Arboriculture & Urban Forestry 45(1): January 2019 Arboriculture & Urban Forestry 2019. 45(1):1–9 1 Profiles of a Non-Calibrated Resistance Drill Compared with Deteriorated Stem Cross Sections Mariana Nagle dos Reis, Raquel Gonçalves, Gustavo Henrique Lopes Garcia, and Leandro Manes Abstract. The drilling resistance test has been widely used in tree inspections and structures since its first demonstration in Germany in 1988. A high correlation to wood density allows a correspondingly clear interpretation and reliable evaluation of the profiles in terms of wood condi- tion. Without such a correlation, it is not clear what the profiles mean. In this study, researchers compared the profiles of a non-calibrated resis- tance drill with pictures of the surfaces of the drilled stem cross sections in order to find out how defects are revealed. In decayed areas, the profiles mostly dropped down and the results showed that advanced stages of decomposition and voids of significant size can be detected reli- ably with this device. There were statistical differences between drilling amplitude among the studied species and, in the heartwood, the values of amplitudes were superior and statistically different from those obtained in the sapwood. However, the depth of the drop, or the changes in the profiles of this device, do not allow users to differentiate between various stages of deterioration. Similarly, it is not clear if all rising profile peaks are caused by locally higher wood density, as compatibilizations zones, or by technical artefacts. Key Words. Decay in Trees; Hazard; Resistance Drilling; Stem Cross Section; Tree Inspection; Tree Risk Assessment. The drilling resistance measurement is a semi- destructive test in which a fast rotating drilling needle is inserted in the wood under inspection. The method has development considerably since the idea was first introduced in the 1970s (Rinn 2014); it has been widely used in tree inspections and structures since 1988 (Rinn et al. 1989). The needle must be very thin to minimize material damage; the needle, however, cannot be so thin that it could suffer from resonance or buckling problems (Tannert et al. 2013). Most machines use a needle with a 3-mm tip diameter where the cutting edges are located, and a 1.5-mm diameter shaft (Tannert et al. 2013). With the rotation, the needle cuts the wood and perforates the material as it advances (Botelho 2006). The tested drills require manual adjustment of the advance speed of the needle (cm/min), as well as its rotation speed (turns/min). For those drills, this adjustment must be done according to the hardness or the density of the wood (Nutto and Biechele 2015). Besides the veloci- ties, the sharpening of the needle tip is also very important to reduce shaft friction, which causes inter- pretation problems of this kind of drill results, espe- cially in dense woods (Nutto and Biechele 2015). While drilling, the needed energy is measured depending on the drilling depth of the needle, and registered in a percent-amplitude graph. The different resistance drills differ strongly in many ways: in handling and practical applicability, in precision and accuracy, and most important, in how their profiles have to be interpreted (Rinn 2012). When drilling at the same spot of a tree with different kinds of resistance drills, the profiles can differ so strongly that users can come to contradictory evalua- tions of wood condition (Rinn 2015). Consequently, there is need for a criterion for how to evaluate the accuracy and reliability of the profiles obtained by the various kinds of resistance drills in terms of wood condition. Considering that the equipment measures the resis- tance offered by the wood to drilling, it is also expected that the equipment’s results can be correlated with ©2019 International Society of Arboriculture
January 2019
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