Material behavior modelling in micro/meso-scale forming process with considering size/scale effects

Lai, Xinmin; Peng, Linfa; Hu, Peng; Lan, Shuhuai; Ni, Jun

doi:10.1016/j.commatsci.2008.02.017

Cited by 167 publications

(80 citation statements)

References 14 publications

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“…( 1) where M is a relevant factor to grain orientation and it is 3.1 for polycrystal according to Taylor Theory, is shear stress, K is a constant, d represents the grain size [20].…”

Section: Hall-peth Relationshipmentioning

confidence: 99%

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Modelling of size effects in microforming process with consideration of grained heterogeneity

Wei

Jiang

et al. 2013

Computational Materials Science

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Size effect is a special phenomenon in metal micro-forming process. As the deformation process is scale down to micro/mesoscale, the characteristics of single grain involved in the deformed region play a significant role on the material mechanical behaviours resulting in the invalidation of classical theories in microforming. This paper presents a newly developed material model in microscale on the basis of the grained heterogeneity (e.g. grain size, shape and deformability) and specimen dimension. Voronoi tessellation has been employed to describe the polycrystalline aggregate. The grain shape is controlled by the centroidal-voronoi algorithm to drive grains into steady state. Hardness of the grains obtained from Nano-indentation is used to identify the scatter of the grained deformability. Applying the new material model, the micro-compression test of pure copper is numerically simulated by finite element method (FEM). The influences of grain size and feature size on the deformation behaviours are discussed. The numerical simulation results are in good agreement with the experimental results in terms of the flow stress curves and profile of deformed parts. Based on the novel material model, a FE model of microcross wedge rolling is established and the obtained results show the strain of specimen core region increases with the magnification of grain size. © 2013 Elsevier B.V. All rights reserved. AbstractSize effect is a special phenomenon in metal micro-forming process. As the deformation process is scale down to micro/meso scale, the characteristics of single grain involved in the deformed region play a significant role on the material mechanical behaviours resulting in the invalidation of classical theories in microforming. This paper presents a newly developed material model in micro scale on the basis of the grained heterogeneity (e.g. grain size, shape and deformability) and specimen dimension. Voronoi tessellation has been employed to describe the polycrystalline aggregate. The grain shape is controlled by the centroidal-voronoi algorithm to drive grains into steady state. Hardness of the grains obtained from Nano-indentation is used to identify the scatter of the grained deformability. Applying the new material model, the micro-compression test of pure copper is numerically simulated by finite element method (FEM). The influences of grain size and feature size on the deformation behaviours are discussed. The numerical simulation results are in good agreement with the experimental results in terms of the flow stress curves and profile of deformed parts. Based on the novel material model, a FE model of micro cross wedge rolling is established and the obtained results show the strain of specimen core region increases with the magnification of grain size.

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“…( 1) where M is a relevant factor to grain orientation and it is 3.1 for polycrystal according to Taylor Theory, is shear stress, K is a constant, d represents the grain size [20].…”

Section: Hall-peth Relationshipmentioning

confidence: 99%

“…1. Lai et al [11] developed a mixed model by combining the modified Hall-Petch relation and surface layer model. Based on the composite and surface layer models, Liu [12] developed a constitutive model considering the grain boundary strain strengthening.…”

Section: Introductionmentioning

confidence: 99%

Modelling of size effects in microforming process with consideration of grained heterogeneity

Wei

Jiang

et al. 2013

Computational Materials Science

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“…Based on the surface grain theory (Lai, et al, 2008), the ratio of surface to total grains number  can be calculated by the following equations.…”

Section: Discussionmentioning

confidence: 99%

Effect of ultrasonic vibration on stress relaxation in micro-compression test with step motion

Yamaguchi

Bai

Shimizu

et al. 2015

Mechanical Engineering Journal

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In this study, to promote stress relaxation effect by the servo actuated step motion that stops the die motion at regular interval, a novel microforming process with combining ultrasonic vibration and the step motion was proposed. To investigate the effect of ultrasonic vibration on stress relaxation by step motion, a micro-compression test was carried out in different scale dimension with the specimen size of 0.5, 1.0 and 2.0mm in diameter and height. Stress relaxation by step motion was repeated for 6 times at constant strain interval. Ultrasonic vibration with amplitude of 1.2 and 2.4 μm was applied on the axial direction during the stress relaxation by step motion. As results, in the all process conditions, the stress drop increased with decreasing the specimen size. To investigate the size dependency of the effect of ultrasonic vibration on stress relaxation, the stress drop in the surface and inner grains was calculated based on the surface grain theory. The result showed that the stress drop in the surface grains was larger than that in the inner grains in similar scale dimension. Additionally, the stress drop in the surface grains increased with decreasing the specimen size. The possibility of improving the material formability by this process was experimentally demonstrated.

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“…ߟ is size factor to express the fraction of inner portion to the whole material area. It can be calculated based on the following equation [20].…”

Section: Constitutive Modelmentioning

confidence: 99%

Grain size effect of thickness/average grain size on mechanical behaviour, fracture mechanism and constitutive model for phosphor bronze foil

Fang

Jiang

Wang

et al. 2015

Int J Adv Manuf Technol

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X. (2015). Grain size effect of thickness/average grain size on mechanical behaviour, fracture mechanism and constitutive model for phosphor bronze foil. International Journal of Advanced Manufacturing Technology, 79 (9-12), 1905Technology, 79 (9-12), -1914 Grain size effect of thickness/average grain size on mechanical behaviour, fracture mechanism and constitutive model for phosphor bronze foil AbstractSize effects play a significant role in microforming process, and any dimensional change can have a great impact on materials' mechanical properties. In this paper, the size effects on deformation behaviour and fracture of phosphor foil were investigated in the form of grain size effect: the ratio of materials' thickness (T) to average grain size (D) by micro tensile tests. The ratio was designed to be closed to but larger than, less than and equal to 1, respectively. The results show that the amount of plastic deformation decreases with the decrease of the ratio of T/D, which indicates that the grain size plays a significant role and grain deformation modes differ when the ratio changes. It is also found that their fractograph reflects different features in terms of micro-dimples and cleavage planes, further demonstrating that when T/D >1, its materials have a tendency to fracture ductilely, while materials would like to conduct brittle fracture when T/D Grain size effect of thickness/average grain size on mechanical behaviour, fracture mechanism and constitutive model for phosphor bronze foil Abstract: In this paper, the size effects on deformation behaviour and fracture of phosphor foil were investigated in terms of the ratio of materials' thickness (T) to average grain size (D) by micro tensile tests. The results show that the amount of plastic deformation decrease with the decrease of the ratio of T/D, which indicates that the grain size plays a significant role and grain deformation modes differ when the ratio changes. It is also found that their fractograph reflect different features in terms of micro-dimples and cleavage planes, further demonstrating that when T/D>1, its materials have a tendency to fracture ductilely, while materials would like to conduct brittle fracture when T/D<1. So the ratio of T/D which is close to 1 can be regards as the divide of ductile fracture and brittle fracture. For T/D<1, a new constitutive model is proposed based on the classic composite model. The model's results are compared with the experimental ones and the efficiency of the developed models is verified.

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Material behavior modelling in micro/meso-scale forming process with considering size/scale effects

Cited by 167 publications

References 14 publications

Modelling of size effects in microforming process with consideration of grained heterogeneity

Modelling of size effects in microforming process with consideration of grained heterogeneity

Effect of ultrasonic vibration on stress relaxation in micro-compression test with step motion

Grain size effect of thickness/average grain size on mechanical behaviour, fracture mechanism and constitutive model for phosphor bronze foil

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