Portevin–Le Chatelier effect

Portevin the Le Chatelier effect ( effect PLC ) is also known as dynamic strain aging. Its discovery is attributed to Albert Portevin Le Chatelier and Henry. Some alloys show at a continuous load a jerky and uneven deformation behavior. In the tensile test for example, shows a jagged over large portions of the stress-strain curve. The plastic deformation occurs unevenly distributed over the sample. The zones of increased plastic deformation also referred to as flow lines.

Cause

Materials which exhibit the PLC effect, have a non-monotonic stress - strain rate dependence. This can be explained as follows: Plastic deformation of metals are largely due to the migration of dislocations, respectively. Lattice defects realized in the crystal lattice. Are the crystal free atoms released, keep these on such a close lattice defects. Consequently, the lattice defects a cloud of impurity atoms must carry along while hiking, so the time required for hiking power or voltage increases. If the lattice defects become detached from the cloud of atoms, a lower voltage at the same time faster walking is required. This non- monotonicity of the voltage - strain rate curve is explained. Dissolves a dislocation from their accompanying foreign atoms, this may affect the " atmosphere " of other dislocations and increases the strain rate, which other dislocations may also break away. By this avalanche reproduction together with the induced voltage through the non- monotonous strain rate dependency of the instability effect is macroscopically visible. The effect is particularly pronounced when the free dislocations with moving dislocations and have a similar mobility. This is the case in a limited temperature - strain rate range, wherein the temperature of the diffusion rate of the impurity and the strain rate controls the speed of the dislocations.

In Fe -Al alloys also be startled voids can cause jerky flow.

Similar to the dry friction, the PLC effect can be described as a stick-slip phenomenon.

Effects

In sheet metal forming caused by the uneven distribution of plastic strain for example, Case vehicle body or aircraft parts unacceptable surface finish. A typical example is aluminum -magnesium alloys, which are interesting due to their low density, in the aircraft.

Others

The PLC effect was observed already in the early 19th century, but his discovery is attributed Portevin Le Chatelier and.