Static and dynamic properties of frictional phenomena in a one-dimensional system with randomness

Static and dynamic frictional phenomena at the interface with random impurities are investigated in a two-chain model with incommensurate structure. Static frictional force is caused by the impurity pinning and/or by the pinning due to the regular potential, which is responsible for the breaking of analyticity transition for impurity-free cases. It is confirmed that the static frictional force is always finite in the presence of impurities, in contrast to the impurity-free system. The nature of impurity pinning is discussed in connection with that in density waves. The kinetic frictional force of a steady sliding state is also investigated numerically. The relationship between the sliding velocity dependence of the kinetic frictional force and the strength of impurity potential is discussed.Comment: RevTex, 14 pages, 6 PostScript figures, to appear in Phys. Rev.

Friction, order, and transverse pinning of a two-dimensional elastic lattice under periodic and impurity potentials

Frictional phenomena of two-dimensional elastic lattices are studied numerically based on a two-dimensional Frenkel-Kontorova model with impurities. It is shown that impurities can assist the depinning. We also investigate anisotropic ordering and transverse pinning effects of sliding lattices, which are characteristic of the moving Bragg glass state and/or transverse glass state. Peculiar velocity dependence of the transverse pinning is observed in the presence of both periodic and random potentials and discussed in the relation with growing order and discommensurate structures.Comment: RevTeX, 4 pages, 5 figures. to appear in Phys. Rev. B Rapid Commu

Dynamical frictional phenomena in an incommensurate two-chain model

Dynamical frictional phenomena are studied theoretically in a two-chain model with incommensurate structure. A perturbation theory with respect to the interchain interaction reveals the contributions from phonons excited in each chain to the kinetic frictional force. The validity of the theory is verified in the case of weak interaction by comparing with numerical simulation. The velocity and the interchain interaction dependences of the lattice structure are also investigated. It is shown that peculiar breaking of analyticity states appear, which is characteristic to the two-chain model. The range of the parameters in which the two-chain model is reduced to the Frenkel-Kontorova model is also discussed.Comment: RevTex, 9 pages, 7 PostScript figures, to appear in Phys. Rev.

Theoretical Study of Friction: A Case of One-Dimensional Clean Surfaces

A new method has been proposed to evaluate the frictional force in the stationary state. This method is applied to the 1-dimensional model of clean surfaces. The kinetic frictional force is seen to depend on velocity in general, but the dependence becomes weaker as the maximum static frictional force increases and in the limiting case the kinetic friction gets only weakly dependent on velocity as described by one of the laws of friction. It is also shown that there is a phase transition between state with vanishing maximum static frictional force and that with finite one. The role of randomness at the interface and the relation to the impurity pinning of the sliding Charge-Density-Wave are discussed. to appear in Phys.Rev.B. abstract only. Full text is available upon request. E-mail: [email protected]: 2 pages, Plain TEX, OUCMT-94-

Colossal electroresistance and colossal magnetoresistive step in paramagnetic insulating phase of single crystalline bilayered manganite(La0.4_{0.4}Pr0.6_{0.6})1.2_{1.2}Sr1.8_{1.8}Mn2_{2}O7_{7}

We report a significant decrease in the low-temperature resistance induced by the application of an electric current on the $ab$-plane in the paramagnetic insulating (PMI) state of (La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$. A colossal electroresistance effect attaining -95% is observed at lower temperatures. A colossal magnetoresistive step appears near 5T at low temperatures below 10K, accompanied by an ultrasharp width of the insulator-metal transition. Injection of higher currents to the crystal causes a disappearance of the steplike transition. These findings have a close relationship with the presence of the short-range charge-ordered clusters pinned within the PMI matrix of the crystal studied.Comment: 4 pages 3 figure

Microstructural Change and Mechanical Property of Neutron Irradiated Ti-Ni Shape Memory Alloy

Microstructural change and mechanical property of Ti-Ni shape memory alloy after neutron irradiation have been studied. The neutron doses were from 1.4×10^ to 1.2×10^n/cm^2, and the irradiation temperature was under 423K. A halo ring was observed after the irradiation of 1.2×10^n/cm^2, which means that amorphous phase was induced by the neutron irradiation. In stress-strain curve, the critical point (σ_M) increased as the dose increased. At the highest dose, the stress-strain curve lost pseudoelasticity. These results indicate that such mechanical properties strongly depend on the amorphous formation

Void-induced cross slip of screw dislocations in fcc copper

Pinning interaction between a screw dislocation and a void in fcc copper is investigated by means of molecular dynamics simulation. A screw dislocation bows out to undergo depinning on the original glide plane at low temperatures, where the behavior of the depinning stress is consistent with that obtained by a continuum model. If the temperature is higher than 300 K, the motion of a screw dislocation is no longer restricted to a single glide plane due to cross slip on the void surface. Several depinning mechanisms that involve multiple glide planes are found. In particular, a depinning mechanism that produces an intrinsic prismatic loop is found. We show that these complex depinning mechanisms significantly increase the depinning stress