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Brno, Czech Republic

Sebek F.,Brno University of Technology | Kubik P.,Brno University of Technology | Petruska J.,Brno University of Technology | Hulka J.,Institute of Applied Mechanics
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

The cutting process is now combined with machining, milling, or drilling as one of the widespread manufacturing operations. It is used across various fields of engineering. From an economical point of view, it is desirable to maintain the process in the most effective way in terms of the fracture surface quality or minimizing the burr. It is not possible to manage this experimentally in mass production. Therefore, it is convenient to use numerical computation. To include the crack initiation and propagation in the computations, it is necessary to implement a suitable ductile fracture criterion. Uncoupled ductile fracture models need to be calibrated first from fracture tests when the test selection is crucial. In the present article, there were selected widespread uncoupled ductile fracture models calibrated with, among others, an extremely low-stress triaxiality test realized through the compression of a cylinder with a specific recess. The whole experimental program together with the cutting process experiment were carried out on AISI 1045 carbon steel. After the fracture models were calibrated and the cutting process was simulated with their use, fracture surfaces and force responses from computations were compared with those experimentally obtained and concluding remarks were made. © 2016 The Minerals, Metals & Materials Society and ASM International Source

Zhu L.,Harbin Engineering University | Li Q.,Harbin Engineering University | Buchholz F.G.,Institute of Applied Mechanics
Journal of Marine Science and Application

Fracture processes in ship-building structures are in many cases of a 3-D character. A finite element (FE) model of an all fracture mode (AFM) specimen was built for the study of 3-D mixed mode crack fracture behavior including modes I, II, and III. The stress intensity factors (SIFs) were calculated by the modified virtual crack closure integral (MVCCI) method, and the crack initiation angle assessment was based on a recently developed 3-D fracture criterion-the Richard criterion. It was shown that the FE model of the AFM-specimen is applicable for investigations under general mixed mode loading conditions, and the computational results of crack initiation angles are in agreement with some available experimental findings. Thus, the applicability of the FE model of the AFM-specimen for mixed mode loading conditions and the validity of the Richard criterion can be demonstrated. © 2011 Harbin Engineering University and Springer-Verlag Berlin Heidelberg. Source

Sebek F.,Brno University of Technology | Kubik P.,Brno University of Technology | Hulka J.,Institute of Applied Mechanics | Petruska J.,Brno University of Technology
European Journal of Mechanics, A/Solids

The performance of ductile fracture criteria often depends on the accuracy of material constants identification. Calibration process of three uncoupled phenomenological models was analysed. All of them contain the strain hardening exponent which is related to material plasticity as one of the fracture criteria parameter. More flexibility, better approximation of the fracture locus and more convenient shape of the fracture envelope might be reached when the strain hardening exponent is considered as another independent parameter of the fracture criteria in the identification process. Results are illustrated on the example of two structural steels, AISI 316L and AISI 1045, respectively. © 2015 Elsevier Masson SAS. All rights reserved. Source

Lin Y.-S.,Institute of Applied Mechanics | Lin J.-H.,National Taiwan University | Lin J.-H.,Academia Sinica, Taiwan | Chang C.-C.,Institute of Applied Mechanics | Chang C.-C.,Academia Sinica, Taiwan
Biophysical Journal

The membrane-bound component F0 which is a major component of the F0F1-ATP synthase, works as a rotary motor and plays a central role in driving the F1 component to transform chemiosmotic energy into ATP synthesis. We conducted molecular dynamics simulations of b 2free F0 in a 1 -palmitoyl-2-oleoyl-phosphatidylcholine lipid bilayer for tens of nanoseconds with two different protonation states of the cAsp-61 residue at the interface of the a-c complex in the absence of electric fields and under electric fields of ± 0.03 V/nm across the membrane. To our surprise, we observed that the upper half of the N-terminal helix of the C1 subunit rotated about its axis clockwise by 30°. An energetic analysis revealed that the electrostatic repulsion between this N-terminal helix and subunit C12 was a major contributor to the observed rotation. A correlation map analysis indicated that the correlated motions of residues in the interface of the a-c complex were significantly reduced by external electric fields. The deuterium order parameter (S CD) profile calculated by averaging all the lipids in the F 0-bound bilayer was not very different from that of the pure bilayer system, in agreement with recent 2H solid-state NMR experiments. However, by delineating the lipid properties according to their vicinity to F0, we found that the SCD profiles of different lipid shells were prominently different. Lipids close to F0 formed a more ordered structure. Similarly, the lateral diffusion of lipids on the membrane surface also followed a shelldependent behavior. The lipids in the proximity of F0 exhibited very significantly reduced diffusional motion. The numerical value of SCD was anticorrelated with that of the diffusion coefficient, i.e., the more ordered lipid structures led to slower lipid diffusion. Our findings will help elucidate the dynamics of F0 depending on the protonation state and electric field, and may also shed some light on the interactions between the motor F0 and its surrounding lipids under physiological conditions, which could help to rationalize its extraordinary energy conversion efficiency. © 2010 by the Biophysical Society. Source

Lo Y.J.,Institute of Applied Mechanics | Lei U.,Institute of Applied Mechanics | Yang P.C.,National Taiwan University
15th International Conference on Miniaturized Systems for Chemistry and Life Sciences 2011, MicroTAS 2011

A method is proposed for selective separation and isolation of particles/cells of similar sizes based on their different Clausius-Mossotti factors using dielectrophoresis and microfluidics via both calculation and experiment. The device is a straight micro channel (PDMS) with grooves (or cavities) on its ceiling for capturing particles, and electrodes on its bottom wall (glass) for generating electric field. A particle may be carried downstream or pushed into the groove depending on a designed local force balance between dielectrophoretic force, fluid drag and buoyancy. A mixture of polystyrene particles and CL1-5 lung cancer cells can be separated within 10% accuracy. Copyright © (2011) by the Chemical and Biological Microsystems Society. Source

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