Finite Element Model Predictions Research Articles

Hydraulic permeability and compressive properties of porcine and human synovium

The synovium is a multilayer connective tissue separating the intra-articular spaces of the diarthrodial joint from the extra-synovial vascular and lymphatic supply. Synovium regulates drug transport into and out of the joint, yet its material properties remain poorly characterized. Here, we measured the compressive properties (aggregate modulus, Young's modulus, and Poisson's ratio) and hydraulic permeability of synovium with a combined experimental-computational approach. A compressive aggregate modulus and Young's modulus for the solid phase of synovium were quantified from linear regression of the equilibrium confined and unconfined compressive stress upon strain, respectively (HA = 4.3 ± 2.0 kPa, Es = 2.1 ± 0.75, porcine; HA = 3.1 ± 2.0 kPa, Es = 2.8 ± 1.7, human). Poisson's ratio was estimated to be 0.39 and 0.40 for porcine and human tissue, respectively, from moduli values in a Monte Carlo simulation. To calculate hydraulic permeability, a biphasic finite element model's predictions were numerically matched to experimental data for the time-varying ramp and hold phase of a single increment of applied strain (k = 7.4 ± 4.1 × 10−15 m4/N.s, porcine; k = 7.4 ± 4.3 × 10−15 m4/N.s, human). We can use these newly measured properties to predict fluid flow gradients across the tissue in response to previously reported intra-articular pressures. These values for material constants are to our knowledge the first available measurements in synovium that are necessary to better understand drug transport in both healthy and pathological joints.

Fire structural performance of thermo-mechanically compressed spruce timber by means experiments and a three-step multi-reactions pyrolysis 3D-finite element modelling

This paper presents experimental and numerical investigations to access the relative fire structural resistance of thermo-mechanically compressed (or densified) spruce wood. First of all, thermal characterization, including thermal conductivity and specific heat, has been undertaken on both compressed and uncompressed spruce wood. The thermal degradation of both compressed and uncompressed wood has been analysed by means thermogravimetric tests using different heating rates. Both compressed and uncompressed spruce samples of dimensions of 100 mm × 100 mm × 19 mm have been subjected to fire in a cone calorimeter under 20 kW/m2 and 75 kW/m2. Finally, a predictive finite element model based on three-step multi-reactions of pyrolysis is proposed for the thermal transfer and degradation analyses of timber material. The simulated thermal profiles, the mass loss as well as the charring depths were compared to the experimentally recorded results showing a fairly good agreement.

Modeling of Forced and Natural Convection Drying Process of a Coffee Seed

HighlightsThe forced and natural convection drying processes of a single coffee grain can be predicted.The moisture distribution profiles depict the drying phenomena and water concentration zones.With accurate predictive drying curves, coffee growers can ensure high-quality coffee beans.Abstract. Different coffee drying technologies face complex tasks in ensuring an acceptable final seed moisture content. This research performed a Finite Element Analysis (FEA) study, simulating a single coffee bean's drying process as a transient mass diffusion model under mechanical and natural convection conditions, so the drying behavior and data of both case scenarios can be foreseen and controlled by a predictive Finite Element Model (FEM). A wet bean was 3D-scanned and digitized as the FEA simulation geometry; the water diffusion between the grain and the atmosphere was defined by a diffusion coefficient subject to the drying air temperature and the grain's moisture content. Three cases were studied: mechanical grain drying at three different temperatures (50, 45, and 40°C) in a forced convection environment; variable natural convection drying under environmental conditions (wet and dry season); and constant natural convection (wet and dry season), including the variation in day/night temperature and relative humidity. The results agree well with the data found in the literature, obtaining the graphical moisture distribution of the phenomena, predictive drying curves, diffusion coefficients, and isotherms. Both simulated drying scenarios provide essential information for coffee growers to improve and control their drying processes, thus obtaining high-quality grains, reducing contamination by microorganisms, and ensuring the integrity of their products. Keywords: Coffea arabica, Coffee Drying, Coffee Seed, Finite Element Model, Moisture Diffusion.

Strut-and-tie and finite element modelling of unsymmetrically-loaded deep beams

A strut-and-tie model (STM) for unsymmetrically-loaded deep beams is proposed in this paper through simplifying the unsymmetrical problem into symmetrical and anti-symmetrical problems. This analytical solution starts with derivations of principal compressive stress fields based on the theory of elasticity. Furthermore, a minimum-strain-energy criterion is adopted to define the optimal STM geometry from the stress field, including the dimensions of struts and nodal zones, and strut angles. The proposed STM is validated against 140 test results, including 14 unsymmetrically-loaded deep beams and 126 symmetric deep and short beams, and finite element models (FEMs) for the 14 unsymmetrical deep beams. The FEM is also used to simulate the load-displacement relationships of unsymmetrical deep beams that could not be modelled by STM. In addition, a worked example is presented to demonstrate in detail the procedure of analysing an unsymmetrically-loaded deep beam using the proposed solution. In summary, the STM predictions are in good agreement with experimental results and FEM predictions. Therefore, the proposed STM is capable of giving accurate and consistent predictions for both symmetrical and unsymmetrical deep and short beams.

Prediction of softening kinetics and recrystallization texture in non-isothermally annealed bulged tubes using CPFEM and CA models

A hierarchically coupled cellular automata (CA) model, crystal plasticity finite element method (CPFEM), and thermal finite element (FE) model is developed to predict the softening kinetics of the bulged steel tube during non-isothermal annealing. Through the developed model, the kinetics of softening mechanisms including static recovery (SRV) and static recrystallization (SRX), as well as the recrystallization texture are predicted. Later, the Johnson-Mehl-Avrami-Kohnogorov (JMAK) model based on the predicted SRX data is developed to interpret the recrystallization behavior of the material. To perform this study, diverse experimental tests including tube hydroforming (THF), annealing, uniaxial tensile test, hardness test, as well as microstructure observations through optical microscopy and Electron Backscatter Diffraction (EBSD) tests on steel tube are performed. The obtained experimental data are utilized to calibrate and verify the implemented CPFEM model for simulation of THF process, thermal FE model for prediction of the local temperature over annealing time, and CA algorithm for modeling of the softening kinetics and texture evolution throughout the annealing process. The study shows that the predicted deformation characteristics, softening kinetics, recrystallization texture and temperature profile during non-isothermal annealing are in good agreement with experimental data. During the annealing process, a total of four stages for the kinetics of softening mechanisms is observed: No softening; SRV only; SRV dominant; and SRX dominant. During the progress of SRX, the behavior of recrystallization is abruptly changed, confirming that two different mechanisms are controlling the kinetics of transformation.

Towards a shape-performance integrated digital twin for lumbar spine analysis

Background: With significant advancement and demand for digital transformation, the digital twin has been gaining increasing attention as it is capable of establishing real-time mapping between physical space and virtual space. In this work, a shape-performance integrated digital twin solution is presented to predict the real-time biomechanics of the lumbar spine during human movement. Methods: A finite element model (FEM) of the lumbar spine was firstly developed using computed tomography (CT) and constrained by the body movement which was calculated by the inverse kinematics algorithm. The Gaussian process regression was utilized to train the predicted results and create the digital twin of the lumbar spine in real-time. Finally, a three-dimensional virtual reality system was developed using Unity3D to display and record the real-time biomechanics performance of the lumbar spine during body movement. Results: The evaluation results presented an agreement (R-squared > 0.8) between the real-time prediction from digital twin and offline FEM prediction. Conclusions: This approach provides an effective method of real-time planning and warning in spine rehabilitation.

The Nail Penetration Behaviour of Carbon Nanotube Composite Electrodes for Energy Storage

The high surface area, electrical and mechanical properties of carbon nanotube (CNT) composites has rendered them promising candidates for structural power composites. Nevertheless, it is important to understand their mechanical behaviour before they are applied in energy storage devices amid the safety concerns. This work explores the nail penetration behaviours of supercapacitor specimens consisting of CNT electrodes and pseudocapacitor specimens with carbon nanotube-polyaniline (CNT/PANI) electrodes. Specimens with and without electrolyte were tested. The dry cells without electrolyte follow a power law behaviour, while the wet cells with the electrolyte exhibit a piece-wise nonlinear relationship. The force, voltage and temperature of the supercapacitor were recorded during the nail penetration test. No temperature change or overheating was observed after short-circuit. Moreover, electrochemical testing is performed before and after the specimen penetration. The cyclic voltammetry shows the dramatic loss of capacitance, changing the cell behaviour from capacitor to resistor-like manner. Johnson-Cook model was used to predict the nail penetration behaviour. The coefficients of Johnson-Cook model are calibrated from the experimental load-displacement curves. The finite element model predictions are in a good agreement with the experimental results.

Response Evaluation of Large-Span Ultradeep Soil─Steel Bridges to Truck Loading

Soil–steel structures are increasingly used as a solution for roadway and railway overpasses because of their relative low cost and ease of construction compared with conventional concrete and steel bridges. Recently, soil–steel arched bridges have been developed to achieve large spans of up to 32.4 m. Current design guidelines for these structures require comprehensive numerical modeling to specifically consider the soil–structure interaction and live loading. This study presents three-dimensional finite-element (FE) analysis for a field monitored full-scale corrugated steel culvert subjected to single-axle loading. The FE model predictions were within 15% of the measured responses. In addition, the behavior of a large-span arched steel culvert using the world's deepest corrugated steel profile was analyzed under the effect of axle loading at different soil cover heights. The straining actions of the steel structure decreased by 30%–35% as the height of soil cover increased from 1.0 to 1.4 m. Furthermore, the effects of the numerical modeling technique on the predicted performance and straining actions were evaluated, including geometric nonlinearity, soil behavior constitutive model, soil–steel interface condition, and construction stages for backfilling. The results demonstrated that incongruous numerical simulation may lead to differences in the results by up to 60% with the anticipated results causing significant impacts on the design and cost of soil–steel structures.

Comparison of structural model reduction methods applied to a large-deformation wing box

AbstractIn this paper, the accuracy and practical capabilities of three different reduced-order models (ROMs) are explored: an enhanced implicit condensation and expansion (EnICE) model, a finite element beam model, and a finite volume beam model are compared for their capability to accurately predict the nonlinear structural response of geometrically nonlinear built-up wing structures. This work briefly outlines the different order reduction methods, highlighting the associated assumptions and computational effort. The ROMs are then used to calculate the wing deflection for different representative load cases and these results are compared with the global finite element model (GFEM) predictions when possible. Overall, the ROMs are found to be able to capture the nonlinear GFEM behaviour accurately, but differences are noticed at very large displacements and rotations due to local geometrical effects.

Finite element modelling of concrete-filled spiral-welded stainless-steel tube columns under concentric and eccentric axial loading

This study investigated the capacity of finite element modelling (FEM) approaches to predict the experimentally obtained behaviour of concrete-filled spiral-welded stainless-steel tube (CF-SWSST) short and long columns. Using the ABAQUS software, FEM was carried out of 24 CF-SWSST column tests. Nominal outside diameter to thickness ratios, effective length to diameter ratios and load eccentricity to diameter ratios equal to 51–114.5, 4.5–12.0, and 0–0.4 had been considered for the tests that were modelled. The distinct spiral weld seam geometry of the SWSST was explicitly considered in the FEM. Widely reported and accepted FEM modelling approaches and material models were adopted for this work. The concrete damaged plasticity model was utilised for the concrete core, while the stress–strain behaviour of stainless-steel was modelled using a modified Ramberg-Osgood relationship. On average, the capacities predicted by the FEM for the CF-SWSST columns were found to be non-conservative. The non-conservativeness was higher for specimens under concentric axial loading and increased with column and section slenderness. The actual to predicted capacity ratios were much closer to 1.0 for eccentrically loaded CF-SWSST columns, with conservative capacities predicted for eccentrically loaded specimens with the smallest section slenderness. For load eccentricity to diameter ratios of 0.15 and 0.4, there was negligible difference in the prediction conservativeness. Compared to analogous concrete-filled spiral-welded mild-steel tube columns, the FEM predictions obtained for the CF-SWSST columns were notably less conservative. This suggested that separate material constitutive models may be warranted for the FEM of CF-SWSSTs compared to their mild-steel counterparts. For the modelled eccentrically loaded specimens, the FEM predicted globally flexurally deformed states which agreed with those obtained experimentally, though the local buckling patterns were not replicated. In addition, the FEM qualitatively captured the experimentally obtained bending stiffness and strain variations. A modelling sensitivity study found that the FEM results were effectively equivalent even when the SWSSTs were modelled as plain seamless tubes.

Finite Element Simulation of Moisture Content Changes of Peeled Banana (Musa x paradisiaca L.) during Drying

This paper presents finite element simulation of drying of peeled banana. A two-dimensional finite element model was developed for simulation of moisture content changes during drying of peeled banana. The finite element simulation model was programmed in Compaq Visual FORTRAN version 6.5. Classical models for moisture diffusivity, sorption isotherm and volumetric shrinkage of peeled banana were experimentally determined and used in the finite element simulation. The finite element model prediction was compared with the experimental data. The agreement between the simulated moisture content changes and the experimental data was in reasonable agreement with a discrepancy in root mean square error being in the range of 2.2-14.6%. Moisture content change profiles inside peeled banana during drying were predicted and these profiles give a good picture of the moisture movement inside peeled banana during drying. Keywords: Drying, Peeled banana, Finite element, Moisture diffusion

Submodeling in wear predictive finite element models with multipoint contacts

AbstractThe application of the submodeling technique to finite element (FE) wear analyses has been recently proposed as an efficient solution to reduce the computational cost of the simulations and provide accurate numerical results. However, the method was validated only on single point contact cases. The present study proposes a generalization of the wear submodeling procedure that can be used to speed up FE wear simulations with multipoint contacts. The modified global–local procedure is applied and evaluated on a double contact pin on plate wear test using three‐dimensional models developed in Ansys® mechanical APDL. Three different model geometries with different curvature radii at the contact regions were considered in order to replicate possible critical scenarios. Results suggest that an additional wear simulation step where the global model is used to simulate the first wear cycles is needed to correctly transfer the boundary conditions to the local models. The new proposed strategy demonstrates the possibility to extend the method to more general FE wear simulations by significantly reducing their computational cost.

Finite Element Model Prediction of Charge Weld Behaviour in AA6082 and AA6063 Extruded Profiles

Charge welds are unavoidable defects of the continuous extrusion process whose extension needs to be accurately predicted in order to avoid profile mechanical failures or to minimize unrequired scrap of material. The aim of this work was then to evaluate the accuracy of the charge welds FEM predictions and their applicability in the industrial field. Two different industrial cases involving A6082 and AA6063 aluminium alloys were analysed. The data of charge welds behaviours were experimentally collected, discussed and then innovatively compared to the predicted outcomes of FEM simulations performed using QForm Extrusion® software and of theoretical formulas reported in the literature. As main results, a very good numerical-experimental matching was found, with a peak discrepancy of 122 mm in terms of charge weld extent, while theoretical formulas returned a significant underestimation.

Plantar fascia loading at different running speed: a dynamic finite element model prediction

Loads on the plantar fascia could be influenced by running speed and relate to its pathology. This study calculated and compared plantar fascia strains under different running speed conditions using a dynamic finite element foot model and computational simulations. The model was previously validated featuring twenty bones, bulk soft tissue, muscles/ligaments, and a solid part of plantar fascia. A runner performed running trials under one preferred speed (PS), two lower (PS - 10% and PS - 20%) and two higher (PS + 10% and PS + 20%) speed conditions. The movement data were processed to drive musculoskeletal modelling and calculated boundary/loading conditions for the subsequent finite element analyses. The results show that peak strains of the plantar fascia increased with increasing running speed. From PS – 20% to PS + 20%, peak strain in the proximal and distal fascia regions increased by 96.78% and 58.89% respectively. Running speed could directly affect plantar fascia loading, which should be considered in running regimens and rehabilitation programmes. However, prescribing speed control for runners is worth pondering as it influences the trade-off between maximum single-step loads and loading frequency, which in coalescence determine the risk of plantar fascia injury and warranted further investigations.

An efficient predictive modeling for simulating part-scale residual stress in laser metal deposition process

Residual stress and deformation are common issues which prevent dimensional accuracy and lead early fatigue of products by laser metal deposition process. Finite element analysis is an efficient means to estimate the temperature history and thermal stress distribution. However, it is extremely challenging to predict thermal history and stress distribution of a practical large and complex geometry if each laser pulse is taken into account as by conventional laser pulse modeling. Therefore, in this study, an efficient predictive finite element model with assumptions on the laser heat source and loading is established to study the evolution of thermal history, residual stresses, and deformations of a test coupon. The efficient predictive model, which is also called as the 2-layer by 2-layer model, simulates two layers at each laser pulse time. This model is compared with conventional laser pulse model in terms of the evolution of thermal history of selected points and residual stresses. Results show that the 2-layer by 2-layer model considerably reduces the simulation time without much compromising the accuracy of the prediction of deformation and thermal stress. In addition, test coupon is designed and fabricated to capture temperature history and observe microstructure change. It is found that microstructure presents certain correlation with cooling rate. Microstructure and residual stress of the test coupon are evaluated and found to be consistent with the prediction by proposed model. This efficient predictive model can shed light on large-scale part fabrication by laser metal deposition process in industry.

On the Prediction of Guided Wave Dispersion Curves in Plates for Health Monitoring Applications

AbstractIn the last years, a significant interest has been pointed out in the capability of ultrasonic guided waves as candidate tool for structural health monitoring (SHM), due to their high damage detection sensitivity and low power consumption. The monitoring of the structural health through the propagation of guided waves is complex: some wave phenomena, namely dispersion and slowness, together with boundary scattered waves, may mask the presence of damages. So, studying the dispersion phenomenon through the dispersion curves may be helpful in understanding the propagation mechanisms. As Lamb waves dispersion equations do not generally have analytical solutions, the development of a predictive finite element (FE) model can be a valuable tool for the improvement of SHM systems, avoiding the high cost of experimental campaigns. Thus, once calibrated with respect to an experimental test case, the developed FE model can be used to simulate and predict guided‐wave propagation mechanisms in a given structure. This leads to the possibility of employing such approach to identify and localize potential structural damages, that is the final aim of an SHM system. In this work, the FE method, together with an in‐house code, has been used to investigate guided wave dispersion phenomenon in plates for possible SHM applications.

An investigation of the elastic cylindrical line contact equations for plane strain and stress considering friction

This work presents a finite-element model-based study of elastic cylindrical contact. The aim is to evaluate the transition between the plane stress and plane strain-based Hertz solutions when each assumption is most applicable. To accomplish this, a range of curvatures, widths, Poisson’s ratios, and friction coefficients are considered. The finite-element model results for the elastic cylindrical contact cases are compared with the Hertz contact model when assuming plane stress or plane strain. Perhaps, surprisingly, the finite-element model predictions show little dependence on Poisson’s ratio and friction coefficient. The finite-element model predictions of force as a function of deflection agree relatively well with the plane stress Hertz prediction for all cases considered. The finite-element model predictions of contact width as a function of force actually fall below all the analytical Hertz predictions. Therefore, an adapted version of the Hertz equations is provided, which shows better agreement with the cases considered in this work.

Correlation of Full-Field Dynamic Strain Measurements with Reverse Engineered Finite Element Model Predictions

Conventionally strain measurements are done in an intrusive way, and, at one or a few discrete points. In this paper, use of a 3D laser measurement system is explored for direct and full-field dynamic strain measurements on compressor and turbine rotor blades. The results are correlated to corresponding FE predictions in a systematic and quantified manner. The ability to measure strain maps on real engine hardware is demonstrated not only for low frequency fundamental modes, but also for challenging high frequency modes. Correlation results show a high degree of agreement between measured and predicted strains, demonstrating the maturity of the technology and the validity of the method of integration used here. The measurements are repeated for a number of different loading amplitudes to assess the variations in strain fields. The actual component geometries are scanned and component-specific FE models are created. By correlating the measurement results to those predicted from the reverse engineered FE models, it is demonstrated that the results are improved when actual geometries are taken into account. Although the application of 3D laser systems to measurements of full-field strain were explored in previous studies, to the best knowledge of the authors, full-field numerical correlation of full-field strain on a wide range of real, sophisticated components to this extent is presented here for the first time.

Investigation on the scale effects of initial bulk and machining induced residual stresses of thin walled milled monolithic aluminum workpieces on part distortions: experiments and finite element prediction model

Thin walled monolithic milled aluminum workpieces are commonly used in the aerospace industry, because of their good properties such as a high overall strength-to-weight ratio. After machining those parts distortions occur. Residual stresses (RS) are the main driver for those distortions. Two types of RS, the initial bulk residual stresses (IBRS) and the machining induced residual stresses (MIRS), contribute to the part distortion. In this study, the scale effects of each RS type and their combined effects on the distortion of milled thin walled aluminum workpieces are evaluated for different wall thicknesses, different IBRS conditions and different MIRS. In this context a finite element model (FEM) is developed to predict the distortion due to the measured RS. A 3D linear elastic model, considering both types of RS as input is presented. The simulation outcome is validated by experiments.It was found that both RS types contribute to part distortion. For parts containing high IBRS, those IBRS dominate the distortion. For stress relieved parts, containing low IBRS, the MIRS dominate the distortion. The investigations showed that the shear RS induced by machining are crucial for the distortion. The developed FEM model is able to predict the distortion due to both RS types.

Impact and Bandgap Characteristics of Periodic Rods With Viscoelastic Inserts and Local Resonators

Abstract A comprehensive theoretical and experimental study is presented of the bandgap behavior of periodic viscoelastic material (VEM) composites subjected to impact loading. The composites under consideration consist of an assembly of aluminum sections integrated with periodic inserts which are arranged in one-dimensional configurations. The investigated inserts are manufactured either from VEM only or VEM with local resonators (LR). A finite element model (FEM) is developed to predict the dynamics of this class of VEM composites by integrating the dynamics of the solid aluminum sections with those of VEM using the Golla-Hughes-Mctavish (GHM) mini-oscillator approach. The integrated model enables, for the first time, the accurate predictions of the bandgap characteristics of periodic viscoelastic composites unlike previous studies where the viscoelastic damping is modeled using the complex modulus approach with storage modulus and loss factor are assumed constants and independent of the frequency or the unrealistic and physically inaccurate Kelvin–Voigt viscous-damping models. The predictions of the developed FEM are validated against the predictions of the commercial finite element package ansys. Furthermore, the FEM predictions are checked experimentally using prototypes of the VEM composites with VEM and VEM/LR inserts. Comparisons are also established against the behavior of plain aluminum rods in an attempt to demonstrate the effectiveness of the proposed class of composites in mitigation of the structural response under impact loading. Close agreements are demonstrated between the theoretical predictions and the obtained experimental results.