Complicated tribological behavior occurs when human fingers touch and perceive the surfaces of objects.In this process,people use their exploration style with different conditions,such as contact load,sliding speed,sl...Complicated tribological behavior occurs when human fingers touch and perceive the surfaces of objects.In this process,people use their exploration style with different conditions,such as contact load,sliding speed,sliding direction,and angle of orientation between fingers and object surface consciously or unconsciously.This work addressed interlaboratory experimental devices for finger active and passive tactile friction analysis,showing two types of finger movement.In active sliding experiment,the participant slid their finger freely against the object surface,requiring the subject to control the motion conditions themselves.For passive sliding experiments,these motion conditions were adjusted by the device.Several analysis parameters,such as contact force,vibration acceleration signals,vibration magnitude,and fingerprint deformation were recorded simultaneously.Noticeable friction differences were observed when comparing active sliding and passive sliding.For passive sliding,stick-slip behavior occurred when sliding in the distal direction,evidenced by observing the friction force and the related deformation of the fingerprint ridges.The employed devices showed good repeatability and high reliability,which enriched the design of the experimental platform and provided guidance to the standardization research in the field of tactile friction.展开更多
In this study, the performance against erosive wear of PVD TiN (titanium nitride) coating was evaluated using an erosion test rig similar to that described in the standard ASTM G76-95. This coating normally has variou...In this study, the performance against erosive wear of PVD TiN (titanium nitride) coating was evaluated using an erosion test rig similar to that described in the standard ASTM G76-95. This coating normally has various industrial applications such as tapping, drilling, dry machining and punching. Angular silicon carbide (SiC) was used as an abrasive particle with a grain size of 350-450 μm. Erosion tests were carried out using different incident angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s, an abrasive flow rate of 0.7 ± 0.5 g/min, and the test temperature was between 35°C and 40°C. The particle velocity and the abrasive flow rate were low in all of the tests to reduce the interaction between the incident and the rebounding particles in the system. The surfaces were examined with a scanning electron microscope (SEM) to characterize the erosive damage. The wear mechanisms identified were brittle fracture characterized by radial cracks on the surface by multiple impact and a few pits at 30°, while a few cracks and the formation of craters in random positions were observed at angles near or at 90°. Elliptical scars were observed at 30° and 45°, which are a characteristic feature when the specimens are impacted at low-incident angles (α ≤ 45°) whereas a roughly circular scar was seen at 60° and 90°. In addition, roughness variations were analyzed using atomic force microscopy (AFM), before and after the erosion tests, and the results exhibited an increase in the roughness as the TiN samples were impacted at angles near or at 90°.展开更多
It is increasingly important to monitor sliding interfaces within machines,since this is where both energy is lost,and failures occur.Acoustic emission(AE)techniques offer a way to monitor contacts remotely without re...It is increasingly important to monitor sliding interfaces within machines,since this is where both energy is lost,and failures occur.Acoustic emission(AE)techniques offer a way to monitor contacts remotely without requiring transparent or electrically conductive materials.However,acoustic data from sliding contacts is notoriously complex and difficult to interpret.Herein,we simultaneously measure coefficient of friction(with a conventional force transducer)and acoustic emission(with a piezoelectric sensor and high acquisition rate digitizer)produced by a steel‒steel rubbing contact.Acquired data is then used to train machine learning(ML)algorithms(e.g.,Gaussian process regression(GPR)and support vector machine(SVM))to correlated acoustic emission with friction.ML training requires the dense AE data to first be reduced in size and a range of processing techniques are assessed for this(e.g.,down-sampling,averaging,fast Fourier transforms(FFTs),histograms).Next,fresh,unseen AE data is given to the trained model and the resulting friction predictions are compared with the directly measured friction.There is excellent agreement between the measured and predicted friction when the GPR model is used on AE histogram data,with root mean square(RMS)errors as low as 0.03 and Pearson correlation coefficients reaching 0.8.Moreover,predictions remain accurate despite changes in test conditions such as normal load,reciprocating frequency,and stroke length.This paves the way for remote,acoustic measurements of friction in inaccessible locations within machinery to increase mechanical efficiency and avoid costly failure/needless maintenance.展开更多
Preventing the accretion of droplets on surfaces is vital and slippery liquid-infused porous surfaces(SLIPS)have promising application prospects,such as surface self-cleaning and droplet transportation.In this work,co...Preventing the accretion of droplets on surfaces is vital and slippery liquid-infused porous surfaces(SLIPS)have promising application prospects,such as surface self-cleaning and droplet transportation.In this work,controllable self-transport of bouncing droplets on ultraslippery surfaces with wedge-shaped grooves is reported.The impact behaviors of droplets on SLIPS under various impact velocities and diameters are explored,which can be classified as hover,total bounce,partial bounce,Worthington jet,and crush.SLIPS with wedge-shaped grooves were designed to transport accreted droplets.An energy and transport model is established to explain the impact and self-transport mechanism,where the Laplace pressure and moving resistance between droplets play a key role.Finally,SLIPS with branched wedge-shaped grooves were designed for droplet self-transport and demonstrated advantages.This work provides a general reference for spontaneous motion control of sessile droplets,droplets with initial impacting velocity,or even liquid films.展开更多
In stress-augmented thermal activation, the activation energy barrier that controls the rate of atomic and molecular processes is reduced by the application of stress, with the result that the rate of these processes ...In stress-augmented thermal activation, the activation energy barrier that controls the rate of atomic and molecular processes is reduced by the application of stress, with the result that the rate of these processes increases exponentially with applied stress. This concept has particular relevance to Tribology, and since its development in the early twentieth century, it has been applied to develop important models of plastic flow, sliding friction, rheology, wear, and tribochemistry. This paper reviews the development of stress-augmented thermal activation and its application to all of these areas of Tribology. The strengths and limitations of the approach are then discussed and future directions considered. From the scientific point of view, the concept of stress-augmented thermal activation is important since it enables the development of models that describe macroscale tribological performance, such as friction coefficient or tribofilm formation, in terms of the structure and behaviour of individual atoms and molecules. This both helps us understand these processes at a fundamental level and also provides tools for the informed design of lubricants and surfaces.展开更多
This paper describes a study of point contact elastohydrodynamic(EHD)lubrication behavior at high speeds(up to 20 m s1).Central film thicknesses were measured by optical interferometry device.The influence of slide-ro...This paper describes a study of point contact elastohydrodynamic(EHD)lubrication behavior at high speeds(up to 20 m s1).Central film thicknesses were measured by optical interferometry device.The influence of slide-roll ratio and operating temperature on the central film thickness was determined.The influence of thermal effects on the reduction of film thickness was discussed via the analysis of numerical simulation method considering thermal effects.Subsequently,the experimental data was used to amend a set of unified parameters for the thermal corrections for different types of oil at high speeds.展开更多
基金Supported by the China Scholarship Council (Grant No.201907000020)the 111 Project (Grant No.B20008)。
文摘Complicated tribological behavior occurs when human fingers touch and perceive the surfaces of objects.In this process,people use their exploration style with different conditions,such as contact load,sliding speed,sliding direction,and angle of orientation between fingers and object surface consciously or unconsciously.This work addressed interlaboratory experimental devices for finger active and passive tactile friction analysis,showing two types of finger movement.In active sliding experiment,the participant slid their finger freely against the object surface,requiring the subject to control the motion conditions themselves.For passive sliding experiments,these motion conditions were adjusted by the device.Several analysis parameters,such as contact force,vibration acceleration signals,vibration magnitude,and fingerprint deformation were recorded simultaneously.Noticeable friction differences were observed when comparing active sliding and passive sliding.For passive sliding,stick-slip behavior occurred when sliding in the distal direction,evidenced by observing the friction force and the related deformation of the fingerprint ridges.The employed devices showed good repeatability and high reliability,which enriched the design of the experimental platform and provided guidance to the standardization research in the field of tactile friction.
文摘In this study, the performance against erosive wear of PVD TiN (titanium nitride) coating was evaluated using an erosion test rig similar to that described in the standard ASTM G76-95. This coating normally has various industrial applications such as tapping, drilling, dry machining and punching. Angular silicon carbide (SiC) was used as an abrasive particle with a grain size of 350-450 μm. Erosion tests were carried out using different incident angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s, an abrasive flow rate of 0.7 ± 0.5 g/min, and the test temperature was between 35°C and 40°C. The particle velocity and the abrasive flow rate were low in all of the tests to reduce the interaction between the incident and the rebounding particles in the system. The surfaces were examined with a scanning electron microscope (SEM) to characterize the erosive damage. The wear mechanisms identified were brittle fracture characterized by radial cracks on the surface by multiple impact and a few pits at 30°, while a few cracks and the formation of craters in random positions were observed at angles near or at 90°. Elliptical scars were observed at 30° and 45°, which are a characteristic feature when the specimens are impacted at low-incident angles (α ≤ 45°) whereas a roughly circular scar was seen at 60° and 90°. In addition, roughness variations were analyzed using atomic force microscopy (AFM), before and after the erosion tests, and the results exhibited an increase in the roughness as the TiN samples were impacted at angles near or at 90°.
文摘It is increasingly important to monitor sliding interfaces within machines,since this is where both energy is lost,and failures occur.Acoustic emission(AE)techniques offer a way to monitor contacts remotely without requiring transparent or electrically conductive materials.However,acoustic data from sliding contacts is notoriously complex and difficult to interpret.Herein,we simultaneously measure coefficient of friction(with a conventional force transducer)and acoustic emission(with a piezoelectric sensor and high acquisition rate digitizer)produced by a steel‒steel rubbing contact.Acquired data is then used to train machine learning(ML)algorithms(e.g.,Gaussian process regression(GPR)and support vector machine(SVM))to correlated acoustic emission with friction.ML training requires the dense AE data to first be reduced in size and a range of processing techniques are assessed for this(e.g.,down-sampling,averaging,fast Fourier transforms(FFTs),histograms).Next,fresh,unseen AE data is given to the trained model and the resulting friction predictions are compared with the directly measured friction.There is excellent agreement between the measured and predicted friction when the GPR model is used on AE histogram data,with root mean square(RMS)errors as low as 0.03 and Pearson correlation coefficients reaching 0.8.Moreover,predictions remain accurate despite changes in test conditions such as normal load,reciprocating frequency,and stroke length.This paves the way for remote,acoustic measurements of friction in inaccessible locations within machinery to increase mechanical efficiency and avoid costly failure/needless maintenance.
基金the support from the National Natural Science Foundation of China(No.51805252)Qingwen Dai acknowledges the support from the Alexander von Humboldt Foundation.Especially,Chuchen Yue thanks Kai Zhuang for critical discussions.
文摘Preventing the accretion of droplets on surfaces is vital and slippery liquid-infused porous surfaces(SLIPS)have promising application prospects,such as surface self-cleaning and droplet transportation.In this work,controllable self-transport of bouncing droplets on ultraslippery surfaces with wedge-shaped grooves is reported.The impact behaviors of droplets on SLIPS under various impact velocities and diameters are explored,which can be classified as hover,total bounce,partial bounce,Worthington jet,and crush.SLIPS with wedge-shaped grooves were designed to transport accreted droplets.An energy and transport model is established to explain the impact and self-transport mechanism,where the Laplace pressure and moving resistance between droplets play a key role.Finally,SLIPS with branched wedge-shaped grooves were designed for droplet self-transport and demonstrated advantages.This work provides a general reference for spontaneous motion control of sessile droplets,droplets with initial impacting velocity,or even liquid films.
文摘In stress-augmented thermal activation, the activation energy barrier that controls the rate of atomic and molecular processes is reduced by the application of stress, with the result that the rate of these processes increases exponentially with applied stress. This concept has particular relevance to Tribology, and since its development in the early twentieth century, it has been applied to develop important models of plastic flow, sliding friction, rheology, wear, and tribochemistry. This paper reviews the development of stress-augmented thermal activation and its application to all of these areas of Tribology. The strengths and limitations of the approach are then discussed and future directions considered. From the scientific point of view, the concept of stress-augmented thermal activation is important since it enables the development of models that describe macroscale tribological performance, such as friction coefficient or tribofilm formation, in terms of the structure and behaviour of individual atoms and molecules. This both helps us understand these processes at a fundamental level and also provides tools for the informed design of lubricants and surfaces.
基金supported by National Nature Science Foundation of China(Grant Nos.51027007,51021064)the International Science&Technology Cooperation Project(Grant No.2011DFA70980)
文摘This paper describes a study of point contact elastohydrodynamic(EHD)lubrication behavior at high speeds(up to 20 m s1).Central film thicknesses were measured by optical interferometry device.The influence of slide-roll ratio and operating temperature on the central film thickness was determined.The influence of thermal effects on the reduction of film thickness was discussed via the analysis of numerical simulation method considering thermal effects.Subsequently,the experimental data was used to amend a set of unified parameters for the thermal corrections for different types of oil at high speeds.
