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Zhu R.,China University of Mining and Technology | Zhou J.,Nanjing University of Technology | Jiang H.,Nanjing University of Technology | Zhang D.,Shanghai Institute of Applied Mathematics and Mechanics
Mechanics of Materials | Year: 2012

Compared with the coarse-grained counterpart, nanocrystalline (NC) metals have higher strength simultaneously with a decrease in ductility, strain localization is a main factor contributed to the early failure of NC metals during plastic deformation. This work deals with the study of shear banding in fully dense electrodeposited NC Ni sheet with sample dimensions at tens of millimeters under quasi-static uniaxial tensile load through the use of a strain gage calculated by digital image correlation technique. Shear band nucleation, broadening process and failure point were recognized. It is identified that maximum shear strain happens in the middle of the shear band where crack initiates first in this experiment. This indicates that the shear banding induces the failure of the NC Ni sample. Meanwhile, physical characteristics of the shear band, such as inclination and width of single full-developed shear band, were determined quantitatively. The results show that the inclination of shear band is about 63°, as well as the width of shear band is in sub-micrometer range. To investigate the micro-mechanisms during the shear banding process in the NC Ni sample, in situ tensile testing in a transmission electron microscope was conducted, the results suggest that grain boundary migration and grain coalescence are the main carriers during the propagation of shear band. © 2012 Elsevier Ltd. All rights reserved. Source

Zhang Z.,University of Shanghai for Science and Technology | Zhang Z.,Tongji University | Zhang Z.,Shanghai Institute of Applied Mathematics and Mechanics | Huang M.,Tongji University
Computers and Geotechnics | Year: 2012

The mechanical behavior prediction for existing pipelines induced by tunneling is usually based on the assumption that the ground is homogeneous. Actually, layered formations with different soil properties are usually encountered in situ and the effects of soil stratification should be taken into account. Based on the boundary element model, a displacement controlled two stage method is presented to predict the deformation behavior of existing pipelines subjected to tunneling-induced deformations in layered soils. The green field displacement profile for layered soils during tunneling is firstly obtained, which is then imposed onto existing pipelines to enable quantifying the interaction effect of tunneling-induced ground movements on pipelines in layered soils. The accuracy of the proposed method is demonstrated with centrifuge model tests, site investigation data, and displacement controlled finite element analyses. The results discussed in this paper indicate that the proposed method can be used to estimate the interaction mechanics for tunnel-soil-pipeline systems in multi-layered soils with higher precision. © 2012 Elsevier Ltd. Source

An B.,Shanghai Institute of Applied Mathematics and Mechanics | An B.,Shanghai Key Laboratory of Mechanics in Energy Engineering | Wang R.,Tongji University | Zhang D.,Shanghai Key Laboratory of Mechanics in Energy Engineering | Zhang D.,Shanghai University
Acta Biomaterialia | Year: 2012

The superior mechanical properties of enamel, such as excellent penetration and crack resistance, are believed to be related to the unique microscopic structure. In this study, the effects of hydroxyapatite (HAP) crystallite orientation on the mechanical behavior of enamel have been investigated through a series of multiscale numerical simulations. A micromechanical model, which considers the HAP crystal arrangement in enamel prisms, the hierarchical structure of HAP crystals and the inelastic mechanical behavior of protein, has been developed. Numerical simulations revealed that, under compressive loading, plastic deformation progression took place in enamel prisms, which is responsible for the experimentally observed post-yield strain hardening. By comparing the mechanical responses for the uniform and non-uniform arrangement of HAP crystals within enamel prisms, it was found that the stiffness for the two cases was identical, while much greater energy dissipation was observed in the enamel with the non-uniform arrangement. Based on these results, we propose an important mechanism whereby the non-uniform arrangement of crystals in enamel rods enhances energy dissipation while maintaining sufficient stiffness to promote fracture toughness, mitigation of fracture and resistance to penetration deformation. Further simulations indicated that the non-uniform arrangement of the HAP crystals is a key factor responsible for the unique mechanical behavior of enamel, while the change in the nanostructure of nanocomposites could dictate the Young's modulus and yield strength of the biocomposite. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Yang X.-D.,Shenyang Institute of Engineering | Zhang W.,Beijing University of Technology | Chen L.-Q.,Shanghai Institute of Applied Mathematics and Mechanics | Chen L.-Q.,Shanghai University | Yao M.-H.,Beijing University of Technology
Nonlinear Dynamics | Year: 2012

The complex natural frequencies for linear free vibrations and bifurcation and chaos for forced nonlinear vibration of axially moving viscoelastic plate are investigated in this paper. The governing partial differential equation of out-of-plane motion of the plate is derived by Newton's second law. The finite difference method in spatial field is applied to the differential equation to study the instability due to flutter and divergence. The finite difference method in both spatial and temporal field is used in the analysis of a nonlinear partial differential equation to detect bifurcations and chaos of a nonlinear forced vibration of the system. Numerical results show that, with the increasing axially moving speed, the increasing excitation amplitude, and the decreasing viscosity coefficient, the equilibrium loses its stability and bifurcates into periodic motion, and then the periodic motion becomes chaotic motion by period-doubling bifurcation. © 2011 Springer Science+Business Media B.V. Source

Zheng X.,Shanghai Institute of Applied Mathematics and Mechanics | Ren J.,Shanghai University
Journal of Theoretical Biology | Year: 2016

Effects of the three-dimensional residual stresses on the mechanical properties of arterial walls are analyzed in this paper, based on the model which considered the bending and stretching both in the circumferential and axial directions of the three distinct arterial layers. Moreover, different constitutive models are proposed to quantify the nonlinear mechanics of the three distinct layers and the important constituents, i.e. elastin, collagen fibers and smooth muscle cells (SMCs), are all taken into account. The stress distributions and pressure-radius curves of the arterial wall are given in details. Results demonstrate that the maximum values of the circumferential stress and the corresponding stress gradient in the media under the mean arterial pressure are reduced significantly as a consequence of the SMCs. The bending in the axial direction of the media and the opening angle of the intima have an obvious impact on the mechanical behaviors of arterial walls. This study may not only develop the understanding of effects of the three-dimensional residual stresses on the arterial wall response, but also can increase the accuracy of the analyses for patient-specific studies used for the treatments of arterial diseases. © 2016 Elsevier Ltd. Source

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