Institute of Applied Mechanics

Brno, Czech Republic

Institute of Applied Mechanics

Brno, Czech Republic
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Jenik I.,Honeywell | Kubik P.,Brno University of Technology | Sebek F.,Brno University of Technology | Hulka J.,Institute of Applied Mechanics | Petruska J.,Brno University of Technology
Archive of Applied Mechanics | Year: 2017

Two alternative methods for the stress–strain curve determination in the large strains region are proposed. Only standard force–elongation response is needed as an input into the identification procedure. Both methods are applied to eight various materials, covering a broad spectre of possible ductile behaviour. The first method is based on the iterative procedure of sequential simulation of piecewise stress–strain curve using the parallel finite element modelling. Error between the computed and experimental force–elongation response is low, while the convergence rate is high. The second method uses the neural network for the stress–strain curve identification. Large database of force–elongation responses is computed by the finite element method. Then, the database is processed and reduced in order to get the input for neural network training procedure. Training process and response of network is fast compared to sequential simulation. When the desired accuracy is not reached, results can be used as a starting point for the following optimization task. © 2017 Springer-Verlag Berlin Heidelberg

Naghipour P.,Ohio Aerospace Institute | Arnold S.M.,NASA | Pineda E.J.,NASA | Stier B.,Institute of Applied Mechanics | And 4 more authors.
Journal of Composite Materials | Year: 2017

The generalized method of cells (GMC) is demonstrated to be a viable micromechanics tool for predicting the deformation and failure response of laminated composites with and without notches subjected to tensile and compressive static loading. Given the axial [0], transverse [90], and shear [+45/-'45] response of a carbon/epoxy (IM7/977-3) system, the unnotched and notched behavior of three multidirectional layups (1) Layup 1: [0,45,90,-'45]2S, (2) layup 2: [60,0,-60]3S, (3) layup 3: [30,60,90,-'30,-'60]2S) are predicted under both tensile and compressive static loading. Matrix nonlinearity is modeled in two ways. The first assumes all nonlinearity is due to anisotropic progressive damage of the matrix only, which is modeled, using the multiaxial mixed mode continuum damage model (MMCDM) within GMC. The second utilizes matrix plasticity coupled with brittle final failure based on the maximum principle strain criteria to account for matrix nonlinearity and failure within NASA's multiscale framework (FEAMAC). Both MMCDM and plasticity models incorporate brittle strain and stress based failure criteria for the fiber. Upon satisfaction of this criterion, the fiber properties are immediately reduced to a nominal value. The constitutive response for each constituent (fiber/matrix) is characterized using a combination of vendor data and the axial, transverse and shear response of unnotched laminates. Then, the capability of the multiscale methodology is assessed, by performing blind predictions of the mentioned notched and unnotched composite laminates response under tensile and compressive loading. Tabulated data along with the detailed results (i.e. stress-strain curves as well as damage evolution states at various ratios of strain to failure) for all laminates are presented. © 2016 SAGE Publications.

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 | Year: 2010

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.

Chen J.Z.,Institute of Applied Mechanics | Li C.-H.,Institute of Applied Mechanics | Cheng I.-C.,National Taiwan University
Thin Solid Films | Year: 2012

We report the thermal stability of room-temperature RF-sputtered Mg 0.4Zn 0.6O thin films and ZnO/Mg 0.4Zn 0.6O superlattices at 600 °C and 800 °C. The phase of room-temperature as-sputtered Mg 0.4Zn 0.6O is crystalline ZnO embedded in an amorphous or short-range-ordered hexagonal MgZnO matrix. Annealing at either 600 °C or 800 °C for 5 min transforms the matrix into a crystalline hexagonal wurtzite structure, leading to a decrease of the optical bandgap (E g) of Mg 0.4Zn 0.6O. This also results in a slight change near the absorption edge of the superlattice transmission spectrum. The films precipitate cubic MgZnO after heating Mg 0.4Zn 0.6O at 800 °C for 5 min; by contrast, precipitations take at least 3 h if the samples are heated at 600 °C. Heating at 800 °C for more than 3 h significantly reduces the film thickness and E g, attributed to the decomposition of superlattices and diffusion of magnesium into the substrate, respectively. On the other hand, annealing the ZnO/Mg 0.4Zn 0.6O superlattice at 600 °C for 12 h also produces an initial slight change in the optical transmission spectra, yet the spectra remain essentially unchanged for the remainder of the annealing process. © 2011 Elsevier B.V. All rights reserved.

Kubik P.,Brno University of Technology | Sebek F.,Brno University of Technology | Hulka J.,Institute of Applied Mechanics | Petruska J.,Brno University of Technology
International Journal of Mechanical Sciences | Year: 2016

The aluminium alloy 2024-T351 and AISI 1045 carbon steel was examined in scope of uncoupled ductile fracture criteria calibration using newly designed specimen. Its novel geometry allowed to reach extremely low stress triaxialities. The analysis of fracture envelopes was carried out with comparison of each criteria cut-off regions after the calibration where one novel criterion, KHPS, has been introduced. Ductile fracture criteria implemented into the commercial finite element code Abaqus through user subroutine VUMAT were applied to simulation of compression of newly designed cylinder with specific recess to show the crack prediction ability using the element deletion technique. Crack initiation loci together with force responses were compared to experimental observations. © 2016 Elsevier Ltd. All rights reserved.

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 | Year: 2016

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

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 | Year: 2016

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.

Radermacher A.,Institute of Applied Mechanics | Reese S.,Institute of Applied Mechanics
Archive of Applied Mechanics | Year: 2013

Computational assistance gains increasing importance in the field of medical surgery. As an example, in the present work, we look at functional endoscopic sinus surgery. Simulations for surgery training programs or online support during surgeries require simulation tools which are characterized by a preferably short simulation time (real time) and a high degree of accuracy. The nonlinear finite element method is most suitable to yield qualitatively and quantitatively reliable results. The problem is, however, to achieve such results in real time. One possibility to reach both, short computational time and high accuracy, is to combine model reduction and finite element techniques. Therefore, in this paper, various projection-based model reduction methods are discussed and compared with respect to their possible application in biomechanics. The modal basis, the load-dependent Ritz and the proper orthogonal decomposition (POD) method were used to reduce the model of a cube under compression considering different material nonlinearities and large deformations. The POD method led to the lowest errors in displacement and stress while providing the largest reduction in CPU time. Further, the influence of different POD parameters was investigated. According to this study, the snapshots upon which the POD is based had to agree as closely as possible with the original deformation of the reduced system. The POD method applied to the finite element model of an inferior turbinate led to an adequate accuracy for surgery simulations within less than one-third of the computational time of the unreduced finite element simulation. © 2013 Springer-Verlag Berlin Heidelberg.

Kebriaei R.,Institute of Applied Mechanics | Vladimirov I.,Institute of Applied Mechanics | Reese S.,Institute of Applied Mechanics
Advanced Materials Research | Year: 2014

In the last decades, manufacturing of layered composite materials has become an interesting topic in industrial development. Joining properties of adhesively bonded materials are characterized by a complex interaction of plastic deformation, thermo-mechano-chemical coupling effects, adhesion and diffusion. Additionally, the interactions between the microstructures involved in the process have to be taken into account. The design of new joining technologies requires a fundamental understanding of the mechanisms which is difficult to achieve by working solely experimentally. The present study therefore deals with modeling the essential effects characterizing joining. Additionally, special attention is paid to the experimental characterization of the involved materials at the macro and micro levels. The microstructure of materials (as e.g. AA1050, AA2024 and AA5754), which have a wide range of applications in engineering structures, is numerically and experimentally investigated. Moreover, a general cohesive zone element formulation in the framework of zero-thickness interface elements is developed. This enables the accurate and efficient modeling of the interface based on an interfacial traction-separation law. © (2014) Trans Tech Publications, Switzerland.

Zhu L.,Harbin Engineering University | Li Q.,Harbin Engineering University | Buchholz F.G.,Institute of Applied Mechanics
Journal of Marine Science and Application | Year: 2011

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.

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