Reduction of the critical shear stress for the multiplication of dislocations upon multiple alternating bending

• Published in: The Journal of physics and chemistry of solids 1965-01, Vol.26 (5), p.861,IN1,863-862,IN2,864
• Main Authors: Garber, R.I., Soloshenko, I.I., Khaldej, O.A.
• Format: Article
• Language: English
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/0022-3697(65)90261-1

Bracket fastened plates of lithium fluoride have been subjected to the alternating bending at constant amplitude of the deflecting force. After a definite number of cycles had been completed newly generated dislocations were revealed by etching. Critical stress for the multiplications of dislocations (τ c ) was defined as a value of the amplitude of shearing stress in the planes {(110)} on those sections of the sample where there appeared a noticeable amount of new etch pits. Most of them are terminations on the flat side of edge dislocations with Burgers vector in the bending plane. Upon a single bending (τ c ) is approximately equal to the static yield stress (600 g/mm 2) however, with the increase in the number of cycles it considerably decreases : with 10 cycles τ c = 250 g/mm 2 and with 100 it reduces to 70 g/mm 2. With the increase in the number of cycles there is also evidence of strain hardening, showing gradual decrease in the number of newly generated dislocations, and the reduction of damping constant of elastico-plastic oscillations. The decrease of (τ c ) may be ascribed to the decrease of the shear stress due to the separation of dislocations caused by pinning of dislocations at point defects, which was supported by the data of the amplitude dependence of the internal friction for the samples, which were previously multiply deformed under fairly low amplitudes of the tension.