A three-dimensional elastic contact problem has been investigated in this article with the emphasis on analysis of the partial slip phenomenon which occurs at certain areas in nominal contact zone when the local shear tractions exceed the limit specified by the friction. The investigation has been made for the contacts between similar or dissimilar materials and under general conditions in which the applied loads consist of a normal load, a tangential force, and a torque normal to the contact plane. The partial slip contact problem is solved through a numerical procedure based on a semi-analytical method. The conjugate gradient method and the fast Fourier transform technique are employed to speed up the computation. The contact pressures, surface shear tractions, stick ratios, tangential body displacements, and rotational angles are analysed under different loads and for similar or dissimilar contact materials. The coupling effects among the normal load, the tangential force, and the twisting moment are studied. Results show that for the contact of dissimilar materials and under a pure torque, the surface shear tractions q x and q y will produce normal deformations until the gross slip occurs. The combined actions of tangential force and twisting moment are prone to cause gross slip in comparison with those under tangential force or twisting moment alone. Moreover, the increasing twisting moment will cause the shrinking of the stick zone, but it evolves in different ways for the contacts of similar or dissimilar materials.
Time-frequency representations (TFR) have been intensively employed for analysing vibration signals in gear fault diagnosis. However, in many applications, TFR are simply utilized as a visual aid to detect gear defects. An attractive issue is to utilize the TFR for automatic classification of faults. A key step for this study is to extract discriminative features from TFR as input feature vector for classifiers. This article contributes to this ongoing investigation by applying morphological pattern spectrum (MPS) to characterize the TFR for gear fault diagnosis. The S transform, which combines the separate strengths of the short-time Fourier transform and wavelet transforms, is chosen to perform the time-frequency analysis of vibration signals from gear. Then, the MPS scheme is applied to extract the discriminative features from the TFR. The promise of MPS is illustrated by performing our procedure on vibration signals measured from a gearbox with five operating states. Experiment results demonstrate the MPS to be a satisfactory scheme for characterizing TFRs for an accurate classification of gear faults.
This paper proposes a novel method of collision-free fixture and tool space design for five-axis grinding, considering tool movement, machine degrees of freedom, the machine envelope, inspection, and related features. The fixture space is designed in three steps. First, the fixture space is generated as the remaining space after cutting out the tooling space (i.e. the sweeping space of the grinding wheel along the profile of the machined features). In this way, the fixture space is naturally collision-free with respect to tool movement. Second, the fixture space is further modified based on the constraints imposed by the grinding machine centre, which include over-travel distance, the positions of coolant nozzle and wheel dresser, and so on. Third, the fixture space is modified again according to measurements conducted by coordinate measuring machines and in-cycle machine probes. Interactions of fixture space with tool space, machine, and inspection are considered.The fixture space design for holding aerofoil blades on a five-axis machining centre Makino A55 for grinding operations is used as a case study, and the results of this study have been verified by computer-aided manufacture (CAM) simulation software Vericut and physical experiments using dummy wheels.
Fixture is a mechanical component to clamp a workpiece and to move it to a specific position. This paper analyses partial slip at the fixture-workpiece interface and addresses the effects of design parameters and working conditions of a fixture-workpiece facility on clamping reliability. A stick ratio, defined as the ratio of the stick area to the entire nominal contact area, is introduced in this study to characterize the clamping reliability. If the value of stick ratio equals to one, the clamping is most reliable, but when it drops to zero, a gross sliding will occur, which means clamping failure. This paper investigates the partial slip phenomenon by solving threedimensional contacts between elastically dissimilar materials, using the conjugate gradient method (CGM) and discrete convolution-fast Fourier transform (DC-FFT) techniques, but focuses on its industrial applications. Results have demonstrated how the inferential factors, such as material property, normal and tangential loads, operational parameters, and geometric features of the fixture, would affect the clamping reliability, which can be used for guiding the design of the fixture, for example, the choice of material, friction coefficient, fixture's opening angle, acceleration in manipulation, and so on.
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