Interfacial Friction Conditions Research Articles

Shear characteristics of root–matrix composites under various interface friction and moisture content conditions

Analysing the composite's adhesion mechanism is necessary to gain a deep understanding of the pipeline blockage phenomenon encountered during negative pressure matrix removal. This study considers the interface suction and liquid bridge changes between the roots and the matrix. In particular, the liquid bridge volume and the interface's effective stress parameters were combined to establish a theoretical model of the shear strength of the root–matrix composite. The main factors affecting root–matrix composite adhesion stability were the root friction coefficient and the composite moisture content. Regarding the influence of the root friction coefficient, the surface structures of the primary and lateral roots were observed using a laser confocal microscope. Using the principal component analysis method, the main factors influencing the friction properties of the root system were identified as the taproot's maximum valley depth (Rv) and the average roughness (Ra) of the profile, as well as the lateral root's maximum peak-to-valley height (Rz) and the average roughness (Rq) of the lateral root profile. The influence of both the main and lateral roots cannot be overlooked when removing inferior seedlings from the substrate. Furthermore, the bond efficiency of the root–matrix composite was calculated, revealing values of 16.03%, 49.87%, and 58.31% under low, medium, and high moisture content conditions, respectively. Finally, direct shear tests were conducted on the complex under dry-wet-dry conditions, yielding an internal friction angle of 14.1656° and a cohesion force of 1.738 ± 0.3 kPa at a water content of 20% (dry-wet). In conclusion, it is recommended to perform the negative pressure removal of inferior seedling substrate blocks during the seedling stage with low water content and underdeveloped root systems. Related research lays the foundation for preventing blockages in negative pressure pipelines.

Analyses of the Suction Anchor–Sandy Soil Interactions under Slidable Pulling Action Using DEM-FEM Coupling Method: The Interface Friction Effect

The microscale mechanisms underlying the suction anchor–sandy soil interaction under slidable pulling actions of mooring lines remain poorly understood. This technical note addresses this knowledge gap by investigating the suction anchor–sandy soil interaction from micro to macro, with a particular emphasis on the effect of interface friction. The discrete element method (DEM) was utilized to simulate the sandy soil, while the finite element method (FEM) was employed to model the suction anchors. The peak pulling forces in numerical simulations were verified by centrifuge test results. The research findings highlight the significant influence of interface friction on the pulling force–displacement curves, as it affects the patterns of suction anchor–sandy soil interactions. Furthermore, clear relationships were established between the magnitude of interface friction, rotation angle, and pullout displacement of suction anchors. By examining the macro-to-micro behaviors of suction anchor–sandy soil interactions, this study concludes with a comprehensive understanding of failure patterns and their key characteristics under different interface friction conditions. The findings proved that the interface friction not only influences the anti-pullout capacity but also changes the failure patterns of suction anchor–soil interactions in marine engineering.

Deformation Mechanism Studies by Varying Height to Diameter Ratio of Al–Mg and Al–Mg–C Metal Matrix Composites

This paper reports deformation mechanism studies by varying height-to-diameter ratio of aluminum (Al), aluminum–magnesium (Al–Mg) and aluminum–magnesium–carbon (Al–Mg–C) metal matrix composites prepared using stir casting technique. Specimen were machined to the required sizes, having different [Formula: see text] ratios (i.e. [Formula: see text], [Formula: see text] and [Formula: see text]). Mechanical properties such as hardness and deformation of the undeformed and deformed specimens were examined. Deformation test was performed under a load of 14 tonnes at different interfacial frictional conditions, i.e. dry, solid lubrication and liquid lubrication. The study revealed significant improvement in densification and hardness behavior in the composites as compared to its base metals and alloys.

The surface effect of ultrasonic vibration in double cup extrusion test

Ultrasonic vibration has been widely studied because of its excellent utility and performance in the plastic forming of metals. The mechanism and effects of ultrasonic vibration on material flow and deformation have therefore become a focus for current research. The mechanisms of ultrasonic vibration as it acts on materials include the volume effect and the surface effect. Double Cup Extrusion (DCE) testing is an ideal method for studying the surface effect but there have been few studies and some conclusions from those studies have been contradictory. For the present study, a new ultrasonic vibration-assisted DCE device was specifically designed and used for the experiment. In the tests, friction factors were calibrated and analyzed using the finite element method (FEM). The results show that ultrasonic vibration can effectively improve interface friction conditions in DCE. By changing ultrasonic loadings, an explanation was found for the ‘illusion’ that ultrasonic vibration increased interface friction, as had previously been reported. It was also shown that ultrasonic vibration exhibits a significant size effect, which can efficiently offset the negative size effect of friction in the micro-forming process. Further, it was found that the ultrasonic effect is influenced by the wall thickness of the formed part—the smaller the wall thickness, the more significant the effect of ultrasonic vibration.

A study on aluminum metal matrix preforms forging into double-hub flange

The present article presents investigation of deformation characteristics during forging (closed-die) of SiCp AMC. The preform (cylindrical) fabricated via liquid metal stir casting manufacturing route were located centrally in closed-die set with respect to its axis and forged into axi-symmetric double-hub flange component. Initial experiments were conducted to examine the mechanical characterization of the AMC preforms under consideration, which also included investigations into interfacial frictional conditions and stress-strain behaviour of the AMC material. Under a controlled die-travel till the die corners were filled completely, during forging of the preforms, corresponding height reductions and die loads were recorded. The complete deformations were considered in two stages, i.e. free barreling and constrained distortion stages. The theoretical expressions (generalized using ‘Upper Bound’ technique) for strain rates, velocity field, various energy dissipations along with average die loads for all the deformation modes considered in the present study were formulated. The variation in die loads, die cavity fills and energy dissipations due to the effect of preform aspect ratio and die velocity were critically examined and experimentally compared the results.

Plastic deformation of a metallic pre form

At work die interface investigators have used stationary die to analyze and predict the pressure and die load distribution. In this paper high speed forging with vibrating die tribological problems during forging operation have been examined. The process is influenced by several process parameters. Mathematical modeling and experimental results of the process parameters can be a useful tool for new product or process development to ascertain the load requirements, velocity fields and interfacial friction conditions, compacted at various load conditions.

Effect of height to diameter (h/d) ratio on the deformation behaviour of Fe–Al2O3 metal matrix nanocomposites

The present paper reports the effect of height to diameter (h/d) ratio on the deformation behaviour of Fe–Al2O3 metal matrix nanocomposites (MMNCs) during bulk processing. Sintered compacts were machined to the required size with different h/d ratios. Test specimens were subjected to deformation at room temperature under three different interfacial friction conditions such as dry, solid and liquid lubrications. Deformed specimens show a significant improvement in the density and hardness. Results also revealed the formation of a nanosize iron aluminate phase due to reactive sintering, which in turn contributes to grain refinement. Experimental density of the specimens was also verified with the theoretical density using the standard equations. It is expected that the present work will be useful in designing and developing MMNC products with better quality at competitive cost.

Closed Die Deformation Behavior of Cylindrical Iron–Alumina Metal Matrix Composites During Cold Sinter Forging

The present paper aims to study the closed die deformation behavior of cylindrical Fe–Al2O3 metal matrix composites (MMCs). Closed die was manufactured by machining the high carbon steel block followed by oil quenching and then finishing. Samples sintered at a temperature of 1100 °C for 1 h were characterized with X-ray diffraction and scanning electron microscopy, which showed the formation of Fe, Al2O3 and nano size FeAl2O4 phases respectively. Density and hardness of the composite samples were determined after sintering. Closed die deformation studies of the prepared composite samples were carried under three different interfacial frictional conditions i.e. dry, solid lubricating and liquid lubricating. Hardness, density and metallographic characterizations were also done for the deformed samples. On comparing the micrographs of the samples before and after deformation it was revealed that in deformed specimens recrystallization has taken place due to the difference in the energy between the strained iron matrix and unstrained alumina reinforcement during closed die forging process. Experimental density of the samples was also verified with the theoretical density using the standard equations. It is expected that the results of the present investigations will be helpful in developing quality MMC components for wide industrial applications.

A numerical approach for determination of flow curve and evaluation of frictional behavior of AZ61 magnesium alloy under elevated temperature forming conditions

The ring compression test can be used for evaluation of both the interfacial friction and the flow curve of a material at the same time. Hence, this test is employed in the paper to simultaneously determination of the flow stress and the friction factor for AZ61 alloy. This alloy can be utilized for manufacturing extruded parts with a higher production rate, compared with other magnesium alloys. Using an iterative procedure and by means of the numerical sigmoid and calibration curves, the flow curve and interfacial friction factor of the magnesium alloy are determined. This was carried out for various temperatures and strain rates. In addition, the flow behavior of as-cast AZ61 is modeled employing an exponential function. It was found that the predictions of the mathematical model were encouragingly very good. Moreover, the influences of the temperature on the interfacial friction condition and numerical sigmoid curves were greater than those of the strain rate.

ADAPTIVE INCREMENTAL FINITE ELEMENT PROCEDURE FOR SOLVING ELASTOPLASTIC FRICTIONAL CONTACT PROBLEMS SUBJECTED TO NORMAL AND TANGENTIAL LOADS

This paper presents a numerical model for analyzing the stresses and displacements of deformable bodies in contact with the presence of friction and material nonlinearity. Based on the finite element method (FEM), the elastoplastic frictional contact problem is formulated as an incremental convex programming model (ICPM) under inequality contact constraints and friction conditions. The classical Coulomb's friction law and the Prandtl–Reuss flow rule with the von Mises yield criterion are used to simulate the interface friction conditions and the elastoplastic behavior of the contacting bodies, respectively. The Lagrange multiplier approach is adopted for imposing the contact constraints. Furthermore, an effective adaptive incremental procedure is developed for solving the elastoplastic frictional contact problems. Examples for the frictional contact having advancing and receding nature are analyzed. The obtained results prove the ability of the developed procedure to investigate the sequence of different events during monotonic application of external loads. In addition, the results elucidate the effect of external side force on the friction behavior in the presence of plastic deformation. Good agreement has been found with published results.

Effects of Surface Finish and Die Temperature on Friction and Lubrication in Forging

In this study, ring compression test was conducted to investigate i) effects of surface topography on friction and lubrication at room temperature with both dry and lubricated conditions, and ii) the effect of die temperature on friction and lubrication by differentiating temperatures of die and ring samples. Findings from experiments and FE results lead to develop a pressure-dependent variable friction model that concurrently changes friction factor during the forming stroke and different contact surface areas. The constant frictional model and this variable friction model were used in FE simulations of ring compression. The prediction results were compared with experimental results in details. The use of variable friction model gave very good correlations of the final ring geometry than other constant friction models in comparison to experiments. This implies that the pressure-dependent variable friction model can better characterize the interfacial friction condition in cold forging applications. In the ring compression with heated dies, the temperature rise was found to degrade the performance of lubricant, which resulted in the tapered shape ring. Therefore, the effect of surface topography and die temperature on interfacial friction condition with lubricant viscosity should be considered for the improved friction model for FE simulations of forging processes with high stroking rates.

마이크로 성형에서 마찰거동의 크기효과에 대한 이론적 및 실험적 연구

Microforming is a very efficient and economical technology to fabricate very small metallic parts in various applications. In order to extend the use of this forming technology for the production of microparts, the size effect, which occurs with the reduction of part size and affects the forming process significantly, must be thoroughly investigated. In this study, the tribological size effect in microforming was studied using modeling and scaled ring compression experiments. A micro-scale friction approach based on the slip-line field theory and lubricant pocket model was used to understand the friction mechanism and explain the tribological size effect. Ring compression tests were performed to analyze the interfacial friction condition from the deformation characteristics of the ring specimens. In addition, finite element analysis results were utilized to quantitatively determine the size-dependent frictional behavior of materials in various process conditions. By comparing theoretical results and experimental measurements for different size factors, the accuracy and reliability of the model were verified.

A slip-line plasticity analysis of abrasive wear of a smooth and soft surface sliding against a rough (fractal) and hard surface

Abrasive wear of a soft and smooth surface sliding against a rough (fractal) and hard surface was analyzed by the slip-line theory of plasticity. The analysis is based on a slip-line model of a rigid spherical asperity (wear particle) plowing through a soft surface and removing material by microcutting. Integration of this single-contact model into a three-dimensional contact mechanics analysis of an abrasive surface exhibiting multi-scale roughness described by fractal geometry yielded relationships of the abrasive wear rate and wear coefficient in terms of the interfacial shear strength (adhesion), topography (fractal) parameters of the hard/rough surface, elastic–plastic material properties of the soft/smooth surface, and total normal load. Analytical results from the single-contact analysis provide insight into the deformation of a perfectly plastic material caused by the abrasive action of a rigid asperity/wear particle under different normal load and interfacial friction (adhesion) conditions. The dependence of the abrasive wear rate and wear coefficient on normal load (global interference), roughness of the abrasive surface, elastic–plastic material properties of the abraded surface, and interfacial shear strength (lubrication effect) is interpreted in the context of numerical results obtained for representative ceramic/ceramic, ceramic/metallic, and metal/metal sliding systems.

Investigation of dynamic effects during cold upset-forging of sintered aluminium truncated conical preforms

The present paper deals with the upper bound analysis, experimental investigation and computer simulation of upset-forging of sintered aluminium truncated conical preforms, which considers heterogeneous deformation due to barreling of preform slant sides, composite die–workpiece interfacial friction conditions, preform densification along with compression and inertia effects. A generalized theoretical expression for average forging load and preform bulged profile based on the exponential velocity field and strain rate has been established. The upset-forging experiments were conducted using the sintered preforms prepared by compacting aluminium metal powder in the closed dies and various deformation characteristics were measured. Finally, the computer simulation of the upset-forging of the sintered aluminium truncated conical preforms was performed using DEFORM software and the deformation behavior velocity, effective strain and effective stress distribution were critically studied. The effect of die speed, i.e. dynamic effects on average die load has been investigated using energy and load factors. The DOE (Design of Experiment) and RSM (Response Surface Methodology) techniques were also used to investigate and determine interrelationships between important upset-forging characteristics and the results were presented graphically. During the present investigations, it was found that inertia energy dissipation and energy factor increases, where as die load and load factor decreases exponentially with die speed. It is expected that the present work will be useful for effective assessment of various deformation characteristics during processing of sintered materials, especially at high-speed.

PREFORM MAP FOR UPSETTING ALUMINUM SPECIMENS AND ITS EXPERIMENTAL VERIFICATION

This study deals with preform maps for near net shape upsetting of aluminum billets. These maps have been developed using finite element analysis results considering 10 interfacial friction conditions and varying geometrical and processing parameters. Preform maps are experimentally verified using aluminum specimens. The proposed approach offers a powerful tool for near net shape upsetting.

Evaluation of interfacial friction condition by boss and rib test based on backward extrusion

Proper consideration of tribological problems at the contact interface between the tool and workpiece is crucial in metal forming, since interfacial friction condition plays an important role in metal forming by influencing the metal flow, forming load, die wear, etc. In order to quantitatively estimate such friction condition, a new friction testing method “Boss and Rib Test” based on the backward extrusion process is proposed in this work. In boss and rib test, a key design is to use a tube-shaped punch so that the boss and rib at the deforming workpiece along the inner and outer surfaces of the punch are formed during backward extrusion. It was experimentally and numerically revealed that the heights of the boss and rib vary according to the friction condition applied. It was also found that the height of the boss is higher than that of the rib when the friction condition at the contact interface is severe. From this finding, the shear friction factor can be evaluated according to lubricant characteristics assigned. In addition, simulation results revealed that calibration curve demonstrating deformation pattern of the workpiece is affected by strain-hardening exponent of the workpiece.

The application of neural networks in the preform design of the upsetting process

Design of the optimum preform for near net shape manufacturing is a crucial step in upsetting process design. In this study, artificial neural networks (ANN) are used to consider different interfacial friction conditions between the top and bottom die and billet interface. Two back propagation neural networks are trained based on finite element analysis results considering ten interfacial friction conditions and varying geometrical and processing parameters, to predict the optimum preform for high strength (HS) steel and commercial aluminum. Neural network predictions were verified for three new problems of both HS steel and commercial aluminum and observed that these are in close match with their simulation counterparts. It was further Experimentally verified with two commercial aluminum specimens and observed that the preform values predicted by ANN are in good agreement with experimental results.

Prediction of flow stress of metallic material and interfacial friction condition at high temperature using inverse analysis

Inverse analysis is a method for determining material parameters by minimizing the difference between experimental and the finite element (FE) simulated results, such as the load-stroke curve and barreling shape of a deformed specimen using an optimum design technique. In this study, ring compression tests were conducted to predict the flow stress of materials and interfacial friction conditions. Cylinder compression tests were conducted under the same process conditions to estimate the validity of the data obtained from the ring compression tests. By comparing the experimental results with the FE simulated results, it was confirmed that flow stress and the interfacial friction condition obtained from the ring compression tests, as well as their inverse analysis, are quite reasonable. The validity of both the flow stress function and the interfacial friction condition using the above procedures was verified by the experiments.

보스-리브 시험 시 마찰보정선도에 대한 펀치형상 및 유동응력의 영향

Recently, boss and rib test based on backward extrusion process was proposed to quantitatively evaluate the interfacial friction condition in bulk forming process. In this test, the tube-shaped punch with hole pressurizes the workpiece so that the boss and rib are formed along the hole and outer surface of the punch. It was experimentally and numerically revealed that the height of boss is higher than that of the rib under the severe friction condition. This work is focused on the effect of the punch design and flow stress on deformation pattern in boss and rib test. From the boss and rib test simulations, it was found that there is slight variation in both the heights of boss and rib according to the length of punch land, nose radius, and face angle. However the hole diameter of the punch and the clearance between the punch and die have a significant influence on the calibration curves showing the heights of the boss and rib. In addition, the effect of flow stress on the calibration curves was investigated through FE simulations. It was found that there is no effect of strength coefficient of the workpiece on the calibration curves for estimation of friction condition. On the other hand, the strain-hardening exponent of the workpiece has a significant influence on the calibration curve.

Experimental Study of Lubrication Influence in the Production of Hydroformed T-Joint Tubes

THF process is a forming technique that consists of tube deformation by means of hydraulic pressure and punches which guarantee the tube ends feeding and sealing. In the last years, this technique found a large and rapid diffusion thanks to its many advantages with respect to conventional processes: parts weight reduction, tighter dimensional tolerances, lower costs or fewer secondary assembly operations. Besides, many lacks in the process knowledge still represent an obstacle and they are usually bypassed by trial and error methods. Therefore, lot of studies were conducted to better understand the influence of the process parameters, such as pressure path, punch stroke or material behaviour. In this paper, an experimental study of tubular T-joints made of copper manufactured by means of THF process is described. The aim of this work is to analyze the tube-die interface friction condition effects on the final part. In fact, material flow during the process is greatly influenced by the friction conditions between tube and die especially due to the high pressure acting inside the tube. Different lubrication types were considered: dry, oil, Teflon, Teflon with oil, Teflon spray and Graphitic oil. Two different experimental campaigns were performed in this investigation. The first one was carried out in order to estimate the lubricant friction coefficients using a Pin on Disk tribometer. The second one was performed to study the effects of the lubrication on the process and the tests were conducted hydroforming T-joints under the different lubrication conditions considered. The collected data allowed to identify how the different lubrication conditions affect the final workpiece geometry. Moreover, a critical aspect of the process related to the tube wrinkling was identified and a solution was proposed.