On elastic gaps in strain gradient plasticity: 3D discrete dislocation dynamics investigation

• DOI: 10.1016/j.actamat.2023.118920
• Publication Date: 2023-04-13T04:16:01Z
• Authors: Yaovi Armand Amou...; Mohamed Jebahi; Marc Fivel; Samuel Forest; Jean-Sebastien Le...; Christophe Schuman; Farid Abed-Meraim
• Keywords: Size effects; Metals and Alloys; [SPI.MECA.MSMECA]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Materials and structures in mechanics [physics.class-ph]; 02 engineering and technology; Elastic gaps; Sciences de l'ingénieur: Mécanique: Mécanique des matériaux; Non-proportional loading conditions; Sciences de l'ingénieur; 620; 510; Discrete dislocation dynamics; Passivation; [SPI]Engineering Sciences [physics]; Sciences de l'ingénieur: Mécanique: Matériaux et structures en mécanique; [SPI.MECA.MEMA]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Mechanics of materials [physics.class-ph]; Strain gradient plasticity; 0210 nano-technology

Although presenting attractive features in dealing with small-scale size effects, strain gradient plasticity (SGP) theories can lead to uncommon phenomena for some boundary value problems. Almost all non-incremental (Gurtin-type) SGP theories including thermodynamically-consistent higher-order dissipation predict elastic gaps under certain non-proportional loading conditions. An elastic gap is defined as a finite change in the equivalent yield stress after an infinitesimal change in the strain conditions, at the occurrence of the non-proportional loading source. The existence of such gaps in reality is largely questioned and represents a major source of uncertainty preventing the development of robust SGP theories for real small-scale applications. Using 3D discrete dislocation dynamics (3D-DDD), the present paper aims at investigating size effects within micron-scale single crystal structures under various non-proportional loading conditions, including tension-compression-passivation, bending-passivation and tension-bending. An in-depth investigation of the occurrence of elastic gaps under these conditions, which are known to entail such gaps when using classical non-incremental SGP theories, is conducted. The obtained 3D-DDD results reproduce well known experimentally confirmed size effects like Hall-Petch effect, Asaro’s type III kinematic hardening and reversible plasticity. However, no evidence of the phenomenon of elastic gaps is found, which constitutes a first indication that this phenomenon may not exist in reality. The simulations are performed on face-centered cubic (FCC) Nickel single grains with cuboid shapes ranging from 2 microns to 15 microns and different orientations.<br/>Agence Nationale de la Recherche (ANR-20-CE08-0010)<br/>