An assessment of the drilling process employed by the hole-drilling method for residual stress measurements

by Mariana Tiemi Tamura

Institution: Universidade Federal de Santa Catarina
Year: 2016
Posted: 02/05/2017
Record ID: 2133939
Full text PDF: https://repositorio.ufsc.br/xmlui/handle/123456789/167751


Abstract: Predictive maintenance is important to prevent catastrophic accidents inoil and gas distribution networks, since failures in pipelines and other mechanical components may lead to serious economic and environmental consequences. A possible approach to perform predictive maintenance isto monitor periodically loads that act on these structures. This task can becarried out through the Hole-Drilling Method to measure residual stresses,a consolidated semi-destructive technique for both in-field and in-lab applications. Standardised by ASTM E837 - 13a, this method is based on ablind hole drilling that relieves local stresses; the stress relief that occurs after material removal induces a microstructure reorganization, settling the material in a new equilibrium state after producing strains on the hole surrounding surface. These strains are related to the stresses that caused them according to Hooke's law in linearly elastic isotropic materials. The measurement result provided by this technique is intrinsically sensitive to the drilling process and produced hole characteristics, since machining induced residual stresses can mislead the true stress value. Besides, the hole geometry may differ significantly from the model recommended by the standard, provoking further errors in stress calculation. This work aims to investigate a cutting tool and cutting parameters combination that presents the best performance for residual stress measurements through the Hole-Drilling Method from two perspectives: machining and Electronic Speckle Pattern Interferometry application to measure strains. Two square end mills (two and four flutes) with TiAlN coating were used to drill the following workpiece materials: aluminium alloy AA 6061, carbon steel AISI 1020 and stainless steel AISI 304L. Chip and burr formation are investigated in preliminary analysis concerning the optical technique application since the seelements can cause loss of correlation and produce unreliable data. Rotational speed and feed rates effects on machining induced residual stresses are analysed through analysis of variance. Chip analysis is performed to assess qualitatively plastic deformation suffered during the process. This information are complemented with microhardness measurements to verify microstructural changes caused by the drilling process. Four-flute end mill presented lower machining induced residual stress absolute values. Particularly, the cutting tool and cutting parameters combination yielded satisfactory results when drilling AA 6061 and AISI 1020. However, AISI304L presented highly compressive machining induced residual stresses for almost all conditions. The most influential cutting parameter on machining induced residual stress introduction was the feed rate in the majority of the tested conditions. ; A manutenção preditiva tem um papel importante na prevenção de acidentes catastróficos em redes de distribuição de petróleo e gás, uma vez que falhas em dutos e componentes mecânicos integrantes destas malhas podem trazer graves… Advisors/Committee Members: Schroeter, Rolf Bertrand (advisor), Gonçalves Júnior, Armando Albertazzi (advisor).