Papers by Keyword: Friction Law

Abstract: The paper presents the results of the study of the friction of the spherical ball made of steel SHKH15 on the flat surface of the prism of steel R6M5. It has been established that as a result of the friction of the rotation according to the “ball-plane” scheme, at a steady wear mode, the torque of the friction of the rotation also becomes steady. It is shown that the change in the friction torque of the rotation from the load does not fit within the limits of one linear dependence, similar to G. Amonton's law. Semi-empirical models of friction rotation are given.

Abstract: Cutting tools made of polycrystalline diamond (PCD) are used for machining of aluminum alloys, fiber-reinforced plastic composites and wood. Compared to cemented carbide tools with geometrically defined cutting edges, PCD tools offer significant advantages with respect to tool life. High demands regarding the cutting edge roughness and the quality of the rake and the flank face usually require a grinding process with diamond grinding wheels. The PCD grinding process, however, is characterized by low material removal rates and high grinding wheel wear. The material removal rate and the grinding wheel wear, in turn, highly depend on the process state variables process force and process temperature. However, the relationship between these process state variables and the process input variables is largely unknown. This work provides a contribution to the closure of this knowledge gap by means of an adapted friction law. A single grain friction test stand using the pin-disk principle was developed, which enables a measurement of the friction force and the contact zone temperature for normal forces and relative speeds that are common in PCD grinding. During the experiments, the specification of the PCD disc, the cross-sectional area of the friction sample made of monocrystalline diamond as well as the process parameters normal force and relative speed were varied. In addition, the tests were carried out without lubrication as well as with a minimum lubrication. A high correlation between the contact force and the coefficient of friction was determined. This relationship was mathematically formulated in a friction law. In addition, a direct influence of the contact force and the relative velocity on the contact zone temperature was identified. The knowledge gained leads to an improved understanding of the PCD grinding process and thus enables a more efficient grinding process design.

Abstract: The subject of this paper was the presentation of a holistic, fully-temperature-coupled FE model of inertia friction welding based on the modified friction law, which divided the friction welding process into beginning friction stage and steady equilibrium friction stage. At each of the stage Coulomb friction model and shear friction model were adopted respectively. The present FE model predicted the temperature of the welding joint as well as variation of friction torque and relative rotating velocity of the work-piece during the welding process. The evolution of friction torque and rotating velocity were compared with the experimental measurement. They showed a good agreement between them.

Abstract: During the pressing step, the clay tiles undergo stresses which result in the appearance of defects. A rheological study, based on free compression tests, allowed to confirm the Elasto-visco-plastic behaviour of the clay. The different constitutive parameters were estimated by fitting the force-displacement experimental curves using the optimisation algorithm (ES Metamodel) implanted in the commercial software Forge 2009®. The influence of the tribological parameters was studied using squeezing numerical simulations of a full tile. The numerical model was validated with experimental squeezing test of technological specimen with a tile lug. Then, we have compared experimental force with the numerical one and deduced that the clay/tool interface is not perfectly sliding. A friction Tresca’s law was used to model the clay/tool interface. Numerical results showed that the actual geometry of tile lug didn’t allow to form correctly the tile. Several areas undergo tensile stress, air traps ,... A new geometry of tile lug was proposed in order to limit this phenomenon. Using a simplified defect criteria (Latham and Cockroft), the numerical model allowed to locate the areas where there is a risk of crack.

Abstract: This paper presents a finite element model for the simulation of aircraft tire rolling. Large deformations, material incompressibility, heterogeneities of the material, unilateral contact with Coulomb friction law are taken into account. The numerical model will allow estimating the forces in the contact patch - even in critical and extreme conditions for the aircraft safety and security. We show the influence of loading parameters (vertical load, velocity, inflating pressure) and slip angle on the Self Aligning torque and on the lateral friction coefficient. A friction coefficient law corresponding to Chichinadze model is considered to take into account thermal effects in the aircraft tire model behaviour.

Abstract: Residual stresses are very important for the lifetime of pieces in their mechanisms. These kind of damages are mainly caused by mechanical, thermal, and metallurgical affectations of the machined material. To control these affectations, we need to link the cutting parameters to the residual stress state observed onto the workpiece surface and depth. These connections can be made with analytical works, experimental works or numerical works. In our case, it has been chosen to work with a numerical support in order to observe and understand precisely the phenomenon involved during cutting operation. While this way of study is really popular, we proposed to model the residual stress generation in a original way by keeping aside the chip formation. This new approach presented in a previous paper was simple and only use a 2D model. This first model moves thermo mechanical loadings onto the workpiece surface to recreate the relative motion between the tool and the workpiece. The new 3D model, presented in this paper, is now improved with an original friction law. It underlines the impact of each passage of the tool onto the others. The physical properties are thermo dependant and the flow stress model is based on a Johnson cook behaviour.

Abstract: The thermo-mechanical simulation of Friction Stir Welding focuses the interest of the welding scientific and technical community. However, literature reporting material flow modeling is rather poor. The present work is based on the model developed by Heurtier [2004] and aims at improving this thermo-fluid simulation developed by means of fluid mechanics numerical and analytical velocity fields combined together. These various velocity fields are investigated separately and especially according to the power dissipated during the flow. Boundary conditions are considered through a new approach based on the kinematic analysis of the thread of the pin. An equilibrium is established between the vertical motion of the bulk material dragged in the depth of the metal sheet, and its partial circulation around the pin. The analyses of the obtained velocity fields enable the understanding of the welded zone asymmetry and highlights the bulk material mixing between the welded coupons in the depth of the sheet. A regression is performed on the relative sliding velocity of the aluminium according to the surface of the tool: shoulder and pin. Two dimension flow lines in the depth of the metal sheet are then obtained and successfully compared with the results obtained by Colegrove (2004) [1].