Finite Element Model Model Research Articles

The effect of laser sintering on the microstructure, relative density, and cracking of sol-gel-derived silica thin films.

Combining sol-gel processing and laser sintering is a promising way for fabricating functional ceramic deposition with high dimensional resolution. In this work, crack-free silica tracks on a silica substrate with a thickness from ~360 nm to ~950 nm, have been obtained by direct exposure to a CO2 laser beam. At a fixed scanning speed, the density and microstructures of the silica deposition can be precisely controlled by varying the laser output power. The porosity of the laser-sintered silica tracks ranged from close to 0% to ~60%. When the thickness of the silica deposition exceeded the critical thickness (eg, ~2.2 μm before firing), cracks occurred in both laser-sintered and furnace-sintered samples. Cracks propagated along the edge of the laser-sintered track, resulting in the crack-free track. However, for the furnace heat-treated counterpart, the cracks spread randomly. To understand the laser sintering effect, we established a finite element model (FEM) to calculate the temperature profile of the substrate during laser scanning, which agreed well with the one-dimensional analytical model. The FEM model confirmed that laser sintering was the main thermal effect and the calculated temperature profile can be used to predict the microstructure of the laser-sintered tracks. Combining these results, we were able to fabricate, predesigned patterned (Clemson tiger paw) silica films with high density using a galvo scanner.

Simulation of fabric drying based on heat and mass transfer theory in porous media

Nowdays, the process of fabric drying inside the drying equipment is critical in practical production, this process affect the quality of dried fabric and energy utilization rate directly. There is a problem that the distribution of the percentage of water in fabric is uneven in drying process in practical production. In order to provide a method to solve this problem, this paper develop an finite element model(FE) on the platform of FLUENT by combining heat and mass transfer theory in porous media and transport theory of gas species organically, On the base of Mathis DHe steaming machine, the FE model is verified by carrying out an experiment.After that, this numerical model is used to study the process of fabric drying and the distribution of the percentage of water. The results indicate that the change of the weight of water in the fabric is nearly linear relationship with time and the percentage of water is low in the margin of fabric in the process of drying. In the later analysis, there have enough confidence that this finite element model can be used to analyse the structure and technological parameters of drying device.

Construction of three-dimensional finite element model and biomechanical study on patient with with cervical spondylotic myelopathy

To establish a three-dimensional finite element model (FEM) of the neck, to analyze the differences in neck biomechanics between patient with cervical spondylotic myelopathy (CSM) and healthy subject and to provide biomechanics basis for the pathogenesis of CSM. Methods: A patient with CSM was enrolled in a mechanical simulation experiment. Three-dimensional CT scan was performed, and three-dimensional FEM of the neck was constructed. A heathy subject was selected as a control according to the patient's age, gender, height, and weight. Three-dimensional FEM was used to compare the stress differences in the vertebral body, intervertebral disc, ligament and spinal cord under the normal stress of the cervical spine and the maximum stress of the posterior reclining motion. Results: Successfully constructed FEM model of CSM patient and control, and performed mechanical analysis, the most obvious difference in cervical vertebral body force was at C5-C6 segment in CSM patients. The maximum stress site of control and patient was at the anterior edge of the vertebral body. The maximum stress of the vertebral body in the CSM patient was less than that of the control. The stress distribution of the intervertebral disc was irregular in the CSM patient, and the maximum stress was concentrated on both sides of the posterior edge of the intervertebral disc. The stress distribution of the ligaments of the CSM patient was uneven. The maximum stress was in the posterior longitudinal ligament. The range of neck movement in extension of the CSM patient was restricted. Conclusion: Compared with the healthy subject, the balance of the vertebral body, intervertebral disc, ligament and limited range of motion of the CSM patient has been changed, which may be related to the mechanical pathogenesis of cervical spondylotic myelopathy.

Characterization of Macroscopic Mechanical Anisotropy of Magnetocaloric Gadolinium Cylinders

The metallographic analysis of polycrystalline gadolinium cylinders revealed a microstructural anisotropy of some included phases in the extrusion and extrusion transversal directions. The amount of those phases in the material is not significant. However, the macroscopic anisotropy of mechanical properties needs to be verified. The strain distribution during compression loading was analyzed using finite element model (FEM) simulations. A FEM for the simulation of the elasto-plastic response of the Gd cylinders was performed. For this purpose, the experimentally obtained typical flow curve in the extrusion direction was used as the input data for the FEM model. Based on the dimensional similarity of the FEM model and the measured specimens, the potential appearance of macroscopic anisotropy is evaluated. Mechanical testing using compression cigar tests, as well as FEM, did not confirm any obvious effect of the elongated inclusions on the mechanical anisotropy of the gadolinium specimens.

An Improved Mass Consistent Model for Three-Dimensional Wind Field Construction

An improved diagnostic mass-consistent finite element model (FEM) has been developed to construct 3D wind fields over irregular terrain. Instead of using constant Gauss precision moduli over the whole domain in the existing mass-consistent models, the improved mass-consistent model adopts different Gauss precision moduli based on the terrain topography gradient associated with atmospheric boundary conditions. These terrain sensitive moduli resolve wind flows over large topographical obstacles more accurately than constant Gauss precision moduli. In this study, a terrain following mesh generator is developed based on digital elevation data from the U.S. Geological Survey, and the data linked to the modified mass-consistent FEM model. The improved model is validated and verified using a benchmark study for flow over a semicylinder. The model is then used to re-examine 3D wind fields previously simulated for the Nellis Dunes area near Las Vegas, NV. Results show that the improved mass consistent modeling system shows better agreement with the recorded meteorological tower data than the previous results obtained using constant moduli.

Material Parameter Extraction for Complex AlScN Thin Film Using Dual Mode Resonators in Combination with Advanced Microstructural Analysis and Finite Element Modeling

AbstractAccurate property determination of the piezoelectric thin film material Al(1−x)Sc(x)N is necessary for designing the next generation of radio frequency resonators in mobile communication, and for testing results of ab initio calculations. Sound velocity and piezoelectric coupling of both longitudinal and shear mode are evaluated from a single dual mode resonator. This assures a compatible set of coefficients. It is observed that AlScN thin films grew differently on small, isolated bottom electrodes. The investigated film starts growing with a slightly tilted, c‐textured microstructure, and switches after 200 nm to a polycrystalline film with irregularly oriented grains having c‐axis tilt angles in the range of 35°–70°, as revealed by transmission electron microscope nanodiffraction mapping. Based on this information, a finite element model (FEM) is constructed that properly reproduces the resonance behavior of the resonator. The relevant elastic and piezoelectric constants are derived by curve fitting and yield somewhat lower stiffness and higher piezoelectric coefficients than ab initio calculations published in the literature. The FEM modeling results show that the upper film part with the abnormally oriented grains is overall piezoelectric, i.e., the misoriented grains maintain the polarity projected onto the growth direction from the starting layer.

Deep learning segmentation of coronary calcified plaque from intravascular optical coherence tomography (IVOCT) images with application to finite element modeling of stent deployment.

Because coronary artery calcified plaques can hinder or eliminate stent deployment, interventional cardiologists need a better way to plan interventions, which might include one of the many methods for calcification modification (e.g., atherectomy). We are imaging calcifications with intravascular optical coherence tomography (IVOCT), which is the lone intravascular imaging technique with the ability to image the extent of a calcification, and using results to build vessel-specific finite element models for stent deployment. We applied methods to a large set of image data (>45 lesions and > 2,600 image frames) of calcified plaques, manually segmented by experts into calcified, lumen and "other" tissue classes. In optimization experiments, we evaluated anatomical (x, y) versus acquisition (r,θ) views, augmentation methods, and classification noise cleaning. Noisy semantic segmentations are cleaned by applying a conditional random field (CRF). We achieve an accuracy of 0.85 ± 0.04, 0.99 ± 0.01, and 0.97 ± 0.01, and F-score of 0.88 ± 0.07, 0.97 ± 0.01, and 0.91 ± 0.04 for calcified, lumen, and other tissues classes respectively across all folds following CRF noise cleaning. As a proof of concept, we applied our methods to cadaver heart experiments on highly calcified plaques. Following limited manual correction, we used our calcification segmentations to create a lesion-specific finite element model (FEM) and used it to predict direct stenting deployment at multiple pressure steps. FEM modeling of stent deployment captured many features found in the actual stent deployment (e.g., lumen shape, lumen area, and location and number of apposed stent struts).

Numerical modeling of Flux assisted Gas Tungsten Arc Welding (F-GTAW) process of Duplex Stainless Steel (DSS)

A three dimensional transient Finite Element Model (FEM) of Flux assisted Gas Tungsten Arc Welding (F-GTAW) to predict the temperature cycle at the weld lineof Duplex Stainless Steel (DSS2205) is proposed in this study using gaussian moving source. Theproposed finite element model is validated using theexperimental results published in the literature. The temperature history plot obtained from the FEM is compared with the experimental data. The results shows that the peak temperature value at a surface node of the FEM is matching with the maximum temperature obtained at the surface of the weld. The proposedmodel has the capability to predict the temperature history of the entire welding cycle. The temperature distribution profile obtained from the FEM of F-GTAW is also compared with the conventional GTAW model. The proposed FEM model has been developed using Ansys software.

Simulation Tools for a Fiber-Optic Based Structural Health Monitoring System

Probability of detection (POD) graphics allow for a change from qualitative to quantitative assessment for every damage detection system, and as such it is a main request for conventional non-destructive testing (NDT) techniques. Its availability can greatly help towards the industrialization of the corresponding Structural health monitoring (SHM) system. But having in mind that for SHM systems the sensors are at fixed positions, and the location of a potential damage would change its detectability. Consequently robust simulation tools are required to obtain the model assisted probability of detection (MAPOD) which is needed to validate the SHM system. This tool may also help for the optimization of the sensor distribution, and finally will allow a probabilistic risk management. INDEUS, simulation of ultrasonic waves SHM system, was a main milestone in this direction. This article deals with the simulation tools for a strain based SHM system, using fiber optic sensors (FOS). FOS are essentially strain/temperature sensors, either with multi-point or with distributed sensing. The simulation tool includes the finite element model (FEM) for the original and damaged structure, and algorithms to compare the strain data at the pre-established sensors locations, and from this comparison to extract information about damage occurrence and location. The study has been applied to the structure of an all-composite unmanned aircraft vehicle (UAV) now under construction, designed at Universidad Politecnica de Madrid for the inspection of electrical utilities networks. Distributed sensing optical fibers were internally bonded at the fuselage and wing. Routine inspection is planned to be done with the aircraft at the test bench by imposing known loads. From the acquired strain data, damage occurrence may be calculated as slight deviations from the baselines. This is a fast inspection procedure without requiring trained specialists, and it would allow for detection of hidden damages. Simulation indicates that stringer partial debondings are detected before they become critical, while small delaminations as those produced by barely visible impact damages would require a prohibited number of sensing lines. These simulation tools may easily be applied to any other complex structure, just by changing the FEM models. From these results it is shown how a fiber optic based SHM system may be used as a reliable damage detection procedure.

The Live Load Capacity of Rectangular Precast Reinforced Concrete Stick Plates

The process of making reinforced cast-in-place concrete plates is a long-term one and it is very expensive. Cast-in-place concrete requires the use of formwork, which raises the cost. An innovation in the field of precast concrete plates will significantly reduce cost and time. The purpose of this study is to investigate the flexural capacity of precast concrete plates as a function of slab thickness, with identical tensile reinforcement. The concrete’s cylindrical compression strength used in this study has been 22.5 MPa. This research has been conducted both experimentally and numerically using a single stick plate specimen with dimensions of 6 cm × 10 cm × 100 cm (ESP-6 and SSP-6) and 8 cm × 10 cm × 100 cm (ESP-8 and SSP-8). ESP stands for the experimentally tested specimen. The flexural test using a-single-point loading system has been performed in order to determine the capacity and the load-displacement responses of the stick plate. On the next step, a finite element model (FEM) has been constructed, and the experimental data obtained from the ESP specimens have been used to validate the SSP model. The FEM model has been further utilized to simulate the behaviour of a range in stick plates (SSP). The numerical models SSP have had a range in thickness from 70, 90 and 100 mm. It has been found that the live load carrying capacity of specimens SSP-6, SSP-7, SSP-8, SSP-9, and SSP-10 has been 63, 91, 127, 138 and 165 kg/m2, respectively. The initial stiffness of the specimens has been identical up till 30% of the ultimate load, while the moment carrying capacity increased as a function of plate thickness, followed a linear path.

Measurement and Simulation of Temperature Field of Concrete Box Girder in Northwest Severely Cold Area

This study evaluated the characteristics of temperature field distribution of the concrete box girder based on the middle bridge of Xiaosha River, and the effects of temperature in severely cold area were determined through experiments and finite element model (FEM) analysis. An FEM model of the concrete box girder considering the temperature field was established based on heat transfer theory to verify the accuracy of the model. Moreover, the calculation of the vertical temperature distribution and the temperature distribution along the web plate was conducted. The distribution along the through-thickness direction of the bottom plate and the temperature drop caused by cold waves was evaluated. Results suggest that the published codes and guidebooks were relevant. The effect of the most unfavorable condition of temperature load was also calculated. The result drawn from this research shows that the distribution of temperature field at the cross sections in the severely cold area differed greatly from that in the current code. However, the temperature difference in the top flange was not evident, whereas it was much larger in the bottom flange. The temperature in the web was higher than that in the top flange under solar radiation and was lower during cooling. The results of the temperature effect were much more critical than the result calculated using the vertical temperature gradient in the current code. The tensile stress produced by temperature load may cause cracks. Consequently, sufficient attention should be paid to the damage of thermal effects when calculating the concrete box girder in the northwest of the severely cold area.

Experimental and Numerical Investigation of the Buckling Performance of Tubular Glass Columns under Compression

This study investigates the buckling performance of tubular glass columns under axial compression. A total of two cases are considered (i) single glass tubular column and (ii) bundled column constructed using structural silicone sealants. A series of compression test were carried out on different geometrical dimensions of these two cases to determine their failure mechanism, load carrying capacity and to evaluate the buckling performance. Prior to the load carrying capacity (LCC) that was measured at the ultimate, a distinctive remaining structural capacity (RSC) was characterized especially for bundled glass based on the first crack. The shear connection in the bundled system was justified in comparison to the monolithic glass. This study showed that the failure mechanisms depended strongly on the slenderness ratio of the columns and that the failure occurred either by crushing or by buckling depending on the lengths of the column. The scatter in the failure load for specimens that had a higher slenderness ratio was much lower than for those that had a lower slenderness ratio. In order to justify the variability of the glass strength, a Weibull statistical distribution was used. Finite element modelling (FE) based on the simplified Riks method was performed using ABAQUS v6.10 to compliment the test results and to provide methods of analysis which could be used as a guideline for structural engineers to predict structural behaviour of tubular glass columns in general. An overestimation was predicted in the FE models which suggested modification of the imperfection factor.

Elastic and fracture characteristics of graphene-silicon nanosheet composites using nonlinear finite element method

A simple and efficient methodology is proposed for computing the nonlinear stress-strain behavior and fracture strength under tensile loading of graphene-silicon nanosheet composites. A nonlinear finite-element model (FEM) is developed to obtain the stress-strain relationships, which in general are computed using the computationally expensive procedure of molecular dynamics (MD) simulations. The modelling method, based on the interconnection of continuum micro-mechanics approaches, incorporates bonded contact at the graphene-silicon interface with the graphene being modelled as the multilinear elastic and the silicon assumed as an isotropic material is fed into an atomistic progressive fracture model. Using this model, we get the nonlinear behaviour of graphene, silicon and its composites, as a nonlinear stress-strain curve with their critical stress at inflection point leading to failure. The obtained results of the stress-strain curves, the elastic modulus and the critical stresses of single layer graphene (SLG), silicon nanosheet and their composites (GSNC) with different thickness of silicon nanosheet are in good agreement with the MD results available in the literature. These results elucidate that the tensile strength and Young’s modulus of the silicon nanosheet increase enormously by putting the graphene layer on the top and bottom surface of the silicon nanosheet. This model is then employed to study the non-linear stress behaviour for the different orientations of silicon with varying thickness and their corresponding composites with graphene and the effect of various chirality of SLGs are also considered. Thus, we try to establish FEM as a reliable numerical method to obtain the mechanical behaviour of graphene-silicon nanosheet composites which for long-time has been solved using the classical approach of MD. The parametric study which is done using the developed FEM model shows that the GSNC helps to enhance the mechanical properties of silicon nanosheet, which in turn is helpful for the silicon-based semiconductor industry. This fact correlates well with the other methods, well-established in the literature.

Nonlinear dynamic modeling of a V-shaped metal based thermally driven MEMS actuator for RF switches

In this paper, we propose a new dynamic model to describe the nonlinear characteristics of a V-shaped (chevron) metallic-based thermally driven MEMS actuator. We developed two models for the thermal actuator with two configurations. The first MEMS configuration has a small tip connected to the shuttle, while the second configuration has a folded spring and a wide beam attached to the shuttle. A detailed finite element model (FEM) and a lumped element model (LEM) are proposed for each configuration to completely characterize the electro-thermal and thermo-mechanical behaviors. The nonlinear resistivity of the polysilicon layer is extracted from the measured current–voltage (I–V) characteristics of the actuator and the simulated corresponding temperatures in the FEM model, knowing the resistivity of the polysilicon at room temperature from the manufacture’s handbook. Both developed models include the nonlinear temperature-dependent material properties. Numerical simulations in comparison with experimental data using a dedicated MEMS test apparatus verify the accuracy of the proposed LEM model to represent the complex dynamics of the thermal MEMS actuator. The LEM and FEM simulation results show an accuracy ranging from a maximum of 13% error down to a minimum of 1.4% error. The actuator with the lower thermal load to air that includes a folded spring (FS), also known as high surface area actuator is compared to the actuator without FS, also known as low surface area actuator, in terms of the I–V characteristics, power consumption, and experimental static and dynamic responses of the tip displacement.

Perfusion double-channel micropipette probes for oxygen flux mapping with single-cell resolution.

Measuring cellular respiration with single-cell spatial resolution is a significant challenge, even with modern tools and techniques. Here, a double-channel micropipette is proposed and investigated as a probe to achieve this goal by sampling fluid near the point of interest. A finite element model (FEM) of this perfusion probe is validated by comparing simulation results with experimental results of hydrodynamically confined fluorescent molecule diffusion. The FEM is then used to investigate the dependence of the oxygen concentration variation and the measurement signal on system parameters, including the pipette’s shape, perfusion velocity, position of the oxygen sensors within the pipette, and proximity of the pipette to the substrate. The work demonstrates that the use of perfusion double-barrel micropipette probes enables the detection of oxygen consumption signals with micrometer spatial resolution, while amplifying the signal, as compared to sensors without the perfusion system. In certain flow velocity ranges (depending on pipette geometry and configuration), the perfusion flow increases oxygen concentration gradients formed due to cellular oxygen consumption. An optimal perfusion velocity for respiratory measurements on single cells can be determined for different system parameters (e.g., proximity of the pipette to the substrate). The optimum perfusion velocities calculated in this paper range from 1.9 to 12.5 μm/s. Finally, the FEM model is used to show that the spatial resolution of the probe may be varied by adjusting the pipette tip diameter, which may allow oxygen consumption mapping of cells within tissue, as well as individual cells at subcellular resolution.

Understanding the mechanics of creep deformation to develop a surrogate model for contact assessment in CANDU® fuel channels

A key element of the fuel channel life cycle management in CANDU® reactors is to prevent contact between the pressure tube (PT) and the calandria tube (CT) and to avoid the development of hydride blisters that lead to delayed hydride cracking of the PT. The PT-CT contact is the result of in-reactor deformation due to irradiation induced creep of the fuel channel assembly, which in turn is affected by uncertainties associated with various parameters like material properties, dimensional changes in the channel and boundary conditions (e.g., end slopes) of the channel. To account for these uncertainties, probabilistic assessment methods are developed to evaluate the risk of PT-CT contact and demonstrate compliance with provisions of the CSA Standard N285.8. Currently, a simulation is based on probabilistic assessments in which input parameters to a finite element model (FEM) of creep deformation are randomly sampled from their respective distributions. A simulation model involves numerous repetitive solutions of the FEM model to determine the probability distribution of PT-CT gap and the time to contact. Since the creep deformation analysis using FEM is computationally involved, this brute force Monte Carlo simulation method is not an efficient way to carry out the probabilistic assessment of the reactor core. This paper proposes a new line of thinking for probabilistic assessments of PT-CT contact in fuel channels, which is based on replacing a full FEM model by a surrogate model of a much simpler analytical form. The surrogate model not only simplifies the creep deformation analysis, but also provides a more logical basis for probabilistic assessments. This paper presents an insightful analysis of creep deformation and shows that a simple surrogate model can be developed to predict the PT-CT gap as a linear function of two primary random variables, namely, a creep factor and end slopes. This simplified representation has a far reaching effect on the probabilistic assessment of fuel channels.

Comparisons of Different Models on Dynamic Recrystallization of Plate during Asymmetrical Shear Rolling.

Asymmetrical shear rolling with velocity asymmetry and geometry asymmetry is beneficial to enlarge deformation and refine grain size at the center of the thick plate compared to conventional symmetrical rolling. Dynamic recrystallization (DRX) plays a vital role in grain refinement during hot deformation. Finite element models (FEM) coupled with microstructure evolution models and cellular automata models (CA) are established to study the microstructure evolution of plate during asymmetrical shear rolling. The results show that a larger DRX fraction and a smaller average grain size can be obtained at the lower layer of the plate. The DRX fraction at the lower part increases with the ascending speed ratio, while that at upper part decreases. With the increase of the offset distance, the DRX fraction slightly decreases for the whole thickness of the plate. The differences in the DRX fraction and average grain size between the upper and lower surfaces increase with the ascending speed ratio; however, it varies little with the change of the speed ratio. Experiments are conducted and the CA models have a higher accuracy than FEM models as the grain morphology, DRX nuclei, and grain growth are taken into consideration in CA models, which are more similar to the actual DRX process during hot deformation.

Seismic Evaluation of A Historical Structure In Kastamonu - Turkey

The Kastomonu province is a seismically active zone. the city has many historical buildings made of stone-masonry. In case of any probable future earthquakes, existing buildings may suffer substantial or heavy damages. In the present study, one of the historical traditional house located in Kastamonu were structurally investigated through probabilistic seismic risk assessment methodology. In the study, the building was modeled by using the Finite Element Modeling (FEM) software, SAP2000. Time history analyses were carried out using 10 different ground motion data on the FEM models. Displacements were interpreted, and the results were displayed graphically and discussed.

Numerical investigation of temperature gradient-induced thermal stress for steel–concrete composite bridge deck in suspension bridges

A 3D finite element model (FEM) with realistic field measurements of temperature distributions is proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system. First, a brief literature review indicates that traditional thermal stress calculation in suspension bridges is based on the 2D plane structure with simplified temperature profiles on bridges. Thus, a 3D FEM is proposed for accurate stress analysis. The focus is on the incorporation of full field arbitrary temperature profile for the stress analysis. Following this, the effect of realistic temperature distribution on the structure is investigated in detail and an example using field measurements of Aizhai Bridge is integrated with the proposed 3D FEM model. Parametric studies are used to illustrate the effect of different parameters on the thermal stress distribution in the bridge structure. Next, the discussion and comparison of the proposed methodology and simplified calculation method in the standard is given. The calculation difference and their potential impact on the structure are shown in detail. Finally, some conclusions and recommendations for future bridge analysis and design are given based on the proposed study.

Comparing heat flow models for interpretation of precast quadratic pile heat exchanger thermal response tests

This paper investigates the applicability of currently available analytical, empirical and numerical heat flow models for interpreting thermal response tests (TRT) of quadratic cross section precast pile heat exchangers. A 3D finite element model (FEM) is utilised for interpreting five TRTs by inverse modelling. The calibrated estimates of soil and concrete thermal conductivity are consistent with independent laboratory measurements. Due to the computational cost of inverting the 3D model, simpler models are utilised in additional calibrations. Interpretations based on semi-empirical pile G-functions yield soil thermal conductivity estimates statistically similar to those obtained from the 3D FEM inverse modelling, given minimum testing times of 60 h. Reliable estimates of pile thermal resistance can only be obtained from type curves computed with 3D FEM models. This study highlights the potential of applying TRTs for sizing quadratic, precast pile heat exchanger foundations.