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R. Citarella et alii, Frattura ed Integrità Strutturale, 34 (2015) 554-563; DOI: 10.3221/IGF-ESIS.34.61 554 Robust design of a polygonal shaft-hub coupling R. Citarella, M. Perrella Department of Industrial Engineering, University of Salerno, via Giovanni Paolo II 132, Fisciano (SA), Italy rcitarella@unisa.it A BSTRACT . In this work, the Taguchi method is applied for the optimal choice of design parameter values for a polygonal shaft-hub coupling. The objective is to maximize a performance function, minimizing, at the same time, its sensitivity to noises factors (robust design). The Design of Experiments (DoE) is adopted to set up a plan of numerical experiments, whose different configurations are simulated using the Boundary Element Method (BEM). K EYWORDS . Robust design; Boundary Element Method; Taguchi method; Polygonal shaft-hub coupling. I NTRODUCTION n polygonal shaft-hub couplings, the torque transmission takes place thanks to normal and friction forces at the interface between the joined components. The common features of these couplings include: compact construction, self-alignment, absence of protruding elements that may cause high stress levels, efficient transmission of static-oscillating torques even with small dimensions, easy hub interchangeability (in case of failure) and, for polygonal shapes, such as those with 4 lobes, the possibility of displacement under load [1]. These types of couplings are highly competitive when compared to traditional ones that use keys, fasteners and splined shafts. Nevertheless, the difficult workability (with steel requiring special grinding machines) and laborious calculation of the stresses, due to the lack of rotation symmetry, along with a tri-axial stress state, discouraged designers and constructors in the past, with them preferring traditional couplings over polygonal ones. The development of CNC grinding machines, the introduction of sintered materials (allowing for production by moulding), along with the improvement of hardware and software resources, making it possible to carry out accurate assessments for the dimensioning, circumvented those drawbacks, making the use of polygonal couplings very appealing. The first analysis of the biaxial stress and strain states in the shaft-hub was proposed by Mechnik that used the Finite Element Method (FEM) [2], followed by many literature works up to recent time [3]. The numerical analysis of the coupling by FEM greatly reduced the simplification of the coupling model, with the results becoming reliable, as highlighted by the comparison of the FEM numerical results against the experimental ones obtained from optical methods [4] and against BEM (Boundary Element Method) numerical results [5]. Mechnik’s study, along with those that followed [6-7], dealt with shaft-hub couplings with the most commonly used P3G normalized polygonal profiles. Figure 1 shows a normalized profile with 3 lobes, whilst its parametric equation, defined in 1959 by Filemon [8] and valid in general for profiles with n lobes is reported in Eq. (1), where the parameters D m and e are, respectively, the diameter and eccentricity of the profile. I