Mustafa Sabuncu

Early Detection of Pitting Damage in Gears using Mean Frequency of Scalogram

A local gear-tooth defect such as a fatigue crack, pit or chip weakens the tooth and causes transient events when that faulty tooth is in mesh. The magnitude and duration of these events depend mainly upon the severity of the defect and the contact ratio of the gear pair. If the tooth fault severity is small and the contact ratio is high, the resulting transient may not show distinctively in the vibration signal; time-frequency analysis can be used to reveal such events. This paper presents the use of a scalogram and its mean frequency variation for the detection and monitoring of pitting faults in gears. Real gear vibrations are obtained from a test rig utilising a two-stage industrial gearbox. Pits representing differing degrees of fault severity are simulated on a few tooth surfaces. Classical processing schemes in the time and frequency domain are firstly employed to obtain general characteristics of the gear vibration. The continuous wavelet transform is then used to obtain a scalogram and its mean frequency variation. It has been found that the presence of a pitting fault cannot be clearly revealed by the time and frequency domain representations unless the fault severity is high. In contrast, the scalogram (and especially its mean frequency variation) provides early indications of presence and progression of pitting faults in gears even when the fault severity is considerably smaller.

LATERAL DYNAMIC STABILITY ANALYSIS OF A CANTILEVER LAMINATED COMPOSITE BEAM WITH AN ELASTIC SUPPORT

In this paper, static and dynamic stabilities of a cantilever laminated composite beam, having a linear translation spring as elastic support whose position is changeable from the free end to midspan of the beam, subjected to periodic vertical end loading, are examined. The beam is assumed to be an Euler beam and the finite element model used can accommodate symmetric and antisymmetric lay-ups. Solutions referred to as combination resonance are investigated for the dynamic stability analysis. The effects of length-to-thickness ratio, the variation of cross-section in one direction, orientation angle, static and dynamic load parameters, stiffness and position of the elastic support on stability are examined.

Investigation of Effectiveness of Some Vibration-Based Techniques in Early Detection of Real-Time Fatigue Failure in Gears

Bending fatigue crack is a dangerous and insidious mode of failure in gears. As it produces no debris in its early stages, it gives little warning during its progression, and usually results in either immediate loss of serviceability or great ly reduced power transmitting capacity. This paper presents the applications of vibration-based techniques (i.e. conventional time and frequency domain analysis, cepstrum, and continuous wavelet transform) to real gear vibrations in the early detection , diagnosis and advancement monitoring of a real tooth fatigue crack and compares their detection and diagnostic capabilities on the basis of experimental results. Gear fatigue damage is achieved under heavy-loading conditions and the gearbox is allowed to run until the gears suffer badly from complete tooth breakage. It has been found that the initiation and progression of fatig ue crack cannot be easily detected by conventional time and frequency domain approaches until the fault is significantly develop ed. On the contrary, the wavelet transform is quite sensitive to an y change in gear vibration and reveals fault features earlie r than other methods considered.

Effects of an edge crack on the free vibration and lateral buckling of a cantilever laminated composite slender beam

The objective of this paper is to investigate the effects of laminate scheme, crack ratio (a/h) and crack position (L1/L) on the free vibration and lateral buckling of a cantilever slender rectangular beam such as an airplane wing or a wind turbine blade with a single edge crack. The local flexibility approach is adopted to model the crack, based on linear fracture mechanics and the Castigliano theorem. The governing matrix equations for free vibration and buckling load are derived from the standard beam element and cracked beam element combined with the local flexibility concept. The results are obtained numerically using the finite element method, based on the energy approach and are given for crack ratios up to 0.5 at crack positions up to 0.9 ratio. Polynomial approximation for displacements gives results with reasonable accuracy.

Dynamic stability of cracked multi-bay frame structures.

ABSTRACT The effects of crack depth and crack location on the in-plane static and dynamic stability of cracked multi-bay frame structures subjected to periodic loading have been investigated numerically by using the finite element method. For the rectangular cross-section beam, a crack element is developed by using the principles of fracture mechanics. In addition, the effect of the number of spans and static and dynamic load parameters on static and dynamic stability analysis are also investigated. For buckling and dynamic stability analyses, the results obtained by using the present model are presented in three-dimensional graphical forms and tables.