Object-oriented Finite Element Research Articles

A Critique on the Role of Object-Oriented Finite Element Analysis (OOF2) in Predicting Thermal and Mechanical Properties in Thermal Sprayed Coatings

A Critique on the Role of Object-Oriented Finite Element Analysis (OOF2) in Predicting Thermal and Mechanical Properties in Thermal Sprayed Coatings

In-situ shrinkage measurement of alkali-activated materials using focused ion beam combined with environmental scanning electron microscopy

Drying shrinkage of alkali-activated slag (AAS) has gained significant attention since the volumetric instability of this material can generate premature cracking and degrade the long-term durability of concrete structures. The unique shrinkage behavior of AAS originates mainly from the particular characteristics of its main hydrated products. However, few studies have even at-tempted to investigate the shrinkage behavior of hydrated products in AAS materials. This paper presented a new method of investigating drying shrinkage behavior of AAS using focused ion beam (FIB) combined with environmental scanning electron microscopy (ESEM). This innovative experimental method allowed the in-situ measurement of phase-specific shrinkage. The results showed FIB/ESEM technique can be successfully implemented to cementitious material to prepare phase-specific samples. Furthermore, object-oriented finite element method (OOF2) has been utilized to compute the shrinkage behavior of AAS concrete using a proposed multi-scale scheme. The computations can be made at multi-scales which highlight the effect of hydration products on shrinkage behaviors. OOF2 calculation at the micro-length scale predicted an increase in the shrinkage due to the well-dispersed hydration products inside the matrix. At larger scale, the decrease in the overall shrinkage is related to the extremely low shrinkage value by aggregates. The findings reveal OOF2 offers the capability to accurately measure local stress and strain distribution within heterogeneous materials, a feature notably absent in conventional numerical homogenization approaches. The importance of this benefit is highlighted particularly in the context of free-restrained shrinkage prediction, as conventional homogenization methods fail to account for stress.

Adaptation of FEM-based open-source software for ship structural analysis

ABSTRACT This paper investigates the challenges and opportunities emerging from the application of finite element method-based open-source software in ship structural analysis. Application of general procedure for development and assessment of FEA software used for ship structures is presented and demonstrated on the new upgrade of open-source FEA software OOFEM (Object-Oriented Finite Element Method). Properties of new quadrilateral shell FEs implemented in OOFEM are presented. The new FEs comply with relevant class requirements and are suitable for the usage in the analysis of real-world ship structures. The implemented software upgrade is validated on a series of test problems ranging from simple engineering structures to a real-world model of one part of megayacht’s superstructure. The benefits of validation tests and challenges encountered in the process of selecting the tests and interpreting their results are also discussed.

An Object-oriented finite element framework for modified cam clay model

In this paper, an object-oriented finite element framework is developed and modified cam clay model, which is an elasto-plastic soil constitutive model, is implemented with it. The paper briefly describes the approach of implementing the steps of finite element analysis in object-oriented programming paradigm. An implicit integration algorithm for modified cam clay model is implemented in the proposed framework, which can be used to solve boundary value problems in geotechnical engineering. The framework ensures the maintainability and extensibility of the program to implement new tasks that may be in the form of the addition of a new constitutive model with different integration algorithms, and hence it can be used for research purposes in the field of geotechnical engineering. Numerical investigations are performed to validate the stability and accuracy of the proposed framework, which also demonstrate the effectiveness of object-oriented programming in finite element analysis. Numerical examples include triaxial compression tests on normally consolidated clay (NCC) and overconsolidated clay (OCC) and bearing capacity evaluation of a flexible strip footing on a homogeneous deposit of clay. As a programming language, C++ is used.

Thermomechanical analysis of 0.94Na1/2Bi1/2TiO3-0.06BaTiO3/ZnO composites using finite element method

Object-oriented finite element (OOF2) analysis has been carried out on composites constituting of 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-6BT) matrix phase and ZnO inclusions (4%, 7.5%, 10.78%, and 14% by volume). The effect of ZnO inclusions on the thermomechanical properties of NBT-6BT is investigated and the results are compared with theoretical methods. The thermal stress and strain variation are analyzed under the homogeneous and heterogeneous temperature conditions as a function of volume fraction of the inclusions. The residual stresses localized at the NBT-6BT/ZnO interface are evaluated using the real microstructure of the composite (SEM micrographs), thus providing an actual spatial distribution of stress in the material. In the case of a gradient temperature application, orientation of the grain also varies the stress concentration. Based on the above, the depolarization temperature of the composite can be further improved if the ZnO nano-wire/nano-rods are used instead of ZnO nanoparticle/powder (depending on the orientation of nanowire). Further, the elastic loading conditions mimic the experimental response and as expected, material failure initiates at the pores thus validating the model.

Spalling in Continuously Reinforced Concrete Pavement in Texas

The performance of continuously reinforced concrete pavement (CRCP) in Texas has been quite satisfactory, primarily thanks to the continuous improvements in design and construction. However, severe spalling has been a major problem, and the Texas Department of Transportation (TxDOT) has sponsored several research projects since 1985 to identify solutions for this serious problem. Even though the research efforts were successful in identifying spalling mechanisms, developing a policy that TxDOT could easily implement has been a challenge. To develop a more practical solution to this problem, TxDOT initiated a research study, and the research efforts consisting of identifying CRCP projects with severe and no spalling, obtaining and conducting materials testing on concrete cores from those projects, analyzing the testing data, and performing theoretical analyses to validate the testing results. Among the material properties evaluated, the coefficient of thermal expansion (CTE) of concrete proved to have the best correlation with spalling. Detailed analyses of mechanistic behavior of concrete conducted with an object-oriented finite element program (OOF2) and commercial finite element program verified the reasonableness of the field-testing results. All concrete cores from CRCP with severe spalling had a CTE larger than 5.5 microstrains/°F, whereas no spalling was observed in concrete with a CTE less than that value. Based on this finding, TxDOT now requires the use of coarse aggregate that will produce concrete with a CTE of less than 5.5 microstrains/°F for CRCP construction. It is expected that this implementation will reduce the spalling in CRCP substantially.

Preliminary design of a novel AlN-Al composite coating used for micro-electronic packaging via finite element modeling

In this study, a novel AlN-Al composite coating (AACC) is proposed for micro-electronic packaging. By adjusting the proportion of AlN in the AACC, the effective thermal conductivity and coefficient of thermal expansion of the AACC can be controlled. The powder of AlN and Al sprayed onto the surface of the W-Cu alloy to form the AACC that acts as a buffer layer to reduce the thermal mismatch between the W-Cu alloy and microchip. Finite element simulation results show that the thermal conductivity decreases from 240.64 to 179.99 W m−1 K−1 with increasing AlN content. The coefficient of thermal expansion ranges from 8.39 to 205 MPa in the case of a selected W-Cu alloy (W70-Cu30). Some microscopic features that affect the thermal conductivity of the coating, such as porosity, pore shape, and pore orientation, have been investigated. Macroscopic properties from an SEM image of real microstructures were studied using the Object-oriented finite element (OOF) analysis.

Characterization of Mechanical Performance of Composites Fabricated Using Innovative Carbon Fiber Wet Laid Process

Recent innovation in production of optimized nonwoven wet laid (WL) carbon fiber (CF) mats raised the question of optimal translation of the performance and isotropy into composites formed through these dry preforms. This work explores the mechanical behavior of composites produced from WL-CF mats in conjunction with the microstructure predicted through Object Oriented Finite Element Analysis (OOF). The mats used for the composites were prepared in two dispersion regimes using 25.4 mm long CF. The mixing regimes discussed in the author’s previous work, are identified as Method 1 for the traditional processing regime and Method 2 for the innovative regime that provided optimal nonwoven WL-CF mats. Composite panels from Method 2 mats showed a normalized tensile strength increase of 52% over those from Method 1 panels. Reproducibility analysis of composites made from Method 2 mats demonstrated a standard deviation of 2% in fiber weight content, 2% in tensile modulus and 9% in tensile strength, while composites made from Method 1 mats demonstrated a standard deviation of 5% in fiber weight content, 5% in tensile modulus and 17% in tensile strength. Systematic study of the microstructure and its analysis through OOF confirmed the isotropy translation of mats produced through method 2 to the composites. This study validated the hypothesis that optimal nonwoven mats lead to a well-balanced composite with optimal performance and that non-optimal nonwoven mats do not pack into a well-balanced composite.

Timber beam in virtual furnace

Purpose This paper aims to present a part of a coupled numerical model for prediction the fire resistance of elements in a horizontal furnace. Temperatures calculated inside the timber beam are compared to measured values from the fire test. Design/methodology/approach The paper presents a part of a coupled numerical model for prediction the fire resistance of elements in a horizontal furnace. The presented part lies in a virtual furnace which simulates temperature environment around tested elements in the furnace. Comparison of results show good agreement in the case when burning of timber is included in the numerical model. Findings The virtual furnace presented in this paper allows to calculate temperature environment around three timber beams. After validation of the fire dynamics simulator (FDS) model, the temperature conditions are passed to the FE model which solves heat transfer to the tested element. Temperatures inside the timber beam which are solved in software Atena Science are compared to measured temperatures from the fire test. The comparison of temperatures in three control points shows good accuracy of the calculation in the point closer to the heated edge. An inaccuracy is shown in points located deeper in the beam cross-section – below the char layer. Research limitations/implications In conclusion, the virtual furnace has a great potential for investigating the thermal behaviour of fire-resistance tests. A huge advantage inheres in the evaluation of the thermal effect throughout the volume of the furnace, which allows an accurate prediction of fire-resistance tests and evaluation of large number of technical alternatives and boundary conditions. However, passing the temperature field from the FDS model into FE model may decrease the level of accuracy. The solution lies in a coupled CFD-FE model. A weakly coupled model including fluid dynamics, heat transfer and mechanical behaviour is under development at Faculty of Civil Engineering, Czech Technical University in Prague. The fluid dynamics part which is presented in this paper is solved by FDS and the thermo-mechanical part is computed by object-oriented finite element model (OOFEM). The interconnection of both software is made owing to MuPIF python library. Practical implications The virtual furnace takes advantage of great possibilities of computational fluid dynamics code FDS. The model is based on an accurate representation of a real fire furnace of fire laboratory PAVUS a.s. located in the Czech Republic. It includes geometry of the real furnace, material properties of the furnace linings, burners, ventilation conditions and tested elements. Gas temperature calculated in the virtual furnace is validated to temperatures measured during a fire test. Social implications The virtual furnace has a great potential for investigating the thermal behaviour of fire-resistance tests. A huge advantage inheres in the evaluation of the thermal effect throughout the volume of the furnace, which allows an accurate prediction of fire-resistance tests and evaluation of large number of technical alternatives and boundary conditions. Originality/value The virtual furnace has a great potential for investigating the thermal behaviour of fire-resistance tests. A huge advantage inheres in the evaluation of the thermal effect throughout the volume of the furnace, which allows an accurate prediction of fire-resistance tests and evaluation of large number of technical alternatives and boundary conditions. However, passing the temperature field from the FDS model into FE model may decrease the level of accuracy. The solution lies in a coupled CFD-FE model. A weakly coupled model including fluid dynamics, heat transfer and mechanical behaviour is under development at Faculty of Civil Engineering, Czech Technical University in Prague. The fluid dynamics part which is presented in this paper is solved by FDS and the thermo-mechanical part is computed by OOFEM. The interconnection of both software is made thanks to MuPIF python library.

Principle and application of OpenGeoSys for geothermal energy sustainable utilization

Numerical simulation is very useful in utilizing large scale geothermal energy,predicting reservoir response and optimizing exploitation procedure.Here we describe the OpenGeoSys(OGS)software used to simulate the complex processes in geoscience and hydrological applications,focusing on its application in geothermal energy utilization.OGS is based on an object-oriented finite element method concept and can deal with numerical simulation of thermo-hydro-mechanical-chemical processes in porous media.Case studies related to shallow geothermal energy(temperature and pressure prediction),hydrothermal energy(optimization on the distance between production well and reinjection well,scaling)and hot dry rock(hydraulic fracturing,permeability evolution)are shown with the purpose to help managing geothermal energy utilization.

Investigation on Relationship Between Microstructural Characteristics and Mechanical Properties of Wire-Arc-Sprayed Zn-Al Coating

Wire arc spraying is a cost-effective thermal spraying technology to deposit a protective coating layer on the surface of industrial components. Mechanical properties of wire arc spraying coatings are mainly influenced by their heterogeneous microstructure, resulting in complex and anisotropic mechanical properties. The objective of this investigation is to characterize the mechanical behavior of wire-arc-sprayed Zn-15Al alloy using an efficient micromechanical–computational scheme. Scanning electron microscopy images were imported to an object-oriented finite element scheme and distinguished into various phases, and then subsequently discretized into finite elements. To examine the validity of this technique, experimental studies, such as Knoop and Vickers microhardness, resonance frequency, and nanoindentation, were conducted on the freestanding coating samples. The elastic modulus of the coating was also calculated using well-known analytical methods. Comparison of the results obtained in this study was used to investigate the relationship between the microstructural features and mechanical properties in coating materials. Image-based finite element analysis showed good agreement with the experimental measurements and proved the effect of splat boundaries on the reduction in mechanical strength between coating layers and, consequently, lower elastic modulus of the wire-arc-sprayed Zn-15Al coating in the longitudinal direction compared to the transversal one.

Numerical Development and Assessment of 3D Quintuple Friction Pendulum Isolator Element Based on Its Analytical and Mathematical Models

ABSTRACT This paper aims to develop, assess, and numerically implement analytical models for the newly introduced Quintuple Friction Pendulum Isolator (QFPI) which can identically capture its real experimental performance and also have the ability to capture the bi-directional, tri-directional, and vertical-horizontal coupling behavior of it, raising the predictive capability of nonlinear response history analyses and also lowering computational and experimental complexity and cost. The mathematical formulation proposed in this paper aims at addressing the variability of the coefficient of friction based on experimentally obtained data from prototype test on QFPI system. The formulation accounts for variation in the coefficient of friction with the instantaneous change of axial load and sliding velocity at the isolator contact interfaces. Furthermore, it considers the experimentally discovered phenomena such as the static frictions developed at the very first initiation of motion, breakaway, or at motion reversals, stick-slip. The proposed model has been coded three-dimensionally by a series model in the object-oriented finite element software OpenSees based on its mathematical formulations. The primary assumptions in developing the friction models and corresponding parameters are validated by available experimental data and suggestions. A case study has been considered to validate the developed element and also to investigate and demonstrate the prediction capability of it when applied to real situations, such as variations have been made in displacement, base shear, and acceleration demand for this system under dynamic behavior of earthquakes. Moreover, the effects of vertical-horizontal coupling behavior of QFP isolated system on its horizontal responses have been investigated numerically and justified analytically under the existence of vertical acceleration, by subjecting the system to a variety of X and XY (horizontal only) and 3D (horizontal plus vertical) input excitations for comparison.

Graphene-reinforced thermoplastic polyurethane nanocomposites: A simulation and experimental study

Multiscale modelling and simulations, based on molecular dynamics (MD) and object-oriented finite element method (OOFEM), are two important simulation tools to predict property enhancement of polymer nanocomposites for designing armor-type components in requisite applications. In this study, MD simulation software (Materials Studio) is used to develop 0.5%, 1%, 2%, 3%, and 4% (by weight) single-layer graphene (SLGR)-reinforced thermoplastic polyurethane (TPU) nanocomposites to find out their mechanical properties (mainly elastic moduli and Poisson’s ratio) using constant strain method. OOFEM simulation software (OOF2) is used for mechanical characterization of 0.5%, 3%, and 4% (by weight) SLGR-reinforced TPU nanocomposites from scanning electron microscopy–generated microstructures. Properties obtained from both the simulations are compared with experimental results to know the nanoreinforcement effect in atomic level as well as in microlevel in the nanocomposites. It is observed that the results based on OOF2 simulation are closer to the experimental results compared with the results obtained from MD simulation in this multiscale modelling and simulation study.

CastLab: an object-oriented finite element toolbox within the Matlab environment for educational and research purposes in computational solid mechanics

The Matlab environment has become widely used among the computational mechanics community, not only for research purposes but also to teach either undergraduate or graduate classes. This paper aims to present a new toolbox devoted to computational mechanics and in particular to solid mechanics. Both recent and well-established numerical formulations have been implemented in it. One of its strengths resides in the fact that it was developed within an object-oriented framework. This key feature makes the CastLab toolbox easy-to-use and with extensive capabilities for customized user developments. After a brief description of the theoretical background related to the problems that can be solved by means of the toolbox, several representative case-studies are presented. These examples have been selected to illustrate not only the numerical efficiency of the toolbox, which is of primary importance for research purposes, but also its strong educational and pedagogic potential.

A novel OpenSees element for single curved surface sliding isolators

The increasing use of curved surface sliding bearings as seismic isolators benefits from the improvement of analytical models that can accurately capture their experimental performance and enhance the predictive capability of nonlinear response history analyses. The mathematical formulation proposed in this paper aims at addressing the variability of the coefficient of friction based on experimental data that can be retrieved from prototype tests on Curved Surface Sliders. The formulation accounts for variation in the coefficient of friction with the instantaneous change of axial load and sliding velocity at the contact interface, and the accumulated heat due to cyclic motion; furthermore, it incorporates new features such as the static friction developed in the transition from the pre-sliding phase to the dynamic sliding condition. The proposed model has been coded in the object-oriented finite element software OpenSees by modifying the standard SingleFPSimple3d element that describes the force – displacement relationship of a bearing comprising one concave sliding surface and a spherical articulation. The main novelties of the new CSSBearing_BVNC element are inclusion of the static friction before the breakaway and degradation of kinetic friction induced by the heat developed during the motion of the articulated slider. The primary assumptions in the development of the friction model and the verification of the newly developed element are validated by agreement with available data. A case study helps to demonstrate the improved prediction capability of the new bearing element over its standard counterpart when applied to real situations, such as estimating a +50% increase in isolator displacement, superstructure drift and base shear demand under high intensity earthquakes, and possible non-activation of the sliding isolators under weak or medium intensity earthquakes.

Material forces: An insight into configurational mechanics

The concept of material or configurational forces, albeit not new, is one of those innovations in theoretical mechanics that has struggled to reach the success of wide-spread acceptance, or even familiarity. Perhaps, one reason for this is to be found in the few available introductory examples or in the non-trivial physical-mathematical approach often taken to establish this concept, although by no means more complex than other treatments in non-linear continuum mechanics. With this work we aim at contributing to the dissemination of configurational mechanics concepts by guiding the reader through an introductory analytical example step by step and comparing it to numerically obtained results. The numerical model is solved with OpenGeoSys (OGS-6), an open-source, C++-based, object-oriented finite element platform for the thermo-hydro-mechanical analysis of coupled processes in fractured porous media. In the spirit of the open-source philosophy, and to enable the readers to reproduce the example themselves, both the source code and the input files are available online. The example highlights—in a simple and intuitive manner—several insightful aspects related to configurational mechanics.

Determining Stress-Strain Behavior of Zr<sub>60</sub>Cu<sub>10</sub>Al<sub>15</sub>Ni<sub>15</sub> Bulk Metallic Glass Using Object Oriented Finite Element Analysis

Determining mechanical properties of Bulk Metallic Glasses (BMGs) requires synthesizing of the alloys in bulk form. However obtaining metallic glass in bulk form is quite challenging due to its tendency towards crystallization. In such circumstances it is beneficial to determine the mechanical properties of materials using finite elemental analysis of microstructures. Thus, in the present investigation, using Object Oriented Finite Element Analysis (OOF2) software package, Stress-Strain analysis has been carried out on Zr60Cu10Al15Ni15 BMG to determine such mechanical properties. Specimen of Zr60Cu10Al15Ni15 BMG exhibiting three microstructurally distinct regions amorphous, partial crystalline and crystalline regions was used for this analysis. The Stress-Strain relationship have been estimated for each of the three distinct phases and the results are validated by determining the Modulus of Elasticity for all the phases and comparing it with the available experimental results from Nano-indentation test.

Thermal Conductivity in Suspension Sprayed Thermal Barrier Coatings: Modeling and Experiments

Axial suspension plasma spraying (ASPS) can generate microstructures with higher porosity and pores in the size range from submicron to nanometer. ASPS thermal barrier coatings (TBC) have already shown a great potential to produce low thermal conductivity coatings for gas turbine applications. It is important to understand the fundamental relationships between microstructural defects in ASPS coatings such as crystallite boundaries, porosity etc. and thermal conductivity. Object-oriented finite element (OOF) analysis has been shown as an effective tool for evaluating thermal conductivity of conventional TBCs as this method is capable of incorporating the inherent microstructure in the model. The objective of this work was to analyze the thermal conductivity of ASPS TBCs using experimental techniques and also to evaluate a procedure where OOF can be used to predict and analyze the thermal conductivity for these coatings. Verification of the model was done by comparing modeling results with the experimental thermal conductivity. The results showed that the varied scaled porosity has a significant influence on the thermal conductivity. Smaller crystallites and higher overall porosity content resulted in lower thermal conductivity. It was shown that OOF could be a powerful tool to predict and rank thermal conductivity of ASPS TBCs.

Characterization and methodology for calculating the mechanical properties of a TRIP-steel submitted to hot stamping and quenching and partitioning (Q&P)

Thermomechanical simulation of quenching, hot stamping, and quenching and partitioning processes of a high-strength TRIP-assisted steel were carried out in a Gleeble®3S50 thermo-mechanical simulator, coupled to the synchrotron X-ray diffraction line. The microstructures and mechanical properties were analyzed using Field Emission Gun Scanning Electron Microscopy (FEG-SEM), X-ray diffraction, and nanoindentation. The microstructures of thermomechanical treated specimens were modeled using the Object Oriented Finite Element (OOF) technique. The modeled microstructures were then fed into a finite element model to predict the mechanical behavior. By using a reverse algorithm method, the elasto-plastic mechanical properties of different microconstituents were determined. This was done through the analysis of instrumented nanoindentation loading-penetration curves. Tensile properties of the thermomechanical processed steels were measured by tensile testing of subsized specimens cut from samples processed on the Gleeble®3S50. The comparison between the experimental results and those of the reverse algorithm and the OOF modeled microstructure showed quite good agreement.

Closed-form effective elastic constants of frame-like periodic cellular solids by a symbolic object-oriented finite element program

In this study, the effective elastic constants of several 2D and 3D frame-like periodic cellular solids with different unit-cell topologies are analytically derived using the homogenization method based on equivalent strain energy. The analytical expressions of strain energy of a unit cell under different strain modes are determined using a generic symbolic object-oriented finite element (FE) program written in MATLAB. The obtained analytical expressions of the strain energy are then used to symbolically compute the effective elastic constants that include Young’s moduli, Poisson’s ratios, and shear moduli. The obtained analytical effective elastic constants are numerically verified using results from an ordinary numerical FE program. The obtained closed-form effective elastic constants are also compared with some existing solutions from the literature. This study demonstrates that symbolic computation platforms can be properly used to provide efficient methodologies for finding useful analytical solutions of mechanical problems. Without the symbolic object-oriented FE program in this study, elaborate and tedious analytical analysis has to be manually performed for each different unit cell. The symbolic object-oriented FE program provides analytical analysis of unit cells that is accurate and fast. The object-oriented programming technique allows the symbolic FE program in this study to be efficiently implemented.