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1

On the yield surface of a typical bending-dominant periodic lattice metamaterial

Wang Yongjun, Liu Jinxing

Journal of Theoretical and Applied Mechanics

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2023

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Vol. 61 nr 1

175--187

EN

A theoretical method for analyzing the initial yield of a typical bending-dominant peri- odic lattice (BDPL) is established. Based on the principle of strain energy equivalence, the macroscopic effective stiffnesses of lattices are calculated. An empirical formula is employed to consider the contributions of both the axial force and bending moment. The initial yield surface of BDPL can be figured out by comparing the effective stress of each strut to the yield strength of the matrix material. The method is applicable to various BDPLs, which we believe is a helpful extension to the method for lattices comprising axial-tension bars in the literature.

2

Modeling of dynamic growth of a micro-scaled void based on strain gradient elasto-plasticity

Ma Xinbing, Liu Jinxing, Wang Jiadong, Pan Hao

Journal of Theoretical and Applied Mechanics

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2020

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Vol. 58 nr 4

927--941

EN

Void initiation and growth serve as an important mechanism in ductile failures in metals. Particularly, on the micron-level, the extra hardening effect associated with strain gradient is accounted for by adopting strain gradient elasto-plasticity instead of the conventional plasticity. Effects of inertial, strain gradient hardening and thermal softening are formulated analytically for the case where a spherical void expands under external hydrostatic stress. As demonstrated by our results, the inertia effect firstly tends to hinder but then promotes the void growth. The threshold stress required for rapid void growth is lifted due to extra hardening of strain gradient so that the growth of a smaller void is delayed more remarkably. A considerable thermal softening phenomenon is observed here, which is caused by plastic work during the deformation process. The final void growth rate is mainly related to the maximum loading, which is consistent with the prediction based on the classical plastic theory.

3

Influence of pre-tension on torsion of microscale Cu wires: a study via strain gradient theory

Ma Xinbing, Liu Jinxing

Journal of Theoretical and Applied Mechanics

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2019

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Vol. 57 nr 4

1055--1065

EN

Nonproportional plastic deformations on the microscale are an emerging topic. A simplified theory of strain gradient elasto-plasticity is developed to study the evolution of yield strength in a copper wire sequentially experiencing tension and torsion. The pre-tension deformation and stress are inherited to the upcoming torsion process, resulting in a nonproportional loading condition. With consideration of the extra hardening effect due to strain gradient, pre-tension weakens the extra hardening effect of the strain gradient and the dependence on the wire radius. Cyclic torsion behavior is also investigated. Anomalous Bauschinger effect and plastic softening are found.