Friction Calibration Research Articles

An Iterative Numerical Approach to Evaluate the Variable Friction Coefficient of Steel AMS5643 Using Ring Compression Tests

The coefficient of friction is an important variable that must be defined to allow the accurate prediction of the forming geometry and stresses involved in metal forming processes. Literature reports have shown that the coefficient of friction does not remain constant with respect to variables including but not limited to contact pressure, sliding speed, surface roughness, and surface morphology. Ring compression tests provide a simple and efficient process by which to measure the variable coefficient of friction present in the bulk-metal process; however, the conventional interpolating method can result in a poor evaluation of the evolution of friction, especially if the coefficient of friction changes significantly during a test. In this article, a novel approach to evaluate the relationship between the coefficient of friction and contact pressure is outlined using friction calibration charts generated via iterative computation models and ring compression tests. This relationship can be programmed into a computational model to allow for the coefficient of friction to behave as a dynamic variable. This approach improves on the prediction of the computational model when compared to conventional interpolation methods.

Frictional behavior of severe plastic deformed copper sample by using friction calibration curves

Equal Channel Angular Pressing (ECAP) known as one of the most significant methods involving in severe plastic deformation. There are not many investigations which focus on the design of dies and its analysis by FEM, considering friction coefficients as die geometry parameters; likewise, only few studies have been reported in which the effect of die shape has been analyzed, for example. One of the challenging problems in industrialization of ECAP is designing and manufacturing of die. To avoid trial and error in the next designs, the measurement of right friction coefficient plays a key role, which is used in finite element method to prevent doing experimental test. The main objective of this study was to investigate and find generalized friction calibration curves utilizing the ring compression test. To perform the ring compression test, which is oxygen-free copper with 99.7%, (BS EN 15079 standard) the standard ring specimen ratio of 6:3:2 was used. With use of different lubricants during the ring compression test the relations between friction coefficients and changes of inner and outer diameters was revealed. To solve complicated plasticity equations with complex geometries and boundary conditions with various friction coefficients, finite element method was used. To use more accurate frictional coefficient values with considering different ECAP passes, friction calibration curves were updated.

Development of Universal Friction Calibration Curve for Ball Ironing Test

The friction calibration curve (FCC) is normally constructed to indirectly approximate the friction value for any simulative friction test based on sensitive friction indicators (i.e., forming load or final geometry) by finite element modeling (FEM). For calculation, these indicators are highly dependent on flow stress data and the techniques to extrapolate them. A universal FCC is preferable with the independence of these factors. In this paper, the sensitivity of the material data and our proposed extrapolation techniques for the ball ironing test (BIT) were studied to construct a new universal FCC. A specific load was proposed as a new friction indicator for this universal FCC. It was used to approximate the friction value for different materials and lubricants. This friction value was also validated to determine the maximum load and geometry for pulley forming. The results obtained from the simulation were in good agreement with the experiment.

Using rapid repeat SAR interferometry to improve hydrodynamic models of flood propagation in coastal wetlands

The propagation of tides and riverine floodwater in coastal wetlands is controlled by subtle topographic differences and a thick vegetation canopy. High-resolution numerical models have been used in recent years to simulate fluxes across wetlands. However, these models are based on sparse field data that can lead to unreliable results. Here, we utilize high spatial-resolution, rapid repeat interferometric data from the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) to provide a synoptic measurement of sub-canopy water-level change resulting from tide propagation into wetlands. These data are used to constrain crucial model parameters and improve the performance and realism of simulations of the Wax Lake wetlands in coastal Louisiana (USA). A sensitivity analysis shows that the boundary condition of river discharge should be calibrated first, followed by iterative correction of terrain elevation specified originally by a Digital Terrain Model derived from LiDAR measurements. The calibration of bed friction becomes important only with the boundary and topography calibrated. With the model parameters calibrated, the overall Nash-Sutcliffe model efficiency for water-level change increases from 0.15 to 0.53 with the RMSE reduced by 26%. In areas with dense wetland grasses, the LiDAR signal is unable to reach the soil surface, but the L-band UAVSAR instrument detects changes in water levels that can be used to infer the true ground elevation. The high spatial resolution and repeat-acquisition frequency (minutes to hours) observations provided by UAVSAR represent a groundbreaking opportunity for a deeper understanding of the complex hydrodynamics of coastal wetlands.

Studies on friction behaviour of aluminium AA4032 alloy during forging using ring compression test

In metal forming, friction has a negative effect on the deformation load & energy requirements, homogeneity of metal flow, quality of formed surfaces, etc.; however, its effect can be reduced through the use of proper lubricants. Mostly, in industrial applications, selection of proper lubricant for specific material is challenging and quantification of magnitude of friction at diework piece interface is essential. Hence, for metallic alloys, a realistic friction factor is needed to be known and used at the diework piece interface for better control of deformation process. Thus, this research, generally, aims at experimental investigation of the friction behavior of aluminum AA4032 alloy and selection of suitable lubricant for its effective processing using ring compression test and finite element (FE) simulations. Meanwhile, the effect of metal surface conditions and different lubricants namely palm oil, grease, emulsion oil and dry conditions on the friction behaviour has been evaluated. A commercial FEM software, DEFORM 3D, is used to analyze the flow of metal, determine the geometry changes of the specimen and generate friction calibration curves. The results revealed that the nature of metal surface and lubricating conditions have significantly affected the metal flow pattern, deformation load requirement, induced effective stress and strain, and geometry of the metal. The friction factor at die-work piece is determined for different lubricating conditions. Among lubricants employed, palm oil is found to be suitable and effective for industrial processing of aluminium AA4032 alloy, specifically for forging. The FE simulation results are in a good agreement with the experimental one.

Friction Evaluation for Combined Drawing and Ironing Process With Thick Sheet by Ball Ironing Test

Abstract Ball ironing test (BIT) was proposed to evaluate the tribological conditions of the combined drawing and ironing process for thick sheets. This process was used to produce the products with controlled thickness at the sidewall, such as pulleys. Finite element modeling (FEM) was utilized to study the effects of the main geometrical parameters on friction from the BIT results and thereby design suitable tooling geometries. Clearance-to-thickness ratio (c/t), inner die radius (rd), and inner diameter of specimen (di) were adopted as process and specimen parameters. The results of the BIT comprised the maximum load and final height of the specimen. Slope sensitivity (λ) in the results was introduced to evaluate the friction sensitivity. According to the simulation, the maximum load was highly sensitive to the friction and was thus used as a friction indicator. Friction calibration curve (FCC) was established and fitted on the basis of a simplified mathematical model as a function of the maximum load and friction factor (m). The BIT with various types of lubricants was performed experimentally to evaluate the performances of the lubricants and approximate the friction factors. The solid lubricant, Zn-Ph coating, provided the least forming with m of 0.03. The liquid lubricant, oil with extreme pressure (EP) additives, performed similarly to the Zn-Ph coating with m of 0.07. In conclusion, the BIT test performed very well in ranking the lubricants and determining the friction value of the combined drawing and ironing process for thick sheets.

Evaluation of friction using double cup and spike forging test for dry-in-place coating and forming oils

The friction characteristics of lubricants were evaluated using the double cup and spike forging tests. Friction calibration curves, i.e., plots of cup height ratio vs. punch stroke and spike height vs. punch stroke, were established through finite element (FE) simulations considering various friction factor values. The friction factor of the lubricants was determined by matching the relationships of the cup height ratio and spike height with the punch stroke obtained from experiments to those obtained from the FE simulations. Under the lubricating condition of dry-in-place coating with forming oil, the results showed that different tribo-testing methods yielded different friction factors. The friction factor determined was applied in the FE simulation of a cold forging process of a claw pole.

FEM Simulation Analysis of Ring Compression Test Using Stationary and Rotating Die under Constant Shear Friction

The main objective of this research was to investigate the effect of friction on the behaviour of the metal flow and ring geometry, using comparisons from a stationary and rotating bottom die. This was carried out using friction calibration curves, compressive force analysis, stress and strain relationships and the reduction ratio of the ring specimen. The ring compression test (RCT) is considered one of the most reliable ways to obtain the friction factor existing in a plastic deformation process. This technique utilizes the dimensional changes of a test specimen to determine the magnitude of the friction factor. The variation of the calibration curve for the stationary die, with a range of m=0.0 to 0.9, and for the rotating die a range of m=0.1, 0.5 and 0.9. The frictional factor is calculated using FEM analysis, friction calibration and reduction ratio curves were generated from the compressive force using the DEFORM software package. The results indicated that the change in the inner diameter is related to the friction conditions and angular velocities at the die-workpiece interface.

The Investigation of the Influence of Friction and Roll Calibration on the Pipe Formation during Plug Rolling

The influence of the friction coefficient and roll calibration on the pipe formation during longitudinal rolling on a short mandrel was investigated using the FEM simulation. The study was carried out for three different roll calibrations: hexagonal, dodecahedral, dioctahedral. Pipe formation was also studied using the Siebel index of friction in the range from 0.1 to 1. The effect of the friction coefficient ψ on the dimensionless parameter determining the shape change was determined, as well as the wall thickness deviation and the “guide mark” defect formation on the inner surface of the pipes. The values of a dimensionless parameter characterizing the appearance of a “guide mark” defect on the inner surface of pipes are determined.

Lubrication efficiency of vegetable oil nano-lubricants and solid powder lubricants

Reducing crude oil reserves and also environmental pollution caused by its excessive use has led to numerous researches to find alternatives to petroleum-based oils. Thus, owing to lower pollution and higher lubrication efficiency, the use of vegetable base lubricants has been widely considered. Due to the unique properties of different nanoparticles such as sphericality and high surface area besides low environmental risk, the subjected nanoparticles can be applied as additives to the base lubricants and create optimal tribological properties. In this study, in order to improve the lubricating efficiency of vegetable base lubricants, SiO2 nanoparticles with different weight concentrations were used in the cold forging process of aluminum alloy. Then, the lubrication proficiency of both nano-lubricants and conventional solid powder lubricants in the forging industry was evaluated. Friction coefficient was determined by standard compression test and friction calibration curves. In order to evaluate the lubricants’ efficiency, two key parameters, namely shear friction coefficient and surface roughness have been considered. Experimental results showed that the presence of SiO2 nanoparticles in the base lubricants significantly increased the lubrication efficiency of the base lubricants and notably reduced both the friction coefficient and surface roughness.

Non Conventional Specimens FEA and Exergy Analysis Effects of Geometrical Parameters in Ring Compression Test

This research aims to investigate the possibilities of alternative non-conventional specimens for friction calibration. From literature survey it is observed that researchers have made attempts to investigate alternate specimens for friction calibration. It is found that ring compression test is recommended as the standard test for determination of coefficient of friction, because it gives reliable results. There is need to search other friction of friction calibration specimens, which are in same conformity as ring compression test. Two different solid geometry specimens are tried for friction prediction using computer simulation techniques. Finite Element analyses of the compression test are carried out in order to study the deformation behaviour with respect to friction. Based on the deformation studies, correlation has been made between diameter ratios and friction. The deformed radii at various locations for different friction conditions are recorded and it can be observed, that there is continuous decrease in end radius with respect to friction. Friction calibration curves for these specimens are generated. In order to validate the predictability of these specimens, real experiments on them are carried out. Rings of standard dimensional ratio 6:3:1 in the same machine. Friction predictions from both specimen are found to be in close match, proposed alternate specimen offers a powerful tool for friction prediction in the absence of ring specimen.

Calibration of snow avalanche mathematical models using the data of real avalanches in the Ile (Zailiyskiy) Alatau Range

The calibration of the dry friction and turbulent friction coefficients is necessary for computer simulation of avalanches. The method of back calculation based on data on actual avalanches is used for this purpose. The article presents the results of the calibration of the Eglit’s and RAMMS models for Ile Alatau range condi‑ tions. The range is located in Kazakhstan. The data on six avalanches in the same avalanche site were used. Five avalanches were dry, and one avalanche was wet. Avalanches volume varied from 2000 to 12000 m3. Maximum speed avalanches were between 15 and 30 m/s, the flow height – from 3 to 10 m. Series of back calculations with different values of the friction coefficients was made to obtain the calibrated coeffi‑ cients. The calibrated coefficients were chosen under condition of the best fit with real avalanches. The cal‑ ibrated coefficients were following. For the Eglit’s model for dry avalanches of the volume 2000–5000 m3 μ = 0.46÷0.48, k = 0.005–0.006, and the volume 8000–12000 m3 μ = 0.38÷0.42, k = 0.002÷0.003. For RAMMS model for dry avalanches of the volume of 2000–5000 m3 μ (dry friction coefficient) = 0.35÷0.4, ξ (viscous friction coefficient) = 1500÷2000 m/s2, and the volume 8,000–12,000 m3 μ = 0.3÷0.35, ξ = 2000÷3000 m/s2. For wet avalanches of the volume 12,000 m3 μ = 0.35, ξ = 1500 m/s2. The work on the calibration will be con‑ tinued to obtain the friction coefficients for the Eglit’s and RAMMS models. The additional data on real ava‑ lanches will be needed for this purpose.

Incremental versus continuous load-lubrication procedure in the determination of friction conditions by the ring compression test

This work presents the differences found when using two types of methodology (continuous and incremental) in the application of load-lubricant during ring compression tests. Friction calibration maps have been obtained by conducting ring compression tests to flat rings of aluminium alloy UNS A97075-T6 with molybdenum disulphide (MoS2) as lubricant. Accordingly, in order to determine the particular values of the Coulomb friction coefficient, the problem was simulated using an elasto-plastic model with the finite element code Abaqus/Standard. A friction coefficients map from experiments and finite element simulation is drawn to compare the friction coefficient values derived from the continuous and incremental procedure. A comparison with experiments done with graphite powder as lubricant is also presented. Results of this investigation show that friction curves are affected by the methodology of load-lubricant application, and some guidelines about the use of these maps depending on the actual process conditions are provided.

Incremental versus continuous load-lubrication procedure in the determination of friction conditions by the ring compression test

This work presents the differences found when using two types of methodology (continuous and incremental) in the application of load-lubricant during ring compression tests. Friction calibration maps have been obtained by conducting ring compression tests to flat rings of aluminium alloy UNS A97075-T6 with molybdenum disulphide (MoS2) as lubricant. Accordingly, in order to determine the particular values of the Coulomb friction coefficient, the problem was simulated using an elasto-plastic model with the finite element code Abaqus/Standard. A friction coefficients map from experiments and finite element simulation is drawn to compare the friction coefficient values derived from the continuous and incremental procedure. A comparison with experiments done with graphite powder as lubricant is also presented. Results of this investigation show that friction curves are affected by the methodology of load-lubricant application, and some guidelines about the use of these maps depending on the actual process conditions are provided.

Assessing the lubrication performance of vegetable oil-based nano-lubricants for environmentally conscious metal forming processes

In metal forming processes, employing lubricants for providing desirable tribological circumstances at tool-workpiece interface is essential to increase the material formability, prolonging tool life and suppressing energy loss. With increasing the awareness and concerns towards the substantial hazardous effects of conventional metal forming lubricants a step forward is crucial to replace them with benign and compatible lubricants with environment. Despite the fact that vegetable oils have an immense potential to be utilized as green lubricants, but the limited tribological characteristics of them restrict their applications. Hence, the biodegradability and non-toxicity privileges of vegetable oils have been incorporated with friction reduction and extreme pressure capabilities of nanoparticle additives in this study, to develop a high performance lubricant with environmentally friendly feature. The CuO and SiO2 nanoparticles were dispersed in soybean and rapeseed oils in diverse concentrations and their lubrication performance were compared with two conventional metal forming lubricants, CM202A press drawing oil and solid lubricant of zinc phosphate plus sodium soap. The standard ring compression test was utilized to evaluate the efficiency of considered lubricants. The performance comparison was made using two key factors of friction coefficient and deformation load. The necessary friction calibration curves for estimating friction coefficient were provided employing finite element simulation. The acquired results convey that the lubricity of vegetable oil is dependent on its chemical structure. With increasing the concentration of nanoparticles, the friction factor and deformation load reach to a minimum for a certain amount of concentration. According to obtained results, the most efficient concentration of nanoparticles was determined within the range of 0.5–0.7 wt%, which provides 21–31% enhancement. It is demonstrated that the vegetable oil-based nano-lubricants which are enriched with optimum amounts of nanoparticles have the friction reduction capability comparable to conventional lubricants. The outcomes of this study can be fruitful in developing more environmentally conscious metal forming processes.

Failure Orientation in Stretch Forming and Its Correlation with a Polycrystal Plasticity-Based Material Model for a Collection of Highly Formable Sheet Steels

Robust design optimization techniques have been developed in recent years within the automotive industry with the aim of reducing scrap rates and improving process stability in sheet metal forming. These new techniques are able to take process variations and other sources of material scatter into account. Among the many material variables and inputs used, the yield criterion is an important aspect and this is used to describe the plastic behavior of sheet metals. To achieve a reliable output in an optimization study, the yield criterion selected must be representative of material response and scatter. However, simple material models that deviate from real material behavior are often used due to a lack of material data, which is usually a requirement when using more complex models. In the present research, a polycrystal plasticity-based CTFP model has been evaluated in stretch forming for a collection of highly formable sheet steel materials. The results demonstrate that the CTFP model can capture the yielding character and also detect the minor deviations presented by different coils. The stretching factor derived from the CTFP model, as opposed to the work hardening and ductility, has a dominant effect on failure for a collection of materials with similar mechanical properties. Results also indicate that plastic deformation causes texture evolution and, consequently, an evolving yield locus. Such changes in the yield locus during deformation have an effect on stretching and friction calibration in FE simulations.

Friction Study in Equal Channel Multi Angular Pressing: Load Curve and Ring Compression tests

The majority of process parameters in different severe plastic deformation (SPD) methods are completely dependent on friction factor. So precise analysis of this complicated factor is always useful. Equal channel multi angular pressing (ECMAP) process, enhances the productivity of equal channel angular pressing process that is the most popular technique among SPD methods. In this article, the frictional behavior of ECMAP process was studied. Route C was selected as the multi-pass route in ECMAP process and samples were prepared from Al5754 alloy. During the process, die and strip surfaces were not in full contact with each other thus making the friction situation complicated. Thus, the values of friction coefficient were obtained by two typical methods: ring compression test and ECMAP load curve test. For the first method, to extract friction calibration curves, FE simulations were done on the compressing ring for different friction coefficients. Also, experimental works were done on prepared rings. The results of both FEM and experimental works were used to acquire the final value of friction coefficient. For the second method, ECMAP process was simulated via FEM by different friction coefficients, leading to different load stroke curves. Also, load stroke curves were achieved from experimental works, using manufactured die. Then the friction coefficient value was extracted from the comparison between the results of experiments and FEM curves. It could be concluded that in the best case scenario, the results of both methods were close to each other but in the weakest situation there was 13.6 % difference between two methods. It was inferred that, in ECMAP practical works, there were some parameters like die clearance or non-uniform lubrication surfaces that had effect on load stroke curves and, as a result on the friction coefficient estimation.

Evaluation of Friction of Powder Metallurgical Al–4 wt% Cu Preforms by Employing Ring Compression Test and FEM in Hot Compression Test

In this investigation, the interface friction behaviour of powder metallurgical (P/M) Al–4 wt% Cu preforms was evaluated by using ring compression tests and finite element (FE) simulations at elevated temperature. P/M Al–4 wt% Cu ring specimens of different initial relative densities, 84, 87 and 90 %, were hot compressed at temperature ranging from 300 to 500 °C under graphite lubricant and dry friction conditions. FE simulation was used to derive the calibration curves, analyze the densification behaviour and geometric changes and to evaluate the metal flow. Different interface heat transfer coefficients were used to generate friction calibration curves for graphite lubricant and dry friction conditions. The results revealed that increase in temperature or decrease in initial relative density increases the interface friction factor between tool and work piece. It was found that the influence of temperature was relatively less significant in dry friction than graphite lubricant condition. In addition, the effect of temperature, initial relative density and lubricating conditions on the densification behaviour, barreling phenomenon and metal flow was evaluated. FE simulations provided detailed and accurate results of the frictional behaviour at the tool-work piece interface, and hence employment of ring compression test with FE simulations is a reliable and feasible way to evaluate interface friction behaviour of P/M components in hot compression test.

Ice-avalanche scenario elaboration and uncertainty propagation in numerical simulation of rock-/ice-avalanche-induced impact waves at Mount Hualcán and Lake 513, Peru

The interest in numerical simulation of cascading processes involving mass movements and lakes has recently risen strongly, especially as the formation of new lakes in high-mountain areas as a consequence of glacier recession can be observed all over the world. These lakes are often located close to potentially unstable slopes and therewith prone to impacts from mass movements, which may cause the lake to burst out and endanger settlements further downvalley. The need for hazard assessment of such cascading processes is continuously rising, which demands methodological development of coupled numerical simulations. Our study takes up on the need for systematic analysis of the effect of assumptions taken in the simulation of the process chain and the propagation of the corresponding uncertainties on the simulation results. We complemented the research of Adv Geosci 35:145-155, 2014 carried out at Lake 513 in the Cordillera Blanca, Peru, by focusing on the aspects of (a) ice-avalanche scenario development and of (b) analysis of uncertainty propagation in the coupled numerical simulation of the process chain of an impact wave triggered by a rock/ice avalanche. The analysis of variance of the dimension of the overtopping wave was based on 54 coupled simulation runs, applying RAMMS and IBER for simulation of the ice avalanche and the impact wave, respectively. The results indicate (a) location and magnitude of potential ice-avalanche events, and further showed (b) that the momentum transfer between an avalanche and the impact wave seems to be reliably representable in coupled numerical simulations. The assessed parameters—initial avalanche volume, friction calibration, mass entrainment and transformation of the data between the models—was decisive of whether the wave overtopped or not. The overtopping time and height directly characterize the overtopping wave, while the overtopping volume and the discharge describe the overtopping hydrograph as a consequence of the run-up rather than the wave. The largest uncertainties inherent in the simulation of the impact wave emerge from avalanche-scenario definition rather than from coupling of the models. These findings are of relevance also to subsequent outburst flow simulation and contribute to advance numerical simulation of the entire process chain, which might also be applied to mass movements other than rock/ice avalanches.

Investigating Friction Factor in Forging of Ti-6Al-4V through Isothermal Ring Compression Test

Isothermal ring compression tests are studied to assess the effects of temperature and deformation rate on the friction factor and calibration curves of Ti-6Al-4V. Using finite element method (FEM) analysis, the calibration curves of Ti-6Al-4V are developed and compared to the calibration curves available in the literature. The results show that the calibration curves of Ti-6Al-4V change with temperature and deformation rate at high friction factors. The experimental results indicate that the friction factor of the glass used as a lubricant increases with increasing temperature. The deformation rate has a significant effect on the friction factor at 850 and 950°C, but its effect is inconsiderable at 900°C. A model is presented for the friction factor value as a function of temperature and platen speed.