Wide Range Measurement of Lubricant Film Thickness Based on Ultrasonic Reflection Coefficient Phase Spectrum

The ultrasonic technique is very effective in measuring lubricant film thickness in a noninvasive manner. To estimate the film thickness with reflection signals, two main ultrasonic models are often applied in cases of different film thicknesses; they are the spring model for thin films and the resonant model for thick films. However, when measuring oil film thicknesses distributed in a wide range, there is an inherent blind zone between these two models. This problem is especially prominent in online monitoring because the abrupt variation of film thickness is highly correlated with the occurrence of abnormal conditions. To address this issue, we further proposed a method using the phase spectrum of reflection coefficient which can cover a wide range of film thicknesses. The slight variation of reflection signal in the blind zone can then be identified and bridged the measurement gap between those two traditional models. A calibration rig was used to verify the theoretical analysis and the results indicated that the developed model is capable of providing reliable ultrasonic measurement of lubricant film thicknesses in a wide range.

A Method for Ultrasonic Characterization of Density, Thickness and Velocity of Homogeneous Coating

This paper provides a nondestructive method for determination of the density, thickness and velocity of homogeneous coating from an inversion of experimental ultrasonic reflection coefficient amplitude spectrum (URCAS). The detailed analyses of the inverse algorithm and sensitivity of URCAS to the density, thickness and velocity are presented, and the sensitivity is identified as a basis for selecting the experimental data used in inversion. An example of the method and experimental measurement for comparison was given for an epoxy coating with the thickness of 0.277 mm. The relative errors between the inversion and reference value of the density, thickness and velocity were found to be 0.5 %, 3.97 %, and 0.97 %, respectively.

Ultrasonic Characterization of EB-PVD Thermal Barrier Coatings Irradiated by HIPIB

High-intensity pulsed ion beam (HIPIB) irradiation at 300 A/cm2 with a shot number of 1, and 5 was performed on the coatings and caused the modification of properties. Porosity and rough surface of EB-PVD (Electron Beam-Physical Vapor Deposition) deposited ZrO2-7%Y2O3 coatings with the thickness of 150 μm on heat-resistant steel have been characterized using the ultrasonic reflection coefficient phase spectrum. With increasing the shot number, the surface remelting and ablating filled gaps and caves between columns, and induced more uniform and compact structure. The ultrasonic measurement was investigated using immersion focusing pulse echo method with a 10 MHz transducer. The ultrasonic reflection coefficient related to frequency, velocity and attenuation coefficient were analyzed based on the acoustic transmission model in a multi-layered structure. For the as-deposited coating and coatings irradiated by HIPIB with the shot number of 1 and 5, the ultrasonic velocity changed from 2950 to 3170, and 3255 m/s respectively. The relationship between the attenuation coefficient and the frequency has been deduced based on the numerical fitting of the phase spectrum. The corresponded expressions are 1.35 α = 0.105 f , 1.2 α = 0.045 f and 1.14 α = 0.035 f , which displays that the attenuation coefficient decreases with the increasing of shot number. The ultrasonic results are in agreement with SEM observations, which have indicated that the coatings became denser and uniform with increasing the shot number. From the velocity and attenuation coefficient, the density, porosity, and microcracks of the coatings can be nondestructively evaluated utilizing the method of this paper.

Monitoring of Lubricant Film Failure in a Ball Bearing Using Ultrasound

A lubricant-film monitoring system for a conventional deep groove ball bearing (type 6016, shaft diameter 80 mm, ball diameter 12.7 mm) is described. A high-frequency (50 MHz) ultrasonic transducer is mounted on the static outer raceway of the bearing. The transducer is focused on the ball-raceway interface and used to measure the reflection coefficient of the lubricant in the “contact” ellipse between bearing components. The reflection coefficient characterizes the lubricant film and can be used to calculate its thickness. An accurate triggering system enables multiple reflection measurements to be made as each lubricated contact moves past the measurement location. Experiments are described in which bearings were deliberately caused to fail by the addition of acetone, water, and sand to the lubricant. The ultrasonic reflection coefficient was monitored as a function of time as the failure occurred. Also monitored were the more standard parameters, temperature and vibration. The results indicate that the ultrasonic measurements are able to detect the failures before seizure. It is also observed that, when used in parallel, these monitoring techniques offer the potential to diagnose the failure mechanism and hence improve predictions of remaining life.

Measurement of the stiffness of joints in a graphite brick assembly

Large, dry-contacting assemblies of graphite blocks are a feature of many nuclear reactors, and the seismic response of these structures is dependent on both the bulk and surface properties of the blocks. The nature of the interblockinterface will influence the load-deflection relationship of the blocks, which is important in understanding the response of the structure to seismic loading. The stiffness of this interface is dependent on surface roughness effects. In this paper, ultrasonic reflection coefficient measurements are used to investigate the stiffness distribution of this interface under various loading conditions. A low-frequency quasi-static spring model of the interface was adopted. This allowed the interfacial stiffness to be determined as a function of applied load, frequency, surface roughness and graphite composition. Cyclical loading of the graphite-graphite interface has also been carried out. This has shown that there is only a slight plastic deformation under normal loading, and also is indicative of a degree of intersurface adhesion at the interface. Direct measurement of the load-deflection relationship of an entire brick was also carried out which, in conjunction with the ultrasonic measurements, suggests that it is the effect of macroscopic surface features rather than microscopic roughness that is the dominant interfacial contribution to brick-tilting stiffness.