The use of the direct impact Hopkinson pressure bar technique to describe thermally activated and viscous regimes of metallic materials

Abstract

The influence of strain rate over domains involving the thermal activation and the viscous drag behaviour of the dislocations is discussed. While it is recognized that the Koslky–Hopkinson technique or split Hopkinson pressure bar technique can generate data up to the upper strain-rate limit of the thermal-activated regime, it is necessary to use a direct impact Hopkinson pressure bar technique to access the viscous regime. Data generated with this technique are presented for a series of metals, including steel, nickel, copper and tungsten alloys. The motivation to generate such data is provided through three industrial applications.

A Modified Eyring Equation for Modeling Yield and Flow Stresses of Metals at Strain Rates Ranging from 10−5to 5 × 104 s−1

“…First we consider two materials, namely, copper and A304L steel, to show the quality of the first-guess material constants. Couque [4] has already reported experimental values of copper and A304L steel yield stresses for strain rates up to ∼20000/s and ∼10000/ s, respectively. In order to achieve so high strain rates a directimpact Hopkinson bar was used [4,5,28].…”

“…Couque [4] has already reported experimental values of copper and A304L steel yield stresses for strain rates up to ∼20000/s and ∼10000/ s, respectively. In order to achieve so high strain rates a directimpact Hopkinson bar was used [4,5,28]. The two-step identification procedure, detailed above, is used to determine the materials constants of (6) for three copper materials and two AA304L steels.…”

“…respectively. The third constanṫwill be determined from the threshold strain rate separating the thermally activated regime from the viscous regime [4]. Denotinĝ̇threshold strain rate, the first guess oḟis defined aṡ…”

“…The split Hopkinson bar was largely applied to evaluate the strain rate sensitivity of materials at high strain rates; that is,̇∼< 5000 s −1 [1][2][3]. At very high strain rates (̇>∼ 5000 s −1 ), the direct-impact Hopkinson bar is now increasingly used [4,5]. Based on the available experimental data, several constitutive equations were proposed in the open literature [6][7][8][9].…”

Прогнозирование Динамического Предела Текучести Металлов С Помощью Двух Структурно-Временных Параметров

“…3. Зависимость предела текучести от скорости дефор-мации для никеля (экспериментальные значения [26] обознач-ны квадратами) по классической модели Джонсона-Кука (6) (кривая 1) и критерию (1) (кривая 2), по модифицированной модели Джонсона-Кука (7) (кривая 3). В представленных эмпирических моделях два пара-метра, также как и в критерии инкубационного времени текучести.…”