Abstract: A depth-sensing indentation system was used to measure the residual stress in a stainless steel plate implanted by Fe2+ ions with an energy of 3 MeV at a dose of 3 x 10(16) cm(-2). Unlike other measurement methods, such as substrate curvature and X-ray diffraction techniques, depth-sensing indentation provides an accurate measurement of local residual surface stresses in the thin ion-implanted layer. Micromechanical analysis was carried out based on the premise that elastic unloading responses during indentation are fully independent of any pre-existing residual stresses at the indented surface. The correctness of this premise was verified by FEM simulation. It is found that the surface stress is proportional to the load shift induced by the surface stress. By using the energy method, a formula was derived for determining the surface stress by depth-sensing indentation studies. The residual surface stress induced by ion implantation was evaluated by using this formula. (c) 2005 Elsevier B.V. All rights reserved.
Abstract: Several different species of ions, An, Fe, Ag, Ti and Si, were implanted into austenite stainless steel sheets at an energy of 3 MeV, respectively. The martensite transformation induced with the ion implantation was investigated with transmission electron microscopy equipped with an energy dispersive X-ray spectrometer. The residual stresses induced with ion implantation were evaluated by the curvature technique. The effects of irradiation doses and ion species on the residual stress near surface induced by ion implantation were investigated. It is found that compressive residual stresses were induced by all the ions, and Fe and An ions, among these ions, produced a higher level of residual stress at the same implantation. It shows that ion implantation can be employed to control and modify the internal stress near surface by changing the irradiation dose and selecting ion specie of the ion implantation.
Abstract: In this paper, the strength of the singular stress field near the ends of the CNTs in composites was analyzed to clarify the effects of the CNT length on stress filed in the CNT reinforced composites when studying the fracture toughness. The singular stress field was separated into two types of singularities, symmetric and skew-symmetric, near the ends of CNTs according to the deformation and loading types. The stress intensity factors of the singular stress field were calculated for these two types of singularities. The effects of the CNT length in CNT reinforced composites on these stress intensity factors were investigated.
Abstract: In this work, we investigated the influences of residual stress on the load shifts, irreversible work from load vs. depth curves. It is found that there are linear relationships between the level of surface residual stress, the load shifts, and the variation of irreversible work for Ni, Ti, TiFe and A316L studied in this work. From these effects of residual stresses on load versus depth curves, depth-sensing indentation can be expected as a non-destructive method for measuring the residual stresses. Using the simulation results, the stresses estimated from the relationship of the level of surface residual stress and the load shifts, agree well with the applied stresses during simulations.
Abstract: Based on the effects of residual surface stress on the unloading curves of indentation load-depth responses, an experimental scheme for determination of the residual stress by depthsensing indentation is proposed. From the point that the elastic unloading portion of the load-depth curves can be expected to be unaffected by the residual stresses, the formula for evaluating surface stress by indentation is derived based on energy method. The proposed formula is verified by using FEM simulated indentation load-depth responses for different surface stress levels. The levels of surface stress evaluated by the proposed formula show a good agreement with the ones used as input parameters in FEM simulation.
Abstract: Ion implantation causes changes in mechanical properties such as hardness and fracture toughness on the ion-implanted surface. The purpose of this study is to experimentally investigate the effects of substrate temperature during ion implantation on the hardness and fracture toughness of an ion-implanted silicon wafer. A silicon (10 0) wafer was implanted by 3 MeV ions of Au and Si at different substrate temperature of 100, 200 and 300 K, respectively. After ion implantation, Vickers indentation experiments were carried out on the ion-implanted surface of the silicon wafer at room temperature. The results of the Vickers indentation tests show a significant decrease of hardness and an increase of fracture toughness of the ion-implanted silicon with decreasing the substrate temperature during ion implantation. It was found that the lower the substrate temperature during implantation, the greater the effectiveness of ion implantation on the changes in mechanical properties of the ion-implanted silicon. (C) 2003 Elsevier B.V. All rights reserved.
Abstract: Residual stress in ion-implanted stainless-steel sheet and the effects of ion species and implantation dose on the residual stress were investigated by using curvature technique based on the Stoney equation. Six species of ions of An, Ag, Fe, Ni, Ti and Si were implanted into the stainless steel sheet with an energy of 3 MeV at the dose of 1.0 x 10(16) to 10(17) ions/cm(2). The depth profile of the ion implantation in the ion-implanted layer was examined by using transmission electron microscopy equipped with an energy-dispersive X-ray spectroscopy. The level of the residual stress evaluated by the Stoney equation was compared with the results of X-ray diffraction. (C) 2004 Elsevier Ltd. All rights reserved.
Abstract: Gold nanoparticles can be used as a catalyst when deposited on a material surface. Adhesion to the support surface is a problem, however, and thus prevents the particles from being an effective catalyst. Adhesion in specified microscale regions is needed in recently developed micro total analysis systems (mu-TAS) and other microchemical systems such as "lab on a chip". Both types of systems have channels, mixers, reactors and analyzing devices. The mixer and reactor devices use chemical reactions and therefore need a catalyst. We previously developed an adhesion process for gold nanoparticles that involves ion implantation and surface etching. In this process, which is called the IISE (ion implantation and surface etching) method, a silicon substrate as a support surface is etched after gold ions (3.1 MeV) are implanted, resulting in gold particles adhering to the support. The catalytic performance of nanoparticles, however, depends on the particle size. To determine the particle size for optimal catalytic performance in mu-TAS, in this study, we used the IISE method to fabricate gold nanoparticles at different ion implantation temperatures, ion doses and etch times. Results showed that the nanoparticle size was independent of implantation temperature, but increased slightly with increasing ion dose and increased significantly with increasing etch time. An ion dose exceeding 3 x 10(16) cm(-2) yielded approximately 10-nm diameter nanoparticles. In conclusion, by adjusting the etch time, the USE method showed good controllability of particle size and concentration. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: In short fiber reinforced composite it is known that the singular stress at the end of fibers causes crack initiation, propagation, and final,failure. The singular stress field is controlled by the generalized stress intensity factors defined at the end of the inclusion. In this study the stress intensity factors are discussed for an elastic cylindrical inclusion in an infinite body under (A) asymmetric uniaxial tension in the x direction, and (B) symmetric uniaxial tension in the z direction. These problems are formulated as a system of integral equations with Cauchy-type or logarithmic-type singularities, where densities of body force distributed in infinite bodies having the same elastic constants as those of the matrix and inclusion are unknown. In the numerical analysis, the unknown body force densities are expressed as fundamental density functions and weight functions. Here, fundamental density functions are chosen to express the symmetric and skew-symmetric stress singularities. Then, the singular stress fields at the end of a cylindrical inclusion are discussed with varying the fiber length and elastic ratio. The results are compared with the ones of a rectangular inclusion under longitudinal and transverse tension.
Abstract: Investigations were carried out on the relation between the martensite transformation and the stress induced by 3 MeV ion implantation in an austenite stainless steel (SS) sheet. Gold ions were implanted into the austenite SS sheet and the implantation dose was varied between 1 x 10(16)/cm(2) and 3 x 10(16)/cm(2). The microstructures in the ion-implanted region were examined by using transmission electron microscopy equipped with an energy dispersive X-ray spectrometer. The depth profile of the martensite volume fraction in the ion-implanted region was obtained by using a modified version of the direction comparison method, and the residual stress in the ion-implanted layer was measured by a low incident beam angle X-ray diffraction method. (C) 2003 Elsevier Science B.V. All rights reserved.
Abstract: In this paper a singular integral equation method is applied to calculate the distribution of stress intensity factor along the crack front of a 3D rectangular crack. The stress field induced by a body force doublet in an infinite body is used as the fundamental solution. Then, the problem is formulated as an integral equation with a singularity of the form of r(-3). In solving the integral equation. the unknown functions of body force densities are approximated by the product of a polynomial and a fundamental density function, which expresses stress singularity along the crack front in an infinite body. The calculation shows that the present method fives smooth variations of stress intensity factors along the crack front for various aspect ratios. The present method gives rapidly converging numerical results and highly satisfied boundary conditions throughout the crack boundary.
Abstract: In short fiber reinforced composite it is known that the singular stress at the end of fibers causes crack initiation and final failure, This paper deals with this end effect in analyzing models of fiber as 2D rectangular and 3D cylindrical inclusions. The body force method is used to formulate the problems as a system of singular integral equations having Cauchy and logarithmic singularities. Initially, numerical solution of the singular integral equations is discussed. Next, interaction of rectangular inclusions are considered. Finally, singular stress at the end of a cylindrical inclusion is analyzed and discussed in comparison with the results of a rectangular inclusion.
Abstract: Investigated is the push-in test used to determine the interfacial strength of fiber-reinforced composites via the method of singular integral equation. Singularity analysis shows that stresses near the end for an intact interface have a power singularity, and the singularity index is only dependent on the material constants of the fiber and the matrix. In order to describe the interfacial strength at the initial debonding of the push-in test, critical interfacial shear stress intensity factor and the related singularity index are adopted. This interfacial strength characteristic parameter is applied to analysis of the push-in test results of carbon fiber reinforced epoxy resin composites.
Abstract: This paper deals with numerical solutions of singular integral equations in interaction problems of rectangular inclusions under various loading conditions. The body force method is used to formulate the problems as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where the unknowns are the densities of body forces distributed in infinite plates having the same elastic constants as those of the matrix and inclusions. In order to analyze the problems accurately, the unknown functions are expressed as piecewize smooth functions using two types of fundamental densities and power series, where the fundamental densities are chosen to represent the symmetric stress singularity of 1/r(1-lambda 1) and the skew-symmetric stress singularity of 1/r(1-lambda 2). Then, newly defined stress intensity factors at the end of inclusions are systematically calculated for various shapes and spacings of two rectangular inclusions in a plate subjected to longitudinal tension, transverse tension, and in-plane shear. The present method is found to be effective for accurate and efficient analysis of rectangular inclusions.
