Advances in Fracture and Materials Behavior

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Authors: Wen Hwa Chen, Hsien Chie Cheng, Yang Lun Liu
Abstract: At the nanoscale, surface effect could cause atomistic structures a pre-stressed or pre-deformed state, which would consequently have a great dependence on their bulk mechanical properties. Besides, according to molecular mechanics [1,2], the effect of the non-bonding interactions among the atoms that are separated by equal or more than two bonds, say, van der Waals (vdW) forces, should be taken into account. Thus, the underlying objective of the study attempts to explore the extent of the surface effect and the in-layer vdW interactions on the mechanical properties of single/multi-walled carbon nanotubes(S/MWCNTs) with two different types of chiralities, including zigzag and armchair. To deal with the problem, an atomistic-continuum modeling (ACM) approach is introduced. The ACM is established by molecular dynamics (MD) simulation and equivalent continuum modeling (ECM). MD simulation is adopted to derive the initial equilibrium state of CNTs due to the surface effect, and the ECM is applied to calculate the mechanical properties of CNTs. The ECM is formulated based on the finite element (FE) approximations, which are composed of three-dimensional beam elements and one-dimensional non-linear spring elements. They basically represent the bonding and non-bonding interactions, respectively. The equivalent material constants of these two types of elements are derived from classical molecular mechanics and beam theory. The present results are also compared with those obtained from other simulations and experiments.
Authors: X.M. Liu, X. You, Zhuo Zhuang
Abstract: Molecular Dynamics (MD) simulations of indentation and scratch over crystal nickel (100) were carried out to investigate the microstructure evolution at nanoscale. The dislocation nucleation and propagation during process were observed preferably between close-packed planes. Dislocation loops are formed under both indentation and scratch process, and indentation and friction energy were transferred to the substrate in the form of phonon of disordered atoms, then part of the energy dissipated and rest is remain in the form of permanent plastic deformation.
Authors: Zhi Ying Ou, Gang Feng Wang, Tie Jun Wang
Abstract: The elastic field around a nanosized spheroidal cavity is derived on the basis of surface elasticity theory. The effects of surface energy, shape and size of the cavity are discussed. It is seen that the stress field near the nanosized cavity depends on the shape and the size of the cavity as well as the properties of the surface. These new characteristics are different from those predicted by the classical elasticity and may illuminate some new mechanisms at nanoscale.
Authors: Li Hua Jia, Mamtimin Gheni, Hazirti Eli, Xamxinur Abdikerem, Masanori Kikuchi
Abstract: In this paper, the iBone (Imitation Bone) model which is coupled with Turing reaction-diffusion system and FEM, is used. The numerical simulation of bone forming process by considering the osteoclasts and osteoblasts process are conducted. The results shown, that the bone mass is increased with increase of the initial load value, then fibula and femur bones are obtained respectively by keeping the required bone forming value. The different bone shapes are obtained by changing the both bone keeping value and the compressing force value. When set larger bone keeping value by keeping larger constant compressing force value, bone shape as a pipe with hole just like femur, when set smaller bone keeping value by keeping the smaller constant compressing force value, it is close to solid pillar as like fibula.
Authors: Dilinaer Mahemuti, Julaiti Maitirouzi, Chun Yuan Kong
Abstract: Purpose: Experiment research and theory analysis to the heat transmission and mechanics property about organism tissue. Method: Heat transmission and the dynamic change of temperature should be survey in the course of sand-therapy, then compare it with simulative result; workpieces were made, buried in different temperature and buried in the sand for 30 minutes, to test its biomechanics property and compare to group without buried in sand. Result: (1) The initial temperature field of the sand was not well mixed. (2) The test spot of the electric thermocouple was inaccuracies when test the temperature. (3) Every parameter of the mathematical model is taken from the bibliography, it may not fix actually to the parameter of the patient. (4) In the model, we did not consider several factors such as sweat transit in the sand. (5) There was some differentiation between parameter of the experiment such as temperature, humidity, wind speed in the natural environment. The very common disease such as rheumarthritis, lumbag and cervical vertebra degeneration brings huge pain to the patients. Medical treatments which are often used by the medical institutions can not obtain efficient results. But sand-therapy, a great part of Uyghur medicine, has obviously effects to these diseases [1, 2]. The sand-therapy provides positive effects in such diseases taking place in the hot sand in Turfan in Xingjiang where special climate, special environment and strong sunshine have. But this treatment is greatly effected by environment and climate and only can take place between July to September. Nowadays, there is little research about the sand-therapy both domestically and internationally, among them concentrated on influence of medical parameter of the human body and exploration to cure the disease mechanism. The sand-therapy is effected by calorific, magnetic and mechanics, etc., involving a lot of disciplines. Some scholars have carried on qualitative analysis to sand-therapy and other heat-therapy in terms of biomechanics [3,4], others have carried on thermal effects by experiment manner and analysis [5,6], still others analysis sand-therapy deeply by animal experiment[7,8,9]. This paper has carried on experiment and theoretical analysis to part of hot-strength effect of Uyghur medicine[10,11] and mechanics of bone tissue by temperature of sand-therapy[12,13], based on thermal-physical model of thermal transmitting among human body and sand and numerical simulation of temperature change in human body and sand in the course of sand-therapy[14].
Authors: Gulbahar Wahap, Tatsuya Kobori, Yoko Takakura, Norio Arai, Yoshifumi Konishi, Kazuaki Fukasaku
Abstract: Recently, the intravascular therapy using microcoils and stents to treat aneurysms has attracted researcher’s interest. In this study, in order to evaluate the effects of the stents, a numerical simulation of two-dimensional flows has been carried out for a pipe with a model of an aneurismal sac. Using aneurismal models with different inclined angles to the pipe, inflow conditions with steady states or pulsations have been applied in the range of Reynolds number in human blood flows. First, the computational results are compared with experiments under the steady inflow condition, which has shown the reliability of the numerical simulation. Furthermore, the mechanism of flows with an aneurismal model is discussed in the case with or without a stent, and consequently the effect of the stent is clarified.
Authors: Yoko Takakura, Gulbahar Wahap, Norio Arai, Yoshifumi Konishi, Kazuaki Fukasaku
Abstract: Recently for the treatment of aneurysms, endovascular therapy with microcoils and stents has started. This study explores the design of better stents by means of numerical computations from the viewpoint of the fluid mechanics. Two-dimensional flows are numerically solved for a stented duct with a model of an aneurysmal sac by changing the distribution of stent filaments under the constraint of a constant porosity for the neck. Stents are assessed by whether the wall shear stress (WSS) on the aneurismal wall and the shear rate (SR) within the aneurysm are made lower. Barometers for the allocation of filaments are sought, and resultant optimized stents are those where filament(s) should be attached to both the distal and proximal wall of the neck, with more filaments to the distal wall, to make the WSS low, and filaments should be appropriately distributed in the off-wall portion of the neck to make the SR low.
Authors: Atsushi Osao, Gulbahar Wahap, Yoko Takakura, Norio Arai, Yoshifumi Konishi, Kazuaki Fukasaku, Nobumasa Kikuchi
Abstract: The purpose of this study is to accumulate data to predict the ruptures of aneurysms on the bifurcation of the middle cerebral arteries at the base of the brain. Particular stress is laid on understanding the elemental nature of branch flows with/without an aneurysm. Therefore, “flow patterns” and “wall shear stress”, which are important factors for the causes of ruptures, are investigated by the three-dimensional experiments in vitro and the two-dimensional numerical simulations with simplified models. In the branch arteries without an aneurysm, there is a possibility of growing aneurysms at the location slightly away from a stagnation point. If an aneurysm forms into a centrosymmetric shape for the inlet axis, it is considered that they tend to grow further in a symmetrical plane. From the viewpoint of the risk of ruptures, recirculation flows become problematic with the lower Reynolds number, while the influence of wall shear stress becomes larger with the higher Reynolds number.
Authors: Xue Feng Yao, P. Wang, H.Y. Yeh
Abstract: The fracture is an important failure behavior of cancellous bone. Three-point-bending experiment was used to study fracture behavior of cancellous bone. Three group specimens were taken from two human femoral head and there was a non-angled crack and an angled crack in every group respectively. By using Digital Speckle Correlation Method (DSCM), the displacement and strain field were obtained at the crack-tip and the full specimen. The initial crack path was always at the maximal strain location and could be predicted by the DSCM. In the macro-scope, the crack propagation paths towards the load tip, and are independent of the initial crack angle.
Authors: Jurat Matruzi, Mamtimin Gheni, Ilham Abdureyim, Xamxinur Abdikerem
Abstract: In this study, the directionally fixed air tunnel testing equipment are used for obtain nearly close natural uniform wind and provide more stable wind speed for tunnel test. The changes of sand ripple moving speed in different location are observed under given wind speed condition. The sand ripple lines formation and moving process are tested on flat surface of sand, in Taklimakan desert. The results shown that the sand ripple forming rapidly from non ripple surface to ripple surface and moving along the wind direction. Though the sand ripples in the testing region have some difference about its moving speed, the sand ripple moving speed appear linearity relationship between sand moving displacement and the moving time. This phenomenon indicate that the sand ripple almost occurs and moving at the same time in the uniform wind stream field.

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