Papers by Keyword: Microscale

Abstract: An innovative method of obtaining thin films of semiconductors and other materials, which is based on the differences in components solubility, density, and atomic mass, is developed. Process of producing a thin film of a substance A starts by choosing of another component – substance B that may form a two-component A–B solid solution. Then, it has to be selected third component – substance C that must dissolve substance B well, but A does not. The selection of the composition and conditions of application of the chemical etching process ensure the removal of C and B dissolved in it from the surface of A. The method provides both low- and high-temperature processes. The proposed new principle of obtaining thin films would be attractive due to their reduced size, tunable properties, proper adhesion, preservation of high reliability, possibility of further miniaturization in electronics, and cost reduction.

Abstract: A micro-scale-based approach for the numerical analysis of cement-based materials, subjected to low-and high-cycle fatigue actions, is presented in this paper. The constitutive model is aimed at describing the evolving microstructural changes caused by cyclic loading protocols. More specifically, statistically representative microscopic geometries are equipped with a fracture-based model combined with a continuous inelastic constitutive law accumulating damage induced by the cyclic stress. The plastic-damage-based model is formulated combining the concepts of fracture-energy theories and damage stiffness degradations, representing the key phenomena occurring in concrete under fatigue. The paper explores the potential of the technique for assessing fatigue microcracks formation and growth, and their influence on the macroscopic behavior.

Abstract: In this paper, we focus on the stress-strain behavior prediction of the bimodal bulk Al5083 series which are comprised of ultra-fine grains (UFG) separated by coarse grain (CG) regions. The CGs in the UFG matrix effectively prevents microcracks from propagation, leading to enhance ductility and toughness while the strength remains high. In this work, initially, XFEM is implemented for bimodal materials considering various fracture criteria for brittle and ductile phases in maximum traction and cohesive law. Then the stress-strain behavior dependency of the model on the CG distribution in a constant volume fraction is investigated by extraction of RVEs from optical microscopy (OM) images of the real material. The solution convergence of such a problem with irregular geometry, plasticity and crack initiation-propagation demanded extreme efforts that accomplished by refining and arranging meshes as well as adding damage stabilizations. As a result of the above procedures, the sensitivity of the modeling procedure to various RVEs is obtained, the crack initiation-propagation pattern in microscale is predicted and consequently, the global stress-strain behavior result is calculated. It is shown that the predicted results are in good agreement with the available experimental results.

Abstract: Metal micro forming is microscale effect in the process of classification and evaluation, for the correct understanding of micro forming and conventional forming difference, it is guiding significance in the course of micro forming technology similar to conventional forming which is applied to the data and experience. The microscale effect is beneficial to accurate grasp of all kinds of microscale effect in the forming reasonable classification and evaluation.Change law of microscale affects the nature of knowledge for the right team which provides effective quantitative data, when determine the major hours of rights, it also can provide the guiding idea for material selection and process optimization.The reasonable classification and evaluation of microscale effect is the experience that conventional forming calculation provides a reality way. In all kinds of process load calculation, as long as the material intrinsic microscale is joined, microscale can be introduced in corresponding few and the process conditions.

Abstract: The nonlinear dynamics of a microbeam with initial axial tension is presented. The nonlocal theory with a small scale effect is applied to the problem model. Considering the axial protraction due to the transverse deformation of the microbeam, a nonlinear partial differential equation that governs the dynamic motion is derived. Explicit solution of transverse amplitude is obtained by the method of multiscale analysis. Both nonlinear and nonlocal effects are found to play significant roles in the vibration behaviors of a microbeam. The results may be helpful for the application and design of various micro-electronic-mechanical devices, where a microbeam acts as a basic element.

Abstract: Contact pressure of porous Al2O3 probed by nanoindentation was investigated by dimensional analysis with special attention paid to scaling effects in the mechanical behavior. It was found that, for sample containing small grains and interconnected pores, the contact pressure is manifest dominated by bonding strength of the porous alumina. Whereas the samples with coarse grain and various porous structures exhibit higher contact pressures and smaller residual deformations, which can be attributed to the mechanical response of the solid-phase under current limited peak loads.

Abstract: The substructure evolution was observed in the range of scales from dozens nanometers to millimeters on the surface of the aluminum single crystalline plates under restricted cyclic tension. The self-similar systems of crossing bands that create the grid-like ordered structures on different scales are assumed to be clear manifestation of their self-organization. The selforganization of these grid-like structures is assumed to be inevitably related to the crystal structure defects (dislocations, point-like defects and their ensembles). The model is proposed for explanation of 2-dimensional rectangular "tweed" and 3-dimensional rhombic "pullover" pattern formations which are related to cooperative arrangement of crystal structure defects.

Abstract: The mechanical properties of various parts of the welding-line material are different, while they play very important role in the welding structures, such as the differences of the melted part and the temperature-affected part. In this paper, a non-contacting laser based technique, ISDG (Interference Strain Displacement Gauge) method, is applied to find out these property differences on very small specimen. The testing is very successful and the whole stress-strain curves in such small scale are obtained on different parts of the welding-line material. The soften phenomena of the temperature-affected part is observed by the comparison of the Young’s modulus and yield stress between the melted part and the temperature-affected part.

Abstract: This work deals with the development of a full-field extensometric method at a micrometric scale in order to precisely identify the local features of a metallic alloy at the scale of the grains. The full-field method that has been chosen is the grid method that applies a spatial phase-shifting algorithm to a periodic pattern. To mark the sample, direct interferometric photolithography was used. The paper presents the basic features of the technique and first mechanical test results are commented.