Arboriculture & Urban Forestry 45(1): January 2019 7 Figure 8. Superposition of the amplitude graph of drilling resistance to the photographic image obtained from the disc, in the position of the needle passage of the resistograph. Species: a) Platanus spp., b) Caesalpinia pluviosa. segment of low amplitudes (Figure 8), according to the behavior indicated by Rinn (1996). CONCLUSIONS For all studied species, the amplitude ranged from 0% to 40%, with the 0% sections corresponding to the voids, as expected, which confirms that this tool is potentially adequate for the detection of the location and the approximate size of voids. In the heartwood, the values of the amplitudes were superior and statis- tically different from those obtained in the sapwood, both with moisture content around 10%~11%. There were also statistical differences between species. The variance analysis showed that the amplitude in deteri- orated regions (with or without voids) was always lower, except in the Coleoptera attacked wood, whose deterioration was not captured by the equipment. In some discs, amplitude-increase peaks observed on the drilling resistance graph were probably associated with compartmentalization zones promoted in the tree tissue to protect themselves from the advance- ment of the deteriorated zone. This behavior, also observed by other researchers, can affect the inspection interpretation by hiding deterioration, for example. The impact of feed rate, rotational speed, and den- sity correlation on the obtained results is critical and must be considered in further research. Curves of the same piece of wood drilled with a different feed rate and rotational speed can differ strongly, making it dif- ficult to clearly interpret the meaning of the result. In the same way, analysis of correlation between the device profiles and real local wood density along the drilling path is necessary in order to clarify analyst interpretation and reliable evaluation of the profiles in terms of wood condition by this device. Acknowledgments. The authors would like to thank the National Council for Scientific and Technological Development (CNPQ) for the scholarship and FAPESP (Proc. 2015/05692-3) for the research funding. They also thank the Environment Directory of UNICAMP for donating the logs used in the tests, and PD Instruments for the help and equipment used in the tests of resistance to drilling. LITERATURE CITED Botelho, J.A. 2006. Avaliação não destrutiva da capacidade resis- tente de estruturas de madeira de edifícios antigos. Thesis, Universidade do Porto, Portugal. Brashaw, B.K., R. Vatalaro, R.J. Ross, X. Wang, S. Schmieding, and W. Okstad. 2011. Historic log cabin structural condition assessment and rehabilitation—A case study. In: International nondestructive testing and evaluation of wood symposium, 17, Hungria. Anais. Hungria: University of West Hungary 2:505–512. Brashaw, B.K. 2013. Nondestructive Testing and Evaluation of Wood Research and Technology Transfer in North America. Proceedings of the 18th International Nondestructive Testing and Evaluation of Wood Symposium, Madison, September 2013. Costello, L.R., and S.L. Quarles. 1999. Detection of wood decay in blue gum and elm: An evaluation of the resistograph and the portable drill. Journal of Arboriculture 25(6):311–318. ©2019 International Society of Arboriculture
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