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Failures of bearing would cause sudden downtime and severe accidents that may require significant maintenance and economic consequences. Therefore, condition monitoring of bearing is extremely important for ensuring reliable and efficient operation. The analysis of electric power supply signals offers a non-intrusive and cost-effective method for detecting various incipient faults in rotary machines. However, using inverter or variable speed drive would influence the electric power supply signals, causing difficulties in detection and diagnosis results. To reduce these influences and develop effective detection techniques, this paper focuses on using electric power supply signals as an approach to detect incipient faults in the bearing of driving induction motor based on high-order bispectral analysis. It takes the advantage of providing abundant information from electric signatures of downstream driving motors to improve the performance of bearing's health monitoring. Modulation signal bispectrum (MSB) and cyclic bispectrum (CCB) exhibit significance to detect normal and abnormal bearing conditions, whereas remarkable effort is dedicated from MSB result due to the inclusion of phase information with amplitude modulation in both lower and higher sidebands. It can conclude that effective measurements of electrical power supply signals utilize reliable fault diagnosis information in the mechanical components of the driving motor. [ABSTRACT FROM AUTHOR]

Due to ignoring the effects of the change of the tooth attachment position caused by the cracks, traditional time vary mesh stiffness (TVMS) calculation models and dynamic simulations for cracked gears will lose their precision in the body crack case. To address this shortcoming, a new analytical TVMS calculation model of cracked gear considering tip relief (TR) is developed based on a proposed variable-angle deformation energy integration method. On this basis, a dynamic model of the gear system for the analysis of fault vibration characteristics is established. The effectiveness and accuracy of the proposed TVMS calculation model are verified by the finite element method. A comprehensive investigation is finally carried out to reveal the effects of the parameters of TR, load and crack on the TVMS and dynamic characteristics of the cracked gears. The study results indicate that the proposed models can meet the accurate TVMS calculation and dynamic simulation for both the tooth- and body-cracked gears, and the influences of the tooth attachment position change caused by the crack cannot be ignored. This study could provide a systematic methodology and meaningful reference for the dynamic modelling, simulation and fault diagnosis of gear systems with crack failures. [ABSTRACT FROM AUTHOR]

Grinding residual stress (GRS) has been understood to have a great impact on the strength of gear fatigue life. However, there are lack of detailed studies on the influences in terms of mechanism and magnitude. To fill this gap, this study proposed a new method based on finite element analysis (FEA) to calculate the overall meshing stress on a gear tooth surface by including both the GRS and elastohydrodynamic lubrication (EHL) film pressure. Applying this method to a spiral bevel gear has resulted in a number of interesting results that GRS produced to reveal its mechanism of action through a full meshing cycle. The acquired understanding would be useful for development of manufacturing processes. [ABSTRACT FROM AUTHOR]

Gearbox condition monitoring (CM) plays a significant role in ensuring the operational reliability and efficiency of a wide range of critical industrial systems such as wind turbines and helicopters. Accurate and timely diagnosis of gear faults will improve the maintenance of gearboxes operating under sub-optimal conditions, avoid excessive energy consumption and prevent avoidable damages to systems. This study focuses on developing CM for a multi-stage helical gearbox using airborne sound. Based on signal phase alignments, Modulation Signal Bispectrum (MSB) analysis allows random noise and interrupting events in sound signals to be suppressed greatly and obtains nonlinear modulation features in association with gear dynamics. MSB coherence is evaluated for selecting the reliable bi-spectral peaks for indication of gear deterioration. A run-to-failure test of two industrial gearboxes was tested under various loading conditions. Two omnidirectional microphones were fixed near the gearboxes to sense acoustic information during operation. It has been shown that compared against vibration based CM, acoustics can perceive the responses of vibration in a larger areas and contains more comprehensive and stable information related to gear dynamics variation due to wear. Also, the MSB magnitude peaks at the first three harmonic components of gear mesh and rotation components are demonstrated to be sufficient in characterizing the gradual deterioration of gear transmission. Consequently, the combining of MSB peaks with baseline normalization yields more accurate monitoring trends and diagnostics, allowing the gradual deterioration process and gear wear location to be represented more consistently. [ABSTRACT FROM AUTHOR]

In accordance with the vibration characteristics of ball screw feed systems, a hybrid modeling method is proposed to study its dynamic behavior. Partially, the ball screw is modeled as a continuous body, and the remaining components are considered lumped masses, allowing for a realistic description of the dynamics of the feed system. The axial, torsional, transverse, and bending vibration models of a ball screw carriage system are established via the Rayleigh-Ritz series method based on the Timoshenko beam assumption. The established model that added the Timoshenko beam assumption obtains the coupling vibration displacement between the transverse and bending vibrations of the lead screw, which is close to real situations. Numerical simulations are conducted to investigate the changes of the natural frequency and modal shapes of ball screw systems with carriage positions. Results show that the carriage position has significant influence on the amplitude and direction of axial and transverse vibrations, substantial influence on the direction of the bending vibration, and minimal influence on the amplitude and direction of torsional vibration. These results indicate that the proposed hybrid model performs well to predict the vibration characteristics of the feed system. Moreover, the carriage position and carriage load also have a remarkable effect on the frequency response of the feed system. These results, along with the modeling approach, provide an important basis for the further study of in-machining monitoring and vibration controller design. [ABSTRACT FROM AUTHOR]

Clinching technology is widely used for joining lightweight materials. It is well known that the fatigue life of clinched joints is outstanding, but its static strength is inferior to other conventional joints such as resistance spot welding joints. In this study, a post-processing method was proposed to enhance the overall mechanical performances of clinched joints in material of steel plate cold commercial steel. Based on the failure mechanism analysis, we performed quenching, a local heat treatment process, on the joining zone to improve the static strength of clinched joints. The static strength and fatigue life of clinched joints before and after quenching were compared via experimental study. The experimental results showed that the tensile–shearing strength of clinched joint increased by 60.65% and the fatigue life was extended when the joint was under high fatigue load levels after local heat treatment. Besides, metallographic test and fracture analysis were conducted to analyze the mechanism of the change of mechanical behaviors. Lath martensite was observed in the cross section of clinched joint after local heat treatment, which is the main reason for the tensile–shearing strength increase as martensite has higher strength than ferrite and pearlite. The fracture analysis showed that the fatigue fracture mode became transcrystalline rupture after local heat treatment when the clinched joint was under low fatigue load levels, which lead to the fatigue behavior of clinched joints weakened. Nonetheless, the overall mechanical properties of clinched joints were improved. [ABSTRACT FROM AUTHOR]

It seems a universally accepted doctrine that chatter resistance of a machining system can be improved with increasing stiffness of its components. However, the viewpoint that the tool stiffness reduction would be beneficial to cutting stability of flexible components has been demonstrated by the compliant tool-workpiece chatter model. This paper presents a comprehensive investigation of the dynamic interaction between the tool and the workpiece during turning operations and its effect on the cutting stability. Following the formulation of the chatter model, the effect of the coupling dynamics of the cutting system on the limiting depth of cut (doc), a conservative but reliable indicator for evaluating the stability level of the machining process, is highlighted. It is shown that stability can be enhanced by judicious increase of the tool flexibility and/or the workpiece damping. Also, an inflexion point generally exists on the cutting position-dependent limiting doc stability curve, revealing that the stability appears to be unchanged once the stiffness of the tool or workpiece is increased to a certain degree. As a result, the analysis results lay the foundation of a tool dynamics adaptation (TDA) approach to machining chatter control. It suggests an adaptive adjustment of the tool dynamics to the machined workpiece to enhance stability. The proposed approach was validated through turning experiments, in which the tool shank was installed parallel to the length of the flexible workpiece. The experimental results have shown an effective extension of the chatter-free cutting margin when tuning dynamics of the compliant tool-workpiece system. Given the reality that there is no absolutely rigid workpiece or tool in industrial applications, the proposed chatter control strategy can be adopted as a generic approach for the turning or boring processes. [ABSTRACT FROM AUTHOR]

In this paper, the propagation of bounded uncertainties in the dynamic response of a misaligned rotor is investigated using a Legendre collocation based non-intrusive analysis method. A finite element rotor model is used and the parallel and angular misalignments are modelled by additions of stiffness and force terms to the system. A simplex meta-model for the harmonic solutions of the vibration problem is constructed to take into account the uncertainties. The influences of uncertainties in the fault parameters are analysed and the calculation performance of the interval method is validated. Different propagation mechanisms of the uncertainties are observed in the interval responses and discussed in case studies. The results of this study will promote the understandings of the nonlinear vibrations in misaligned rotor systems with interval variables. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) has been studied for monitoring the condition of mechanical seals by many researchers, however to the best knowledge of the authors, typical fault cases and their effects on tribological behaviour of mechanical seals have not yet been successfully investigated. In this paper, AE signatures from common faults of mechanical seals are studied in association with tribological behaviour of sealing gap to develop more reliable condition monitoring approaches. A purpose-built test rig was employed for recording AE signals from the mechanical seals under healthy and faulty conditions. The collected data was then processed using time domain and frequency domain analysis methods. The study has shown that AE signal parameters: root mean squared (RMS) along with AE spectrum, allows fault conditions including dry running, spring out and defective seal faces to be diagnosed under a wide range of operating conditions. However, when mechanical seals operate around their transition point, conventional signal processing methods may not allow a clear separation of the fault conditions from the healthy baseline. Therefore an auto-regressive (AR) model has been developed on recorded AE signals to classify different fault conditions of mechanical seals and satisfactory results have been perceived. [ABSTRACT FROM AUTHOR]

Chatter happens frequently in turning of flexible parts, jeopardizing the dynamic stability of the operation. The chatter stability prediction is dependent on the accurate estimation of the structural parameters of the cutting system. This paper aims to quantify the influence of the support conditions on dynamics of the flexible parts in straight turning. Given the time-varying cutting tool position during machining, first, the chatter stability of the cutting system along the cutting path is analyzed, and the critical stiffness expression for chatter onset prediction is deduced. Then, two models of the spindle-workpiece-tailstock system using analytical and numerical methods are constructed and compared. The simulation results showed that increasing the spindle bearing or tailstock support stiffness cannot effectively improve the stiffness distribution and the eigenfrequency of the machined rod, whereas the frequency of the system tends to be increased evidently with the chuck size decreased. In comparison with the experimental results, it has been shown that the model involving the effect of spindle bearing and center support enables to produce more accurate modal parameters estimation and chatter onset location prediction than the simplified model. Besides, the measured displacement signals demonstrate a good mapping relation with the theoretical analysis results. The present study could provide an in-depth understanding of the dynamic behavior of flexible workpieces in turning operations. [ABSTRACT FROM AUTHOR]

Mechanical clinching is a connection technology that is widely used in different industrial fields because it has several advantages, including easy preparation, an excellent fatigue property and environmental friendliness. In this study, tensile-shear tests and fatigue tests were conducted to characterize the mechanical properties of clinched joints using aluminium alloys. The experimental results showed that the fracture regions were concentrated in the indentations of the lower sheets. The failed surfaces were examined using a scanning electron microscope and an energy-dispersive X-ray machine to study the fretting fatigue failure mechanisms of the clinched joints. Two types of fretting wear modes were observed: the neck fretting wear mode and indentation-surrounding fretting wear mode. The results also showed that the proportions of these two fretting wear modes could be impacted by the applied load levels. [ABSTRACT FROM AUTHOR]

The inevitable deterioration of the lubrication conditions in a gearbox in service can change the tribological properties of the meshing teeth. In turn, such changes can significantly affect the dynamic responses and running status of gear systems. This paper investigates such an effect by utilizing virtual prototype technology to model and simulate the dynamics of a wind turbine gearbox system. The change in the lubrication conditions is modeled by the changes in the friction coefficients, thereby indicating that poor lubrication causes not only increased frictional losses but also significant changes in the dynamic responses. These results are further demonstrated by the mean and root mean square values calculated by the simulated responses under different friction coefficients. In addition, the spectrum exhibits significant changes in the first, second, and third harmonics of the meshing components. The findings and simulation method of this study provide theoretical bases for the development of accurate diagnostic techniques. [ABSTRACT FROM AUTHOR]

Clinching is a widely used sheet material connection technology in different industrial fields. The effects of annealing and quenching on the mechanical performances of clinched titanium alloy joints were investigated in this research. Tensile-shear tests were carried out to study the join ability, load-bearing capacity, energy absorption, and failure modes of different clinched titanium alloy joints. The F-N curves were obtained from fatigue tests to characterize the fatigue properties of different types of clinched joints. The typical fracture interfaces were analyzed by scanning electron microscopy. Results show that the tensile-shear strength of the clinched titanium alloy joints was severely decreased by quenching, but both tensile-shear strength and energy absorption were improved by annealing. For all types of joints tested, fatigue cracks always appeared near the indentation of the upper sheet. Analysis of the microstructure suggested that the plasticity of the titanium was improved by annealing. [ABSTRACT FROM AUTHOR]

Self-piercing riveting is a relatively new high-speed mechanical joining technique. The present paper deals with the join-ability of similar and dissimilar titanium sheets by self-piercing riveting and the mechanical properties of the self-piercing riveted joints. Tensile-shear tests were carried out to characterize the mechanical properties of different self-piercing riveted joints made of the similar titanium sheets and the dissimilar metal sheet combinations. The normal hypothesis tests were performed to examine the rationality of the test data. The load-bearing capacity, energy absorption, and failure modes of different titanium sheet self-piercing riveted joints were studied. Results showed that the load-bearing capacity of self-piercing riveted joints with titanium as upper sheets are higher than that of the self-piercing riveted joints with titanium as lower sheets. [ABSTRACT FROM AUTHOR]

With an increasing application of clinching in different industrial fields, the demand for knowledge of static and dynamic characteristics of clinching is increased. In the present work, the extensible die clinching process was numerically investigated using finite element method. To validate the computational simulation of the extensible die clinching process, experimental tests on extensible die clinched specimens have been carried out. Good agreement is achieved between the predictions and the experimental results. Monotonic tensile tests were carried out to measure the ultimate tensile strengths of the extensible die clinching joints and clinching-bonded hybrid joints. Deformation and failure of the extensible die clinched joints under monotonic tensile loading were studied. The normal hypothesis tests were performed to examine the rationality of the test data. This work was also aimed at evaluating experimentally and comparing the strength and energy absorption of the extensible die clinched joints and clinching-bonded hybrid joints. [ABSTRACT FROM AUTHOR]

Self-piercing riveting (SPR) is a new high-speed mechanical fastening technique which is suitable for point-joining dissimilar sheet materials, as well as coated and pre-painted sheet materials. With an increasing application of SPR in different industrial fields, the demand for a better understanding of the knowledge of static and dynamic characteristics of the SPR joints is required. In this paper, the SPR process has been numerically simulated using the commercial finite element software LS-Dyna. For validating the numerical simulation of the SPR process, experimental tests on specimens made of aluminium alloy have been carried out. The online window monitoring technique was introduced in the tests for evaluating the quality of SPR joints. Good agreements between the simulations and the tests have been found, both with respect to the force-travel (time) curves as well as the deformed shape on the cross-section of the SPR joint. Monotonic tensile tests were carried out to measure the ultimate tensile strengths of the bonded joints, SPR joints and SPR-bonded hybrid joints. Deformation and failure of the joints under monotonic tensile loading were studied. The normal hypothesis tests were performed to examine the rationality of the test data. This work was also aimed at evaluating experimentally and comparing the strength and energy absorption of the bonded joints, SPR joints and SPR-bonded hybrid joints. [ABSTRACT FROM AUTHOR]

As novelty detection works when only normal data are available, it is of considerable promise for health monitoring in cases lacking fault samples and prior knowledge. We present two novelty detection methods for health monitoring of turbopumps in large-scale liquid-propellant rocket engines. The first method is the adaptive Gaussian threshold model. This method is designed to monitor the vibration of the turbopumps online because it has minimal computational complexity and is easy for implementation in real time. The second method is the one-class support vector machine (OCSVM) which is developed for post analysis of historical vibration signals. Via post analysis the method not only confirms the online monitoring results but also provides diagnostic results so that faults from sensors are separated from those actually from the turbopumps. Both of these two methods are validated to be efficient for health monitoring of the turbopumps. [ABSTRACT FROM AUTHOR]

Self-piercing riveting (SPR) is a high-speed mechanical fastening technique which is suitable for point-joining advanced lightweight sheet materials that are dissimilar, coated, and hard to weld. Major advances have been made in recent years in SPR technique. Latest literature relating to finite element analysis (FEA) of SPR joints is reviewed in this paper. The recent development in FEA of SPR joints are described with particular reference to three major factors that influence the success of SPR technique: SPR process, failure mechanism, and mechanical behavior of SPR joints. The main FE methods used in FEA of SPR joints are discussed and illustrated with brief case studies from the literature. Areas where further useful progress can be made are also identified. [ABSTRACT FROM AUTHOR]