Plastic Friction Research Articles

Dynamic Response of Mold Oscillator Interacting with Steel Slabs

A mathematical model to show the dynamic response of the mold oscillator was suggested. The model considered a frictional interaction between the mold oscillator and slab as several connected nodes. The governing equation considered the slab as a multi-degree-of-freedom (DoF) system, and included a hysteresis model to describe elastic-plastic behavior of the slab; the mold oscillator was given two DoF by utilizing pressure and displacement experiment data. Simulations indicate that the mold and slab execute various vibrations, and that mold oscillation marks are caused by a stick-and-slip phenomenon during intervals, in which the slab contacting the mold moves downward compared to the other slab (negative strip time). The slab shows the formation of mold oscillation marks to previous formation criterion equally when the mold velocity is faster than the casting speed about downward. The oscillation mark will grow up over 2 Hz exciting frequency with constant 4 mm stroke in simulations. Finally, the negative strip time was compared to the frictional force, hysteresis variable, and plastic force to investigate formation mechanism of the oscillation marks.

An experimental investigation on effect of minimum quantity cooling lubrication (MQCL) in machining titanium alloy (Ti6Al4V)

During the machining operation, elevated temperatures are achieved at the cutting interface due to the presence of high plastic deformation and friction in between the tool and chip contacting area. Efficient heat dissipation from the cutting interface is required to achieve better machining performance. Elevated temperature in the cutting area results in lower tool life as it facilitates different types of wear mechanisms. Metal working fluids (MWFs) are employed to reduce heat and friction in the cutting zone, simultaneously to help in the flushing of waste particles. The MWFs are based on either water or petroleum oil and include several additives which make them non-biodegradable and toxic in nature. The minimum quantity lubrication (MQL) method offers a feasible substitute to the MWF-based conventional flood cooling method. In this study, a vegetable oil-based MQL system was mixed with sub-zero temperature air to design a new minimum quantity cooling lubrication (MQCL) system. The study investigates the machinability of Ti6Al4V using an MQCL system under various oil flow rates and compared its machining performance with both dry cutting and conventional flood cooling. For further evaluation, the study investigated surface roughness, flank wear, and associated wear mechanisms. It was found that in the MQCL system (60–70 ml/h), oil supply rates provided reliable machining performance at higher feed levels.

Numerical Simulation of Friction Stir Spot Welding

Friction Stir Spot Welding (FSSW) is a solid state joining process that relies on frictional heating and plastic deformation realized at the interaction between a non-consumable welding tool that rotates on the contact surfaces of the workpieces. Friction Stir Spot Welding (FSSW) is an evolving technique that has received considerable attention from automotive industries to replace electric resistance spot welding, which shows poor weldability for advanced high-strength steels as well as aluminium alloys. Because of the interest shown by the industry towards this process, an attempt to optimize it is imperative. But the experiments are often time consuming and costly. To overcome these problems, numerical analysis has frequently been used in the last years. The purpose of this paper is to develop a three-dimensional fully coupled thermal-stress finite element (FE) model of FSSW process for thin aluminium alloy Al 6061-T6. Numerical simulation being helpful for better understanding and observation of the influence of input parameters on the resulting phenomena. It is described the algorithm and are presented the activities needed to be performed in order to develop a valid numerical model for FSSW. The validation of the numerical model being achieved by comparing the resulted temperatures from the numerical simulation with the experimentally determined temperatures for the same material

Damage and plastic friction in initially anisotropic quasi brittle materials

A three dimensional micro-mechanical model is developed for modeling micro-crack growth and plastic frictional sliding in initially anisotropic quasi brittle materials under compressive loading. Macroscopic strains are attributed to elastic deformation of matrix and displacement discontinuity on micro-cracks. Effective elastic properties of cracked materials are determined using a Eshelby's solution based linear homogenization technique by considering micro-cracks as spheroidal inclusions. An efficient numerical method is used to calculate Hill polarization tensor for spheroidal micro-cracks arbitrarily embedded in transversely isotropic solid matrix. Based on this, the plastic strain related to frictional sliding on closed micro-cracks is determined by combining irreversible thermodynamics and homogenization method. A specific plastic friction criterion is formulated in terms of the local stress field on crack surfaces. The presence of a back stress tensor allows description of material hardening and softening without any additional functions. A specific damage evolution law is finally proposed. The evolutions of the friction-related plastic strain and crack-propagation induced damage are inherently coupled. A series of numerical assessments are presented for various loading paths such as uniaxial compression, triaxial compression and shear. The obtained numerical results clearly reveal that the macroscopic behaviors of cracked materials are strongly affected by the initial anisotropy. Finally, the performance of the proposed micro-mechanical model is verified by comparing numerical results and experimental data for a typical rock-like materials, shale.

A thermodynamically consistent cohesive-frictional interface model for mixed mode delamination

A new interface constitutive model based on damage mechanics and frictional plasticity is presented. The model is thermodynamically consistent, it is able to accurately reproduce arbitrary mixed mode debonding conditions and it is proved that the separation work is always bounded between the fracture energy in mode I and the fracture energy in mode II. Analytical results are given for proportional loading paths and for two non-proportional loading paths, confirming the correct behavior of the model for complex loading histories. Numerical and analytical solutions are compared for three classical delamination tests and frictional effects on 4ENF are also considered.

Theoretical prediction and numerical studies of expanding circular tubes as energy absorbers

This work investigated the energy absorption behavior of expansion circular tubes. This kind of energy absorption device dissipates the impact of kinetic energy through plastic deformation and friction. A finite element model (FEM) was established with reference to the size of the coupler, which was used for connecting two vehicles. A special case was designed to validate the accuracy of the FEM. Furthermore, a theoretical prediction model that took into consideration the additional shear deformation and expansion ratio enlargement was compared with the steady compressional force of the experiment and numerical simulation. The theoretical prediction was accurate. Based on this valid FEM, a series of parameter studies was developed. Specifically, a list of conical mandrels with different angles from 5° to 40° was established, and the coefficient of friction varied from 0 to 0.3. Both had great influence on energy absorption. The relationship between the expansion angle and steady compressional force is nonlinear, while the friction coefficient and steady compressional force are linear. With friction, the inflection point of force curve existed between 10° and 20°.

Molecular dynamics simulation on the tribology properties of two hard nanoparticles (diamond and silicon dioxide) confined by two iron blocks

The tribology behaviors of diamond and silicon dioxide (SiO2) nanoparticles were examined via molecular dynamics simulations; four cases were simulated. At low velocity and low load, the nanoparticles separated the two blocks from each other and acted as ball-bearings. The plastic deformation, temperature distribution, and friction force were all improved due to the action of the nanoparticles. However, the crushing of the SiO2 nanoparticles was accompanied by deformation-induced loss of the rolling effect, when the load was increased. Without nanoparticles, a transfer layer formed at high velocity and low load. The two nanoparticles provided support for a certain duration. However, at high velocity and high load, the support effect of these nanoparticles was lost in a short sliding time.

Tribology behavior during indentation and scratch of thin films on substrates: effects of plastic friction

When friction stress on a contact surface reaches material yield strength in shear, contact slippage can occur even if the slipping condition for Coulomb friction is not satisfied. In this paper, a three-dimensional (3-D) scratch model is proposed, which considers combined Coulomb and plastic friction. Influences of plastic friction are discussed for two continuous displacement loading steps: indentation and scratch. For indentation, initially the sliding on the contact surface can not take place and the complete cohesion condition should be employed; then as the indenter is further compressed down to the coating surface, plastic friction instead of Coulomb friction prevails in most of the contact region. For scratch, the previous complete cohesion at the initial indentation is substituted by plastic or Coulomb slipping, and the slippage becomes plastic-sliding governed for a slightly large indentation depth. The effects of the indentation depth and the Coulomb friction coefficient on the scratch friction coefficient are discussed in detail. Several experimental phenomena are interpreted, which include that with an increase of the normal loading, the scratch friction coefficient reduces for the soft coating but grows for the hard coating; and with the growth of hardness after heat treatment, the scratch friction coefficient increases due to weak plastic slippage. Obtained results help to elucidate tribological behaviors during scratch and are helpful for the interpretation of experimental phenomena and the improvement of numerical simulations for the scratch process.

Analysis of hot strip rolling using exponent velocity field and MY criterion

Rolling force and torque are critical in hot strip rolling process and they affect the setup rolling schedule, the thickness accuracy and the final product profile. In order to obtain the accurate rolling force and torque, a new exponent velocity and corresponding strain rate field are firstly proposed in this paper. The fields and linear MY (mean yield) criterion, as well as the co-line vector inner product method are used respectively in integration of the internal plastic deformation and friction power terms. Ultimately, an analytical solution of total power functional is given. The analytical expressions of rolling torque, rolling force and stress effective factor are obtained by minimizing the total power functional. To verify the validity of the proposed analytical solution, the calculated rolling forces are compared with on-line measured ones in a hot strip rolling plant. Results show that the analytical solutions are in good agreement with the actual measured ones, and the relative errors are less than 8.39%. Besides, the effects of various rolling conditions such as friction factor, reduction rate and shape factor, on rolling force and torque, location of neutral point, and stress state coefficient are discussed.

Upper bound analysis of rolling force and dog-bone shape via sine function model in vertical rolling

The control of the slab width in actual production is realized by the widely use of vertical rolling (edge rolling). According to the incompressibility condition, the sine function dog-bone model is firstly proposed in this paper for steady state deformation in vertical rolling with flat rolls combined with the actual conditions. Based on the first variation principle of rigid-plastic material, the variable upper bound integration method is used to integrate plastic deformation, shear and friction power terms. The upper bound solutions of rolling force and dog-bone shape are solved numerically, and this process is carried out using Matlab Optimization Toolbox by minimizing the total power functional. Results show that the rolling force increases and the dog-bone shape size become larger while engineering strain, initial thickness, or roll radius increases. The results obtained from sine function model are compared with those of experimental data in reference and FEM simulation, and a good agreement is found. The comparison shows that it is possible to determine the required optimum rolling force and dog-bone shape by using sine function model.

Development of Surface Nanocomposite Based on Al-Ni-O Ternary System on Al6061 Alloy by Friction-Stir Processing and Evaluation of Its Properties

In this study, an Al/Al2O3-Al3Ni hybrid nanocomposite was developed on the surface of Al6061-T6 plate with preplaced NiO powder on its surface using friction-stir processing (FSP). The x-ray diffraction results showed that NiO particles were reduced by Al during FSP and Al3Ni and Al2O3 were formed as in situ reaction products. A thermodynamic analysis indicated that the reaction is thermodynamically possible and exothermic. Thus, the reaction that is initiated by the severe plastic deformation and friction associated with FSP could continue by the heat that is generated by the exothermic reaction. During each FSP pass, the FSP products are detached quickly from the interface and the growth of the particles is limited and nanometer-sized reinforcements were produced. The presence of facet and hexagonal nanoparticles in transmission electron microscopy micrographs of the stir zone confirmed the formation of Al3Ni and Al2O3 nanoreinforcements, respectively. Mechanical test results showed that the microhardness and ultimate tensile strength in the stir zone of nanocomposite decreased due to the dissolution of precipitates in Al6061-T6 during FSP. The tribological properties of Al6061 at 350°C were significantly improved by developing surface Al/Al2O3-Al3Ni nanocomposite.

Analysis of heat transfer and material flow in reverse dual-rotation friction stir welding

Reverse dual-rotation friction stir welding (RDR-FSW) is a novel variant of conventional FSW process. The key feature is that the tool pin and the assisted shoulder rotate reversely and independently during the process; thus, it has great potential to improve the weld quality and lower the welding loads through adjusting the rotating speeds of the tool pin and the assisted shoulder independently. In this study, a 3D model of RDR-FSW process is developed to conduct the numerical simulation of heat generation, material flow, and temperature profile during the process. Heat generated due to plastic deformation and friction at the tool-workpiece contact interfaces are both considered. Streamlines show that there are two material flows with reverse direction, which is beneficial to the uniformity of both the temperature and the microstructure at the advancing side and retreating side. The simulation results show that rotating speeds of the assisted shoulder and the tool pin have great effects on the shape and size of the thermo-mechanically affected zone (TMAZ). The calculated peak temperatures at typical locations match with the experimentally measured ones. It lays solid foundation to optimize the process parameters in RDR-FSW.

Novel material and structural design for large-scale marine protective devices

Abstract Large-scale protective devices must endure the impact of severe forces, large structural deformation, the increased stress and strain rate effects, and multiple coupling effects. In evaluation of the safety of conceptual design through simulation, several key parameters considered in this research are maximum impact force, energy dissipated by the impactor (e.g. a ship) and energy absorbed by the device and the impactor stroke. During impact, the main function of the ring beam structure is to resist and buffer the impact force between ship and bridge pile caps, which could guarantee that the magnitude of impact force meets the corresponding requirements. The means of improving anti-collision performance can be to increase the strength of the beam section or to exchange the steel material with novel fiber reinforced polymer laminates. The main function of the buoyancy tank is to absorb and transfer the ship’s kinetic energy through large plastic deformation, damage, or friction occurring within itself. The energy absorption effect can be improved by structure optimization or by the use of new sandwich panels. Structural and material optimization schemes are proposed on the basis of conceptual design in this research, and protective devices constructed of sandwich panels prove to have the best anti-collision performance.

A finite element study on effect of frictional heating in the taylor rod impact problem

In an impact phenomenon the material is subjected to very short duration high force levels resulting large plastic deformations and rise in temperature at high strain rates. A circular rod impacting against a rigid surface called as Taylor rod impact test is widely used for determining the mechanical behaviour of materials subjected to high strain rates with associated increase in temperature. A three-dimensional large deformation, thermo-elasto-plastic, dynamic, contact, finite element formulation is developed to study the effect of temperature rise due to plastic deformation and surface friction on the deformation and stress fields. It is found that the predicted equivalent plastic strain values are influenced by temperature generated due to plastic deformation and surface friction. The values of the coefficient of friction have a profound effect on the location of fracture initiation on the impacting face in a circular rod.

Molecular dynamics investigation of the effect of copper nanoparticle on the solid contact between friction surfaces

This study investigated the effect of copper (Cu) nanoparticles on the solid contact between friction surfaces by applying a molecular dynamics method to reveal the mechanisms responsible for the favorable friction properties of nanoparticles. Two models were built, which were named model A (without Cu) and model B (with Cu), respectively. The differences in the mechanical properties between these two models were compared. The simulation results demonstrated that the improvement in friction properties by Cu nanoparticles was more obvious at low velocity than at high velocity. At low velocity, a Cu nano-film was formed on the friction surface, which accommodated the velocity gradient and plastic deformation. Due to the good lubrication effect of the nano-film, the plastic deformation, defect structures and friction force of model B were improved compared with model A. Under high velocity conditions, a transfer layer appeared adjacent to the interface in both models. Because of this, the friction forces of the two models decreased with increased velocity. The fluid mechanics theory was used to explain why the friction force in model B was lower than that in model A at high velocity. The effect of the load on friction properties was also analyzed and the results showed that the mechanisms of anti-wear and friction reduction by Cu nanoparticles under a low load were the same as those under a high load.

Characterization of bi-planar and ploughing failure mechanisms in footwall slopes using numerical modelling

Footwall slopes refer to unbenched rock slopes in which the slope face is parallel to a set of persistent discontinuities (e.g. bedding planes, foliation, faults). These are commonly encountered in weak, thinly bedded, orthogonally jointed, sedimentary rock sequences. Common failure mechanisms include bi-planar failures where shallow dipping crosscutting structures daylight near the slope toe, enabling sliding to occur along steep dipping bedding planes. In the absence of crosscutting structures, failure occurs through deformation and rock mass yielding involving the formation of inter block shear and toe breakout surfaces. Because of the complexity of the toe breakout mechanism, evaluation methods are not well understood. An improved understanding of the failure mechanism, the role of adverse discontinuities, and characterization of the discontinuity, intact rock and rock mass strength properties are key for a successful footwall stability analysis. This paper investigates the development of the inter block shear and toe breakout surfaces with three approaches: i) continuum-based frictional plasticity theory; ii) discontinuum-based distinct-element modelling with Voronoi tessellation using the commercial software UDEC; and iii) hybrid continuum/discontinuum finite-/discrete-element brittle fracture modelling using the commercial software ELFEN. Numerical simulations using ELFEN and UDEC demonstrated a good agreement with frictional plasticity theory. Ploughing failure of footwall slopes is also evaluated, specifically the influence of cross-cutting discontinuity dip angle relative to the slope face. The effects of different geometrical parameters (e.g., slope angle and depth/height ratio) on bi-planar and ploughing failure are assessed using a sensitivity analysis approach. A “Damage Intensity” parameter is introduced and used to quantify damage in the numerical simulations using ELFEN.

Modelling of Inertia Friction Welding Using Finite Element Analysis and Computational Fluid Dynamics

Inertia Friction Welding (IFW) is a solid-state joining process where one rotating (connected to an inertia) and one stationary part are brought together under an axial load, causing frictional heat generation and plastic deformation at the interface; upon cooling a weld is formed between the components. There is evidence in welds between dissimilar materials which show a flow regime that may keep impurities at the weld interface and may have implications for weld strength and fatigue life. Numerical modelling of IFW using Finite Element Analysis (FEA) has allowed the successful prediction of temperature profile, upset (length loss) and flash shape and process parameters such as flywheel slowdown. However, due to the lack of knowledge of the behaviour of the severely plasticised zone (shear zone) and the fluid-like nature of the material near the interface, the use of Computational Fluid Dynamics (CFD) has been considered. This paper presents a method to utilise both FEA and CFD modelling techniques to provide a better modelling strategy for the IFW processes. By using the results of an FEA model as the boundary/initial conditions for the CFD, simple models have allowed comparison between the two numerical approaches and have validated the implementation and consistency of material properties and modelling methodology for both. A model of the interface has been produced with CFD with this method which illustrates the possible material behaviour and material flow in that zone.

Investigation of pile-up during a rigid ball sliding on coated surface based on elastic–plastic analysis

A three-dimensional finite element model (FEM) is used to study the development of pile-up and contact situation during nano-indentation and sliding indentation of elastic–plastic coated solids. The FEM results were verified by nano-indentation and sliding indentation tests which were carried out on TiN specimens. Then, the influence of elastic–plastic deformation, penetration depth, contact friction and strain hardening on pile-up was investigated for a wide range of materials with different elastic modulus, yield stresses, strain-hardening exponents and friction coefficients. The results indicated that the pile-up/sink-in geometry depends on the relative amounts of elastic and plastic deformation characterized by (E/σy), in a way that pile-up grows by increasing (E/σy). At small non-dimensional penetration depth (h/R), the deformation is only elastic, then by increasing the load, the plastic zone grows and spreads upward and the sink-in diminishes. It was found that friction severely enhances pile-up only in small amounts of strain hardening exponent. In addition, the influence of a unified parameter on pile-up was utilized to investigate some parameters simultaneously for various strain hardenings which depicted that increasing strain hardening exponent leads to smaller pile-up. The finite element results may be used as a first estimate of the pile-up/sink-in behavior if the material parameters are known.

Strain-induced phase transformation under compression in a diamond anvil cell: Simulations of a sample and gasket

Combined high pressure phase transformations (PTs) and plastic flow in a sample within a gasket compressed in diamond anvil cell (DAC) are studied for the first time using finite element method. The key point is that phase transformations are modelled as strain-induced, which involves a completely different kinetic description than for traditional pressure-induced PTs. The model takes into account, contact sliding with Coulomb and plastic friction at the boundaries between the sample, gasket, and anvil. A comprehensive computational study of the effects of the kinetic parameter, ratio of the yield strengths of high and low-pressure phases and the gasket, sample radius, and initial thickness on the PTs and plastic flow is performed. A new sliding mechanism at the contact line between the sample, gasket, and anvil called extrusion-based pseudoslip is revealed, which plays an important part in producing high pressure. Strain-controlled kinetics explains why experimentally determined phase transformation pressure and kinetics (concentration of high pressure phase vs. pressure) differ for different geometries and properties of the gasket and the sample: they provide different plastic strain, which was not measured. Utilization of the gasket changes radial plastic flow toward the center of a sample, which leads to high quasi-homogeneous pressure for some geometries. For transformation to a stronger high pressure phase, plastic strain and concentration of a high-pressure phase are also quasi-homogeneous. This allowed us to suggest a method of determining strain-controlled kinetics from experimentation, which is not possible for weaker and equal-strength high-pressure phases and cases without a gasket. Some experimental phenomena are reproduced and interpreted. Developed methods and obtained results represent essential progress toward the understanding of PTs under compression in the DAC. This will allow one optimal design of experiments and conditions for synthesis of new high pressure phases.

Implicit Geometry Meshing for the simulation of Rotary Friction Welding

The simulation of Rotary Friction Welding (RFW) is a challenging task, since it states a coupled problem of phenomena like large plastic deformations, heat flux, contact and friction. In particular the mesh generation and its restoration when using a Lagrangian description of motion is of significant severity. In this regard Implicit Geometry Meshing (IGM) algorithms are promising alternatives to the more conventional explicit methods. Because of the implicit description of the geometry during remeshing, the IGM procedure turns out to be highly robust and generates spatial discretizations of high quality regardless of the complexity of the flash shape and its inclusions.A model for efficient RFW simulation is presented, which is based on a Carreau fluid law, an Augmented Lagrange approach in mapping the incompressible deformations, a penalty contact approach, a fully regularized Coulomb-/fluid friction law and a hybrid time integration strategy. The implementation of the IGM algorithm using 6-node triangular finite elements is described in detail. The techniques are demonstrated on a fairly complex friction welding problem, demonstrating the performance and the potentials of the proposed method. The techniques are general and straight-forward to implement, and offer the potential of successful adoption to a wide range of other engineering problems.