Novel analysis for nanoindentation size effect using strain gradient plasticity

2005 ◽  
Vol 53 (10) ◽  
pp. 1135-1139 ◽  
Author(s):  
Hunkee Lee ◽  
Seonghyun Ko ◽  
Junsoo Han ◽  
Hyunchul Park ◽  
Woonbong Hwang
Keyword(s):  
Size Effect ◽  
Strain Gradient ◽  
Strain Gradient Plasticity ◽  
Gradient Plasticity

Experimental Evaluation and Modeling Analysis of Micromilling of Hardened H13 Tool Steels

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Hongtao Ding ◽  
Ninggang Shen ◽  
Yung C. Shin
Keyword(s):  
Tool Wear ◽  
Size Effect ◽  
Strain Gradient ◽  
Chip Formation ◽  
Experimental Evaluation ◽  
Strain Gradient Plasticity ◽  
Fe Model ◽  
Tool Steels ◽  
Gradient Plasticity ◽  
Continuous Chip

This study is focused on experimental evaluation and numerical modeling of micromilling of hardened H13 tool steels. Multiple tool wear tests are performed in a microside cutting condition with 100 μm diameter endmills. The machined surface integrity, part dimension control, size effect, and tool wear progression in micromachining of hardened tool steels are experimentally investigated. A strain gradient plasticity model is developed for micromachining of hardened H13 tool steel. Novel 2D finite element (FE) models are developed in software ABAQUS to simulate the continuous chip formation with varying chip thickness in complete micromilling cycles under two configurations: microslotting and microside cutting. The steady-state cutting temperature is investigated by a heat transfer analysis of multi micromilling cycles. The FE model with the material strain gradient plasticity is validated by comparing the model predictions of the specific cutting forces with the measured data. The FE model results are discussed in chip formation, stress, temperature, and velocity fields to great details. It is shown that the developed FE model is capable of modeling a continuous chip formation in a complete micromilling cycle, including the size effect. It is also shown that the built-up edge in micromachining can be predicted with the FE model.

Experimental Verification of the Strain-Gradient Plasticity Model for Indentation

2005 ◽  
Vol 20 (11) ◽  
pp. 3150-3156
Author(s):  
Linmao Qian ◽  
Hui Yang ◽  
Minhao Zhu ◽  
Zhongrong Zhou
Keyword(s):  
Size Effect ◽  
Yield Stress ◽  
Strain Gradient ◽  
Indentation Size Effect ◽  
Linear Increase ◽  
Strain Gradient Plasticity ◽  
Plasticity Model ◽  
Gradient Plasticity ◽  
Indentation Size ◽  
Tensile Yield Stress

The indentation size effect of pure iron samples with various pre-plastic tensile strains has been experimentally investigated and analyzed. With the increase in the strain, the indentation size effect of iron samples becomes weak, accompanied by the multiplication of the statistically stored dislocations. All of the hardness (H) versus indentation depth (h) curves fit the strain-gradient plasticity model for indentation of Nix and Gao well. Two fitting parameters, the hardness in the limit of infinite depth (H0) and the characteristic length (h*), were obtained for each curve. The hardness (H0) of iron samples can also be estimated as the microhardness (H) at a very large depth, h ≅ 10h*. Both the fitted H0 and the measured H0′ increase linearly with the tensile yield stress σy of iron samples, indicating a dependence of H0 on the statistically stored dislocation density through σy. Furthermore, 1/√h* shows a linear increase with the tensile yield stress σy, which also agrees qualitatively with the general prediction of the Nix and Gao theory. Therefore, our experiments and analysis demonstrate that the strain-gradient plasticity model for indentation of Nix and Gao can interpret the indentation size effect with satisfied precision.

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