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Collaborators

Prof. D.j. Dunstan  of QUML
​
Prof. Yuming He of HUST
​
Prof. Markus J. Buehler of MIT
​
Dr. E Martinez-Paneda of Cambridge
​
Dr. Xu Zhang of  Southwest Jiaotong University
 
Dr. Juan Guan of Beihang University
 
Prof.  Jie Liu of Hubei University
 
Dr. Anna Tarakanova of MIT

Objectives of TORWIRE

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 704292. The size effects (smaller is stronger) and Bauschinger effects (plastic recovery) at room temperature have been extensively documented experimentally at the micro/nano-scale. However, the underlying deformation mechanisms remain ambiguous, particularly in the presence of strain gradients. A long term goal of this project is to exploit the size effect in novel high-strength, lightweight materials through “length-scale engineering”. The main objectives are: • To integrate the different micro-torsion/ tension experimental methods, and so that it can be used at high temperatures. • To perform (cyclic) torsion and tension tests on thin metallic wires/tubes at elevated temperature. • To integrate the complementary theoretical methods, used to understand the corresponding physical mechanisms for the observed phenomena. • To test existing theories for micro-scale plasticity by using the homemade samples, e.g. thin wires/tubes prepared with different grain sizes and diameters.

Main Results

Main Results

During the performance of the project, five main works have been done. They are:

(1) Two micro-torsion testers based on different principle have been developed.

(2) The torsional properties of single fibers/wires, e.g. copper wires, carbon fiber, human hair, spider silk, etc. have been studied by using the torsion testers.

(3) The physical basis and the magnitude of the material length scale in theories of strain gradient plasticity are elucidated based on the critical thickness theory.

(4) The critical thickness phenomenon occurred in single-crystal wires under torsion is predicted by the continuum dislocation theory quantitatively. This links the continuum dislocation theory to the underlying physical picture of Matthews’ critical thickness theory.

(5) The physical nature of the flow rule for strain gradient plasticity theory proposed by Nix and Gao is discussed based on the thermodynamics paradigm developed by Gurtin and Anand. It is shown that the Nix-Gao flow rule is a combination of constitutive laws for the microstresses, balance law and a constraint.

Related Publications

  1.  Song Guo, Yuming He*, Jian Lei, Zhenkun Li, and Dabiao Liu*. Individual Strain Gradient Effect on Torsional Strength of Electropolished Microscale Copper Wires. Scripta Materialia, 130 (2017), 124-27.

  2. Dabiao Liu, Yuming He, Peng Hu, and Huaming Ding. Characterizing Torsional Properties of Microwires Using an Automated Torsion Balance. Experimental Mechanics, 57 (2017), 297-311.

  3. Dabiao Liu, Kai Peng, and Yuming He*. Direct Measurement of Torsional Properties of Single Fibers. Measurement Science and Technology, 27 (2016), 115017.

  4. Dabiao Liu*, and D. J. Dunstan. Material Length Scale of Strain Gradient Plasticity: A Physical Interpretation. International Journal of Plasticity, 98 (2017), 156-47.

  5. Dabiao Liu, Longteng Yu, Yuming He*, Kai Peng, Jie Liu, Juan Guan, and D. J. Dunstan. Peculiar Torsion Dynamical Response of Spider Dragline Silk. Applied Physics Letters, 111 (2017), 013701.

  6. Shimin Zheng, Dabiao Liu*, and Yuming He. The Influence of Fiber Migration on the Mechanical Properties of Yarns with Hierarchical Helical Structures. The Journal of Strain Analysis for Engineering Design, 53 (2018), 88-105.

  7. Dabiao Liu*, Xu Zhang, Yuan Li, and D. J. Dunstan. Critical Thickness Phenomenon in Single-Crystalline Wires under Torsion. Acta Materialia, 150 (2018), 213-23.

  8. A. S. Borokinni, Dabiao Liu*, Thermodynamics applied to strain gradient plasticity: the physical nature of Nix-Gao flow rule, In preparation.

  9. Song Guo, Yuming He*, Zhenkun Li, Dabiao Liu*, Size effect in the torsional stress relaxation of thin copper wires at room temperature, In preparation.

  10. W. Ali, D. Liu, N. Herrada, X. Chen, D. Mills, R.A. Owen, P. Burton, D. Dong, G. Gannaway, A.J. Bushby and D.J. Dunstan, Nanostrain sensitivity in a torsion experiment, Review of Scientific Instruments, In preparation.

  11. Dabiao Liu, Yuan Li, and D.J. Dunstan, Stress jump and size effect in the bending of thin foils with passivation, J. Mech. Phys. Solids, In preparation.

  12. Dabiao Liu*, Anna Tarakanova, Claire C. Hsu, Miao Yu, Shimin Zheng, Longteng Yu, Jie Liu, Yuming He, D. J. Dunstan, Markus J. Buehler, Spider dragline silk as torsional motor driven by humidity, Nature Communications, Under Review.

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