Static Finite Element Model Research Articles

Predicting pressure distribution between transfemoral prosthetic socket and residual limb using finite element analysis

A static implicit nonlinear finite element model (FEM) was created and analysed to determine the pressure distribution between the residual limb and the prosthetic socket of a transfemoral amputee. This analysis was performed in an attempt to develop a process allowing healthcare providers and engineers to simulate the fit and comfort of transfemoral prosthetics to reduce the number of re-fittings. The FEM considered the effects of donning and body weight and included geometric nonlinearity due to large deflections, nonlinear contacts due to friction, and nonlinear hyper-elastic material properties for the residual limb's soft tissue. The results attained can provide prosthetic fitting clinicians customised information on where the prosthetic fits too tight, and how stress concentrations would change as a result of geometric modifications to the prosthetic. This knowledge can improve patients' comfort levels by providing well targeted and more accurate modifications to the prosthetic, minimising the need for numerous refittings.

Predicting pressure distribution between transfemoral prosthetic socket and residual limb using finite element analysis

A static implicit nonlinear finite element model (FEM) was created and analysed to determine the pressure distribution between the residual limb and the prosthetic socket of a transfemoral amputee. This analysis was performed in an attempt to develop a process allowing healthcare providers and engineers to simulate the fit and comfort of transfemoral prosthetics to reduce the number of re-fittings. The FEM considered the effects of donning and body weight and included geometric nonlinearity due to large deflections, nonlinear contacts due to friction, and nonlinear hyper-elastic material properties for the residual limb's soft tissue. The results attained can provide prosthetic fitting clinicians customised information on where the prosthetic fits too tight, and how stress concentrations would change as a result of geometric modifications to the prosthetic. This knowledge can improve patients' comfort levels by providing well targeted and more accurate modifications to the prosthetic, minimising the need for numerous refittings.

Numerical and Experimental Investigation of Aircraft Panel Deformations During Riveting Process

In collaboration with Airbus-UK, the dimensional growth of aircraft panels while being riveted with stiffeners is investigated. Small panels are used in this investigation. The stiffeners have been fastened to the panels with rivets and it has been observed that during this operation the panels expand in the longitudinal and transverse directions. It has been observed that the growth is variable and the challenge is to control the riveting process to minimize this variability. In this investigation, the assembly of the small panels and longitudinal stiffeners has been simulated using static stress and nonlinear explicit finite element models. The models have been validated against a limited set of experimental measurements; it was found that more accurate predictions of the riveting process are achieved using explicit finite element models. Yet, the static stress finite element model is more time efficient, and more practical to simulate hundreds of rivets and the stochastic nature of the process. Furthermore, through a series of numerical simulations and probabilistic analyses, the manufacturing process control parameters that influence panel growth have been identified. Alternative fastening approaches were examined and it was found that dimensional growth can be controlled by changing the design of the dies used for forming the rivets.

An Evaluation of Primer Preseating in Small Caliber Cartridge Production

This work presents the findings of a study to quantify the relative effectiveness of the primer preseating operation in small caliber cartridge production. In theory, primer preseating would enable cartridge stamping tools to achieve deeper stamping penetration depths and subsequently, greater primer retention forces. This is because, with preseating incorporated in the existing small caliber cartridge production process, a cartridge stamping tool would be fully dedicated to performing the case stamping operation (rather than the simultaneous primer seating and case stamping operations it currently performs). The findings presented in this work include measured percentages of total stamping tool force dedicated to primer seating, stamping tool penetration depths with and without primer preseating and primer retention forces with and without primer preseating. These findings and their underlying principles were produced through a static force equilibrium analysis and finite element modeling and simulation studies.

Delivery and intracellular turnover of insulin-like growth factor I (IGF-I) delivered to human placenta using quantum dots

This paper presents a hybrid explicit finite element (FE)/eigenstrain model for predicting the residual stress generated by arrays of adjacent/overlapping laser shock peening (LSP) shots where the use of a completely explicit FE analysis may be impractical. It shows that for a given material, the underlying eigenstrain distribution (in contrast to the resulting stress field) representing a laser shock peen is primarily dependent on the parameters of the laser pulse and the number of overlays rather than the precise component geometry. Consequently the residual stress introduced by complex laser peening treatments can be built up by using static FE models and superposition of individual eigenstrain distributions without recourse to further computationally demanding explicit FE analyses. It is found that beneath a small LSP array the magnitude of the compressive residual stress is higher than for a wider array of LSP shots and that with increasing numbers of layers the compressive stress increases as does the depth of the compressive zone. The model predictions for the eigenstrain distributions are compared well with experimental measurements of plastic strain (full-width-at-half-maximum) obtained by neutron diffraction. The eigenstrain method is also extended to construct the full residual stress field using measured residual elastic strains at a finite number of measurement locations in a component.

Cellular buckling in stiffened plates

An analytical model based on variational principles for a thin-walled stiffened plate subjected to axial compression is presented. A system of nonlinear differential and integral equations is derived and solved using numerical continuation. The results show that the system is susceptible to highly unstable local–global mode interaction after an initial instability is triggered. Moreover, snap-backs in the response showing sequential destabilization and restabilization, known as cellular buckling or snaking, arise. The analytical model is compared with static finite element (FE) models for joint conditions between the stiffener and the main plate that have significant rotational restraint. However, it is known from previous studies that the behaviour, where the same joint is insignificantly restrained rotationally, is captured better by an analytical approach than by standard FE methods; the latter being unable to capture cellular buckling behaviour even though the phenomenon is clearly observed in laboratory experiments.

A Computationally Efficient Method to Determine Iron and Magnet Losses in VSI-PWM Fed Axial Flux Permanent Magnet Synchronous Machines

For electrical machines with a 3-D geometry, such as axial flux permanent magnet machines, the computation of iron and magnet losses in the case of pulsewidth modulation (PWM) supply could be performed by a transient 3-D finite element model (FEM) coupled with an electrical circuit. To reduce the CPU time, in this paper, these losses are computed with acceptable accuracy without using a 3-D transient FEM. The multislice technique is used with a 2-D static FEM, combined with a state space model of the machine. A Preisach hysteresis model is considered to evaluate the iron loss during minor loops. The loss in the electrical steel and in the magnets is evaluated for several PWM frequencies as well as for different segmentations of the magnets.

Web crippling failure using quasi-static FE models

This paper presents an investigation on the use of quasi-static analyses with explicit integration to evaluate the web crippling behaviour of cold-formed steel beams. Web crippling failure occurs due to the application of transverse concentrated loads, which can be applied statically or dynamically. In the majority of the examples found in the literature, the web crippling phenomenon has been investigated by means of purely static shell finite element (SFE) models with implicit integration. In this work, the ABAQUS code was employed to implement SFE models aimed at replicating an experimental test and quasi-static analyses with an explicit integration scheme were adopted. First, a brief literature review on the topic of the numerical investigation of web crippling of cold-formed steel members is presented. Then, the paper addresses the characterisation of the quasi-static analysis concept with particular emphasis on the control of dynamic effects and the SFE model of a lipped channel beam under External Two Flange (ETF) loading is described. Several conventional parameters of standard SFE analysis, such as the SFE type, mesh selection, steel model, hardening effects due to cold-forming, residual stresses, initial imperfections and support conditions are explained, as well as additional specifications pertaining to the adoption of quasi-static analyses, such as the load rate, mass scaling, contact and friction, smoothed amplitude curves and inhibition of inertia (noise) effects. Finally, the results obtained are presented in the context of the ETF case, including load–displacement curves, curves of kinetic-to-internal energy ratio vs. displacement and beam deformed shapes (failure modes). It is concluded that explicit analysis leads to rigorous simulations of experimental test results, in terms of ultimate load, post-collapse load–deflection curve and failure mechanism. The failure mode obtained with the quasi-static analysis provides a better approximation of the one observed experimentally than its non-linear static analysis counterpart. Indeed, the failure mechanism emerges considerably more clearly when the quasi-static analysis is adopted.

Comparison of eight published static finite element models of the intact lumbar spine: Predictive power of models improves when combined together

Finite element (FE) model studies have made important contributions to our understanding of functional biomechanics of the lumbar spine. However, if a model is used to answer clinical and biomechanical questions over a certain population, their inherently large inter-subject variability has to be considered. Current FE model studies, however, generally account only for a single distinct spinal geometry with one set of material properties. This raises questions concerning their predictive power, their range of results and on their agreement with in vitro and in vivo values.Eight well-established FE models of the lumbar spine (L1-5) of different research centers around the globe were subjected to pure and combined loading modes and compared to in vitro and in vivo measurements for intervertebral rotations, disc pressures and facet joint forces.Under pure moment loading, the predicted L1-5 rotations of almost all models fell within the reported in vitro ranges, and their median values differed on average by only 2° for flexion-extension, 1° for lateral bending and 5° for axial rotation. Predicted median facet joint forces and disc pressures were also in good agreement with published median in vitro values. However, the ranges of predictions were larger and exceeded those reported in vitro, especially for the facet joint forces. For all combined loading modes, except for flexion, predicted median segmental intervertebral rotations and disc pressures were in good agreement with measured in vivo values.In light of high inter-subject variability, the generalization of results of a single model to a population remains a concern. This study demonstrated that the pooled median of individual model results, similar to a probabilistic approach, can be used as an improved predictive tool in order to estimate the response of the lumbar spine.

Toward a real time multi-tissue Adaptive Physics-Based Non-Rigid Registration framework for brain tumor resection

This paper presents an adaptive non-rigid registration method for aligning pre-operative MRI with intra-operative MRI (iMRI) to compensate for brain deformation during brain tumor resection. This method extends a successful existing Physics-Based Non-Rigid Registration (PBNRR) technique implemented in ITKv4.5. The new method relies on a parallel adaptive heterogeneous biomechanical Finite Element (FE) model for tissue/tumor removal depicted in the iMRI. In contrast the existing PBNRR in ITK relies on homogeneous static FE model designed for brain shift only (i.e., it is not designed to handle brain tumor resection). As a result, the new method (1) accurately captures the intra-operative deformations associated with the tissue removal due to tumor resection and (2) reduces the end-to-end execution time to within the time constraints imposed by the neurosurgical procedure. The evaluation of the new method is based on 14 clinical cases with: (i) brain shift only (seven cases), (ii) partial tumor resection (two cases), and (iii) complete tumor resection (five cases). The new adaptive method can reduce the alignment error up to seven and five times compared to a rigid and ITK's PBNRR registration methods, respectively. On average, the alignment error of the new method is reduced by 9.23 and 5.63 mm compared to the alignment error from the rigid and PBNRR method implemented in ITK. Moreover, the total execution time for all the case studies is about 1 min or less in a Linux Dell workstation with 12 Intel Xeon 3.47 GHz CPU cores and 96 GB of RAM.

Static and Dynamic Finite Element Model Updating of a Rigid Frame-Continuous Girders Bridge Based on Response Surface Method

Using the static and dynamic test data simultaneously to update the finite element model can increase the available information for updating. It can overcome the disadvantages of updating based on static or dynamic test data only. In this paper, the response surface method is adopted to update the finite element model of the structure based on the static and dynamic test. Using the reasonable experiment design and regression techniques, a response surface model is formulated to approximate the relationships between the parameters and response values instead of the initial finite element model for further updating. First, a numerical example of a reinforced concrete simply supported beam is used to demonstrate the feasibility of this approach. Then, this approach is applied to update the finite element model of a prestressed reinforced concrete rigid frame-continuous girders bridge based on in-situ static and dynamic test data. Results show that this approach works well and achieve reasonable physical explanations for the updated parameters. The results from the updated model are in good agreement with the results from the in-situ measurement. The updated finite element model can accurately represent mechanical properties of the bridge and it can serve as a benchmark model for further damage detection and condition assessment of the bridge.

Eigenstrain modelling of residual stress generated by arrays of laser shock peening shots and determination of the complete stress field using limited strain measurements

This paper presents a hybrid explicit finite element (FE)/eigenstrain model for predicting the residual stress generated by arrays of adjacent/overlapping laser shock peening (LSP) shots where the use of a completely explicit FE analysis may be impractical. It shows that for a given material, the underlying eigenstrain distribution (in contrast to the resulting stress field) representing a laser shock peen is primarily dependent on the parameters of the laser pulse and the number of overlays rather than the precise component geometry. Consequently the residual stress introduced by complex laser peening treatments can be built up by using static FE models and superposition of individual eigenstrain distributions without recourse to further computationally demanding explicit FE analyses. It is found that beneath a small LSP array the magnitude of the compressive residual stress is higher than for a wider array of LSP shots and that with increasing numbers of layers the compressive stress increases as does the depth of the compressive zone. The model predictions for the eigenstrain distributions are compared well with experimental measurements of plastic strain (full-width-at-half-maximum) obtained by neutron diffraction. The eigenstrain method is also extended to construct the full residual stress field using measured residual elastic strains at a finite number of measurement locations in a component.

Finite element analysis of magnetostrictive vibration energy harvester

PurposeThe paper aims to analyze the behavior of the Galfenol rods under bending conditions that are employed in a vibration energy harvester by illustrating the spatial variations in stress and magnetic field.Design/methodology/approachThis paper describes a 3‐D static finite element model of magnetostrictive materials, considering magnetic and elastic boundary value problems that are bidirectionally coupled through stress and field dependent variables. The finite element method is applied to a small vibration‐driven generator of magnetostrictive type employing Iron‐Gallium alloy (Galfenol).FindingsThe 3‐D static finite element modeling presented here highlights the spatial variations in magnetic field and relative permeability due to the corresponding stress distribution in the Galfenol rods subjected to transverse load. The numerical calculations show that about 1.1 T change in magnetic flux density is achieved which demonstrates the effectiveness of the inspected vibration‐driven generator in voltage generation and energy harvesting. The model predictions agree with the experimental results and are coherent with the magnetostriction phenomenon.Originality/valueThis paper fulfils the behavior analysis of Galfenol rods under transverse load that includes both compression and tension. The compressive and tensile stresses contributions to change in magnetic flux densities in the Galfenol rods were calculated by which the effectiveness of the inspected vibration‐driven generator in voltage generation and energy harvesting is demonstrated.

Static Finite Element Model Updating for Special-Shaped Bridge Based on Response Surface Method

The establishment of an effective finite element model for bridge structure is essential in the health monitoring system for Bridge. A new updating method for static model using response surface method is proposed in this paper, and the main procedures are given with an example of a special-shaped bridge. Firstly, the bridge deflection and strain data in designed load case are obtained. Several groups of combined parameters which are chosen based on the principle of uniform design method are selected to conduct calculation through finite element software. Finally through response surface fitting and optimization, the updated bridge finite element model is obtained. The results show that the updated model is approximate to the real bridge and this updating method is rational and practical.

Modeling and design of magnetostrictive vibration‐powered generator using finite element method

ABSTRACTThis work investigates the design of a vibration‐powered generator with one rod (unimorph) of iron–gallium (galfenol) and compares it with its two‐rod (bimorph) counterpart. Galfenol is a promising magnetostrictive material that combines high magnetic susceptibility and desirable mechanical properties and therefore very suitable for harvesting the vibration energy that involves bending stresses. In this study, an energy‐based magnetoelastic model, so‐called Armstrong model, is employed to predict the behavior of galfenol under multiaxial stresses. The Armstrong model of galfenol is implemented into a static 3D finite element model of the energy harvester by which the performances of the devices are predicted and experimentally observed. Copyright © 2012 John Wiley & Sons, Ltd.

Simulation of the vertical bending fatigue test of a five-link rear axle housing

This study seeks a practical method for simulating the vertical bending fatigue test of the BANJO housing of a five-link rear axle. Linear static and transient dynamic finite element models are constructed for the rear axle in which the rubber bushings and the bearings of the axle shafts are reasonably modeled with solid and shell elements, respectively, for simplicity. The calculated results are compared with the measured strain histories, and the results indicate that the finite element models constructed are reasonable. The hypothesis of equal fatigue damage is applied to determine the Hainan proving ground driving life prediction that is equivalent to the constant amplitude fatigue life in the vertical bending fatigue test.

Study on Fatigue Characteristic of Double Block Ballastless Track under Coupling Loads

Regarding double block ballastless track as research subject, three mechanical models were established, which include steel bar and concrete interaction mechanical model, spatial finite element static model of double block ballastless track, train-double block ballastless track vertical coupling dynamics model. According to concrete and steel bar stress time-dependant curves under axial even temperature and shrinkage load, temperature grads load and train load, fatigue load spectrum under coupling loads was obtained by using rain-flow counting method. Based on steel bar and concrete S-N curve, and Palmgren-Miner linear fatigue damage accumulation rule, track concrete layer fatigue life predicting model of double block ballastless track was established. Taking Changsha climatic condition for an example, the fatigue life of double block ballastless track is predicted, and the effects of design parameters to fatigue life are analyzed.

Curved Girder Deformation Prediction Effectiveness Using First-Order, Linear Geometric Finite-Element Models

This study examines whether a first-order, linear geometric finite-element static model analysis is capable of accurately predicting the deflection and rotation response of a curved steel I-girder bridge and curved steel I-girders. Girder deflections obtained during the erection of a horizontally-curved steel I-girder bridge and deflection and rotation data from curved-beam laboratory tests were used to determine if a linear geometric finite-element analysis could accurately predict their static behavior. Results indicate that the first-order, linear geometric finite-element model accurately predicts the deflection behavior of a horizontally-curved steel I-girder bridge and a curved steel I-girder beam tested under point loads. The results also indicate that the first-order, linear geometric finite-element model predicted the general rotation trends of the experimental beam accurately. However, the model overpredicted peak flange-tip displacements when compared with the experimental results.

Study and Application of Bridge Structure Finite Element Model Updating Based on Static-Load Testing

A method for continuous box-girder bridge structure finite element (FE) model updating based on static-load testing is proposed. The procedure includes field static-load testing, FE modeling, FE model (parameter) updating, etc. Based on this procedure, the structure FE model updating for an expressway 5-span pre-stressed concrete continuous box-girder bridge is conducted. And the bridge structure static FE model, which is consistent with the static-load testing actual measure response, is gained. The updated FE model (parameter) is foundation of structural performance evaluation for the bridge.

Eigenstrain modelling of residual stresses generated by laser shock peening

This paper presents an eigenstrain (misfit strain) model of the residual stresses generated by laser shock peening (LSP). The shock wave is first modelled as a dynamic pressure load in an explicit finite element (FE) model and the stabilised plastic strain distribution is extracted. This strain distribution is then incorporated as an eigenstrain distribution in a static FE model and the residual stresses generated by the original shock wave are obtained as the elastic response to the eigenstrain. In order to focus on the basic mechanics, an elastic-perfectly plastic material model is assumed. Similarly, a simplified pressure/time variation (a triangular ramp with the peak pressure occurring at the half the total pulse duration) is assumed in order to characterise the pressure pulse. The peak pressure and the duration of the pressure pulse are determined in a way that they are consistent with experimental results. The analysis is extended to study the case of multiple pulses and the results show that the process generates compression in a surface layer of about 1.5–2mm deep. Furthermore, the results demonstrate that the magnitudes of subsurface tensile stresses are of the order of one fifth of the material's yield strength for typical peening conditions.