Quantifying Spray Deposition from a UAV Configured for Spot Spray Applications to Individual Plants

HighlightsSpot spraying is a method for applying pesticides to individual tree crowns.A new method is presented to quantify and analyze the two-dimensional spot spray deposit pattern produced by a UAV.A bivariate normal distribution provided a good fit to the observed deposition data for all treatments.Model parameters effectively described the shape of the ground deposits.Abstract. The purpose of this study was to develop a method for quantifying and analyzing the two-dimensional spray deposit pattern produced from a UAV spot spraying system for applying pesticides to individual plants with crown diameters in the range of 1 to 2 m. An XAG P20 UAV was flown over the center of a sampling grid, and spray deposits from three droplet size treatments, with nominal volume median diameters (VMDs) of 335, 430, and 1150 µm, were measured using horizontal steel plate collectors placed on blocks on the ground. A colorimetric tracer in the spray mix was used to quantify spray deposition. The positioning accuracy of the UAV was excellent, but the droplet sizes produced were much larger than expected. A bivariate normal distribution provided a good fit to the observed deposition data for all treatments. Model parameters effectively described the shape of the ground deposits. Displacement of the deposit distribution center was in a downwind direction. While there were no statistically significant effects of wind speed on the shape or degree of displacement of the center of mass of the observed ground deposit pattern, this was probably a result of the low wind speeds during the study, which were often close to or below the lower sensitivity threshold of the anemometer used. The actual spray coverage on a 2 m tall artificial tree target of 1 or 2 m diameter placed in the center of the plot was consistent across the range of droplet sizes and operating conditions tested. Nevertheless, it is hypothesized that targeting could be further improved if the UAV was slightly offset in an upwind direction and, conceptually, the degree of this displacement would increase as wind speed increased. A sampling grid spacing of 1.0 m would have produced results similar to the 0.5 m spacing actually used. Keywords: Aerial spraying, Pesticides, Spot spraying, Spray deposition, UAV, Unmanned aerial vehicle.

A Method of Fracture Toughness Measurement and Effect of Partial Annealing on Monolithic Thick Cold Sprayed Aluminum 6061 Deposits

Cold spray is a solid-state material deposition method that can create thick (>10mm) metal layers that adhere metallurgically to a base part or a substrate. Numerous potential applications exist, such as returning worn mechanical parts to their original dimension, extending their service life. For fatigue applications the fracture properties of cold spray deposited material must be known but little to no literature has been found on the fracture behavior of cold spray deposited material alone, which prompted the study presented here. Fracture toughness specimens were manufactured by depositing thick cold-sprayed layers of powdered aluminum 6061 onto an aluminum 6061 substrate using N2 as the carrier gas. The substrate was then machined away, and monolithic miniature compact tension fracture toughness specimens were machined from the cold spray deposit itself, following ASTM E-1820. The fracture behavior of the cold sprayed material was then experimentally determined using the elastic-plastic J-resistance method for compact test specimens described in ASTM E-1820. Two specimen conditions were successfully tested, “as-sprayed” and “partially annealed”. The results are that the Mode-I elastic-plastic stress intensity factor JI has been successfully measured for cold-spray deposited material alone, and that partially annealing a cold-spray deposit can dramatically increase its fracture toughness.