The minimum shear stress needed to move a dislocation against the resistance of the lattice in an otherwise perfect crystal. It is large for screw dislocations in BCC metals and causes the strong temperature dependence of their yield stress.
Japanese name: パイエルス応力
Peierls stress appears in 2 practice questions across 2 topics, including Mechanical properties and fracture, Strengthening mechanisms and dislocations.
Answer: C. Ferritic carbon steel (BCC)
In BCC metals, the stress needed to move dislocations (the Peierls stress) rises sharply as temperature falls, so at low temperatures cleavage fracture occurs before yielding and the absorbed energy in the Charpy impact test drops abruptly over a certain temperature range. This is the ductile-to-brittle transition, and ferritic carbon steel is the classic example. FCC austenitic stainless steels and aluminum alloys have many slip systems and dislocations remain mobile at low temperatures, so they show no distinct transition and are used for cryogenic applications such as liquefied gas tanks. The transition temperature is lowered by grain refinement and raised by neutron irradiation and similar damage.
Answer: C. The cores of screw dislocations in BCC metals spread over several planes and move with difficulty, overcoming the lattice resistance with the help of thermal fluctuations, so more stress is needed at lower temperature
The cores of screw dislocations in BCC metals do not spread flat on a single plane but take a three-dimensional form extending over several {110} planes, so the Peierls stress, the resistance of the lattice to dislocation motion, is large. Dislocations cross this barrier a little at a time with the help of thermal fluctuations (formation of kink pairs), so as the temperature falls this help diminishes and the yield stress rises steeply. This is one reason for the ductile-to-brittle transition of BCC steels. Dislocations in FCC metals are dissociated flat on the close-packed planes, the Peierls stress is small and the yield stress depends little on temperature. The option in which the yield stress falls at low temperature contradicts the facts, and high-purity BCC metals free of carbon and nitrogen show the same temperature dependence, so the option attributing it mainly to Cottrell atmospheres is also wrong.
In BCC metals, the stress needed to move dislocations (the Peierls stress) rises sharply as temperature falls, so at low temperatures cleavage fracture occurs before yielding and the absorbed energy in the Charpy impact test drops abruptly over a certain temperature range.
Which material shows a distinct ductile-to-brittle transiti…The cores of screw dislocations in BCC metals do not spread flat on a single plane but take a three-dimensional form extending over several {110} planes, so the Peierls stress, the resistance of the lattice to dislocation motion, is large.
The yield stress of BCC metals such as iron rises sharply a…Dislocation Stainless steel Bauschinger effect Critical resolved shear stress Dispersion strengthening Orowan mechanism Schmid factor Taylor factor