Type Friction Research Articles

Discontinuous Galerkin schemes for Stokes flow with Tresca boundary condition: iterative a posteriori error analysis

In two dimensions, we propose and analyse an iterative a posteriori error indicator for the discontinuous Galerkin finite element approximations of the Stokes equations under boundary conditions of friction type. Two sources of error are identified here, namely; the discretisation error and the linearization error. Under a smallness assumption on data, we prove that the devised error estimator is reliable. Balancing these two errors is crucial to design an adaptive strategy for mesh refinement. We illustrate the theory with some representative numerical examples.

Vertical bearing behavior and pile group effect for cemented-soil composite pile groups based on on-site experiments

Bearing characteristics and interactions of a pile group are complex. and there is almost no on-site full-scale test data for cemented-soil composite pile group. In this research, vertical static load tests were conducted on two isolated pile, two-pile group and six-pile group for long-core SDCM pile. The bearing behavior of long-core SDCM pile and the interaction between pile groups have been studied. The results indicate that the long-core SDCM single pile is a typical friction type pile, and cemented soil provides most of the lateral friction resistance for the bearing capacity. In pile groups, pile spacing is the main factor affecting the pile group effect. The model calculation results based on the equivalent pier method are verified using on-site test data and the key parameters in the pile group for long-core SDCM pile including pile spacing Sij, cemented soil Elastic modulus Ec and PHC pipe pile Elastic modulus Ep are analyzed using a mathematical model. Parameter analysis results indicate that the pile group interaction for long-core SDCM pile is mainly reflected in settlement. Group effect is inapparent at pile spacing greater than 4 D. The appropriate value of Ec and Ep are taken in the range of 1.2–1.6 GPa and 30–40 GPa.

Analysis of methods of hardening and restoration of worn parts

The restoration of worn parts is an important aspect in the field of machine repair and maintenance of machinery. It allows you to significantly reduce repair costs and is a priority issue in the development of a machine maintenance and repair system. The main causes of performance loss products are abrasive wear, fatigue breakdowns, corrosion and other types of destruction. When choosing a recovery method, the type of coupling, types of friction and operating conditions of the machines are important factors. An increase in wear resistance can be achieved by changing the chemical composition of the material, mechanical influences and the application of wear-resistant coatings.

On the existence and Lipschitz-like property of the solution map to parametric equilibrium problems governed by trifunction with applications

In this paper, we study a class of parametric equilibrium problems governed by a trifunction. We apply the Fan-KKM theorem under new type of monotonicity and coercivity conditions for trifunctions to obtain the existence result of a solution for the equilibrium problem. For the solution map of parametric equilibrium problems, we obtain the Hölder-type Lipschitz-like property relative to a closed and convex set, which generalizes some existing results in the literature. We illustrate the application of our abstract results in the study of a new model of a fluid flow problem with slip and leak boundary conditions of frictional type.

Molybdenum Disulfide (MoS2) Film Formation and Friction Properties of Molybdenum Phosphate Additive in Combined Condition with Zinc Dialkyldithiophosphate (ZnDTP)

This article describes experimental studies on low friction film formation of molybdenum phosphate (MoP) in combination with zinc dialkyldithiophosphate (ZnDTP). The spinning type friction tests were conducted, and in the test procedure, the test using ZnDTP containing oil was conducted following the test using MoP oil. The results showed that after switching to ZnDTP, the friction coefficient steeply decreased and reached approximately 0.06 in 1,353 ppm of sulfur concentration, and minimum friction coefficient depended on the concentration of sulfur in the oil with ZnDTP. Moreover, it is shown that the friction coefficient gradually increased, and that the coefficient at 1 h after switching to ZnDTP corresponded to that in ZnDTP alone. Raman spectroscopy demonstrated that, at 5 min after switching to ZnDTP, the molybdenum disulfide (MoS2) film was formed on the contact surface. Also, energy dispersive x-ray spectroscopy (EDX) analysis results indicated that at 1 h after switching to ZnDTP, the film derived from ZnDTP was composed of phosphorus, oxygen, and sulfur. These results suggest the film formation mechanism of MoS2: molybdenum oxide, such as iron (II) molybdate (FeMoO4), formed in the test of MoP, was then transformed into MoS2 by sulfur or a sulfur containing compound from ZnDTP decomposition.

Optimal investment with insurable background risk and nonlinear portfolio allocation frictions

We study optimal investment and insurance demand in a continuous-time model that combines risky assets with an insurable background risk. This risk takes the form of a jump-diffusion process that reduces the return rate of the agent's wealth. The main distinctive feature of our model is that the agent's decision on portfolio choice and insurance demand causes nonlinear friction in the dynamics of the wealth process. We use the HJB equation to find the optimal conditions for the agent to fully, partially, or totally insure against the background risk. We consider different types of friction, such as differential borrowing and lending rates. We also show a mutual-fund separation result and provide numerical examples.

“Good” and “bad” frictions in customer experience: Conceptual foundations and implications

AbstractBusinesses often strive for frictionless customer experiences, assuming that customers always desire seamless interactions. However, recent academic and practitioner discussions suggest that not all forms of friction are detrimental. Reconciling the conflicting views, we propose a framework that defines friction as simply the effort customers exert to complete tasks related to their consumption goals. Furthermore, drawing from the goal striving theory and customer experience literature, we identify and propose four types of friction based on dimensions of task desirability and task value: frustrating, constructive, preference‐based, and rewarding. Our framework challenges the prevailing business practice of eliminating all friction, as evidenced by a topic modeling analysis of announcements related to achieving frictionless customer experiences. Instead, we posit that while frustration friction should be minimized, the other three types of friction offer opportunities for businesses to enhance customer value. Particularly, we caution managers that eliminating constructive friction (i.e., customer effort in low‐desirability, high‐value tasks) may hinder value creation. We also recommend that managers find opportunities to infuse rewarding and preference‐based friction to enhance customer experience. By understanding these nuances, businesses can strike a balance between friction reduction and value optimization in their customer experience designs.

Modelling and Forecasting Interregional Migration for Multiregional Population Projections

In this paper we focus on modelling and forecasting gross interregional migration in a way that can be embedded within multiregional population projections. We revisit, and apply, a family of spatial interaction models first formulated during the 1970s. The classic gravity model—in which migration is positively related to the populations of sending and receiving areas, but inversely related to various types of spatial friction associated with migrating between them—is a special case that is nested within this family of models. We investigate which member of the family of models gives the best fit when modelling five-year migration flows between the 66 Territorial Authorities (TAs) of Aotearoa New Zealand, using 2013 and 2018 census data. We find that predicting migration between two TAs can be improved by taking into account, firstly, an index of the ‘draw’ from all other TAs when modelling out-migration of any TA and, secondly, an index of the ‘competitiveness’ of a TA vis-à-vis all other TAs when modelling in-migration of any TA. We highlight the properties of the statistically-preferred model by simulating the impact on internal migration of an exogenous increase in Auckland’s population. In this model, such a population change affects not only migration flows from and to Auckland, but also migration between other TAs. The usefulness of this approach for population projections is assessed by forecasting the 2013–18 migration matrix by means of 2013 census data only. In this specific case, the model outperforms the classic gravity model in terms of forecasting gross migration, but not net migration.

ANALYTICAL STUDY OF DURABILITY AND CONTACT CHARACTERISTICS OF METAL-POLYMER COMPOSITE SLIDING BEARINGS FOR MEANS OF TRANSPORT

The field of application of metal-polymer bearings is vast: transport of various types, processing industry equipment, medical equipment, various types of maintenance equipment, etc. With the use of the developed generalized author's analytical method of metal-polymer plain bearings on the basis of which it is laid the author's research methodology of materials wear kinetics at sliding friction (dry, lubricated), calculation of their durability is carried out. Contact parameters are also determined. Metal-polymer bearings with a bushing made of PA6, PA66 polyamide and PA6 based composites filled with glass (PA6 + 30GF) and carbon (PA6 + 30CF) dispersed fibres, molybdenum disulphide (PA6 + MoS2) and oil filled cast polyamide (PA6 + oil) are considered. These polyamides (unfilled and filled), as self-lubricating materials, are widely used in this type of dry friction sliding bearings. The predictive estimation of durability of investigated bearings depending on loading, polymer materials Young's modulus, their wear resistance and sliding friction coefficient is executed. Regularities of change from the specified factors of bearing's durability and the maximum contact pressures are established. Experimental indicators, diagrams, and wear resistance characteristics of the specified polymeric materials are presented. The results of researches of sliding friction coefficient and modulus of elasticity for carbon steel (0.45%C) – polyamides tribocouples are presented.

Tribological Properties of Polytetrafluoroethylene (PTFE)/Aramid Fabric Composite Liner Modified by PAO40/Polysulfone/SiO2 Hybrid Shell Microcapsules

Hybrid shell microcapsules have been incorporated into polytetrafluoroethylene (PTFE)/aramid fabric composite liners to enhance the tribological behavior of self-lubricating spherical plain bearings. PAO40/polysulfone/SiO2 hybrid shell microcapsules were synthesized utilizing a combination of Pickering emulsification technology and solvent evaporation. The modified liner with 9 wt% microcapsules exhibited the highest reduction in the average friction coefficient and wear rate, which were 31.1% and 47.9% lower than the unmodified liner. Furthermore, the tribological behavior of modified liners was investigated under different loads and sliding speeds. The friction process of the modified liner and the formation process of the transfer film were analyzed. Investigations into the friction reduction mechanism revealed that the PAO-40# released from microcapsules transitioned the friction type from dry to mixed. SiO2 particles are conducive to forming a denser transfer film by the PTFE abrasive. The results of this study have important scientific significance.

Stabilised finite element method for Stokes problem with nonlinear slip condition

This work introduces a stabilised finite element formulation for the Stokes flow problem with a nonlinear slip boundary condition of friction type. The boundary condition is enforced with the help of an additional Lagrange multiplier representing boundary traction and the stabilised formulation is based on simultaneously stabilising both the pressure and the traction. We establish the stability and the a priori error analyses, and perform a numerical convergence study in order to verify the theory.

Preparation and properties of FeS/iron-based self-lubricating materials by chemical nickel plating-mechanical alloying

PurposeThis paper aims to investigate the effect of chemical nickel plating and mechanical alloying on the mechanical and tribological properties of FeS/iron-based self-lubricating materials as well as the wear mechanism of the materials.Design/methodology/approachSurface modification of FeS powder was carried out by chemical nickel plating method and mechanical alloying of mixed powder by ball milling. The mechanical properties of the material were tested by tribological testing by M-200 ring block type friction and wear tester. Optical microscope was used to observe the surface morphology of the material and the transfer film on the surface of the mate parts, and scanning electron microscope and EDS were used to characterize the wear surface.FindingsMechanical alloying ball milling was carried out so that the lubricating particles in the matrix are uniformly dispersed; nickel-plated layer enhances the interfacial bonding of FeS and the matrix, and the combination of the two improves the mechanical properties of the material, and at the same time the friction side of the surface of the lubrication of FeS lubricant transfer film formed is denser and more intact, and the friction coefficient of friction side and the wear rate of the material have been greatly reduced.Originality/valueThis work aims to improve the mechanical and tribological properties of FeS/iron-based self-lubricating materials and to provide a reference for the preparation of materials with excellent overall properties.

Analysis of the development of friction and wear testing machine based on complex working conditions

Friction is one of the three main factors leading to the failure of metal materials. In order to improve the service life of machinery and reduce unnecessary losses in industrial production, it is necessary to study the friction and wear properties of industrial materials. Simultaneously in order to explore the impact of various environmental conditions on material properties, friction and wear testing machine war born as the times require. This paper mainly introduces the experimental principles and application scenarios of several universal friction and wear testing machines. At the same time, this paper also explores the situation of several special friction and wear testing machines that adapt to complex environments by organizing the industrial needs generated by the rapid development of technology. This paper collects and organizes literature on the current status and development of friction and wear testing machine in recent years. The paper has found that adding or improving special equipment to the special type of friction and wear testing machine on the basis of the universal model can better meet the needs of actual working conditions.

Experimental and numerical studies of mechanical performance of an assembled friction type structural underpinning joint

This paper proposed an assembled underpinning joint (UPJ) based on the interfacial friction action between the underpinned concrete member and the underpinning steel beams (UPSBs). To investigate the mechanical performance and failure modes of the proposed UPJ, 20 specimens with different concrete strengths were fabricated and tested with varied preloading levels. Experimental results showed that the proposed UPJs could effectively transfer the vertical loads in the concrete columns through the friction action and all specimens failed due to the slip between the underpinned concrete column and the UPSBs. The failure loads of the specimens were in a positively linear relationship with the preloading levels and an interfacial friction coefficient of 0.46 was found. Numerical models were also created to further examine the detailed structural behaviours of each components in the UPJs, which confirmed that, the UPSBs were subjected to a composite action mainly combining both bending and torsion. The frictional stresses between the UPSBs and the concrete column were concentrated in the regions of the web of UPSBs near flanges and stiffeners. The load transfer mechanisms of the proposed UPJs under complex loading conditions were clarified. The damages, occurred at the corners of concrete columns due to high stress and strain concentrations, should be alleviated or prevented by protective measures in practice.

The Effects of Weaving Process on the Damage Formation of the E- Glass Yarn

The woven fabric production can be executed in the weaving machine by the using of different mechanisms, which are working simultaneously. Because of the weaving mechanisms, the yarn has under tension and changed between the determined range within the repetitive cycles. The mechanisms and unsteady tension cause to damage on the yarns in the woven fabric production process. The breakable fibers like carbon or glass are more sensitive to degrade in the weaving machine because of their low friction resistance in comparison with the traditional fibers. The several of studies had been carried out to determine the tension of yarns and their damage mechanisms in the weaving process. However, they focused on the damage evolutions of warp yarns in the weaving process. In addition to the warp yarns, the damage evolution of weft yarns was investigated for industrial production in this study. The prevalent weft tensioning systems were evaluated, and the spring yarn tensioning system shown the best performance. Moreover, the yarn- to- machinery part type of friction was determined as the main reason to degrade warp yarns in the industrial production of glass woven fabric.

On well-posedness of Navier–Stokes variational inequalities

In this paper, well-posedness is carried out on variational inequalities in a general form for the stationary Navier–Stokes equations modeling viscous incompressible fluid flows with a nonsmooth slip boundary condition of friction type. For a special form of the variational inequality commonly studied in existing literature, our proof technique leads to a substantial improvement on the well-posedness condition.

LUBRICATION BEHAVIOR OF THE POE/R452A MIXTUREAT DIFFERENT SLIDING VELOCITIES UNDER STARVED LUBRICATION CONDITIONS

There are no international standards guiding tribological testing in oil-refrigerant mixtures. The conditions fortribological tests, including sliding velocity, are chosen arbitrarily. The article presents an attempt to examinethe influence of the sliding velocity of friction pair elements on the coefficient of friction and lubricatingproperties of compressor polyester oil (POE) and its mixture with the R452A refrigerant (POE/R452A) understarved lubrication conditions. The R452A refrigerant is currently widely used in transportation refrigeration.The authors’ original test procedure with the use of a model block-on-ring type friction pair was applied toevaluate the lubricating properties of the oil-refrigerant mixture. Tests were conducted in three operationalsituations: no lubrication, starved lubrication with POE oil, and starved lubrication with the POE/R452Amixture. In each case, the tests were performed at different sliding velocities and the same sliding distance.A series of tests was also conducted where the load was increased in steps by 20 N to determine the relationshipbetween the coefficient of friction, sliding velocity, and load on the friction pair.The results support the potential use of higher sliding velocities and the reduction in test duration. For starvedlubrication with the POE oil and the POE/R452A mixture, the differences in wear at specific velocities forthe same sliding distance reached up to 30%, and the rankings of lubricating properties at different velocitiesremained unchanged.

On a Stokes hemivariational inequality for incompressible fluid flows with damping

In this paper, a Stokes hemivariational inequality is studied for incompressible fluid flows with the damping effect. The hemivariational inequality feature is caused by the presence of a nonsmooth slip boundary condition of friction type. Well-posedness of the Stokes hemivariational inequality is established through the consideration of a minimization problem. Mixed finite element methods are introduced to solve the Stokes hemivariational inequality and error estimates are derived for the mixed finite element solutions. The error estimates are of optimal order for low-order mixed element pairs under suitable solution regularity assumptions. An efficient iterative algorithm is introduced to solve the mixed finite element system. Numerical results are reported on the performance of the proposed algorithm and the numerical convergence orders of the finite element solutions.

Analysis of the exponential stability of a beam-string-beam transmission problem with local damping on the string

We consider a beam-string-beam problem, where two undamped beams are coupled to a locally damped string (first by a damping of frictional type and then by one of Kelvin–Voigt (K–V) type) by transmission conditions. We show that for this structure, the dissipation produced by the frictional part is strong enough to produce an exponential decay of the solution no matter how small is its size, but the semigroup associated with the system is not exponentially stable when we apply a some localized K–V damping on the string, given by a suitable discontinuous function and certain condition under the length of the parts of the structure. However, when we impose hinged conditions on the beams on the interface points, the dissipation produced by a some localized K–V damping, given by a suitable continuous function, is strong enough to produce an exponential decay of the system solution. For the proof of these three results we use a frequency-domain method of semigroup theory, where in the proofs of exponential stability we also use a contradiction argument.

Bond-Damaged Prestressed AASHTO Type III Girder-Deck System with Retrofits: Parametric Study

This research describes an in-depth analysis of the flexural strength of a strengthened AASHTO Type III girder-deck system with debonding-damaged strands based on the finite element software ABAQUS 6.17. To investigate the stand-debonding impact and retrofit, two strengthening techniques by the separate use of carbon fiber-reinforced polymer (CFRP) and steel plate (SP) were proposed. A detailed finite element analysis (FEA) model considering strand debonding, material deterioration, and retrofitting systems was developed and verified against relevant experimental data obtained by other researchers. The proposed FEA model and the experimental data were in good agreement. The sensitivity of the numerical model to the mesh size, element type, dilation angle and coefficient of friction was also investigated. Based on the verified FEA model, 156 girder-deck systems were studied, considering the following variables: (1) debonding level, (2) span-to-depth ratio (L/d), (3) strengthening type, and (4) strengthening material amount. The results indicated that the debonding level and span-to-depth ratio had a major effect on both load–deflection behaviors and the ultimate strength. The relationships between the enhancement of the ultimate strength and the thickness of the strengthening material were obtained through regression equations with respect to the CFRP- and SP-strengthened specimens. The coefficient of determination (R2) was 0.9928 for the CFRP group and 0.9968 for the SP group.