Effects Of Friction Conditions Research Articles

Characterization of friction behavior under cryogenic conditions: Ti–6Al–4V

Friction phenomena at the chip/tool/workpiece interfaces during machining of material impacts significantly the cutting process. In this article, the effect of friction conditions (dry, emulsion, cryogenic) on the tribological performance of uncoated tungsten carbide tools is investigated when machining titanium alloy Ti–6Al–4V. Friction tests were conducted to analyze the impact of sliding speed and cooling on the evolution of the friction coefficient. To determine the real friction coefficient (adhesive friction coefficient), a numerical simulation using the Lagrangian method was employed. After a comparative study of various simulation methods (“Lagrangian”, “CEL”, and “ALE”), the Lagrangian method was identified as the most relevant. The obtained results reveal that an increase of sliding velocity significantly influences the friction coefficient. Additionally, the application of cryogenic fluid (LN2) reduces the friction coefficient compared to both dry and emulsion-based friction. Adhesion phenomena play a crucial role in the nature of the contact, especially at high sliding velocities.

Effect of Frictional Conditions in Deep Drawing on Formability

This study investigated the stress and strain behavior caused in the forming process via simulation analysis using the finite element method, for suppressing punch shoulder and head plate thickness reduction die shoulder stress concentration by controlling the friction conditions. The following findings were obtained: The thickness of the blank head and punch shoulder decreased with the forming process. Due to the increase in the coefficient of friction with the punch side, the plate thickness reduction ratio decreases, and is the lowest when it is close to non-lubrication; Stress concentration occurs at the die shoulder with forming processing. With the increase in the friction coefficient value, forming limit parameter (FLP) increases slightly, but as it does not reach the limit value of 1, the forming process can be safely performed without mechanical damage; When the formability is comprehensively evaluated using the plate thickness reduction ratio and FLP, the friction coefficient μ = 0.4 to 0.5 is reasonable.

Effect of friction conditions on phase transformation characteristics in hot forging process of Ti-6Al-4 V turbine blade

This work is motivated by the fact that friction has a significant impact on the microstructures of titanium forged parts, further influencing their mechanical properties. In this paper, a 3D FE model is developed to investigate the phase transformation characteristics of Ti-6Al-4V turbine blade in the hot forging process. Then, the effect of friction conditions on temperature and phase transformations within the forged blade are analyzed numerically and verified by experiments. The results reveal that compared with a less influence on lamellar α+β phase, a good lubricated condition obviously increases the average volume fraction of α phase, while decreases the average values of temperature and β phase volume fraction as well as the distribution uniformities of α and β phases.

Friction-condition-dependent sulfide and sulfate evolution on dialkylpentasulfide tribofilm studied by XANES

The effects of friction conditions, such as rotational speed, frictional time, and applied load, on the evolution mechanism of sulfide and sulfate on the top and bottom layers of tribofilm were investigated by total electron yield (TEY) and fluorescence yield (FY) mode X-ray absorption near-edge structure (XANES) spectra in the same beam line (4B7A). The results demonstrated that the top and bottom layers of tribofilms were covered by sulfide and sulfate. The addition of dialkylpentasulfide (DPS) could form complex nonuniform tribofilm. In addition, the friction condition (speed, load, or time) has its unique role in the generation of sulfide and sulfate at a specific depth on the tribofilm surface. The enhancement of friction conditions could promote the sulfur tribochemical reaction in a comparatively large range and alter the relative intensity of sulfurization and the sulfur-oxidizing process.

Effect of Friction conditions on Material Flow in FE Analysis of Al Piston Forging Process

In the hot forging process of aluminum piston using water-soluble lubricants, the lubricant layer is often peeled off due to excessive deformation of the material during forming, which may result in direct contact between the material and the die, thereby partially increasing the friction. The constant friction in the Finite element (FE) analysis of this process sometimes results in a completely different result from the actual material flow. Therefore, this study was designed to investigate the friction condition to accurately predict the material flow in the FE analysis. The FE analysis was performed for various material temperatures and friction parameters and the proper friction condition was also derived to remove forging defects. Finally, the forging test was carried out for the initial specimens produced by three different methods to verify the analytical results and eliminate the forging defects. The results showed that the friction depends on the effective strain in the FE analysis and the critical value to increase friction is approximately 1.5–1.8. In addition, among the three different specimens, the shot peened specimen can remove the forging defect by increasing the amount and uniformity of the lubricant on its surface.

Effect of Friction Conditions on Triboluminescence of Polymers

Effect of Friction Conditions on Triboluminescence of Polymers

A Finite Element Study of Thermo-Mechanical Fields and Their Relation to Friction Conditions in Al1050 Ring Compression Tests

The most accepted method for determining friction conditions in metal forming is the ring compression test (RCT). At high temperatures, extraction of the friction coefficient, μ, commonly requires numerical analysis due to the coupling between the mechanical and thermal fields. In the current study, compression tests of cylindrical specimens and RCT experiments were conducted on commercially pure aluminium (Al1050) at several temperatures, loading rates, and lubrication conditions. The experiments were used in conjunction with a coupled thermo-mechanical finite element analysis to study the dependence of the friction coefficient on those parameters. It is demonstrated that due to the coupling between friction conditions and material flow stress, both μ and flow stress data should be determined from the cylinder and ring specimens simultaneously and not subsequently. The computed friction conditions are validated using a novel method based on identification of the plastic flow neutral radius. It is shown that, due to heat loss mechanisms, the experimental system preparation stage must be incorporated in the computational analysis. The study also addresses the limitation of the RCT in the presence of high friction conditions. The computational models are finally used to examine the thermo-mechanical fields, which develop during the different processes, with an emphasis on the effect of friction conditions, which were then correlated to the resulting microstructure in the RCTs.

Ultra-Fine and Nano-Crystalline Structure Induced by Sliding Friction of Carbon Steel

Sliding friction is one of the most powerful processes for microstructural evolution in the sub-surface, including grain refinement and recrystallization of deformed structure. Pin-on-disc sliding tests were carried out for 0.45 mass % carbon steels, and TEM microstructure and hardness of the specimens were investigated. Particularly effects of friction conditions on the microstructure at the surfaces and wear properties of the friction induced microstructure were studied. It was found that ultra-fine equi-axed grains in the 30 - 50 nm size range were produced in the case of a high friction speed of 5.0 m/s in an air atmosphere. Moreover, nano-crystalline microstructure can be produced in a vacuum atmosphere even if the friction speed was low. The friction induced nano-crystalline surface layers, which exhibited significant high hardness, showed good wear resistance.

Microstructure and Wear Properties of Friction Induced Nano-crystalline Surface Layers of Carbon Steels

Pin-on-disc sliding friction tests were carried out for 0.45 mass % carbon steels, and TEM microstructure and hardness of the sub-surfaces of the friction specimens were investigated. Particularly effects of friction conditions on the microstructure at the surfaces and wear properties of the friction induced microstructure were studied. It was found that ultra-fine equi-axed grains in the 30 - 50 nm size range were produced in the case of a high friction speed of 5.0 m/s in an air atmosphere. Moreover, nano-crystalline microstructure can be produced in a vacuum atmosphere even if the friction speed was low. The friction induced nano-crystalline surface layers, which exhibited significant high hardness, showed good wear resistance.

The Combination of Advanced Tools for Parameters Investigation and Tools Maintenance in Flow Forming Process

In this work, the authors present an investigation on technological parameters affecting the flow forming process of aluminum alloy 6060 tubular structures and to discuss about the tools maintenance. Flow forming tests were carried out by mounting a single roller on a lathe machine. A 3D thermo-mechanical finite element model was developed to analyze the interaction between the roller and the workpiece in terms of forces, strains and thermal distribution. The effects of friction conditions were investigated through the FE model results and comparing them with acquired thermal maps. The model was validated by comparing the geometrical characteristics of the workpieces, such as the axial elongation, the inner and outer tube diameter. Aluminum spring-back was taken into account with material model adopted in the numerical algorithm. Once collected a complete information on the process parameters, some thermal images were acquired on roller in order to find a parameters set able to reduce the stresses acting on it as far as to obtain the maximum elongation with the minimum number of passes.

Determination of FLD for Ti-6Al-4V Titanium Alloy Sheet

Ti-6Al-4V is the most widely applied titanium alloy in technology and medicine due its good mechanical properties combined with low density and good corrosion resistance. However, poor technological and tribological properties make it very difficult to process, including the problems with sheet-metal forming. The best way to evaluate sheet drawability is to use Forming Limit Diagram (FLD), which represents a line at which failure occurs. FLD allows for determination of critical forming areas.The FLDs can be determined both theoretically and experimentally. Recently, special optical strain measurement systems have been used to determine FLDs.In this study, material deformation was measured with the Aramis system that allows for real-time observation of displacements of the stochastic points applied to the surface using a colour spray. The FLD was determined for Ti-6Al-4V titanium alloy sheet with thickness of 0.8 mm. In order to obtain a complete FLD, a set of 6 samples with different geometries underwent plastic deformation in stretch forming i.e. in the Erichsen cupping test until the appearance of fracture.The real-time results obtained from the ARAMIS software for multiple measurement positions from the test specimen surface were compared with numerical simulations of the cupping tests. The numerical simulations were performed using the PamStamp 2G v2012 software dedicated for analysis of sheet-metal forming processes. PamStamp 2G is based on the Finite Element method (FEM). The major and minor strains were analysed. The effect of friction conditions on strain distribution was also taken into consideration

Study of Localized Thinning of Copper Tube Hydroforming in Square Section Die: Effect of Friction Conditions

The friction conditions are responsible of the thickness distribution in a part realized by tube hydroforming. Then it is essential to have a good evaluation of the friction coefficient for running predictive finite element simulations. The tube expansion in a square die is one of tests proposed for the friction evaluation. In the literature, several analytical models have been developed for this specific test. The present paper concentrates on one of this model and results obtained from the analytical analysis, FE simulations and experiments are compared. The repartition of the thickness over the shaped tube and its evolution during the process are studied. The tendencies are in agreement but some complementary evaluations are proposed for using the proposed approach for the evaluation of the friction coefficient with the analytical model.

On the Friction Effect on the Characteristics of Hydroformed Tube in a Square Section Die: Analytical, Numerical and Experimental Approaches

A focus on the effect of friction condition on tube hydroforming during corner filling in a square section die is proposed. Three approaches have been developed: an analytical model from the literature has been programmed, finite element simulations have been conducted and experiments have been carried out. Effect of friction coefficient on the thickness distribution in the square section of the hydroformed tube is studied. Critical thinning is found to take place in the transition zone between the straight wall and the corner radius and this minimal thickness seems to be the more appropriate parameter for the evaluation of the friction coefficient.

Stability Analysis of Chatter in Tandem Rolling Mills—Part 1: Single- and Multi-Stand Negative Damping Effect

Many different modes of chatter in rolling and their possible causes have been identified after years of research, yet no clear and definite theory of their mechanics has been fully established and accepted. In this two-part paper, stability of tandem mills is investigated. In Part 1, state-space models of single- and multi-stand chatter are formulated in a rigorous and comprehensive mathematical form. Then, the stability of the rolling system is investigated in the sense of the single- and multi-stand negative damping effects. First, a single-stand chatter model in state-space representation is proposed by coupling a dynamic rolling process model with a structural model for the mill stand. Subsequently, a multi-stand chatter model is developed by incorporating the inter-stand tension variations and the time delay effect of the strip transportation based on the single-stand chatter model. Stability criteria are proposed and stability analyses are performed to create corresponding stability charts in terms of the single- and multi-stand negative damping mechanism through numerical simulations. Particularly, the effect of friction conditions on chatter is examined and an explanation is given for the existence of an optimum friction condition. In Part 2, the regenerative effect and resulting instabilities are examined. Suitable stability criteria for each mechanism are established and stability charts are demonstrated in terms of relevant rolling process parameters.

Crystal Plasticity Finite Element Analysis of Texture Evolution during Rolling of fcc Polycrystalline Metal

Localized strain and crystallographic orientation distribution during rolling process have a significant effect on anisotropic flow behavior in sheet forming of aluminum alloy, resulting in local thinning. In this study, crystal plasticity finite element method (CPFEM), which incorporates a crystal plasticity constitutive law into the three-dimensional finite element method, was used to investigate strain localization and textural evolution during the flat rolling process of the face-centered-cubic material. A rate-dependent polycrystalline theory based on the Taylor model was fully implemented into an in-house program, CAMProll3D. The through-thickness texture evolution depending on the degree of draught was predicted by using the developed CPFEM program and compared well with the experimental data available in the literature. The orientation distributions not only in the thickness direction but also in the width direction of the flat rolled sheet were investigated depending on the amount of reduction during the multi-pass flat rolling in terms of pole figure, orientation distribution function and flow potential surface in the 3-plane. Finally, the effect of friction condition between the rolls and the material on rotation about the transverse direction was found to be important to determine the texture evolution at the surface of the rolled sheet. [doi:10.2320/matertrans.M2012346]

Effect of friction conditions on change of sheet surface roughness during deep drawing

The application of radial and axial-centrifugal compressors in turboprop, turboshaft and turbofan engines may require the construction of small diameters diffuser in order to obtain lower weight and smaller frontal area. Conventional exhaust diffusers typically have large outlet diameters for exit Mach numbers lower than 0.2 and low swirl flow to the combustor, hence the design of channel of the low-diameter diffusers called controlled-contour, fishtail-shaped diffuser or diffusing trumpet is complex. The cross-sectional shape of these channels is varied from circular to oval to elliptic and to rectangular. The paper presents an original method for determining the flow parameters in the channel and at the outlet section of the downstream diffusing trumpet for a pipe diffuser, which constitutes the downstream duct of the radial or axial-centrifugal compressor with the pipe diffuser. It also illustrates a new method for determining the geometrical parameters of the diffuser. Mentioned methods (for conceptual design of a compressor with pipe diffuser) are based on Pythagorean theorem, properties of ellipse, equation of continuity, energy equation, first law of thermodynamics, Euler’s moment of momentum equation, gasodynamic functions and definitions used in theory of turbo-machines. The final part of the article includes principles of selection of the computational value pressure ratio for the compressor with the pipe diffuser.

1307 すべり摩擦時に発生するAEに及ぼす摩擦条件の影響(OS01-2 機械要素とトライボロジー,オーガナイズドセッション 1:「機械要素とトライボロジー」)

1307 すべり摩擦時に発生するAEに及ぼす摩擦条件の影響(OS01-2 機械要素とトライボロジー,オーガナイズドセッション 1:「機械要素とトライボロジー」)

Numerical Simulation for Effects of Friction on Deformation Behaviors in a 3-Dimensional Hot Upsetting Process

The friction between the die and workpiece plays an important role in determining the quality of the finished products during the hot deformation. Based on the experimental results, a rigid-viscoplastic finite element model was made to study the effects of friction conditions on the strain distribution and microstructural evolution in high strength low alloy steel during hot upsetting process. Also, the effects of friction conditions on the forging loadings and shape geometry of the deformed specimen were also investigated. The results show that: (1) the deformation of specimen is inhomogeneous, and the degree of deformation inhomogeneity decreases with the increase of friction coefficient; (2) the dynamic recrystallization volume fraction decreases with the increase of friction coefficient; (3) the distribution of the average grain size is inhomogeneous in the deformed specimen, and the average grain size increase as the friction coefficient is increased; (5) the effects of friction conditions on the peak forging loading and shape geometry of the deformed specimen are significant.

Parameter study of stretch—blow moulding process of polyethylene terephthalate bottles using finite element simulation

In this paper, the analysis of the stretch—blow moulding (SBM) process of polyethylene terephthalate (PET) bottles is studied by the finite element method (FEM). In this simulation, owing to the symmetry of bottle geometry, the parts are considered as an axisymmetric model. A hyperelastic constitutive behaviour was calibrated using material data available in literature in variant high temperatures and strain rates and was used in the numerical simulation. Hydrostatic pressure with convention heat transfer has been used instead of a blowing process. Comparisons of numerical results with experimental observations demonstrate that the model can predict an overall trend of thickness distribution, especially in regions between 30 mm to 90 mm from the bottle bottom. However, some differences can be seen in regions 10 mm and 125 mm. These results can be used for an overall prediction of bottle properties such as final bottle thickness and a defect-free production because they are governed by orientation and crystallinity, which are highly temperature and strain dependent. Also, with definition of the critical area in bottle forming, the parametric studies are conducted on the effect of friction condition, heat transfer coefficient, and initial pre-blowing air entrance time delay on bottle thickness. Through the study, it becomes clear that the proposed model is applicable for simulating the stretch-blow moulding process of PET bottles, and is capable of offering helpful knowledge in the production of bottles and the design of an optimum preform.

Effects of Friction on Precision Forging Process of Blade with a Damper Platform

A blade with a damper platform, with excellent anti-vibration characteristic and high efficiency, has become one of the most important types of blades being developed in the aeronautical engines. During the precision forging process of this blade, the friction between dies and workpiece has important effects on metal flow, deformation defects, load and energy etc. So researching the effects of friction conditions on the forging process of blade with a damper platform has been a crucial problem urgent to be resolved. In this paper, the precision forging process of titanium alloy blade with a damper platform under different friction conditions has been simulated and analyzed based on the DEFORM-3D software platform. The obtained results reveal the influence laws of friction on temperature field and load-stroke curves, and provide a significant basis for determining technological parameters of the blade forging process.