Pest birds have long been a significant source of crop loss for grape growers, especially during the critical weeks leading up to harvest when grape sugar levels are high. In Oregon’s Willamette Valley, vineyards have seen a marked increase in crop loss in the last few years despite widespread use of intrusive gas cannons/shotguns and expensive netting systems. In order to deter this pest bird population, we have created an Unmanned Aerial Vehicle (UAV) package capable of autonomous flight, which incorporates common pest bird scare tactics into this dynamic platform. The system has been designed to launch, complete its mission waypoints, and land completely under autonomous control. By using this autonomous guidance system, we are able to employ visual, auditory, and predator mimicry pest bird control techniques in such a way as to discourage habituation. While radio controlled UAVs have been used for bird control in airport settings for many years, these systems require a trained operator to constantly guide the aircraft. The autonomous UAV system was designed for operation by an existing vineyard employee with minimal training. To capture widely accepted pest bird control techniques and management culture of Willamette Valley vineyards and gain information for design, implementation, and industry acceptance of this UAV project, we surveyed the owners of 225 local vineyards. Survey results indicated that vineyard owners are open to implementing innovative pest bird control methods that do not affect the terroir of their vineyards and that could replace the use of netting, which they do not view favorably despite its being the most effective pest bird control method to date. Results also indicated that pest birds are most damaging to a vineyard’s perimeter and that many vineyards employ someone to patrol this perimeter with a shotgun loaded with cracker shells. The UAV system is able to traverse the airspace above this perimeter without interfering with neighboring homes or beneficial predators in the area. By using proven pest bird control methods in an autonomous UAV system, we designed a device that brings an innovative solution to vineyard owners.
Understanding fracture behavior at the interfaces of brittle composite materials requires appropriate measurement techniques for fracture toughness. Due to their simplicity and convenience, indentation techniques are attractive solutions. One such technique is the interface indentation fracture (IIF) test, which measures the relative toughness of interfaces between brittle materials by introducing a series of indents at various angles of incidence (0–90°) to the interface, from which crack growth will either be by penetration through the interface or by deflection (debonding) along it. Larger angles of incidence promote penetration and smaller angles promote deflection, so by noting the critical angle at which propagation changes from penetration to deflection, the IFF test can make inferences about relative fracture toughness of different interfaces tested under similar conditions. However, as previous work by Parmigiani and Thouless has shown, the penetration vs. deflection behavior of a crack incident to an interface is a function not only of interface fracture toughness but also of interface strength. Interface cohesive zone elements in a finite element model incorporating both fracture toughness and strength criteria were used to study the propagation behavior of cracks normally incident to brittle composite interfaces. In the follow up work presented here, the cohesive zone method (CZM) has been extended to study cracks that occur at varying angles of incidence to these interfaces. Results show that IIF testing does not always result in unique values for relative fracture toughness; when interface strength is varied, it is possible for identical IIF-test critical angles to correspond to differing interface toughness values and, conversely, for differing critical angles to correspond to identical fracture toughness values. To properly employ the IFF test method, this phenomenon must be taken into account.
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