Modeling Silicon under Contact Loading Conditions: Aspects of Non-Associated Flow

Technologically relevant abrasive machining techniques (lapping, sawing, grinding) for silicon (Si) are based on (sub-)surface crack formation triggered by contact events. Therefore, the understanding of the inelastic deformation of Si under contact (indenter-)loading is essential to improve machining results. It has been long established that Si undergoes a series of stress driven phase transitions under compression. During subsequent pressure release part of the transformation strain is recovered. The present paper highlights the importance of the direction of inelastic flow for modeling (partially) reversible stress induced phase transitions in materials such as silicon. A phenomenological constitutive model for Si under contact loading, which captures both the cd−Si → −Si transition upon compression and the −Si → a−Si transition upon rapid decompression has been recently presented (Budnitzki and Kuna, 2012). It is shown that indentation experiments are particularly well suited to determine material parameters for this model. Further, material parameters obtained from indentation experiments with Berkovich indenter are confirmed to be valid for the numerical simulation of Knoop indentation, thus verifying a certain predictive capability of the constitutive model

Electrostatic method to measure the size of the sprayed droplets

In the paper is presented the new method the measurement of the main parameters the atomised stream of liquid. This method base on the measurement of the electric charge carried by water drops charged by high voltage. The electrostatic sensor to measure of the droplets size, is associated with precision mechanic system scanning the sprayed surface. The amplified and conditioned signals from electrostatic sensor are send to the computer system equipped in virtual instrument to analyse the size and spatial distribution of droplets. The virtual instrument control also the scanning system

A PVDF Sensor for the In-situ Measurement of Stress Intensity Factors During Fatigue Crack Growth

AbstractSeveral analytical and numerical studies of inverse analysis are performed to verify the feasibility and accuracy of the proposed K-sensor. At first, the application to cracks in sheets under in-plane stresses is investigated and compared with the analytical solution for the GRIFFITH's crack under mixed mode. It was found that the convergence radius, where the electrodes have to be placed, must be smaller than half of the crack length, which is sufficient for real cracks of several millimeters. The obtained accuracy of crack tip location and (KI, KII)-factors is better than 1%. Second, the technique is applied to cracks in thin-walled plates of KIRCHHOFF type under bending and torsion moments. In this case, the plate intensity factors (k1, k2) are of interest. Again, the inverse identification procedure is studied by synthetic analytical and numerical solutions of simple crack configurations. Due to the assumptions of the KIRCHHOFF plate model, the sensors have to be placed outside a radius of 3 times plate thickness h. The obtained accuracy in position and intensity factors is quite sufficient as well. The practical realization of the K-factor sensor requires good electric signal measurement and amplification. Its experimental testing on components is ongoing work

A Finite Element Procedure for Three-dimensional Analyses of Thermopiezoelectric Structures in Static Applications

The development and application ofsmart structures and smart composite materials require eflicient numerical tools to evaluate the thermopiezoelectric behavior and stress state. In this paper, finite element techniques are suggested for three-dimensional coupled thermo-electromechanical static analyses. The actual thermopiezoelectric responses subjected to thermal loadings can be determined by adopting a procedure TPESAP. The detailed implementation is presented with emphasis on the integration with software ABAQUS. Several verification example problems are discussed, including the benchmark problem ofafive-layer hybrid plate

General estimate of the first eigenvalue on manifolds

Ten sharp lower estimates of the first non-trivial eigenvalue of Laplacian on compact Riemannian manifolds are reviewed and compared. An improved variational formula, a general common estimate, and a new sharp one are added. The best lower estimates are now updated. The new estimates provide a global picture of what one can expect by our approach.Comment: 19 page

Novel Quaternary Dilute Magnetic Semiconductor (Ga,Mn)(Bi,As): Magnetic and Magneto-Transport Investigations

Magnetic and magneto-transport properties of thin layers of the (Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor grown by the low-temperature molecular-beam epitaxy technique on GaAs substrates have been investigated. Ferromagnetic Curie temperature and magneto-crystalline anisotropy of the layers have been examined by using magneto-optical Kerr effect magnetometry and low-temperature magneto-transport measurements. Postgrowth annealing treatment has been shown to enhance the hole concentration and Curie temperature in the layers. Significant increase in the magnitude of magnetotransport effects caused by incorporation of a small amount of Bi into the (Ga,Mn)As layers revealed in the planar Hall effect (PHE) measurements, is interpreted as a result of enhanced spin-orbit coupling in the (Ga,Mn)(Bi,As) layers. Two-state behaviour of the planar Hall resistance at zero magnetic field provides its usefulness for applications in nonvolatile memory devices.Comment: 10 pages, 3 figures, to be published in the Proceedings of ICSM-2016 conferenc

Evaluation of Craniometric Methods for Determination of Vertical Dimension of Occlusion

In clinical practice, fully precise method for exact determination of vertical relation of occlusion still does not exist. This study examines the relationship between different craniofacial distances and the distance subnasale– gnathion (Sn–Gn), which represents the lower third of the face in vertical relation determination. The highest coefficient of correlation was (r = 0.8678, p < 0.05) between the distance eye–ear (E–E = lateral border of the ocular orbit–medial opening of the meatus of the external auditory canal) and Sn–Gn. The prediction of the distance Sn–Gn could be determined through the formula: Sn–Gn = E–E / 1.08 or through the regression analysis: Sn–Gn = 1.9197 + 0.6449 x E–E. None of the calculated coefficients of correlation was 1, but was < 1, so that the prediction of the distance Sn–Gn by craniometric distances is not absolutely reliable, although it is considerably helpful. Our results point at the variations of craniofacial distances in the Croatian population. Yet, craniometry could still be recommended in everyday clinical practice for prediction of vertical relation of occlusion, as it is a simple, economic and non-invasive method, however in combination with some other methods, which have proved to be helpful

Experimental and numerical study of interaction between particle loaded fluid and a rough wall with micropillars

© 2014 Elsevier Ltd. All rights reserved. Experimental and numerical studies of the behavior of a slurry in a shear flow over a rough surface with a defined micro-structure are presented. A new ring shear device was built which contains an optically transparent test chamber. Its bottom wall contains arrays of micro-cantilever force sensors simulating a defined surface roughness created by deep-etching of micro-pillars in a silicon wafer. The results of visual observation of the interaction of the suspension with the structured surface during severe deformation are shown. Observations comprise the liquid phase motion, i.e., the interaction between the liquid phase and solid particles, the movement of separate particles and their interactions with the micro-pillars. Abrupt changes in rotational motion and translational velocity of particles are observed that induce mutual collisions and successive formation and break-up of cluster structures of various types. In addition to the experiments the process was simulated with discrete element (DEM) simulations. Many characteristics found in the experiments are reproduced by the simulations. Furthermore the physical quantities of the process like contact forces or velocities can be quantified which helps us to develop more detailed models of the abrasive behavior of slurries