Carlos Morillo

Motor Bearing Fault Detection Using Spectral Kurtosis-Based Feature Extraction Coupled With K -Nearest Neighbor Distance Analysis

Bearing faults are the main contributors to the failure of electric motors. Although a number of vibration analysis methods have been developed for the detection of bearing faults, false alarms still result in losses. This paper presents a method that detects bearing faults and monitors the degradation of bearings in electric motors. Based on spectral kurtosis (SK) and cross correlation, the method extracts fault features that represent different faults, and the features are then combined to form a health index using principal component analysis (PCA) and a semisupervised k-nearest neighbor (KNN) distance measure. The method was validated by experiments using a machinery fault simulator and a computer cooling fan motor bearing. The method is able to detect incipient faults and diagnose the locations of faults under masking noise. It also provides a health index that tracks the degradation of faults without missing intermittent faults. Moreover, faulty reference data are not required.

Detection and Reliability Risks of Counterfeit Electrolytic Capacitors

Counterfeit electronics have been reported in a wide range of products, including computers, medical equipment, automobiles, avionics, and military systems. Counterfeiting is a growing concern for original equipment manufacturers (OEMs) in the electronics industry. Even inexpensive passive components such as capacitors and resistors are frequently found to be counterfeit, and their incorporation into electronic assemblies can cause early failures with potentially serious economic and safety implications. This study examines counterfeit electrolytic capacitors that were unknowingly assembled in power supplies used in medical devices, and then failed in the field. Upon analysis, the counterfeit components were identified, and their reliability relative to genuine parts was assessed. This paper presents an offline reliability assessment methodology and a systematic counterfeit detection methodology for electrolytic capacitors, which include optical inspection, X-Ray examination, weight measurement, electrical parameter measurement over temperature, and chemical characterization of the electrolyte using Fourier Transform Infrared Spectroscopy (FTIR) to assess the failure modes, mechanisms, and reliability risks. FTIR was successfully able to detect a lower concentration of ethylene glycol in the counterfeit capacitor electrolyte. In the electrical properties measurement, the distribution of values at room temperature was broader for counterfeit parts than for the authentic parts, and some electrical parameters at the maximum and minimum rated temperatures were out of specifications. These techniques, particularly FTIR analysis of the electrolyte and electrical measurements at the lowest and highest rated temperature, can be very effective to screen for counterfeit electrolytic capacitors.

Rolling element bearing fault diagnosis using simulated annealing optimized spectral kurtosis

To diagnose the bearing fault using vibration signal, methods like envelope analysis have been used. These methods need to locate the optimum frequency band to perform the analysis. Researchers have developed spectral kurtosis through kurtogram to detect the optimum frequency band. However, kurtogram uses a rigid structure of frequency filter bank and when the optimum frequency band does not match any of the frequency bands in the structure the fault may not be detected. In this paper a method based on simulated annealing is developed to locate the optimum frequency band. The method models spectral kurtosis as a function of the variables of a band-pass filter. Firstly the analysis result from the kurtogram is obtained as a start point, and then the central frequency and the bandwidth are optimized by maximizing spectral kurtosis through simulated annealing. Finally, the test signal is band-pass filtered by the optimized filter, and the envelope analysis is applied to complete the diagnosis. Experimental study shows that the method can diagnose the fault for different fault types. Being able to detect the real optimum frequency band, this method can strengthen the detection of the fault feature frequency component.

Detection of capacitor electrolyte residues with FTIR in failure analysis

Detecting leakage from liquid aluminum electrolytic capacitors is not easy. Typically there is very little evidence of leakage because the electrolyte is volatile and leaves behind only trace residues. Liquid aluminum electrolytic capacitors are known to cause catastrophic failures where there is complete loss of functionality due to a short or open circuit. In the study presented in this paper, printed circuit board assemblies from a test and measurement system used in a clean room environment failed. Two units failed, causing burning in a particular area on the printed circuit board assembly. The failure area included several surface mount liquid aluminum electrolytic capacitors, and several others were mounted very close to the burnt region. A study was initiated to evaluate the cause of failure. Careful optical inspection revealed some residues on the outer side of the rubber seals of two of the electrolytic capacitors. Through using Fourier transform infrared analysis and a process of experimentation and analysis, it was determined that the residues were produced by liquid electrolyte that leaked out of the capacitor at some point in the field. The leaked electrolyte that came out of the capacitor was believed to be the cause of failure that led to the burning of the printed circuit board assembly.

Viscoplastic properties of pressure-less sintered silver materials using indentation

Nanoindentation has been popular since the 1970s for querying material behavior at extremely small length scales. This paper focuses on using a combination of indentation and FEA methods for characterizing the viscoplastic behavior of composite materials and sintered materials, which pose additional challenges because of the heterogeneous morphology. In particular, this paper focuses on two forms of pressure-less sintered silver interconnect materials: an adhesive-based particulate composite for low temperature applications and a porous sintered version for high-temperature applications. By use of indentation methodology to bound the bulk viscoplastic properties for both of these heterogeneous morphologies, both sintered materials in this study are estimated to be less creep resistant than SAC 305 at operational stress levels, at room temperature.

Tribological analysis of Al2O3/TiO2/ZrO2 nanocomposites as an alternative for THR materials

This work studied the microstructure and tribological behavior of Al2O3/TiO2/ZrO2 nanocomposites to be used in hip joint replacements. To increase the fracture toughness of alumina and enhance the tribological properties, nanometer sized particles of TiO2 and ZrO2 were added. The specimens contained 10 mol% of TiO2, different percentages of ZrO2 (0, 2.5, 5, 7.5, 15 and 20 mol %), and alumina as a remainder. Disks were hot pressed at 1500 °C and 25 MPa, in an Argon atmosphere for 1 hour. Given the fact that the sample containing 7.5 mol% of ZrO2 showed the lowest wear volume, it was hot pressed again at 1500, 1400, 1300 and 1200 °C to assess the best temperature condition for sintering. For a composition of 7.5 mol% of ZrO2 the lowest coefficient of friction (0.1-0.3) and the lowest wear volume (0.0046 mm3) were achieved. A direct relation between mechanical and tribological properties was not found. However, these nanocomposites may be considered as a candidate for a new generation of hip joint replacement material.

Wear Mechanisms of PTFE in Humidified Hydrogen Gas

PTFE is used as sealing material of machine elements in hydrogen utilizing machine systems, such as fuel cell vehicles and related infrastructures. It is necessary to know the tribological property of sealing materials in hydrogen gas to realize safety and reliability of machine elements operated in hydrogen environment. In this study, humidity in gases was focused on and its effects on the friction and wear of rubbing pair of PTFE pin and AISI 316L disk was investigated in pin-on-disk wear apparatus. The result indicated that the humidity in hydrogen gas had little effect on the friction coefficient between PTFE and AISI 316L. However, the specific wear rate of unfilled PTFE was clearly affected by the humidity. The amount of PTFE transfer film formed on the stainless surface gradually decreased with decreasing the humidity in hydrogen gas. The similar results could be obtained in inert argon gas as well. Water molecules remained in gaseous environments would be included in the formation process of PTFE transfer film affect on formation of PTFE transfer film. The humidity in hydrogen gas should be regulated to ensure the tribological behavior of the PTFE/stainless sliding pair being used in the hydrogen environment.Copyright

Tribological analysis of alumina nanocomposites for orthopedics applications

In this study the tribological analysis of Al2 O3 nanocomposites/Al2 O3 pair; proposed as a candidate material to fabricate hip prostheses was carried out. Nanopowders of Al2 O3 (AKP 50, 300 nm), TiO2 (PS-25, 50 nm) and Co metallic powder (Nilaco, 28 nm) were mixed and hot pressed. Wear test was carried out in a pin-on-plate tribometer, with a frequency of 1 Hz, a load of 49 N, for 4h; the counterface used was Al2 O3 . Mechanical properties as Vickers hardness, fracture toughness and Young’s modulus were estimated using the indentation method. Distilled water and fetal bovine serum solution (FBSS) were used as environment. It was found that the specific wear rate of Al2 O3 nanocomposites was about 10−8 mm3 /N*m and the coefficients of friction were around 0.3–0.5 for FBSS. Worn surfaces were observed using SEM.Copyright

Microstructure and Wear Properties of Al2O3/TiO2 Nanocomposites

Microstructure and tribological behavior for Al 2 O 3 /TiO 2 nanocomposites have been studied. In order to increase the mechanical properties of alumina, TiO 2 of nanometer size was added. The specimens contain 0, 5, 10, 15, 20, and 25 mol % of TiO 2 on alumina as remainder. Samples were hot pressed at 1500 °C and 25 MPa, in Ar atmosphere for 1 h. The microstructural characterization was carried out with Scanning Electron Microscope and X-ray Diffraction and EDX for chemical analysis. Fracture toughness and Vickers hardness were estimated with indentation method. Relative density was acquired using Archimedes method in toluene medium. Determination of wear behavior was carried out in a ball-on-disc tribometer, using nitride balls and distilled water at 37 °C for 24 h. Wear volume was calculated, and it was found the lower value at 10 mol% of TiO 2 . Also, the highest Vickers hardness of the nanocomposites (12.97 GPa) was achieved for this composition, but this values is lower than that monolithic alumina. The highest fracture toughness (7.15 MPa.m 1/2 ) was obtained at 20 mol% of TiO 2 . It was found both intergranular and transgranular fracture mode in all the samples (monolithic alumina and nanocomposites).