For Finite Element Analysis Research Articles

Temperature Dependence of the Yield Stress in <i>α</i>-Titanium Investigated with Crystal Plasticity Analysis

The effect of the activated slip systems on the temperature dependence of yield stress was investigated in α-Ti by using crystal plasticity finite element method. A model for finite element analysis (FEA) was constructed based on experimental results. The displacement in FEA was applied up to the nominal strain of 4% which is the same strain as the experimental one. Stress-strain curves were obtained, which corresponds to experimental data taken every 50 K between 73 K and 673 K. The used material constants which are temperature dependent were elastic constants, and lattice friction stresses. The lattice friction stresses of basal slip systems were set to be higher than that of pyramidal slip systems at 73 K. Then, the lattice friction stresses were set to be closer as the temperature increases. It was found that the activation of slip systems is strong temperature dependent, and that the yield stress depends on the number of active slip systems.

Virtual structural analysis of tibial fracture healing from low-dose clinical CT scans

Quantitative assessment of bone fracture healing remains a significant challenge in orthopaedic trauma research. Accordingly, we developed a new technique for assessing bone healing using virtual mechano-structural analysis of computed tomography (CT) scans. CT scans from 19 fractured human tibiae at 12 weeks after surgery were segmented and prepared for finite element analysis (FEA). Boundary conditions were applied to the models to simulate a torsion test that is commonly used to access the structural integrity of long bones in animal models of fracture healing. The output of each model was the virtual torsional rigidity (VTR) of the healing zone, normalized to the torsional rigidity of each patient’s virtually reconstructed tibia. This provided a structural measure to track the percentage of healing each patient had undergone. Callus morphometric measurements were also collected from the CT scans. Results showed that at 12 weeks post-op, more than 75% of patients achieved a normalized VTR (torsional rigidity relative to uninjured bone) of 85% or above. The predicted intact torsional rigidities compared well with published cadaveric data. Across all patients, callus volume and density were weakly and non-significantly correlated with normalized VTR and time to clinical union. Conversely, normalized VTR was significantly correlated with time to union (R2 = 0.383, p = 0.005). This suggests that fracture scoring methods based on the visual appearance of callus may not accurately predict mechanical integrity. The image-based structural analysis presented here may be a useful technique for assessment of bone healing in orthopaedic trauma research.

Stochastic reconstruction and microstructure modeling of SMC chopped fiber composites

To establish an integrated Processing-Microstructure-Property workflow for the prediction of material behaviors, this paper presents a new stochastic pseudo-3D microstructure reconstruction method for Sheet Molding Compounds (SMC) chopped fiber composites. The proposed method captures the bi-level microstructural features of SMC composites. At the higher level, a Voronoi diagram-based algorithm is developed to reconstruct the unique substructure features of SMC fiber tows. The geometry of Voronoi cells is adjusted by a Simulated Annealing (SA) algorithm to match the geometrical statistics of the real fiber tows. At the lower level, the algorithm assigns fiber orientation to each Voronoi cell (which represents a fiber tow). The fiber orientation angles are recovered from a statistical fiber orientation tensor. The proposed method is employed to establish a multi-layer pseudo-3D SMC Representative Volume Element (RVE) model for Finite Element Analysis (FEA) of SMC microstructure. This model enables the prediction of mechanical properties based on the material processing information (e.g. fiber orientation tensor obtained from compression molding simulation), and the microstructure information obtained from microscopic imaging for an SMC composite. The predicted properties are successfully validated by experimental tensile tests.

Geometry simplification of open-cell porous materials for elastic deformation FEA

Estimation of mechanical properties of porous materials is central for their medical and industrial application. However, the massive size of accurate boundary representations (B-Rep) of the foams makes the numerical estimations intractable. Even for small domain sizes, the mesh generation for finite element analysis (FEA) may not terminate. Current efforts for simulating porous materials use statistical predictions of the material structure. The simulated and actual materials present different geometry and topology, with consequences on the simulation results. To overcome these limitations, this manuscript presents a method, which (1) synthesizes an accurate truss abstraction from the raw geometry data, (2) executes efficient FEA simulations, and (3) processes nodal displacements to estimate apparent mechanical moduli of the porous material. The method addresses materials whose ligaments have circular cross-sections. The iso-surface present in the Computer Tomography (CT) scan of the porous material is used to synthesize a truss graph whose edges are truncated cones. Then, optimization and simplification methods are applied to produce a topologically and geometrically correct truss representation for the foam domain. Comparative FEA load simulations are conducted between the full B-Rep and truss representations of the material. The truss model proves to be significantly more efficient for FEA, departing from the Full B-Rep FEA by a maximum of 16% in the estimation of equivalent mechanical moduli. Geometric assessments such as porosity and Hausdorff distance confirm that the truss abstraction is a cost-effective one. Ongoing efforts concentrate on point set geometric algorithms for enforcement of standardized material testing.

Evaluation of shear bond strength and shear stress on zirconia reinforced lithium silicate and high translucency zirconia.

This study evaluated the shear stress distribution on the adhesive interface and the bond strength between resin cement and two ceramics. For finite element analysis (FEA), a tridimensional model was made using computer-aided design software. This model consisted of a ceramic slice (10x10x2mm) partially embedded on acrylic resin with a resin cement cylinder (Ø=3.4 mm and h=3mm) cemented on the external surface. Results of maximum principal stress and maximum principal shear were obtained to evaluate the stress generated on the ceramic and the cylinder surfaces. In order to reproduce the in vitro test, similar samples to the computational model were manufactured according to ceramic material (Zirconia reinforced lithium silicate - ZLS and high translucency Zirconia - YZHT), (N=48, n=12). Half of the specimens were submitted to shear bond test after 24h using a universal testing machine (0.5 mm/min, 50kgf) until fracture. The other half was stored (a) (180 days, water, 37ºC) prior to the test. Bond strength was calculated in MPa and submitted to analysis of variance. The results showed that ceramic material influenced bond strength mean values (p=0.002), while aging did not: YZHT (19.80±6.44)a, YZHTa (17.95±7.21)a, ZLS (11.88±5.40)b, ZLSa (11.76±3.32)b. FEA results showed tensile and shear stress on ceramic and cylinder surfaces with more intensity on their periphery. Although the stress distribution was similar for both conditions, YZHT showed higher bond strength values; however, both materials seemed to promote durable bond strength.

Multiscale finite element modeling of sheet molding compound (SMC) composite structure based on stochastic mesostructure reconstruction

Predicting the mechanical behavior of the chopped carbon fiber Sheet Molding Compound (SMC) due to spatial variations in local material properties is critical for the structural performance analysis but is computationally challenging. Such spatial variations are induced by the material flow in the compression molding process. In this work, a new multiscale SMC modeling framework and the associated computational techniques are developed to provide accurate and efficient predictions of SMC mechanical performance. The proposed multiscale modeling framework contains three modules. First, a stochastic algorithm for 3D chip-packing reconstruction is developed to efficiently generate the SMC mesoscale Representative Volume Element (RVE) model for Finite Element Analysis (FEA). A new fiber orientation tensor recovery function is embedded in the reconstruction algorithm to match reconstructions with the target characteristics of fiber orientation distribution. Second, a metamodeling module is established to improve the computational efficiency by creating the surrogates of mesoscale analyses. Third, the macroscale behaviors are predicted by an efficient multiscale model, in which the spatially varying material properties are obtained based on the local fiber orientation tensors. Our approach is validated through experiments at both meso- and macro-scales, such as tensile tests assisted by Digital Image Correlation (DIC) and mesostructure imaging.

Stress and strain distributions on short implants with two different prosthetic connections – an in vitro and in silico analysis

Objective: An ideal biomechanics minimizes the stress between implant and bone that can provide success for osseointegrated implants. This study evaluated the strain concentration in surrounding tissue and stress in the components of two implants with different prosthetic connections through an in vitro and in silico methods. Methods: Twenty polyurethane blocks were divided into two groups (n=10) followed by the installation of internal hexagon (IH) (AS Technology – Titanium Fix, São José dos Campos, Brazil) or locking taper implants (LT) (Bicon Dental Implants). For strain gauge (SG) method, four sensors were placed around the implants. For finite element analysis (FEA), the same block was modeled and analyzed. An axial load (30 kgf) was applied for both methodologies. The values of stress and strain were analyzed for correlation to SG. Results: For SG, LT presented a mean of strain most aggressive (-932) than IH (-632). For FEA, LT showed less stress (-547) then IH (-1169). Conclusion: For two implant’s system, microstrain values capable to induce unwanted bone remodeling were not measured. However, for IH implant, the presence of a retention screw has the disadvantage to concentrate stress while a solid abutment dissipates the axial load through the implant that suggests a better performance for LT group. Keywords: Finite elements analyses; Dental implant; Strain gauge.

A method for analysis of head cover deformation and vibration amplitude in Francis hydro-turbine system by combination of CFD and FEA

It is of great importance to predict the deformation and vibration characteristics of the hydro-turbine structure accurately for the stable operation when the turbine is running under the alternating load of the flow field. In this paper, we proposed a methodology for analysis of the head cover deformation and vibration amplitude in the high-head Francis hydro-turbine system, in which Computational fluid dynamics (CFD) is employed to simulate the complex flow field in the head cover flow passage and the CFD-captured pressure distribution is provided for Finite element analysis (FEA) as a new load input to obtain more accurate head cover deformation and vibration calculation results. The results obtained by this method are compared with the results of the conventional algorithm and laboratory experimental results, demonstrated a better consistency. The great advantage of this method is that it allows vibration amplitude analysis and predictions under varied working conditions by adjusting the flow field parameters according to the specific working conditions. Therefore, it has supportive significance in optimization of the hydro-turbine structural turbine design as well as stabilizing operations at hydropower stations.

The Relationship Between Surface Curvature and Abdominal Aortic Aneurysm Wall Stress.

The maximum diameter (MD) criterion is the most important factor when predicting risk of rupture of abdominal aortic aneurysms (AAAs). An elevated wall stress has also been linked to a high risk of aneurysm rupture, yet is an uncommon clinical practice to compute AAA wall stress. The purpose of this study is to assess whether other characteristics of the AAA geometry are statistically correlated with wall stress. Using in-house segmentation and meshing algorithms, 30 patient-specific AAA models were generated for finite element analysis (FEA). These models were subsequently used to estimate wall stress and maximum diameter and to evaluate the spatial distributions of wall thickness, cross-sectional diameter, mean curvature, and Gaussian curvature. Data analysis consisted of statistical correlations of the aforementioned geometry metrics with wall stress for the 30 AAA inner and outer wall surfaces. In addition, a linear regression analysis was performed with all the AAA wall surfaces to quantify the relationship of the geometric indices with wall stress. These analyses indicated that while all the geometry metrics have statistically significant correlations with wall stress, the local mean curvature (LMC) exhibits the highest average Pearson's correlation coefficient for both inner and outer wall surfaces. The linear regression analysis revealed coefficients of determination for the outer and inner wall surfaces of 0.712 and 0.516, respectively, with LMC having the largest effect on the linear regression equation with wall stress. This work underscores the importance of evaluating AAA mean wall curvature as a potential surrogate for wall stress.

Homogenization Method Based on Model Order Reduction for FE Analysis of Multi-Turn Coils

This paper presents a homogenization method based on the model order reduction (MOR) for finite element (FE) analysis of multi-turn coils. The multi-turn coils are replaced by a homogenous material with the complex permeability that is expressed by a rational polynomial of frequency. After the MOR process, the complex permeability can readily be computed at any frequency. It is shown that the present method can drastically reduce the computational time without loss of accuracy.

Strict upper and lower bounds for quantities of interest in static response sensitivity analysis

• A CRE-based technique is proposed for goal-oriented error estimation in sensitivity analysis. • Strict bounds for quantities associated with sensitivity derivatives are obtained. • The bounding property is exemplified by model problems. In this paper, a goal-oriented error estimation technique for static response sensitivity analysis is proposed based on the constitutive relation error (CRE) estimation for finite element analysis (FEA). Strict upper and lower bounds of various quantities of interest (QoI) that are associated with the response sensitivity derivative fields are acquired. Numerical results are presented to assess the strict bounding properties of the proposed technique.

Verification of the elastic material characteristics of Norway spruce and European beech in the field of shear behaviour by means of digital image correlation (DIC) for finite element analysis (FEA)

Abstract Norway spruce (Picea abies L. Karst.) and European beech (Fagus sylvatica L.) samples were loaded in shear mode aimed at testing their elastic material characteristics applicable in finite element analysis (FEA). More precisely, experimental and numerical analyses of uniaxial tensile test parallel to grain in longitudinal-radial (LR) or longitudinal-tangential (LT) shear of plane are described. The elastic material models in the FEA are based on own experimental data and those of the literature. The verification of material characteristics was performed by 3D numerical models with the same parameters as for the experimental tests. The fully orthotropic elastic material model was applied in the uniaxial tensile tests. The digital image correlation (DIC) method served for verification of the numerical models with proposed elastic material characteristics. Good correlation was found between numerically predicted and experimentally measured data. The minor differences between the two data sets could be mainly attributed to certain natural wood characteristics, which were neglected in the proposed models, i.e. especially variation of earlywood and latewood density. The proposed elastic material models offer general data sets for the evaluation of mechanical response of timber structures and especially in timber connexions.

Influence of Additive Manufactured Scaffold Architecture on the Distribution of Surface Strains and Fluid Flow Shear Stresses and Expected Osteochondral Cell Differentiation.

Scaffolds for regenerative medicine applications should instruct cells with the appropriate signals, including biophysical stimuli such as stress and strain, to form the desired tissue. Apart from that, scaffolds, especially for load-bearing applications, should be capable of providing mechanical stability. Since both scaffold strength and stress–strain distributions throughout the scaffold depend on the scaffold’s internal architecture, it is important to understand how changes in architecture influence these parameters. In this study, four scaffold designs with different architectures were produced using additive manufacturing. The designs varied in fiber orientation, while fiber diameter, spacing, and layer height remained constant. Based on micro-CT (μCT) scans, finite element models (FEMs) were derived for finite element analysis (FEA) and computational fluid dynamics (CFD). FEA of scaffold compression was validated using μCT scan data of compressed scaffolds. Results of the FEA and CFD showed a significant impact of scaffold architecture on fluid shear stress and mechanical strain distribution. The average fluid shear stress ranged from 3.6 mPa for a 0/90 architecture to 6.8 mPa for a 0/90 offset architecture, and the surface shear strain from 0.0096 for a 0/90 offset architecture to 0.0214 for a 0/90 architecture. This subsequently resulted in variations of the predicted cell differentiation stimulus values on the scaffold surface. Fluid shear stress was mainly influenced by pore shape and size, while mechanical strain distribution depended mainly on the presence or absence of supportive columns in the scaffold architecture. Together, these results corroborate that scaffold architecture can be exploited to design scaffolds with regions that guide specific tissue development under compression and perfusion. In conjunction with optimization of stimulation regimes during bioreactor cultures, scaffold architecture optimization can be used to improve scaffold design for tissue engineering purposes.

Shear buckling analysis of laminated plates on tensionless elastic foundations

The current study addresses the local buckling analysis of an infinite thin rectangular symmetrically laminated composite plate restrained by a tensionless Winkler foundation and subjected to uniform in-plane shear loading. An analytic method (i.e., one-dimensional mathematical method) is used to achieve the analytical solution estimate of the contact buckling coefficient. In addition, to study the effect of ply angle and foundation stiffness on the critical buckling coefficients for the laminated composite plates, the parametric studies are implemented. Moreover, the convergence for finite element (FE) mesh is analysed, and then the examples in the parametric study are validated by the FE analysis. The results show that the FE analysis has a good agreement with the analytical solutions. Finally, an example with the analytical solution and FE analysis is presented to demonstrate the availability and feasibility of the presented analytical method.

The Effect of Position and Different Size of Radial Hole on Performance of Cannulated Pedicle Screw

Cannulated Pedicle Screw (CPS) is the instrumentation that has been introduced in Biomedical field in order to stabilize the spine structure and also to enhance the pullout strength in osteoporotic patient. The cement is injected through the CPS which is flow from the screw head to the radial hole and then distributed around the CPS to give higher performance of pullout strength. However, the fracture still reported to happened around the radial hole. This paper is aim to focus on the effect of the position and different diameter of radial hole on the CPS. Three designs were constructed using SolidWork software where two of it are the current models whereas the third was the proposed design which the radial holes were position differently (skewed to each other) and its size is smaller than the current model, 1.0 mm and 1.5mm respectively. The software used for Finite Element Analysis (FEA) is Ansys workbench 16.0. The Finite Element Models were verified with FEA result of the previous research. The FEA results of torsional stress for current and proposed design were then compared to obtain the maximum torque that both designs are able to resist before fracture. It can be concluded that the performance of CPS can be improved by the proposed design which is 2 radial hole skewed to each other and smaller radial hole diameter (1.0mm) than the current cannulated pedicle screw (1.5mm).

Finite Element Analysis of Bend Test of Sandwich Structures Using Strain Energy Based Homogenization Method

The purpose of this article is to present a simplified methodology for analysis of sandwich structures using the homogenization method. This methodology is based upon the strain energy criterion. Normally, sandwich structures are composed of hexagonal core and face sheets and a complete and complex hexagonal core is modeled for finite element (FE) structural analysis. In the present work, the hexagonal core is replaced by a simple equivalent volume for FE analysis. The properties of an equivalent volume were calculated by taking a single representative cell for the entire core structure and the analysis was performed to determine the effective elastic orthotropic modulus of the equivalent volume. Since each elemental cell of the hexagonal core repeats itself within the in-plane direction, periodic boundary conditions were applied to the single cell to obtain the more realistic values of effective modulus. A sandwich beam was then modeled using determined effective properties. 3D FE analysis of Three- and Four-Point Bend Tests (3PBT and 4PBT) for sandwich structures having an equivalent polypropylene honeycomb core and Glass Fiber Reinforced Plastic (GFRP) composite face sheets are performed in the present study. The authenticity of the proposed methodology has been verified by comparing the simulation results with the experimental bend test results on hexagonal core sandwich beams.

A CAD/CAE-integrated structural design framework for machine tools

In this paper, a novel integrated framework for design and optimization of a machine tool structure is presented, which can greatly improve the design quality and efficiency by combining knowledge-based design and multi-stage optimization with the CAD/CAE integration technique. To realize this framework, a topology architecture model has been developed to integrate the configuration design and geometric modeling knowledge as well as the static and dynamic evaluation knowledge of machine tools with a specific topology architecture type; an analysis feature model is proposed for the integration between commercial CAD and CAE software, in which analysis features can be automatically converted to a script code for finite element analysis (FEA) through feature mapping. Based on the topology architecture model and feature-based CAD/CAE integration methodology, a two-stage design optimization process is proposed to perform the conceptual structural design of machine tools. In the first stage, the principal parameters which critically affect the performance of an entire machine are determined; then, the static and dynamic stiffness matching designs are performed to obtain the reasonable stiffness and weight of each structural part and functional component based on the stiffness model and dynamic model. In the second stage, the arrangement of ribs is determined by inferring the design knowledge; FEA is used to evaluate the performances of structural parts, and the response surface method (RSM) is applied to optimize the structural parameters to approach the stiffness and mass close to the allocated values obtained from the first stage. Re-design of a four-axis horizontal machining center with a box-in-box architecture was carried out to illustrate the design procedure in detail and to verify the feasibility and efficacy of the proposed framework. By applying the proposed framework, the total weight of the entire machine is minimized while sufficient stiffness is maintained. The results also show that the proposed framework facilitates the conceptual structural design and optimization process of machine tools.

Analysis on the effect of phase boundary in meso-cutting of AISI1045 based on the microstructure-level simulation

In this paper, in order to discover the mechanism of chip formation in meso-cutting, an equivalent homogenous material (EHM) model and a microstructure-level model based on the real microstructure were built up for finite element analysis (FEA) of the meso-cutting process of hot-rolled AISI1045. The advantage of the microstructure-level model over the EHM ones includes its capability in revealing the hidden phenomena and mechanisms related to grain, grain boundary, and phase structure besides the higher prediction precision. And these phenomena and mechanisms are very important for the correct understanding of meso- and micro-cutting. After experimental verification, the microstructure-level model was used to analyze the effects of phase boundary on the chip morphology, strain, stress, etc. in the meso-cutting. It was found that large strain took place in the interior of the ferrite and built up the plumps on the free chip surface. And large strain gradient formed around the phase boundaries by the combining effects of the generation of geometrically necessary dislocations for meeting the deformation compatibility between grains, image force, and pile-up of dislocations. In addition, the reversal of the strain, stress, and strain rate across the phase boundary was noticed as well. At last, the size effect was analyzed from the perspective of the strengthening of material due to the variation of the hydrostatic pressure with the ratio (λ) of ap/re and its effect on defects along the phase boundaries and shear stress.

Finite Element-Based Mechanical Assessment of Bone Quality on the Basis of In Vivo Images

Beyond bone mineral density (BMD), bone quality designates the mechanical integrity of bone tissue. In vivo images based on X-ray attenuation, such as CT reconstructions, provide size, shape, and local BMD distribution and may be exploited as input for finite element analysis (FEA) to assess bone fragility. Further key input parameters of FEA are the material properties of bone tissue. This review discusses the main determinants of bone mechanical properties and emphasizes the added value, as well as the important assumptions underlying finite element analysis. Bone tissue is a sophisticated, multiscale composite material that undergoes remodeling but exhibits a rather narrow band of tissue mineralization. Mechanically, bone tissue behaves elastically under physiologic loads and yields by cracking beyond critical strain levels. Through adequate cell-orchestrated modeling, trabecular bone tunes its mechanical properties by volume fraction and fabric. With proper calibration, these mechanical properties may be incorporated in quantitative CT-based finite element analysis that has been validated extensively with ex vivo experiments and has been applied increasingly in clinical trials to assess treatment efficacy against osteoporosis.

3D Reconstruction and Thermal Stress Analysis of Re-Oxidized Ni-YSZ Anode Functional Layer of Solid Oxide Fuel Cells

Nickel (Ni) has been widely used in the anode of solid oxide fuel cells (SOFCs) because of its high electrocatalytic activity towards oxidation of H2, good electronic conductivity, and formation of pores when initial nickel oxide (NiO) is reduced to Ni. When SOFCs operate at high temperature (> 800 °C), Ni can be re-oxidized to NiO when there is an interruption of fuel supply, air inflow due to deterioration of seals, or excessive supply of H2O in fuels. Volume expansion of Ni can occur significantly during this re-oxidization, and it can induce severe stress which may cause cracks and changes in anode’s microstructure. In this study, re-oxidized Ni-YSZ anode functional layer (AFL) was 3D reconstructed by using image data obtained from focused ion beam-scanning electron microscopy (FIB-SEM), which is powerful technique to separate the elements and visualize the 3D structure. Then, microstructural properties such as volume fraction, phase boundary density, and connectivity were analyzed using image processing tool. 3D mesh model for finite element analysis (FEA) was generated and thermal stress was analyzed at various temperature. In thermal FEA, we calculated and found some NiO-YSZ interfaces exhibited large thermal stress with magnitude larger than 317 MPa, which is the ultimate tensile stress of Ni phase. This is because the lack of porosity in NiO-YSZ AFL inhibits the release of thermal stresses generated at high temperature. Thus, this high thermal stress could cause critical failure on the cell structure because re-oxidized Ni-YSZ anode still contains Ni phase (< 10 vol %). The details of the 3D reconstruction, image processing, and FEA results will be presented in the conference.