Glide plane | EPFL Graph Search

In geometry and crystallography, a glide plane (or transflection) is a symmetry operation describing how a reflection in a plane, followed by a translation parallel with that plane, may leave the crystal unchanged. Glide planes are noted in the Hermann–Mauguin notation by a, b or c, depending on which axis the glide is along. (The orientation of the plane is determined by the position of the symbol in the Hermann–Mauguin designation.) If the axis is not defined, then the glide plane may be noted by g. When the glide plane is parallel to the screen, these planes may be indicated by a bent arrow in which the arrowhead indicates the direction of the glide. When the glide plane is perpendicular to the screen, these planes can be represented either by dashed lines when the glide is parallel to the plane of the screen or dotted lines when the glide is perpendicular to the plane of the screen. Additionally, a centered lattice can cause a glide plane to exist in two directions at the same ti

Mechanical spectroscopy of interface stress relaxation in magnesium matrix composites

Abu Salek Md. Fahim Chowdhury

Magnesium matrix composites made of pure (99.98%) magnesium reinforced with long carbon (Mg/C) and stainless steel (Mg/steel) fibers were processed by low pressure infiltration method. Mg/C composites were then oriented from the crystallographic point of view by Bridgman technique and finally three composites were obtained with γ = 0°, 45° and 90° (γ is the angle between the matrix-fiber interface and the normal to the basal plane). The results show that the damping level in the composite for γ = 0° is almost 3 and 7 times higher than that of the composites with γ = 45° and γ = 90°, respectively. From the result analysis it was possible to conclude that the damping originates in the hysteretic motion of dislocations in the magnesium matrix. As such a mechanism is not thermally activated, high damping is observed over a broad frequency range. The complete evolution of the mechanical loss as a function of the vibration amplitude has been measured. The obtained result has been found to be in excellent agreement with the Granato-Lücke model for dislocation breakaway. The fit of the experimental points with the theoretical curve and the straight Granato-Lücke plot confirm that the microstructure evolution is controlled by the breakaway of dislocation segments from randomly segregated point defects (hysteretic damping). According to the Granato-Lücke model the critical stress for the breakaway could be estimated. As a consequence of this analysis, the transient damping due to interface thermal stress relaxation has been interpreted by a model based on a solid friction mechanism. It has been shown that the model of Mayencourt and Schaller justifies the whole mechanical loss behavior. The model predicts two fit parameters C1 and C2, which account for the respective evolution of the mobile dislocation density and interfacial strength. An anomalous behavior is observed for the parameter C2 as well upon heating as upon cooling, which is being reflected in the shear modulus evolution. This anomalous behavior is due to a "bonding-debonding" mechanism at the fiber-matrix interface due to the motion of dislocations, which depends on the orientation of the glide plane. Also, at high temperature, the interface is strong, which helps in creep resistance of the composite, and at low temperature, the interface is weak, which is positive for improving toughness by interface crack deflection.

EPFL2009

Atomistic simulation of the a(0) < 1 0 0 > binary junction formation and its unzipping in body-centered cubic iron

Seyed Masood Hafez Haghighat

Molecular dynamics simulation is used to study the formation of the a(0) < 1 0 0 > binary dislocation junction in body-centered cubic Fe. Results show that under an applied strain two intersecting 1/2 a(0) < 1 1 1 > dislocations, one mobile edge and one immobile screw, form an a(0) < 1 0 0 > binary junction of mixed character in the glide plane of the mobile edge dislocation. It appears, however, that the binary junction does not necessarily lay in one of the three possible {1 1 0} glide planes of the screw dislocation. The binary junction starts to unzip as the impinging edge dislocation bows around and moves away, which results in the formation of a screw dipole along its Burgers vector. The dipole eventually annihilates, completing the unzipping process of the junction, which liberates the edge dislocation. The effects of temperature and strain rate on the unzipping of the junction are quantified by the critical release stress needed to detach the edge dislocation from the screw one. The critical stress decreases when the temperature increases from 10 to 300 K, whereas it increases with increasing applied strain rate, or dislocation speed. The interaction mechanism and strength of the a(0) < 1 0 0 > binary junction as an obstacle to the edge dislocation are compared to that of other types of defect, namely nanosized voids, Cu and Cr precipitates, and dislocation loops in Fe. It appears that the binary junction strength is in the lowest range, comparable to that of a coherent Cr precipitate. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2014

Obstacle strength of binary junction due to dislocation dipole formation: An in-situ transmission electron microscopy study

Seyed Masood Hafez Haghighat

We report the experimental observation of the 1/2 < 111 > edge dislocation dipole formation and annihilation in ultra-high purity Fe using transmission electron microscopy (TEM) in-situ straining. The observation is confirmed by TEM image simulations. The edge dipole is formed by the interaction of a moving screw dislocation with an obstacle of dislocation character. It results from the glide of the two arms of the dislocation on two different glide planes, which stabilizes the dipole that is closed by a jog. The dipole is later released from the obstacle and disappears, presumably by gliding of the dipole's edge segments along their Burgers vector and freeing the mobile screw dislocation from the jog. This mechanism. leads to enhanced obstacle strength of the immobile dislocation well above Orowan critical stress, promoting forest strength. (C) 2015 Elsevier B.V. All rights reserved.

Elsevier Science Bv2015

Mechanical spectroscopy of interface stress relaxation in magnesium matrix composites

Abu Salek Md. Fahim Chowdhury

EPFL2009