Aspect ratio, friction forces and normal forces in strip rolling

A study of silver-nickel electrical contact materials : L.Janqiong et al, (Guilin Research Inst. for Electrical Appliance Science, China.) PM Technology, Vol 9, No 4, 1991, 209–214. (In Chinese.)

The friction force between nanoparticles and a silicon wafer is a crucial parameter for cleaning processes in the semiconductor industry. However, little is known about the pH-dependency of the friction forces and the shear strength at the interface. Here, we push polystyrene nanoparticles, 100 nm in diameter, with the tip of an atomic force microscope and measure the pH-dependency of the friction, adhesion, and normal forces on a silicon substrate covered with a native silicon dioxide layer. The peak force tapping mode was applied to control the vertical force on these particles. We successively increased the applied load until the particles started to move. The main advantage of this technique over single manipulation processes is the achievement of a large number of manipulation events in short time and in a straightforward manner. Geometrical considerations of the interaction forces at the tip-particle interface allowed us to calculate the friction force and shear strength from the applied normal force depending on the pH of an aqueous solution. The results clearly demonstrated that particle removal should be performed with a basic solution at pH 9 because of the low interaction forces between particle and substrate.

Study of scratching Mg-based BMG using nanoindenter with Berkovich probe

Friction force measurements relevant to de-inking by means of atomic force microscope

Lowering friction coefficient under low loads by minimizing effects of adhesion force and viscous resistance

Geckos can run rapidly on walls and ceilings, requiring high friction forces (on walls) and adhesion forces (on ceilings), with typical step intervals of approximately 20 ms. The rapid switching between gecko foot attachment and detachment is analyzed theoretically based on a tape model that incorporates the adhesion and friction forces originating from the van der Waals forces between the submicron-sized spatulae and the substrate, which are controlled by the (macroscopic) actions of the gecko toes. The pulling force of a spatula along its shaft with an angle between theta 0 and 90 degrees to the substrate, has a "normal adhesion force" contribution, produced at the spatula-substrate bifurcation zone, and a "lateral friction force" contribution from the part of spatula still in contact with the substrate. High net friction and adhesion forces on the whole gecko are obtained by rolling down and gripping the toes inward to realize small pulling angles between the large number of spatulae in contact with the substrate. To detach, the high adhesion/friction is rapidly reduced to a very low value by rolling the toes upward and backward, which, mediated by the lever function of the setal shaft, peels the spatulae off perpendicularly from the substrates. By these mechanisms, both the adhesion and friction forces of geckos can be changed over three orders of magnitude, allowing for the swift attachment and detachment during gecko motion. The results have obvious implications for the fabrication of dry adhesives and robotic systems inspired by the gecko's locomotion mechanism.

Whereas for sliding friction the Amonton-Coulomb law clearly states the proportionality between the friction force and the normal force, the rolling friction torque and normal force dependency is assumed linear in some references and nonlinear in others. The coefficient of rolling friction can be obtained using various pendula, based on the assumption of linear dependence between the rolling friction torque and normal force. The theoretical models lead to a linear decrease of angular amplitude (confirmed experimentally for the dry sliding friction case) while the experimental damping of amplitude is nonlinear for any of the employed pendula. The basis for finding the rolling friction coefficient is the equality between the theoretical and experimental slopes of the decreasing angular amplitude of the pendulum. Due to this nonlinearity, the value of the coefficient of rolling friction depends on the launching amplitude of the pendulum. In the present paper the equation of motion of the evolvent pendulum is obtained based on the hypothesis that the dependency of resistant torque on normal force is a power law. Experimental tests performed with the new heavy pendulum have confirmed a nonlinear, exponential attenuation of angular amplitude. Thus, finding the coefficient of rolling friction for the least favourable situation was aimed. This happens when the launching amplitude of the pendulum has the highest possible value and occurs when the ratio between the tangential force and the normal force equals the coefficient of sliding friction. A technique is proposed for obtaining the critical value of the coefficient of rolling friction.

We measured normal and friction forces simultaneously using a recently developed cantilever-based optical interfacial force microscope technique for studies of interfacial structures and mechanical properties of nanoscale materials. We derived how the forces can be incorporated into the detection signal using the classical Euler equation for beams. A lateral modulation with the amplitude of nanometers was applied to create the friction forces between tip and sample. We demonstrated its capability by measuring normal and friction forces of interfacial water at the molecular scale over all distance ranges.

Echelle gratings, a specialized type of diffraction grating, feature a periodic groove pattern that exhibits excellent light-splitting capabilities. These gratings are characterized by a low density of lines per millimeter and a significant blaze angle. The primary substrate for echelle gratings in mechanical scratching is an aluminum film with a layered structure, which is determined by the coating process. However, the unique interlayer structure of the layered aluminum film, combined with the challenges posed by deep and high-precision triangular diffraction grooves, complicates the control of the scratching process. This article aims to investigate the material removal process and the thermal field-assisted scratching mechanism in the nano-scratching of polycrystalline layered aluminum films, with a particular emphasis on the material removal mechanism involved in nano-scratching. It discusses the influence of the thermal field and grain size on the mechanical response and the material removal process, while thoroughly examining their effects on the accuracy of groove formation. The results indicate that as the temperature increases, both the frictional and normal forces exhibit a decreasing trend. Additionally, a reduction in grain size corresponds to smaller frictional and normal forces. This decrease in scratching force contributes to minimizing the deformation of the workpiece during the scratching process, which is advantageous for precise control of groove shape and enhances the scratching quality of large-area gratings. As the temperature increases, the number of atoms removed from the polycrystalline layered aluminum film rises, leading to an enhanced material removal rate. Consequently, the accuracy of the diffraction grating groove also improves. Concurrently, the presence of delaminated grain boundary interfaces impedes the downward propagation of defects such as dislocations and can accommodate these dislocations. As temperature rises, the total length of dislocation lines decreases. Elevated temperatures promote the transformation of the crystal structure into an amorphous state. The grain boundaries and interlayer grain boundaries at the delamination restrict the movement of dislocations. The deformation behavior suggests that grain boundaries significantly contribute to the suppression of strain and stress propagation, resulting in a gradient distribution at the layered grain boundary interface, which further impedes stress transmission. Stress and strain are concentrated not only in the contact area between the tool tip and the substrate but also within the grain boundaries and their adjacent regions.

An analytical formulation for the vectors of contact forces and the stiffness matrix of the non-linear friction contact interface is developed for the analysis of multi-harmonic vibrations in the frequency domain. The contact interface elements provided here an exact description of friction and unilateral contact forces at the interacting surfaces, taking into account the influence of the variable normal load on the friction forces, including the extreme cases of separation of the two surfaces. Initial gaps and interferences at the contact nodes, which affect the normal force, as well as the unilateral action of the normal force at the contact surface, are all included in the model. The accurate calculation of the force vector and the tangent stiffness matrix provides a very reliable and fast convergence of the iteration process used in the search for the amplitudes of nonlinear vibrations of bladed discs. Numerical investigations demonstrate excellent performance with respect to speed, accuracy and stability of computation.

Pile-up and heat effect on the mechanical response of SiGe on Si(0 0 1) substrate during nanoscratching and nanoindentation using molecular dynamics

A modified rough interface model considering shear and normal elastic deformation couplings

Characteristics of force transmission in cohesive agglomerates impacting a rigid surface

Frictional forces for disc-type pigging of pipelines

Normal and tangential forces coexist between rough surfaces in engineering components under most operating conditions. Accurate measurement of contact forces (both normal and tangential forces) on rough surfaces is critical for the safety and stability of engineering equipment, as interfaces are typically discontinuous regions within mechanical systems. However, existing contact mechanics and electrical contact models mostly neglect tangential force effects, hindering their application to shearing behavior research and precluding the development of a contact force measurement methodology applicable to simultaneous normal and tangential force quantification. Inspired by the yield criterion for material damage, a contact mechanics model was developed that simultaneously accounts for the effects of normal and tangential forces. Then, a new principle of contact forces measurement is developed by correlating the contact resistance with the real contact area, which enables the simultaneous measurement of normal and tangential forces between rough surfaces based on the single contact resistance under steady-state contact conditions. By proposing a “static friction surface”, the static and dynamic friction stage is effectively differentiated, and the reasons for the sudden drop in friction force and the sudden increase in contact resistance during the static and dynamic transition stages are given. This work proposes a novel explanation for the friction mechanism in terms of mechanical deformation and electrical resistance changes.