Effects of gear mesh fluctuation and defaults on the dynamic behavior of two-stage straight bevel system Driss Yassine, Hammami Ahmed, Walha Lassaad ⁎, Haddar Mohamed Laboratory of Mechanics, Modelling and Manufacturing (LA2MP) Mechanical Engineering Department, National School of Engineers of Sfax, BP 1173-3038 Sfax, Tunisia article info abstract Article history: Received 28 February 2014 Received in revised form 22 July 2014 Accepted 24 July 2014 Available online xxxx This paper presents a three-dimensional model of two-stage straight bevel gear system. Periodic fluctuations of the gear meshes' stiffness are the main sources of excitation for the faultless gear system. First, dynamic response is calculated using Newmark method which is step-by-step time integration. The numerical results are presented in both the frequency and time domains. After that, we introduce some defects in the developed model such us the eccentricity defect, pro- file error and cracked tooth. The dynamic behavior of the defected gear system is compared with that of the faultless system. The numerical results from this work have applications in the design phase or maintenance of this type of bevel gear transmission. © 2014 Elsevier Ltd. All rights reserved. Keywords: Bevel gear Gear meshes' stiffness Eccentricity defect Profile error Cracked tooth 1. Introduction Gears are an excellent mechanism for power transmission due to their uses and works that are devoted. In addition to these benefits, bevel gear allows the transmission angle changing. Indeed, most studies are devoted to the dynamic behavior of a single stage gearbox. Merzouk [1] modeled one spur gear system by the finite element method concentrates. Yakhou [2] addressed the problems of gearboxes with helical teeth; he cited different sources of radiated noise of these boxes. Bruyere [3] achieved a statistical tolerance analysis of straight bevel gear. Li Yinong [4] studied the influence of asymmetric mesh stiffness on dynamics of spiral bevel gear Transmission System. In addition to these research works for the single stage model, there are studies on double or multistage model. Lian and Parker [5] modeled mesh stiffness in two stage spur gear systems. Walha [6] studied nonlinear dynamics behavior of two stage spur gear system. J. Kimotho [7] modeled a multi-stage spur gear Systems as a tool for design optimization. Driss [8] studied the effects of defects on helical two-stage gear system behavior. Modeling of bevel gears is limited to one stage [3,4] although we found mechanisms of two stage bevel gears in processing ma- chine such as the heads of milling, in special gearboxes and in transportation like helicopter. This work is devoted to a two-stage straight bevel gear which is modeled as faultless system in the first case and as a defected system in the second case in order to facilitate the diagnosis of this type of gear boxes. In this research article, a two-stage straight bevel gear system was modeled. In the first, the dynamic behavior of a faultless system is presented. Then, we modeled the mesh stiffness depending on the angular position of contact's point and we calculated the tooth Mechanism and Machine Theory 82 (2014) 71–86 ⁎ Corresponding author. E-mail addresses: yacindris@gmail.com (D. Yassine), ahmed_hammami@voila.fr (H. Ahmed), walhalassaad@yahoo.fr (W. Lassaad), mohamed.haddar@enis.rnu.tn (H. Mohamed). http://dx.doi.org/10.1016/j.mechmachtheory.2014.07.013 0094-114X/© 2014 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Mechanism and Machine Theory journal homepage: www.elsevier.com/locate/mechmt