Multiaxial Fatigue of Aluminum Drill Pipes—Experiments and Numerical Analyses

Abstract

Abstract This article presents an experimental test program and numerical analyses conducted on aluminum alloy drill pipes with two different geometries. Small-scale characterization tests were conducted to determine both the material mechanical properties and the fatigue S–N curves. Full-scale fatigue tests of the components are also presented. A finite element model of the drill pipes, including the tool-joint region, was developed. The model simulates, through different load steps, the tool-joint hot-assembly and the experimental loads to obtain the actual stress distribution during the full-scale tests. Maximum stress amplitude in the aluminum pipes was found to be coincident with the edge of the connector, at the same location where failure was observed in full-scale tests. The study revealed that such pipes present a complex stress state near their connection to the steel tool-joints due to their geometry and the residual stresses induced during the assembly of the steel connectors onto the aluminum pipes. Finally, multi-axial fatigue models were calibrated with the results of the small-scale tests and applied to the stress–strain state obtained numerically. Theoretical predictions were correlated with full-scale fatigue test results.