Abstract
Infrared thermography and two-exposure speckle interferometry have been used to study the plastic deformation of low-carbon steel under the action of pulsed electric current. It was established that external electric effect leads to an increase in velocity of plastic waves by 65 %. Analysis of the velocity distribution patterns showed that they have the profile of “shock transition”. At the origin, velocity of the material is zero (motionless gripping), and at the right end of the curve material velocity is equal to stretching speed specified by testing machine. The effect of electric current leads to splitting of the displacements velocities, both at moving and stationary ends of the samples. It is assumed that the observed splitting is related to the Stark splitting of energy levels of the deformed system. This splitting leads to a decrease in the potential barrier for the motion of defects in crystal lattice. Thermographic studies have shown presence of a temperature gradient directed from clamps to center of the sample, which does not coincide with pattern of displacement distribution. It was determined that during the primary treatment with high power current pulses in the central area of the sample, sample temperature reaches 351 K, and 330 K in the area adjacent to clamps. Subsequent treatments result in a slight increase in temperature. This behavior of temperature can be explained by the fact that heat does not dissipate at a repetition rate of 10 Hz. On an average, sample temperature increases by 30 K. Theoretical calculation has shown that the Joule effect leads to an increase in temperature of the sample by 21 K per pulse, which is practically in agreement with experimental results. Estimates of thermal energy and energy of elastic deformation have shown that the fastest channel for converting the energy of electric pulse is structural changes in deformable system, which lead to the observed decrease in deforming force.
Highlights
It was established that external electric effect leads to an increase in velocity of plastic waves by 65 %
Estimates of thermal energy and energy of elastic deformation have shown that the fastest channel for converting the energy of electric pulse is structural changes in deformable system, which lead to the observed decrease in deforming force
Баранникова С.А., Косинов Д.А., Зуев Л.Б., Громов В.Е., Коновалов С.В
Summary
Испытания на растяжение были выполнены на плоских образцах в форме двойной лопатки с размерами рабочей части 50×10×2 мм, которые вырезали из полос холодной прокатки после отжига в печи при температуре 600 °С в течение 60 мин. Для исследований макроскопической локализации пластического течения использовали технику двухэкспозиционной спекл-фотографии [20], которая сочетает в себе возможности наблюдения всего деформируемого образца в целом (характерный размер поля зрения примерно 100×100 мм) с разрешающей способностью приблизительно 1 мкм. Импульсный электрический ток подавали от генератора однополярных токовых импульсов [24]. Для ее защиты от воздействия токовых импульсов были разработаны специальные диэлектрические переходные втулки. 100 мкс и частотой следования 10 Гц подавали в течение 30 с после достижения площадки текучести. Из зависимостей координат очагов локализации X от времени t определяли пространственный λ и временнóй T периоды соответствующих процессов, а затем вычисляли скорость движения очагов локализованной пластичности.
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