Observations of Acoustic Emission Under Conditions of Varying Specific Film Thickness for Meshing Spur and Helical Gears

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
R. I. Raja Hamzah ◽  
Khamis R. Al-Balushi ◽  
D. Mba
Keyword(s):  
Acoustic Emission ◽  
Film Thickness ◽  
Liquid Nitrogen ◽  
Gear Wheel ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Helical Gears ◽  
Experimental Findings

This paper presents experimental findings on the generation of acoustic emission (AE) from operational spur and helical gears as a function of specific film thickness (λ). The latter was varied while the gears were operating by spraying liquid nitrogen onto the rotating gear wheel over a range of load and speed conditions. It was observed that the level of AE activity was dependent on the specific film thickness (λ) and consequently the level asperity contact. The presented finding on both spur and helical gears is the first known attempt at correlating friction, film thickness, and gear operating conditions with AE.

Acoustic Emission and Elastohydrodynamic Film Thickness for Meshing of Spur and Helical Gear

2007 ◽  
Author(s):  
R. I. Raja Hamzah ◽  
D. Mba
Keyword(s):  
Acoustic Emission ◽  
Film Thickness ◽  
Experimental Evidence ◽  
Liquid Nitrogen ◽  
Gear Wheel ◽  
Helical Gear ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Helical Gears ◽  
Test Conditions

This paper presents experimental evidence of the correlation between Acoustic Emission (AE) activity and the specific film thickness (λ) for operational spur and helical gears. Whilst recording AE activity for a range of test conditions the specific film thickness was varied during operation by spraying liquid nitrogen onto the rotating gear wheel. It was noted that the AE activity reduced significantly as the theoretically estimated specific film thickness increased. It is concluded that the measurements of AE activity may offer an opportunity to quantify the level of asperity contact for meshing gears under a range of operating conditions.

Elastohydrodynamic Film Thickness and Acoustic Emission for Meshing of Spur and Helical Gears

2007 ◽  
Author(s):  
R. I. Raja Hamzah ◽  
D. Mba
Keyword(s):  
Acoustic Emission ◽  
Film Thickness ◽  
Experimental Evidence ◽  
Liquid Nitrogen ◽  
Gear Wheel ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Helical Gears ◽  
Test Conditions ◽  
Elastohydrodynamic Film Thickness

This paper presents experimental evidence of the correlation between Acoustic Emission (AE) activity and the specific film thickness (λ) for operational spur and helical gears. Whilst recording AE activity for a range of test conditions the specific film thickness was varied during operation by spraying liquid nitrogen onto the rotating gear wheel. It was noted that the AE activity reduced significantly as the theoretically estimated specific film thickness increased. It is concluded that the measurements of AE activity may offer an opportunity to quantify the level of asperity contact for meshing gears under a range of operating conditions.

Acoustic Emission and Specific Film Thickness for Operating Spur Gears

2007 ◽  
Vol 129 (4) ◽  
pp. 860-867 ◽  
Author(s):  
R. I. Raja Hamzah ◽  
D. Mba
Keyword(s):  
Acoustic Emission ◽  
Film Thickness ◽  
Liquid Nitrogen ◽  
Operating Temperature ◽  
Gear Wheel ◽  
Operating Conditions ◽  
Experimental Results ◽  
Asperity Contact ◽  
Spur Gears ◽  
Meshing Gears

This paper presents experimental results correlating acoustic emission (AE) activity and the specific film thickness (λ) for operational spur gears. This relationship was established by spraying liquid nitrogen onto a rotating gear wheel, thereby reducing its operating temperature and controlling the specific film thickness for a range of load and speed conditions. It is concluded that the level of AE activity is dependent on the specific film thickness and the source of AE during meshing is predominately due to asperity contact. Furthermore, measurements of AE activity may offer an opportunity to quantify the level of asperity contact for meshing gears under a range of operating conditions.

A Mixed-Lubrication Study of Journal Bearing Conformal Contacts

1997 ◽  
Vol 119 (3) ◽  
pp. 456-461 ◽  
Author(s):  
Qian (Jane) Wang ◽  
Fanghui Shi ◽  
Si C. Lee
Keyword(s):  
Film Thickness ◽  
Contact Pressure ◽  
Contact Area ◽  
Numerical Solutions ◽  
Mixed Lubrication ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Lubricant Film Thickness ◽  
Asperity Contacts

Numerical analyses of finite journal bearings operating with large eccentricity ratios were conducted to better understand the mixed lubrication phenomena in conformal contacts. The average Reynolds equation derived by Patir and Cheng was utilized in the lubrication analysis. The influence function, calculated numerically using the finite element method, was employed to compute the bearing deformation. The effects of bearing surface roughness were incorporated in the present analysis for the calculations of the asperity contact pressure and the asperity contact area. The numerical solutions of the hydrodynamic and asperity contact pressures, lubricant film thickness, and asperity contact area were evaluated based on a simulated bearing-journal geometry. The calculations revealed that the asperity contact pressure may vary significantly along both the width and the circumferential directions. It was also shown that the asperity contacts and the lubricant film thickness were strongly dependent on the bearing width, asperity orientation, and operating conditions.

Experimental Study of Real Roughness Features Within EHD Point Contacts

2005 ◽  
Author(s):  
I. Krˇupka ◽  
M. Hartl ◽  
M. Lisˇka
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Thickness Distribution ◽  
Operating Conditions ◽  
Phase Shifting ◽  
Accurate Information ◽  
Asperity Contact ◽  
Phase Shifting Interferometry ◽  
Wide Range ◽  
Surface Irregularities

A combination of thin film colorimetric interferometry and phase shifting interferometry has been used to study the effect of slide-to-roll ratio on the micro-elastohydrodynamic action and asperity-contact mechanism on the real asperity scale. The phase shifting interferometry was used to measure in-situ initial undeformed rough surface profiles and thin film colorimetric interferometry provided accurate information about micro-EHD film thickness behaviour over a wide range of operating conditions. Lubricant film thickness distribution within mixed EHD contact has been found to change significantly as a function of a slide-roll ratio. A high resolution color camera has enabled a closer look at film thickness changes in the vicinity of surface irregularities that helped to describe these processes in detail. Obtained results indicate the presence of either a boundary film less than 1 nm thick or some solid-like contact in front of roughness features for positive slide to roll ratios. No such a local film thickness reduction has been found for negative slide-to-roll ratio conditions.

scholarly journals Ultrasonic Measurement for Film Thickness and Solid Contact in Elastohydrodynamic Lubrication

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
R. S. Dwyer-Joyce ◽  
T. Reddyhoff ◽  
J. Zhu
Keyword(s):  
Film Thickness ◽  
Bulk Modulus ◽  
Liquid Layer ◽  
Contact Stiffness ◽  
Point Contact ◽  
Ultrasonic Waves ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Solid Contact ◽  
Mixed Regime

The reflection of ultrasound can be used to determine oil film thickness in elastohydrodynamic lubricated (EHL) contacts if the opposing surfaces are fully separated by the liquid layer. The proportion of the wave amplitude reflected depends on the stiffness of the liquid layer, which is a function of its bulk modulus and thickness. However, in many practical applications, boundary or mixed film lubrication is a common occurrence as the nominal thickness of the separating film is of a similar order to the height of the surface asperities. The reflection is then dependent on both the liquid contact and solid contact parts and the total interfacial stiffness is the controlling parameter. In this paper an investigation was carried to study the reflection of ultrasonic waves from the lubricated contact between a sliding steel ball and a flat steel disc when substantial solid contact occurs. To interpret the ultrasonic reflection results, a mixed regime model for a circular point contact was established. The liquid film stiffness was calculated by using a predicted film thickness and a bulk modulus estimated from published rheological models of lubricants under high pressure. Solid contact stiffness was predicted using a statistical rough surface contact model. Under all operating conditions, the prediction of fluid stiffness was found to be much greater than the solid contact stiffness. The total stiffness predicted by the model showed good agreement with experimental measurements for kinematic cases. The model was used to separate the stiffness contributions from the asperity contact part and lubricant layer part from the experimental data. For contact pressures ranging from 0.42 to 0.84 GPa and sliding speed from zero to 2 m/s, the film thickness was found to vary from 0.01 to 0.8 μm, and the proportion of the load supported by asperity contact varied from 50% to 0%.

Effect of shape/size and distribution of microgeometries of textures on tribo-performance of crankpin bearing

2021 ◽  
pp. 135065012110105
Author(s):  
Nguyen Van Liem ◽  
Wu Zhenpeng ◽  
Jiao Renqiang
Keyword(s):  
Friction Coefficient ◽  
Friction Force ◽  
Contact Force ◽  
Distribution Density ◽  
Hydrodynamic Lubrication ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Combined Model ◽  
Obvious Effect ◽  
Area Density

The effect of the shape/size and distribution of microgeometries of textures on improving the tribo-performance of crankpin bearing is proposed. Based on a combined model of the slider-crank mechanism dynamic and hydrodynamic lubrication, the distribution density, area density, and shape of spherical textures, square-cylindrical textures, wedge-shaped textures, and a hybrid between spherical texture and square-cylindrical texture on the crankpin bearing's tribo-performance are investigated under different operating conditions of the engine. The tribological characteristic of the crankpin bearing is then evaluated via the indexes of the oil film pressure p, asperity contact force, friction force, and friction coefficient of the crankpin bearing. The research results show that the distribution density with n = 12 and m = 6, and area density with α = 30% of various microtextures have an obvious effect on ameliorating the crankpin bearings tribo-performance. Concurrently, at the mixed lubrication region, the shape of the square-cylindrical texture on improving the tribo-performance is better than the other shapes of the spherical texture, wedge-shaped texture, and spherical and square-cylindrical texture. Particularly, all the average values of the asperity contact force, friction force, and friction coefficient with a square-cylindrical texture are significantly reduced by 14.6%, 19.5%, and 34.5%, respectively, in comparison without microtextures. Therefore, the microtextures of the spherical texture applied on the bearing surface can contribute to enhance the durability and decrease the friction power loss of the engine.

scholarly journals The effect of liquid nitrogen cooling on coal cracking and mechanical properties

2018 ◽  
Vol 36 (6) ◽  
pp. 1609-1628 ◽  
Author(s):  
Chengzheng Cai ◽  
Feng Gao ◽  
Yugui Yang
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Acoustic Emission ◽  
Liquid Nitrogen ◽  
Wave Velocity ◽  
Count Rate ◽  
Initial State ◽  
Nitrogen Injection ◽  
Strength Tests ◽  
Liquid Nitrogen Cooling

Liquid nitrogen is a type of super-cryogenic fluid, which can cause the reservoir temperature to decrease significantly and thereby induce formation rock damage and cracking when it is injected into the wellbore as fracturing fluid. An experimental set-up was designed to monitor the acoustic emission signals of coal during its contact with cryogenic liquid nitrogen. Ultrasonic and tensile strength tests were then performed to investigate the effect of liquid nitrogen cooling on coal cracking and the changes in mechanical properties thereof. The results showed that acoustic emission phenomena occurred immediately as the coal sample came into contact with liquid nitrogen. This indicated that evident damage and cracking were induced by liquid nitrogen cooling. During liquid nitrogen injection, the ring-down count rate was high, and the cumulative ring-down counts also increased rapidly. Both the ring-down count rate and the cumulative ring-down counts during liquid nitrogen injection were much greater than those in the post-injection period. Liquid nitrogen cooling caused the micro-fissures inside the coal to expand, leading to a decrease in wave velocity and the deterioration in mechanical strength. The wave velocity, which was measured as soon as the sample was removed from the liquid nitrogen (i.e. the wave velocity was recorded in the cooling state), decreased by 14.46% on average. As the cryogenic samples recovered to room temperature, this value increased to 18.69%. In tensile strength tests, the tensile strengths of samples in cooling and cool-treated states were (on average) 17.39 and 31.43% less than those in initial state. These indicated that both during the cooling and heating processes, damage and cracking were generated within these coal samples, resulting in the acoustic emission phenomenon as well as the decrease in wave velocity and tensile strength.

An Accurate Solution of the Gas Lubricated, Flat Sector Thrust Bearing

1977 ◽  
Vol 99 (1) ◽  
pp. 82-88 ◽  
Author(s):  
I. Etsion ◽  
D. P. Fleming
Keyword(s):  
Film Thickness ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Thickness Distribution ◽  
Maximum Load ◽  
Accurate Solution ◽  
Operating Conditions ◽  
Thrust Bearings ◽  
Practical Design ◽  
Minimum Film Thickness

A flat sector shaped pad geometry for gas lubricated thrust bearings is analyzed considering both pitch and roll angles of the pad and the true film thickness distribution. Maximum load capacity is achieved when the pad is tilted so as to create a uniform minimum film thickness along the pad trailing edge. Performance characteristics for various geometries and operating conditions of gas thrust bearings are presented in the form of design curves. A comparison is made with the rectangular slider approximation. It is found that this approximation is unsafe for practical design, since it always overestimates load capacity.

Sign in / Sign up

Export Citation Format

Share Document