Sticking Phenomena Research Articles

Uncovering the mechanism of Tenofovir amibufenamide fumarate punch sticking by combining direct compression experiment and computational simulation

Punch sticking during tablet manufacturing is a prevalent issue for many active pharmaceutical ingredients (APIs) encountered by the pharmaceutical industry. Tenofovir amibufenamide fumarate (TMF), a heavyweight drug for the treatment of hepatitis B, was selected as a model drug due to its tendency to punch sticking during tablet compression. In this study, the cause of sticking was explored by investigating crystal habits, excipients and structure characteristics. The difference in sticking of three crystal habits can be visually represented through direct compression experiments on powdered samples and analysis of crystal surfaces. The excipients play a direct role in decreasing the probability of sticking, and the extent of sticking can be assessed by measuring the tensile strength of the tablet. Additionally, the plasticity index was utilized to theoretically analyze the potential enhancements of four excipients. These experimental results indicate that the block-shaped crystals have superior ability of anti-sticking and that suitable excipients can significantly improve the sticking situation of TMF. Ultimately, the phenomenon of punch sticking was additionally examined through computational calculations, focusing on the mechanical characteristics of TMF molecules and intermolecular interactions. The strategy of combining experiments and simulation calculations has broader significance for the study of drug production.

Oblique impact dynamic analysis of wedge friction damper with Dankowicz dynamic friction

<abstract> <p>Aiming at the wedge friction damper for freight train bogie, considering Dankowicz dynamic friction, the mechanical model of a three-degree-of-freedom inclined impact vibration system with gap and dynamic friction, is simplified. The mechanical model of the system is established, the motion equation of the system is obtained, and the motion state and conditions of the system are analyzed. The Poincare map is constructed by selecting a fixed collision section, and the response of the system is solved by the fourth-order Runge-Kutta numerical method with variable step size. The transition process of the system motion and the phenomenon of sticking and chatter are analyzed by numerical simulation when the external excitation frequency changes. The results show that: 1) Under certain parameters, with the change of excitation frequency, the system undergoes periodic doubling bifurcation, inverse periodic doubling bifurcation, Grazing bifurcation and Hopf bifurcation, and there is a "periodic bubble" phenomenon in the system motion. When the system excitation frequency is between 3.35–3.55, 4.425–6.12, and 7.34–7.758, the system motion has chatter and sticking phenomena; when the system excitation frequency is between 1.75–3.24 and 3.92–4.425, the sticking phenomenon disappears, and only the chatter phenomenon exists. 2) When other parameters remain unchanged, and the mass ratio decreases from 1.15 to 0.85, nonlinear dynamic phenomena such as the transition between periodic bubbles and chaotic bubbles will be found. In this paper, the bifurcation and chaos characteristics of the impact vibration system of the wedge friction damper are studied, and the rich friction-induced vibration forms such as chatter and sticking are revealed, which provides a reference for improving the stability of vehicle operation and the selection of parameters in vehicle vibration reduction design in engineering practice.</p> </abstract>

Hydrothermal carbonization of sludge: Effect of steam release on products properties and wall sticking phenomenon

In order to understand hydrothermal carbonization (HTC) process more effectively, the effect of steam-release process at different temperatures (160, 180, 200, and 220 °C) on product properties and wall sticking phenomenon were studied. Experimental results indicated that the approximate equilibrium moisture content (AEMC) of hydrochar obtained with (SRHC) and without (HC) steam-release process were both negatively correlated with zeta potential (R = −0.96326 for HC and R = −0.95825 for SRHC). More importantly, the absolute value of the zeta potential of SRHC was lower than HC indicating steam-release process significantly improve dewatering performance of sludge after HTC treatment. The results of FE-SEM and N2 adsorption–desorption experiments indicated steam-release process was favorable for the formation of porous hydrochar. The variation of surface functional groups showed that the intensity of all peaks in SRHC was significantly lower than HC, indicating steam-release process which significantly affects surface chemical properties of samples. As for liquid, TOC, TN and COD value of the condensate were lower than filtrate, indicating steam-release process which produces “cleaner” condensed liquid with less organic matter content. The wall sticking phenomenon in the steam-release process became more severe with increasing temperature and the amount of sticky wall sample (SWS) increased from 0.392 g at 160 °C to 2.131 g at 220 °C, which indicated that temperature was key factor affecting the sticking phenomenon on the inside wall of the reactor. The contact angle of SWS and SRHC decreased from 60.083° and 77.283° at 160 °C to 51.317° and 67.967° at 220 °C, and the polar free energy of SWS (12.52–14.00 mN/m) was significantly higher than that of SRHC (1.85–4.53 mN/m), indicating increasing hydrophobicity and reducing polar free energy of sample were key factors in improving sticking phenomenon.

Numerical analysis of frictional contact between crack lips in the framework of Linear Elastic Fracture Mechanics by a mesh-free approach

In this paper, a mesh-free approach is presented for the numerical analysis of frictional contact in the framework of Linear Elastic Fracture Mechanics (LEFM). This approach (WLS-HOCM) is obtained by combining a Weighted Least Square approximation (WLS) under a strong formulation with a High Order Continuation Method (HOCM), the Coulomb friction model and the visibility criterion to investigate the contact that occurs between the crack lips under compression loads. The contact between the crack lips is regarded as boundary conditions, and a regularization technique is used to replace these no-smoothed conditions with smoothed ones. We were able to avoid the numerical integration encountered in the weak formulation by using the strong formulation. The stick and slip phenomena of closed cracks are studied using numerical examples. The numerical results obtained demonstrate the effectiveness and precision of the suggested method for computing frictional self contact problems.

Correlating Electrode Degradation with Weldability of Galvanized BH 220 Steel during the Electrode Failure Process of Resistance Spot Welding

Electrode degradation in the continuous resistance spot-welding process of baked hardening (BH) 220 steel was evaluated by an electrode life test, and weldability tests were conducted by geometry feature measurement, mechanical property analysis, and electrode diameter measurement with 88 or 176 weld intervals. The analysis of weld geometry shows that the heat-affected zone (HAZ) width, nugget diameter, and nugget area tend to decrease rapidly, while the nugget height tends to increase with the weld repetitions until the welding heat input becomes too small to form an effective nugget. The maximum displacement and failure energy of the welded joints show a decreasing trend during the welding electrode failure process, while the peak load increases slightly until the 88th weld and then decreases. The cavities and pores in the nugget mainly appear after the 176th spot weld. The electrode diameter increases during welding. The reason for the increase in electrode diameter may be that the contact area between the electrode and the BH 220 steel sheets becomes smaller in the welding process, which causes the continuous sticking phenomenon between the electrode and the BH 220 steel sheets. In the absence of alloying, the edge of the electrode is geometrically deformed, while Cu–Zn–Fe alloying occurs in the area in contact with the BH 220 steel sheet.

Experimental identification of wheel-surface model parameters: various terrain conditions.

Since the wheel interaction with a certain terrain cases (asphalt, concrete) are known and well described in case of straightforward motion and non-slip and slip cornering conditions, the skid-steered wheeled vehicles case needs to be analyzed. Side-slip for various attack angle has to be investigated. The main area of interest of research that is shown in the project is energy demand calculation of skid-steered wheeled vehicles in various terrain conditions. Certain cases of all-electric vehicles with individual electric motors per wheel demand a precise assessment of longitudinal and lateral forces in order to perform the fully controlled turn. Experimental stand designed and developed by authors allows to test the wheel-surface interaction for various terrain conditions and different driving directions. Test data were acquired for dry and wet sand and granite pavement. Traction and side forces were acquired and used to identify the wheel-soil interaction model parameters for unpropelled wheel. Results in a form of time series including longitudinal and lateral forces show the relation between attack angle, load and surface conditions in terms of stick and slip phenomenon that is essential for skid-steering dynamics calculations. Measurement results are then used for calculation of longitudinal and lateral forces coefficients as a function of attack angle and vertical load. Test were performed in natural environment, thus they are affected by changeable conditions. Multiple runs are used for elimination of that influence. Described experiments are a part of the project that includes results generalization using test validated FEM model. Described work is not intended to develop new ground-tire interaction models, it is focused on numerically efficient traction effort calculation method for various conditions including passive mode—unpropelled wheel.

Measuring the Frictional Behavior and Adhesion of PET Bottles

Polyethylene terephthalate (PET), due to its excellent physical and chemical properties, has become a widely used packaging material for liquids across many consumer market segments. However, one of the most common problems met in bottle manufacturing is the pile-up of bottles during conveying, due to static electrification caused by localized friction. To minimize such phenomena, a thin lubricant layer is applied onto the bottles. The absence of a thin lubricant layer increases the risk of localized sticking phenomena and pileups. In this work, an attempt is made to study the frictional behavior of commercially available PET bottles, with and without lubrication by using a high precision and light load technique. By analyzing the complete tribological pattern of the tangential force and not just averaged values, localized sticking events can be identified. In addition, by performing indentation-retraction measurements the electrostatic forces in a bottle-to-bottle contact can be measured. By combining light load friction and adhesion methods, a better understanding of PET sticking phenomena can be achieved which then can be translated in optimizing (minimizing) the amount of lubricant to be used.

Synchronous properties of the friction phenomenon

The phenomenon of frictional slipping and sticking is one of crucial problems in mechanical engineering. This paper is focused on the numerical analysis of vibrations induced by friction in oscillator model which assumes an influence of the normal degree of freedom on the friction force. Analysis of Poincare maps, time courses and corresponding spectrum of Lyapunov exponents of the proposed three degrees of freedom dynamical system is demonstrated. It is revealed that the friction force, acting on the main slider, reflects dynamic behavior of the system response, i.e., some synchronous correlation between them is observed, even in the range of hyperchaotic behavior of the system, characterized by two positive Lyapunov exponents. On the other hand, an interesting effect of the coexistence of irregular friction force at the contact point of the frictional brush and ground surface with the regular response of the system in the quasi-periodic regime is reported.

Experimental study of machined surface quality in ultrasonic vibration-assisted turning of 5A06 Al-Mg alloy

The 5A06 Al-Mg alloy is a soft material, and the phenomenon of knife sticking is extremely serious during cutting, likewise, it is easy to generate build-up edges. Therefore, it is difficult to acquire good surface quality in turning. For this purpose, the ultrasonic theory and cutting theory are fully combined in this study, and the machining mechanism of conventional turning (CT) is changed by applying ultrasonic vibration (UV) to the cutting tool, so as to build up the machining results. The turning experiments of 5A06 Al-Mg alloy with or without UV are carried out under different process parameters, and through which the effects of ultrasonic amplitude (UA), feed rate (FR), cutting depth (CD) and cutting speed (CS) on the surface roughness of machined workpiece are investigated and analyzed. The consequences show that the process parameters have a different degree of effect on surface roughness. And there are special process parameters suitable for UV assisted turning (UAT), under which the processing results of UAT is obviously better than that of CT. In addition, it is found that by contrast experiment of surface topography under ideal process parameters built-up edges, surface scratches and other phenomena are not easy to arise in UAT to obtain the better surface topography than CT.

Direct assembly of nanowires by electron beam-induced dielectrophoresis

Controllable self-assembly is an important tool to investigate interactions between nanoscale objects. Here we present an assembly strategy based on 3D aligned silicon nanowires. By illuminating the tips of nanowires locally by a focused electron beam, an attractive dielectrophoretic force can be induced, leading to elastic deformations and sticking between adjacent nanowires. The whole process is performed feasibly inside a vacuum environment free from capillary or hydrodynamic forces. Assembly mechanisms are discussed for nanowires in both one and two layers, and various ordered organizations are presented. With the help of moisture treatment, a hierarchical assembly can also be achieved. Notably, an unsynchronized assembly is observed in two layers of nanowires. This study helps with a better understanding of nanoscale sticking phenomena and electrostatic actuations in nanoelectromechanical systems, besides, it also provides possibilities to probe quantum effects like Casimir forces and phonon heat transport in a vacuum gap.

A heat equation with memory: Large-time behavior

We study the large-time behavior in all Lp norms of solutions to a heat equation with a Caputo α-time derivative posed in RN (0<α<1). These are known as subdiffusion equations. The initial data are assumed to be integrable, and, when required, to be also in Lp.We find that the decay rate in all Lp norms, 1≤p≤∞, depends greatly on the space-time scale under consideration. This result explains in particular the so called “critical dimension phenomenon” (cf. [21]).Moreover, we find the final profiles (that strongly depend on the scale). The most striking result states that in compact sets the final profile (in all Lp norms) is a multiple of the Newtonian potential of the initial datum.Our results are very different from the ones for classical diffusion equations and show that, in accordance with the physics they have been proposed for, these are good models for particle systems with sticking and trapping phenomena or fluids with memory.

On formation of dry spots in heated liquid films

Here, the phenomenon of food sticking when frying in a frying pan is experimentally explained. Thermocapillary convection causes a dry spot formation in the center of the frying pan upon heating of the sunflower oil film. It is shown that the speed of formation of a dry spot is similar to the speed of receding motion of the edge of a droplet upon impact and spreading on a solid surface. This allows theoretical determination of the speed of dewetting. For the thin liquid film flowing vertically over a solid surface, the critical volumetric flow rate qcr partitions two regimes: metastable or subcritical, when small perturbation of the film free surface results in the film rupture (q &amp;lt; qcr) and stable or supercritical at q &amp;gt; qcr. For the falling thin liquid film, the critical volumetric flow rate qcr partitions two regimes: metastable or subcritical (q &amp;lt; qcr) and stable or supercritical at q &amp;gt; qcr. At q &amp;lt; qcr, small deformations of the film free surface result in the film rupture. For the case of the temperature distribution in the form of a unit step function, the fundamental solution G1(x) describing the deformation of the film free surface has been derived by the perturbation technique. This solution is important by itself since it describes the most “dangerous” film surface profile at a prescribed value of the temperature drop. For an arbitrary surface temperature distribution θ (ξ), the convolution of G1(ξ) and θ ′(ξ) yields the film thickness profile.

Influence of Tool Offset on Performance of Thin Al–Cu Dissimilar Metal Friction Stir Butt Welded Joint

The 1-mm-thick Al to Cu friction stir welding is successfully performed at the tool offsets toward Al side ranging from 0 to 2 mm. With increasing tool offset, the phenomenon of material sticking to tool shoulder surface is restricted and the area of Al–Cu mixing zone is reduced progressively. As the tool offset is increased from 0 to 1 mm, the weld shows a variation of intermetallic phases from CuAl2 + Cu9Al4 to CuAl2 and exhibits a lowering in hardness and tensile properties. The 2-mm-offset weld without intermetallic phases discernible exhibits the highest hardness due to the thinness of Cu lamellar and Al-rich compound layers, and the joint featured by a failure at the relatively soft region adjacent to harder Al–Cu mixing zone in a ductile pattern shows the best tensile strength equivalent to 80% of that of the base material.

Estimation of reservoir lithology in field “A” using modeling of anisotropy parameter

The heterogeneity and anisotropy of rocks in the field is a necessity. Moreover, the existence of clay and carbonate sediment in Indonesia almost dominate the existing oil and gas reservoir. Ironically, the processing of seismic data is still much done by treating reservoir rocks as an isotropic homogeneous medium. Inaccuracies of results, therefore, always haunt the failure of exploration. Hockey stick phenomenon is the result of anisotropic medium that often appears on the far offset. Demand for the implementation of an anisotropic rock medium is now increasing and more important amid the exhaustive oil and gas reserves. NMO correction by using hyperbolic travel time on anisotropic media still displays the phenomenon of hockey stick at the remote offset. Usually this phenomenon will be muted on the processing of seismic data with the approach of isotropic earth models. This will result in the loss of some lithologic information. Therefore, this study was conducted using anisotropic approach to reduce residual moveout for data which has a very long offset. The method is to calculate the anisotropy parameter model of η which is controlled by core data. The results of this study showed that the Alkhalifah and Tsvankin method of non-hyperbolic travel time was better in the NMO correction for anisotropy medium with a long offset compared to the method of hyperbolic travel time. In addition, Alkhalifah and Tsvankin method can also estimate the lithology of a reservoir. The value of anisotropy parameter η from the equation itself has the same pattern as the gamma ray log. In reservoir, the sand has negative η value and shale has positive η value.

Effect of slime and dust emission on micro-cutting when processing carbon-carbon composites

Results of theoretical and experimental studies aimed at establishing features of micro-cutting with abrasive grains characterized by active emission of slime and dust particles were presented. The slime particles are just partially withdrawn from the interaction zone and partially change surfaces of the tool and the workpiece of a carbon composite material, in particular, of carbon-carbon and carbon-polymer groups. The above materials possessing a complex of unique physical and mechanical properties are used in high-tech production though composites remain difficult to process materials. The problems manifest themselves to their utmost in making various apertures, shoulders, cutting of holes, processing edges. The study has shown that the phenomenon of dust and slime emission in abrasive processing of carbon-based non-dense composites and plastics results from sliding fracture and cyclic weakening of the surface non-dense layer which exhibits quasi-brittle properties under the action of fast-moving micro-indenters. Conditionality of the average slime particle sizes by normal stresses in the cutting zone and the magnitude of protrusion of diamond grains above the cutting surface of the tool was revealed. Since it was found that the particles formed during cutting are only partially withdrawn outside the cutting zone and the degree of removal decreases with an increase in the processing time, a conclusion on the cause of change in the state of the tool surface was drawn. The remaining slime and dirt change topography of the surface which results in the cutting zone temperature rise to critical values. It was shown that the use of tools with cyclic advance makes it possible to partially improve the condition of material processing which is relevant for the implementation of the processes of ring diamond drilling, processing with diamond saw blades. It was proved that the intermittent application of areas of the diamond-bearing layer reduces the phenomenon of dirt particle sticking to the surface of the working tool. Thus, the tool stays free of dirt for longer and the machining process is more efficient

Oblique derivative problems and Feller semigroups with discontinuous coefficients

This paper is devoted to the functional analytic approach to the problem of existence of Markov processes with an oblique derivative boundary condition for second-order, uniformly elliptic differential operators with discontinuous coefficients. More precisely, we construct Feller semigroups associated with absorption, reflection, drift and sticking (or viscosity) phenomena at the boundary. The approach here is distinguished by the extensive use of the ideas and techniques characteristic of the recent developments in the Calderon–Zygmund theory of singular integral operators with non-smooth kernels.

License Plate Character Segmentation Algorithm Based on Improved Regression Model

Many character segmentation algorithms in license plate recognition system are not very good for segmentation of complex characters, and there is a phenomenon of character sticking, which results in slow recognition speed and not very good recognition effect of the license plate with complex characters. For such problems, a segmentation algorithm based on the improved regression model on statistical characteristics is presented. Compared with other algorithms, experimental results show that less time is consumed and segmentation effect is better. The recognition rate of license plate can be improved effectively.

PMSM speed control method based on Kalman filter and dynamic fuzzy control in electric vehicle

Electric vehicles are widely used today, however, the phenomenon of sticking and shaking often occurs during starting, crawling and shifting. The cause of this phenomenon from the perspective of motor control was analyzed in this paper. In view of the disadvantages of low measurement accuracy of position sensor and traditional PID control, a dynamic fuzzy control speed control system based on Kalman filter optimal measurement was proposed. The principle of the system is simple, with good dynamic and static performance, which improves the accuracy of vehicle starting, crawling and gear shifting, and shortens the adjustment time.

Marine Propeller Shaft Bearings under Low-Speed Conditions: Water vs. Oil Lubrication

The bearings used in shipbuilding, hydropower, and water pumps have undergone a metamorphosis in recent decades. Due to environmental regulations, lubrication with grease or mineral oil is prohibited. Thus, the standard solutions include water-lubricated bearings with polymer bushings or sealed systems lubricated with oil. When properly designed, assembled, and operated, bearings can operate reliably for years. However, specific operating conditions, such as a low rotational speed of the shaft, may result in intensive wear and premature failure. In this study, four sliding bearings approved for use in shipbuilding were experimentally tested. The test results showed that the choice of the bearing type has a key effect on friction during low-speed operation. Some of the tested bearings had significant static friction with intense slip–stick phenomena; they should not be used in applications requiring low-speed operation.

Variations in Reaction Force of the Center of a Sleeve depending on Coiling Conditions in a Coiling Process

Coiling is a process to wind a steel strip around a mandrel or sleeve. To wind a coil safely and efficiently, coiling tension σ and coiling speed v are important, but their relationships with the outcome have not been established clearly. Especially, too non-linear behavior among contact layers has been treated as a big task. To be possible to operate the coiling flexibly, this paper establishes a finite element model of the coiling process, and suggests that reaction force FR on the sleeve is a key variable in the dynamic characteristics of the coiling process to know slip and stick (S&S) phenomenon among contact layers according σ and v. Based on the finite element model, FR is investigated by frequency analysis and parametric analysis. Even though FR signal is too non-linear to be described clearly, this paper suggests the coiling status criterion by checking the direction cosine θload of the FR vector in the time–frequency domain according to σ and v, and by separating frequencies of the FR signal into the natural frequencies of the strip, and the slip phenomenon between the sleeve and the strip. Epecially, critical σ that changes the general frequency distribution of FR was selected by using mean squared coherence and used to calculate minimum required σ at each the outer radius ro of a wound steel coil. When σ is sufficient, θload of the FR vector is applied at ~ 0° horizontally to the center of the sleeve by simulating the finite element models and by comparing dynamic responses to a 1-DOF mass–spring system with the S&S phenomenon. As σ increases, unsteady vibrations of FR also decrease. However, when σ decreases, the natural frequencies of the strip predominate. This trend is reversed in case of v. Based on these facts, a novel σ profile according to ro is derived in case of the real operating condition. The results of this paper suggest that a sensor for measuring displacement, velocity, or acceleration should be installed on the housing of the bearing to detect the unusual coiling vibrations by checking the translational vibrations of the housing and by analyzing vibrations with this method in real time. Moreover, the suggested σ profile reduces radial stress on the sleeve, so maintenance costs and fraction defective can be minimized by preventing the sleeve and the coil from dents.