1 Fundamental Science on Aircraft Structural Mechanics and Strength Laboratory, Northwestern Polytechnical University, Xi’an 710072, China 2 School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China 3 College of Materials Science and Engineering, Xi’an Shiyou University, Xi’an 710065, China
Tensile behaviors of Ti/Ni nanolaminate with model-I crack are investigated by molecular dynamics simulations. The Ti/Ni nanolaminates with center crack either in Ti layer or in Ni layer under different loading directions are utilized to systematically study the mechanical performance of the cracked material. The results indicate that pre-existing crack dramatically changes the plastic deformation mechanism of the Ti/Ni nanolaminate. Unlike the initial plastic deformation originating from the interface or weak Ti layer of the crack-free samples, the plastic behavior of cracked Ti/Ni nanolaminate first occurs at the crack tip due to the local stress concentration. Subsequent plastic deformation is dominated by the interaction between the crack and interface. The Ti/Ni interface not only impedes the movement of the initial plastic deformation carriers (dislocation, slip band, and deformation twinning) from the crack tip, but also promotes the movement of interfacial dislocations in the tension process. Microstructure evolution analysis further confirms that the plastic deformation mechanism transition is ascribed to the orientation-dependent tensile behavior at the crack tip, which is intrinsically attributed to the anisotropy of the certain crystal structure and loading direction of the cracked Ti/Ni nanolaminate. In addition, by analyzing the effects of different plastic deformation carriers on crack propagation in specific crystal, it can be discovered that the interfacial dislocations moving towards the crack tip can further promote the crack growth.
Received: 08 May 2020
Revised: 13 June 2020
Accepted manuscript online: 06 July 2020
Fund: the National Natural Science Foundation of China (Grant No. 11572259), the Program for International Cooperation and Exchanges of Shaanxi Province, China (Grant No. 2016KW-049), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2019JQ-827), and the Scientific Research Program Funded by Shaanxi Provincial Education Department, China (Grant No. 19JK0672).
Meng-Jia Su(宿梦嘉), Qiong Deng(邓琼)†, Min-Rong An(安敏荣), and Lan-Ting Liu(刘兰亭) Plastic deformation mechanism transition of Ti/Ni nanolaminate with pre-existing crack: Molecular dynamics study 2020 Chin. Phys. B 29 116201
Fig. 1.
Schematic diagram of cracked and crack-free Ti/Ni nanolaminates with tension loading applied along (a) Y direction and (b) Z direction. Atoms are colored according to the CNA method. And coordinate systems represent the initial crystalline orientation of Ti and Ni, respectively.
Fig. 2.
Stress–strain curves of disparate Ti/Ni nanolaminates in different loading directions: (a) Y direction and (b) Z direction.
Fig. 3.
Microstructure evolutions and atomic stress evolutions of crack-free Ti/Ni nanolaminate with tension loading applied along the Y direction, showing [(a) and (b)] relaxation configuration of Ti/Ni interface, (c)–(f) microstructure evolutions at various tensile strains, where atoms are colored according to the CNA method, (a′)–(f′) corresponding atomic stress evolutions, where atoms are colored according to the value of the Virial stress.
Fig. 4.
Microstructure evolutions and atomic stress evolutions of Ti/Ni nanolaminate with crack in Ti layer under tension loading applied along Y direction, showing [(a)–(d)] microstructure evolutions at various tensile strains, atoms are colored according to CNA method, (a′)–(d′) corresponding atomic stress evolutions, atoms are colored according to Virial stress value.
Fig. 5.
Interactions between crack and Ti/Ni interface at strain (a) 0.101, (b) 0.106, (c) 0.127, and (d) 0.171. Top panels are atomic configurations of Ti/Ni interface in Ni layer, middle panels are microstructure evolutions of cracked nanolaminate, and bottom pictures are corresponding defect propagations at various tensile strains. Atoms are colored according to CNA method.
Fig. 6.
Microstructure evolutions and atomic stress evolutions of Ti/Ni nanolaminate with crack in Ni layer under tension loading applied along Y direction, showing [(a)–(d)] microstructure evolutions at various tensile strains, where atoms are colored according to CNA method, [(a′)–(d′)] corresponding atomic stress evolutions, where atoms are colored according to Virial stress value.
Fig. 7.
Microstructure evolutions of Ti/Ni nanolaminates with tension loading perpendicular to the interface, showing (a) Ti/Ni nanolaminate with crack in Ti layer, (b) Ti/Ni nanolaminate with crack in Ni layer, (c) crack-free Ti/Ni nanolaminate, where atoms are colored according to CNA method. Insets display enlarged details in the tensile process.
Fig. 8.
Crack propagations in different loading directions for Ti/Ni nanolaminates, with crack in (a) Ti layer and (b) Ni layer with loading applied along Y direction, and crack in (c) Ti layer and (d) Ni layer with loading applied along Z direction. In panel, number 1 or 2 shows the atomic configuration, which is colored according to the CNA method, 3 or 4 displays corresponding defect distribution, which is identified by the DXA method. In panel, 1 or 2 shows the atomic configuration, which is colored according to the CNA method, 3 or 4 displays the corresponding defect distribution, which is identified by the DXA method.
Orientation
Models
Crack
Plastic behavior
Burgers vector
Y direction (parallel to the interface)
in Ti
phase transformation and partial dislocations
–
Ti/Ni nanolaminates
(FCC-Ti)
1/6〈112〉
in Ni
full dislocations and multiple dislocations
1/2〈110〉
–
pure Ti
phase transformation and partial dislocations
–
(FCC-Ti)
1/6〈112〉
pure Ni
full dislocations
1/2〈110〉
Z direction (perpendicular to the interface)
Ti/Ni nanolaminates
in Ti
slip bands grain reorientation and twinning
–
in Ni
partial dislocations
1/6〈112〉
pure Ti
slip bands grain reorientation and twinning
–
pure Ni
partial dislocations and full dislocations
1/6〈112〉 1/2〈110〉
Table 1.
Main plastic behavior around crack tip in different loading directions.
Fig. 9.
Variations of crack length with tensile strains under different loading directions, showing tension loading applied along (a) Y and (b) Z directions, with brackets in the legend indicating crack at a certain internal layer.
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