice less than the specified one. The calculation method of residual service life of the sprayer boom under maneuver loading mode conditions has been developed on the basis of the well-known energy approach. The method under discussion has revealed that the above-mentioned mode in case of sprayers broadcast booms (of certain parameters) made of steel Ст3пс can reduce its residual service life in approximately three times. A nontraditional calculation model to determine the boom service life involving the combination of operational and physical-chemical factors has been proposed. Here, the boom service life is represented as a sum of periods of crack initiation and subcritical growth in the weakest boom component. Under specified possible operational conditions (cyclic loading and corrosion medium Nurelle D) the boom service life of 836 operation hours has been found (approximately 1,5 seasons). It is completely unsatisfying service life in comparison with the standard service life of the sprayers – 7 seasons, and has proved the need of the boom vibrations removal, its strengthening and service life increase. The calculation method of the sprayer boom residual service life at the metal structure loading under maneuver mode conditions and taking into account the mechanism of insecticide Nurelle D solution corrosion medium action has been developed. It was found that under such conditions of the sprayer operation the boom residual service life was 5 times lower. A new design of the boom downpipe which has increased its stabilization characteristics under oscillations caused by different agricultural background conditions has been developed. Some completely new dynamic models of operation have been constructed for the above-mentioned boom downpipe. The theoretical papers, calculation methods and experimental tests procedures have been used by the design bureaux of machine building plants.