Advances in Fracture and Materials Behavior

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Authors: Chieh Tang Chuang, Rong Shun Chen
Abstract: This paper presents a high sensitivity micro capacitive tactile sensor that can detect normal forces which is fabricated using deep reactive ion etching (DRIE) bulk silicon micromachining. The tactile sensor consists of a force transmission plate, a symmetric suspension system, and comb electrodes. The sensing character is based on the changes of capacitance between coplanar sense electrodes and it can reach the aim of large sensing range. High sensitivity is achieved by using the high aspect ratio comb electrodes with narrow comb gaps and large overlap areas. In this paper, the sensor structure is designed, the capacitance variation of the proposed device is analyzed, and the finite element analysis of mechanical behavior of the structures is performed.
Authors: Cheng Wen Fan, Jhih Hua Huang, Chyan Bin Hwu, Yu Yang Liu
Abstract: In this paper, the mechanical properties, such as the axial and radial Young’s moduli, shear moduli, buckling loads and natural frequencies, of single-walled carbon nanotubes, are estimated by a finite element approach. Each carbon nanotube is simulated as a frame-like structure and the primary bonds between two nearest-neighboring atoms are treated as isotropic beam members with a uniform circular cross-section. In the modeling work, the BEAM4 element in commercial code ANSYS is selected to simulate the carbon bonds and the atoms are nodes. As to the input parameters of the BEAM4 element, they are determined via the concept of energy equivalence between molecular dynamics and structural mechanics, and represented in terms of the force constants of the carbon bonds found in molecular mechanics. Based on this modeling concept, finite element models of both armchair and zigzag types of carbon nanotubes with different sizes are established and the mechanical properties of these tubes are then effectively predicted. Most of the computed results which can be compared with existing results show good agreement. Moreover, the effects of tube diameter, length etc., on the mechanical properties are also investigated.
Authors: Xi De Li, Zhao Zhang
Abstract: In recent years with the development of MEMS and NEMS, various micro and nano scale experiments are required. In general, the smaller the sample, the smaller the force is in the measurement. But it is difficult to load and measure such small force. We developed a probe-type loading and force sensor system to measure micro/nano samples. The system employs a semiconductor strain gauge of a cantilever type sensor and a micro manipulator. A highly sensitive, stable sensing cantilever beam made of single crystal silicon is ion implanted to form the P-type resistor (strain sensor). A tungsten probe with 100 nm radius of curvature was attached to the end of the cantilever as the micro loading tip. We constructed the measurement system and investigated its properties, such as linearity, dynamic response and stability. We also employed microspeckle interferometry to calibrate the force sensor. In preliminary experiments, we successfully obtained the force resolution 0.7 μN and applied our probe-type microforce sensor to calibrate an atomic force microscope (AFM) probe beam and test a single silkworm filament.
Authors: Dian Wu Huang, Feng Zhan, Qi Jian Zhu
Abstract: A modified model of simply supported ultrathin film for incorporating the surface effects and geometrically nonlinear conditions is proposed on basis of Kirchhoff’s hypothesis. The governing equations and non-classical boundary conditions are derived via using Hamilton’s principle. The residual membrane force and bending moment, in which the contributions of surface stresses and nonlinear terms are taken into account, are explicitly expatiated. Comparison between the modified model and conventional plate theory is also given. Using the simply supported bending strip-like film as an example, results indicate that the mechanical behaviors of the film are size-dependent when the thickness of the film is nanometer.
Authors: S.Y. Kim, S. Im, Y.Y. Earmme
Abstract: We examine the mobility of an edge dislocation pair on the shuffle plane in Si using action-derived molecular dynamics (ADMD). ADMD is one of the specially designed schemes for finding out the reaction pathways passing through transition states in the landscape of potential energy surfaces. Via ADMD calculations, the various structural changes of dislocation line with atomic resolution and their corresponding energy barriers are evaluated during the dislocation motion. The energy barrier for the movement of an edge dislocation pair on shuffle plane is about 0.24 eV. In this case, one bond between the atoms at the dislocation line is broken first, and then a new bond is formed with the neighboring atom. The movement of the dislocation line is achieved by a sequence of making new bond after bond-breaking of concerned atoms, which occur layer by layer. When the dislocation moves through this mechanism, energy barrier for the dislocation movement does not depend on the length of dislocation line. Thus the present result enables one to surmount the inherent limitation of Peierls-Nabarro’s two-dimensional continuum model, which may fail to describe successfully dislocation motion on the atomistic level.
Authors: Chun Yi Chu, Chung Ming Tan, Yung Chuan Chiou
Abstract: The stress induced in a workpiece under nanocutting are analyzed by an atomic-scale model approach that is based on the energy minimization. Certain aspects of the deformation evolution during the process of nanocutting are addressed. This method needs less computational efforts than traditional molecular dynamics (MD) calculations. The simulation results demonstrate that the microscopic cutting deformation mechanism in the nanocutting process can be regarded as the instability of the crystalline structure in our atomistic simulations and the surface quality of the finished workpiece varies with the cutting depth.
Authors: Bong Bu Jung, Seong Hyun Ko, Hun Kee Lee, Hyun Chul Park
Abstract: This paper will discuss two different techniques to measure mechanical properties of thin film, bulge test and nano-indentation test. In the bulge test, uniform pressure applies to one side of thin film. Measurement of the membrane deflection as a function of the applied pressure allows one to determine the mechanical properties such as the elastic modulus and the residual stress. Nano-indentation measurements are accomplished by pushing the indenter tip into a sample and then withdrawing it, recording the force required as a function of position. . In this study, modified King’s model can be used to estimate the mechanical properties of the thin film in order to avoid the effect of substrates. Both techniques can be used to determine Young’s modulus or Poisson’s ratio, but in both cases knowledge of the other variables is needed. However, the mathematical relationship between the modulus and Poisson's ratio is different for the two experimental techniques. Hence, achieving agreement between the techniques means that the modulus and Poisson’s ratio and Young’s modulus of thin films can be determined with no a priori knowledge of either.
Authors: Cho Chun Wu, Rong Shun Chen, Meng Ju Lin
Abstract: There are two kinds of microsprings often used: box microsprings and zig-zag (serpentine) microsprings. Box microsprings are considered with larger spring constant k and more symmetric structure keeping balance than zig-zag microspring. Density of spring number, N, is defined as the numbers of turns within a constant total spring length to investigate performance of box microspring. With applying the same force, the relation between spring constants and microspring sizes are discussed. Under different size parameters of box microsprings: B, W, T, and L, the spring constants decrease like exponential decay and approach a limit value as density of spring number increasing. The results show density of spring number has significant effect on spring constant. Rate of change on spring constant, Kt, is defined as the ratio of spring constant between N=1 and N=10. It means normalization of spring constant that increase density of spring number from minimum to maximum. The results show Kt decreases when B and W increase and increase as T and L increasing. Therefore, the spring constant is coupled affected by different size parameters due to different tendency as results shown. Such that the results can apply in microspring design by adjusting these size parameters to obtain the spring constant.
Authors: Fan Yang, Wei Yang
Abstract: A computation sample of nanocrystallion metal with a crack is proposed in this work. The structural evolution scheme is employed to model the mass flow, the grain boundary cavitation, and the crack growth of the specimen under remote loading. The scheme leads to a system of ordinary differential equations that can be solved by Euler integration. The simulation validates the proposal that the ductile versus brittle transition of nano-grained metals is dictated by the competition of creep deformation promoted by grain-boundary kinetics, and the decohesion of grain boundaries.
Authors: Seong Hyun Ko, Young Deuk Kim, Na Young Shin, Hyun Chul Park, Kun Hong Lee
Abstract: Anodic alumina has exhibits a homogeneous morphology of parallel pores that can be easily controlled between 10 and 400 nm. AAO(Anodic Aluminum Oxide) structure is the transversely isotropic material due to the parallel pores. In this study, mechanical properties of the AAO structures are measured using the nano-indentation method. Nano-indentation technique is one of the most effective methods to measure mechanical properties of nano-structures. Investigation of mechanical properties, such as the indentation modulus and hardness of the AAO structure with varying nano-pore sizes, was performed using the nano-indentation method. The results showed that the indentation modulus and hardness decreases monotically as the pore size increases.

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