T. Fakhfakh

Dynamic analysis of a planetary gear failure caused by tooth pitting and cracking

Planetary gears are widely used in aeronautic and industrial applications that require compactness and high torque-to-weight ratios. Despite these advantages, the severe conditions under which such gears are typically used may lead to failure. Tooth pitting and cracking are frequently encountered failure modes. The defects are modeled and discussed for a planetary gear set. The influence of tooth defects on gear mesh stiffness is scrutinized. Healthy planetary gear dynamic response and the response of planetary gears containing tooth defects are compared in both the time and frequency domains and in the joint time-frequency domains by use of the Wigner-Ville distribution.

Backlash effect on dynamic analysis of a two-stage spur gear system

Gearbox dynamics are characterized by a periodically changing stiffness due to multiple teeth contacts. In real gear systems, a backlash also exists that can lead to a loss in contact between the teeth. Due to this loss of contact, the gear has piecewise linear stiffness characteristics. This paper examines the effect of backlash in the two-stage gear system. A purely torsional gear system is formed by three shafts connected to each other by two spur gear pairs. Using standard methods for nonlinear systems (Newton-Raphson algorithm), the dynamic behavior of a gear system with backlash is examined. Amplitude jumps in systems due to backlash are observed.

Failure analysis of a misaligned and unbalanced flexible rotor

Shaft misalignment and rotor unbalance are major concerns in rotating machinery. In order to understand the dynamic characteristics of these machinery faults, a model of a complete motor flexible-coupling rotor system capable of describing these failures was developed. Generalized system equations of motion for a rotor under misalignment and unbalance conditions were derived using the finite element method. A spectral method was developed for resolving the equation of motion. This allows one to obtain and analyze the dynamic response and consequently to identify misalignment and unbalance faults.

Effect of Load Shape in Cyclic Load Variation on Dynamic Behavior of Spur Gear System

Transmissions including spur gears are widely used in several industrial applications. They are characterized by high efficiency and capability to transmit high torques. A special attention should be made for transmissions running under varying loading conditions which have to be well monitored. The presence of this variability associated with defects that may occur in the transmission will complicate its condition monitoring. The first step to overcome this difficulty is to identify and characterize the dynamic response of the transmission in healthy conditions subjected to variable loading conditions. In this paper, a model based approach is presented in order investigate the influence of the loading shape on the vibration characteristics of the transmission. A dynamic model of a one stage spur gear transmission including a time varying loading conditions is developed. Two cases of loading conditions are considered. A parametric study is achieved and main conclusions are discussed.

Analysis of Double Reducer Stage Using Substructuring Method

Global dynamics of a coupled system are synthesized using a substructuring technique based on the transfer functions of the subsystems. In this chapter, the substructuring method was applied in transmission system. The Frequency-Based Substructuring (FBS) methods are considered to identify the dynamic behavior of a structural system. Impedance coupling technique is applied to a double reducer stage, which is based on the Frequency Response Functions (FRFs) of each substructure and constraint conditions in the connection coordinates. The FRF-based substructuring technique has been previously proposed for computing the vibration modes of complex structural system by coupling the FRF of each subsystem. The effect of damping on substructuring method was discussed. Finally, the coupling technique is validated by comparing the present results with the full system ones. The major interest of using this method is that it allows replacing each subsystem by another subsystem without repeating the computation of the full system.