FEM-based Approach Research Articles

A new FEM-based approach on the modeling of stress-induced velocity shift of piezoelectric surface acoustic wave resonators

A new FEM-based approach on the modeling of stress-induced velocity shift of piezoelectric surface acoustic wave resonators

IGA-based topology optimization in the design of stress-constrained compliant mechanisms

Topology design of compliant mechanisms has gained wide popularity among the scientific community, and their use in the mechanical engineering field is being of upmost importance. In this paper, an isogeometric analysis (IGA) formulation is used to solve the topology optimization problem of compliant mechanisms. Stress constraints are introduced in the problem to guarantee the attainment of realistic solutions. For this purpose, an overweight constraint is considered for the design process, replacing the use of local stress constraints. The material distribution in the domain is modeled with quadratic B-splines and with a uniform relative density within each element of the mesh. These strategies to define the material layout are used to compare the IGA-based formulation with the finite element (FEM) formulation. The IGA formulation provides several advantages with respect to the classical FEM-based approaches that are shown and analyzed with an input-parameters sensitivity analysis. The sensitivity analysis and the assessment of the importance of introducing of stress constraints in the problem are developed by solving two benchmark problems. Regarding the sensitivity analysis of input parameters, the results show that the ratio between the material and the springs stiffnesses is the parameter with the largest influence on the solutions of the problem. Moreover, the advantages of the IGA formulations over FEM formulations are related with the computational time, the smoothness of the structural borders, and the non-appearance of the checkerboard patterns. With respect to the stress constraints, the results show that they have to be considered in order to avoid instability and structural integrity problems.

Investigation of bead morphology and mechanical behaviour for metal inert gas welding-based WAAM in pulsed mode metal transfer on 316LSi stainless steel

Bead geometry plays a significant role in the fabrication of artefacts via the wire arc additive manufacturing (WAAM) route especially with respect to the dimensional characteristics, surface properties, and part density. It also substantially affects the material penetration, part accuracy, and thickness of subsequent layers. The present study focuses on the effect of processing parameters on single-bead geometry for fabricating 316LSi stainless steel in pulsed-mode metal transfer WAAM. Models were developed by utilizing multiple regression modelling, machine learning (ML) based on back propagation neural network (BPNN), and finite element modelling (FEM) with four process parameters, wire feed rate (WFR), torch travel speed (TTS), voltage (V), and contact tip-to-substrate distance (CTSD), each considered at three levels. Response surface methodology was utilized for design of experiments to obtain three-bead geometry responses, namely width of weld bead (WWB), height of weld bead (HWB), and depth of penetration (DOP). The results confirm that all three proposed models predict bead geometry reasonably. However, accuracy of ML-based BPNN method is better as compared to the regression and FEM-based approaches. For multi-objective optimization, a desirability function approach is used, which predicts the optimal conditions at WFR of 4.0 m/min, TTS of 284.545 mm/min, voltage of 18.0 V, and the CTSD of 12.0 mm for minimum WWB, maximum HWB, and minimum DOP. A multi-layered wall of SS316LSi is fabricated with optimized process parameters, and it is found that the ultimate tensile strength, yield strength, and percentage elongation are 546.3 MPa, 440.1 MPa, and 43.7%, respectively. WAAM-deposited structure reveals stable deposition, no debonding/delamination, and complete fusion between layers. The results of the present article will go a long way in aiding the researchers/industrial personnel in arriving on the optimal modelling approach and deposition conditions for WAAM-fabricated SS316LSi parts with enhanced mechanical properties and productivity.

Stress analysis of aluminium die-cast parts including the STL-data of pores

PurposePores and shrink holes are unavoidable defects in the die-casting mass production process which may significantly influence the strength, fatigue and fracture behaviour as well as the life span of structures, especially if they are subjected to high static and dynamic loads. Such defects should be considered during the design process or after production, where the defects could be detected with the help of computed tomography (CT) measurements. However, this is usually not done in today's mass production environments. This paper deals with the stress analysis of die-cast structural parts with pores found from CT measurements or that are artificially placed within a structure.Design/methodology/approachIn this paper the authors illustrate two general methodologies to take into account the porosity of die-cast components in the stress analysis. The detailed geometry of a die-cast part including all discontinuities such as pores and shrink holes can be included via STL data provided by CT measurements. The first approach is a combination of the finite element method (FEM) and the finite cell method (FCM), which extends the FEM if the real geometry cuts finite elements. The FCM is only applied in regions with pores. This procedure has the advantage that all simulations with different pore distributions, real or artificial, can be calculated without changing the base finite element mesh. The second approach includes the pore information as STL data into the original CAD model and creates a new adapted finite element mesh for the simulation. Both methods are compared and evaluated for an industrial problem.FindingsThe STL data of defects which the authors received from CT measurements could not be directly applied without repairing them. Therefore, for FEM applications an appropriate repair procedure is proposed. The first approach, which combines the FEM with the FCM, the authors have realized within the commercial software tool Abaqus. This combination performs well, which is demonstrated for test examples, and is also applied for a complex industrial project. The developed in-house code still has some limitations which restrict broader application in industry. The second pure FEM-based approach works well without limitations but requires increasing computational effort if many different pore distributions are to be investigated.Originality/valueA new simulation approach which combines the FEM with the FCM has been developed and implemented into the commercial Abaqus FEM software. This approach the authors have applied to simulate a real engineering die-cast structure with pores. This approach could become a preferred way to consider pores in practical applications, where the porosity can be derived either from CT measurements or are artificially adopted for design purposes. The authors have also shown how pores can be considered in the standard FEM analysis as well.

Incremental design process for vehicle structural components using thermoplastic-based composites: A simulation-guided approach for door anti-intrusion beams

The design of safety-related structural components in automobiles is a critical phase. Most car manufacturers are aiming at reducing vehicle weight considering continuous fiber-reinforced thermoplastics as candidate to replace metal-based structural components. However, this replacement cannot compromise the safety level already achieved by metal-based designs. A good example is the side door anti-intrusion beam, which is a passive safety component to protect the passengers under a lateral impact. This paper presents an incremental design process to achieve a functional side door anti-intrusion beam fully made of glass fiber reinforced thermoplastic conceived to replace metal-based ones. The reader is guided along the design challenges, where the mechanic-based reasons to adapt the part geometry and composite layout are explained in detail. This incremental design process uses a fully FEM-based approach allowing to reach a standard-defined absorbed energy of 1000 J in a lateral collision. From the simulation analysis, it was found that by implementing essential modifications in the beam’s cross-section corrugation, the damage progression can be slowed down leading to an increase of absorbed energy. Additionally, the enhancement of one extra ply in the proper direction solves severe fracture in the clamping area. The final composite design not only performs similarly to its metal-based counterpart, but also considers aspects of production feasibility. This trip along the design process concludes with the production of the simulate-designed component and its effectiveness under lateral impact is demonstrated. To meet the safety regulations, the model is thoroughly validated against the real impact test by analyzing the response in force, intrusion, energy and damage.

Geometrically nonlinear buckling analysis of truss with length imperfection subjected to mechanical and thermal load using hybrid FEM

This paper presents a novel hybrid FEM-based approach to establish the mathematical model for solving the nonlinear buckling problem of truss systems with length imperfection under mechanical and thermal load. due to constant temperature change-based hybrid FEM. The proposed approach deals with establishing hybrid types of truss elements, including perfect truss elements without thermal deformation and truss elements with length imperfection and thermal deformation. The equilibrium equation of both truss elements is established based on compatibility relationships considering geometric nonlinearity. The hybrid global equilibrium equations of truss systems are developed by assembling constructed perfect truss elements without thermal deformation and truss elements with length imperfection and thermal deformation. The incremental-iterative algorithm based on the arc-length method is used to establish calculation programs to solve the hybrid global equilibrium equation for investigating the geometrically nonlinear buckling behavior of the truss system. The numerical test is presented to investigate the buckling and post-buckling behavior of truss systems having some elements with length imperfection under thermal and mechanical load.

Review on Needle Insertion Haptic Simulation

Purpose of ReviewThis short review updates an exhaustive one written by Correa et al. in 2019 about haptic training simulation on needle insertion in the medical field.Recent FindingsLatest works refine well-known models and enhance setups and methods to facilitate generically getting experimental data.SummaryWe provide a complementary focus on device specifications and recent models to render this specific haptic feedback on computer-based simulators. Assessment approaches and the issues encountered when introducing such simulators into curricula are also discussed. FEM-based approaches still do not permit real-time computation but hybrid approaches as proposed by Wittek et al. in 2020 may become a good compromise. Nonetheless, psychophysical studies should be performed to determine the haptic fidelity of the various approaches found in the literature, and embed them efficiently in medical curricula. This would permit to delay the necessary final hands-on training on patients that raises ethical issues.

A Comparative Study of Conventional and FEM-Based Approach for Dynamic Analysis of Large Reciprocating Compressor Foundation Including Soil-Foundation Interaction

AbstractThis paper aims to present a comparative study of dynamic response of a machine foundation supporting gas-lift reciprocating compressor using a conventional lumped parameter method and an F...

A time-saving FEM-based approach for structural topology optimization with exact boundary representation

A time-saving FEM-based approach for structural topology optimization with exact boundary representation

Application of sub-miniaturized bending tests to extract tensile properties from neutron-irradiated metallic alloys

In this work, we demonstrate the applicability of sub-miniaturized three-point bending (3PB) testing for the extraction of tensile plastic properties of metallic materials, such as yield stress and work hardening rate. The approach is developed and validated on the example of tungsten. For this, dedicated finite element method (FEM) simulations are performed to reveal the correlation between the flexural stress-strain response in 3PB tests and yield stress in tensile tests. Furthermore, a dedicated inverse FEM procedure utilizing rate-sensitive isotropic physical model is developed to extract both yield stress and work hardening rate from the available set of bending tests. Both FEM-based approaches are first benchmarked on unirradiated materials and then validated using neutron-irradiated tungsten grades. The accuracy of the tensile properties extracted using both methods is discussed along with the estimation of a number of 3PB tests required to reach a target precision. The applicability of 3PB geometry for the extraction of tensile properties from unirradiated bending tests below ductile-to-brittle transition temperature (DBTT) is also addressed.

Equivalent Geometric Imperfections for Local Buckling of Slender Box-section Columns

Determining the plate or the local buckling resistance is highly important in designing steel buildings and bridges. The EN 1993-1-5Annex C provides a FEM-based design approach to calculate the buckling resistance based on numerical design calculations (geometrical and material nonlinear analysis - GMNIA). Within the GMNIA analysis-based stability design, the application of the imperfections has a special role. Thus, the applicability of the EN 1993-1-5 based buckling curve (Winter curve) has been questioned for pure compression, and previous investigations showed the buckling curve of EN 1993-1-5 Annex B is more appropriate for the design of slender box-section columns subjected to pure compression, the magnitude of the equivalent geometric imperfection to be applied in numerical models for local buckling is also questioned and investigated by the authors within the current paper. The aim of the current research program is to investigate the necessary equivalent geometric imperfections to be applied in FEM-based design calculations using GMNIA calculations. A numerical parametric study is executed to investigate the imperfection sensitivity of box-section columns having different local slenderness. The necessary imperfection magnitudes are determined to each analyzed geometry leading to the buckling resistance predicted by the standardized buckling curves. Based on the numerical parametric study, a proposal for the applicable equivalent geometric imperfection magnitude is developed, which conforms to the plate buckling curves of the EN 1993-1-5 and giving an improvement proposal to the local buckling imperfection magnitudes of the prEN 1993-1-14, which is currently under development.

Hybrid finite element formulation for geometrically nonlinear buckling analysis of truss with initial length imperfection

This paper presents a novel hybrid FEM-based approach for nonlinear buckling analysis of truss with initial length imperfection. The contribution deals with establishing two types of truss finite element (perfection and imperfection element) considering large displacement based on displacement formulation and mixed formulation. Therefore, the hybrid global equation system is developed by assembling perfection and imperfection truss elements. The incremental-iterative algorithm based on the arc-length method is used to establish calculation programs for solving geometrically nonlinear buckling analysis of truss with initial length imperfection. Using a written calculation program, the numerical test is presented to investigate the equilibrium path for plan truss with initial member length imperfection.

A FEM based methodology to simulate multiple crack propagation in friction stir welds

In this work a numerical procedure, based on a finite element approach, is proposed to simulate multiple three-dimensional crack propagation in a welded structure. Cracks are introduced in a friction stir welded AA2024-T3 butt joint, affected by a process-induced residual stress scenario. The residual stress field was inferred by a thermo-mechanical FEM simulation of the process, considering temperature dependent elastic-plastic material properties, material softening and isotropic hardening. Afterwards, cracks introduced in the selected location of FEM computational domain allow stress redistribution and fatigue crack growth. The proposed approach has been validated by comparison with numerical outcomes provided by a consolidated FEM-DBEM procedure, available in literature. The discussed procedures are substantially equivalent in terms of SIFs evaluation along the crack front at the cracks insertion, as well as with respect to crack sizes measured in three different points for each propagation step. This FEM-based approach simulates the fatigue crack propagation by considering accurately the residual stress field generated by plastic deformations imposed on a structural component and has general validity.

A macroscale FEM-based approach for selective laser sintering of thermoplastics

A numerical approach to model the selective laser sintering (SLS) of polypropylene is proposed. A 3D thermal model was developed and thus enables the prediction of the temperature fields and the extension of the sintered area in the powder bed taking into account the phase change during multiple laser passes. Powder–liquid, liquid–solid and solid–liquid phase changes were modelled during the SLS and the subsequent cooling processes. Then, a 3D thermomechanically coupled model was set up based on the temperature results of the thermal model in order to predict the distortion of the produced parts after cooling down. Different pre-heating temperatures were considered, highlighting their influence on the final part properties.

An FEM-based approach for tool wear estimation in machining

This study presents an FEM-based approach to predict the rate of flank wear evolution for uncoated cemented carbide tools in longitudinal turning processes. This novel approach combines the concept of experimental design and Response Surface Methodology (RSM) with Finite Element (FE) modelling of the cutting process, which allows for a fairly accurate tool wear prediction with a significantly lower computational cost compared to other available numerical methods.In the current approach, a series of three dimensional (3D) FE simulations were initially performed for different combinations of cutting data and tool flank geometries. The obtained results were used to establish the quadratic relation between the input variables and the responses required for tool wear prediction, such as interface temperature. Later, the flank wear rate equation was developed based on the relation between the volume loss due to wear and the dimensions of the worn tools. The results of the FE simulations were finally integrated with the established wear rate equation to estimate the flank wear evolution. The credibility of the presented approach was then assessed through estimation of the flank wear evolution rate for a wide range of cutting conditions. The predicted flank wear rates showed a good agreement with experimental measurements in most cases. The reasons for minor deviations from the experimental results were finally outlined.

AN EFFICIENT FINITE ELEMENT MODEL FOR ANALYSIS OF SINGLE WALLED BORON NITRIDE NANOTUBE-BASED RESONANT NANOMECHANICAL SENSORS

In this paper, the dynamics analysis of single walled boron nitride nanotubes (SWBNNT) as a resonant nanomechanical sensor by using the finite element method has been reported. Molecular structural mechanics-based finite element model (FEM) has been developed by using three-dimensional elastic beams and point masses, such that the proximity of the model to the actual atomic structure of nanotube is significantly retained. Different types of armchair layups of SWBNNTs are considered with cantilevered and bridged end constraints. By implementing the finite element simulation approach, the resonant frequency shift-based mass sensitivity analysis is performed for both types of end constraints for considered armchair form of the SWBNNTs with different aspect ratios. For both types of end constraint, continuum mechanics-based analytical formulations, considering effective wall thickness of nanotubes are used to validate the present FEM-based simulation approach. The intermediate landing position of the added mass is analyzed, considering variations in resonant frequency shifts of the different fundamental modes of vibrations for both types of end constraints. The FEM-based simulation results for both types of end constraints found in good agreement with the continuum mechanics-based analytical results for the aspect ratio of range of 9–15. The mass sensitivity limit of 10-1 zg is achieved for SWBNNT-based resonant nanomechanical sensors. The resonant frequency shift for higher-order fundamental vibrational modes become stable as the attached mass moves away from the fixed ends for particular magnitude of attached mass. The present finite element-based approach is found to be effectual in terms of dealing different atomic structures, boundary conditions and consideration of added mass to analyze the dynamic behavior of the SWBNNT-based resonant nanomechanical sensors.

A Monolithic, FEM-Based Approach for the Coupled Squeeze Film Problem of an Oscillating Elastic Micro-Plate Using 3D 27-Node Elements

In this study we describe an FEM-based methodology to solve the coupled fluid-structure problem due to squeeze film effects present in vibratory MEMS devices, such as resonators, gyroscopes, and acoustic transducers. The aforementioned devices often consist of a plate-like structure that vibrates normal to a fixed substrate, and is generally not perfectly vacuum packed. This results in a thin film of air being sandwiched between the moving plate and the fixed substrate, which behaves like a squeeze film offering both stiffness and damping. Typically, such structures are actuated electro-statically, necessitating the thin air gap for improving the efficiency of actuation and the sensitivity of detection. To accurately model these devices the squeeze film effect must be incorporated. Extensive literature is present on mod- eling squeeze film effects for rigid motion for both perforated as well as non-perforated plates. Studies which model the plate elasticity often use approximate mode shapes as input to the 2D Reynolds Equation. Recent works which try to solve the coupled fluid elasticity problem, report iterative FEM-based solution strategies for the 2D Reynolds Equation coupled with the 3D elasticity Equation. In this work we present a FEM-based single step solution for the coupled problem at hand, using only one type of element (27 node 3D brick). The structure is modeled with 27 node brick elements of which the lowest layer of nodes is also treated as the fluid domain (2D) and the integrals over fluid domain are evaluated for these nodes only. We also apply an electrostatic loading to our model by considering an equivalent electro-static pressure load on the top surface of the structure. Thus we solve the coupled 2D-fluid-3D-structure problem in a single step, using only one element type. The FEM results show good agreement with both existing analytical solutions and published experimental data.

TH-F-211-01: A Finite Element Method-Based Multisource Model for Near-Infrared Laser-Mediated Plasmonic Heating with Optically-Tunable Gold Nanoparticles

Purpose: To develop a computational model based on the finite element method (FEM) that can be used to predict spatiotemporal heat distributions for near-infrared (NIR) laser-based thermal imaging and therapy applications involving highly heterogeneous gold nanoparticle (GNP) distributions in tissue. Methods: The absorption of external light in tissue can be greatly enhanced with the use of GNPs tuned to strongly absorb in the NIR region. Previously, a multisource heat model was developed to compute temperature elevation due to plasmonic heat generation from individual GNPs, treating each GNP as an independent heat source. However, it was implemented by a ‘multi-step approach’, computing the temperature increase due to each individual GNP by Green's function method and that due to laser light by FEM via optical diffusion approximation, separately. In the current investigation, a ‘one-step’ approach was developed to compute the full spatiotemporal temperature distribution due to multiple heat sources all together by solving the weak-form of the heat equation using FEM. This approach was applied to predict temperature increase inside a GNP-filled cavity mimicking a small breast tumor within a breast gel phantom. For the purpose of comparison, calculations were also performed using a ‘multi-step approach’. Results: The results from the one-step approach matched those from the multi-step approach to within 1.2% along the central axis of the laser. Conclusions: A multisource heat model was successfully solved by FEM-based one-step approach. Computational results from the one-step approach were found identical to those from the multi-step approach. Both models showed great flexibility in handling any heterogeneous distribution of GNPs without requiring prior knowledge of the optical properties a GNP-filled medium. The proposed one-step approach will facilitate the prediction of temperature change within GNP-filled tissue during NIR laser-based clinical applications. This work was supported by DOD/BCRP, W81XWH-08-1-0686. DOD/BCRP, W81XWH-08-1-0686.

On error control in the element-free Galerkin method

The paper investigates discretisation error control in the element-free Galerkin method (EFGM) highlighting the differences from the finite element method (FEM). We demonstrate that the (now) conventional procedures for error analysis used in the finite element method require careful application in the EFGM, otherwise competing sources of error work against each other. Examples are provided of previous works in which adopting an FEM-based approach leads to dubious refinements. The discretisation error is here split into contributions arising from an inadequate number of degrees of freedom e h , and from an inadequate basis e p . Numerical studies given in this paper show that for the EFGM the error cannot be easily split into these component parts. Furthermore, we note that arbitrarily setting the size of nodal supports (as is commonly proposed in many papers) causes severe difficulties in terms of error control and solution accuracy. While no solutions to this problem are presented in this paper it is important to highlight these difficulties in applying an approach to errors from the FEM in the EFGM. While numerical tests are performed only for the EFGM, the conclusions are applicable to other meshless methods based on the concept of nodal support.

Simulation of tribological functionality of heterogeneous tribomaterials

We simulated the tribological functionality of two heterogeneous tribomaterials used in conformal contacts by means of a FEM-based approach: journal bearing material AlSn20 and polymeric sealing material PTFE with bronze filler particles. For AlSn20, the emergency running capability, which is based on the activation (melting) of the soft phase tin, was simulated taking into account thermo-elasto-plastic behaviour of the material. For the PTFE bronze compound, we analysed the load bearing capacity of the particle-structured surface with varying volumetric fraction of particles, temperature, load and creep behaviour of the PTFE Matrix. The results show benefit of heterogeneous designs over homogeneous materials.