scholarly journals Finite Element Modeling of Magnitude and Location of Brain Micromotion Induced Strain for Intracortical Implants

2022 ◽  
Vol 15 ◽  
Author(s):  
Ali Al Abed ◽  
Jason Amatoury ◽  
Massoud Khraiche
Keyword(s):  
Finite Element ◽  
Polyvinyl Acetate ◽  
Tissue Injury ◽  
High Stress ◽  
Element Model ◽  
Neural Population ◽  
Order Of Magnitude ◽  
Tissue Interface ◽  
Main Determinants ◽  
Cortical Implants

Micromotion-induced stress remains one of the main determinants of life of intracortical implants. This is due to high stress leading to tissue injury, which in turn leads to an immune response coupled with a significant reduction in the nearby neural population and subsequent isolation of the implant. In this work, we develop a finite element model of the intracortical probe-tissue interface to study the effect of implant micromotion, implant thickness, and material properties on the strain levels induced in brain tissue. Our results showed that for stiff implants, the strain magnitude is dependent on the magnitude of the motion, where a micromotion increase from 1 to 10 μm induced an increase in the strain by an order of magnitude. For higher displacement over 10 μm, the change in the strain was relatively smaller. We also showed that displacement magnitude has no impact on the location of maximum strain and addressed the conflicting results in the literature. Further, we explored the effect of different probe materials [i.e., silicon, polyimide (PI), and polyvinyl acetate nanocomposite (PVAc-NC)] on the magnitude, location, and distribution of strain. Finally, we showed that strain distribution across cortical implants was in line with published results on the size of the typical glial response to the neural probe, further reaffirming that strain can be a precursor to the glial response.

Quantify Resonance Inspection With Finite-Element-Based Modal Analyses

2010 ◽  
Author(s):  
K. Lai ◽  
X. Sun ◽  
C. Dasch
Keyword(s):  
Finite Element ◽  
High Stress ◽  
Mesh Size ◽  
Element Model ◽  
Sensitivity Study ◽  
Production Level ◽  
Mode Shapes ◽  
Resonance Spectroscopy ◽  
Frequency Spectra ◽  
Resonance Frequencies

Resonance inspection uses the natural acoustic resonances of a part to identify anomalous parts. Modern instrumentation can measure the many resonant frequencies rapidly and accurately. Sophisticated sorting algorithms trained on sets of good and anomalous parts can rapidly and reliably inspect and sort parts. This paper aims at using finite-element-based modal analysis to put resonance inspection on a more quantitative basis. A production-level automotive steering knuckle is used as the example part for our study. First, the resonance frequency spectra for the knuckle are measured with two different experimental techniques. Next, scanning laser vibrometry is used to determine the mode shape corresponding to each resonance. The material properties including anisotropy are next measured to high accuracy using resonance spectroscopy on cuboids cut from the part. Then, finite element model (FEM) of the knuckle is generated by meshing the actual part geometry obtained with computed tomography (CT). The resonance frequencies and mode shapes are next predicted with a natural frequency extraction analysis after extensive mesh size sensitivity study. The good comparison between the predicted and the experimentally measured resonance spectra indicate that finite-element-based modal analyses have the potential to be a powerful tool in shortening the training process and improving the accuracy of the resonance inspection process for a complex, production level part. The finite element based analysis can also provide a means to computationally test the sensitivity of the frequencies to various possible defects such as porosity or oxide inclusions especially in the high stress regions that the part will experience in service.

Ultimate Strength Assessment of Semi-Submersible Platform Under Different Load Conditions

2017 ◽  
Author(s):  
Yangzhe Yu ◽  
Guoqing Feng ◽  
Huilong Ren
Keyword(s):  
Finite Element ◽  
Ultimate Strength ◽  
High Stress ◽  
Initial Imperfection ◽  
Element Model ◽  
Nonlinear Finite Element ◽  
Main Bearing ◽  
Strength Assessment ◽  
Hull Structure ◽  
Load Conditions

The nonlinear finite-element method has been widely used in evaluating the ultimate strength of stiffened plates and part of hull girders, considering the effect of boundary conditions, geometrical initial imperfection and welding-induced residual stress in recent years. However, available research on the ultimate strength of large-sized structures, especially of semi-submersible platform is limited. New large-sized semi-submersible platform has been designed with lateral brace structure and square cross-section columns. The investigation of ultimate strength of the whole structure is of paramount importance in assessing the safety and design of such large structure. Therefore, in this paper, a three-dimensional nonlinear finite element model was developed to investigate the ultimate strength of a new generation of semi-submersible platform under different load conditions and its behavior after collapse using explicit dynamic solvers. Results showed that the time dependent dynamic explicit method was reliable and feasible for the calculation of ultimate strength of such complicated structure. For the target platform, the bracings and upper hull structure were the main bearing component and were critical for the ultimate strength of the whole structure. High stress occurred in connection areas and special attention shall be paid for.

Quick Aeromechanical Assessment of Turbine Blades Based on Shell Element Based Models

2014 ◽  
Author(s):  
Suryarghya Chakrabarti ◽  
Letian Wang ◽  
K. M. K. Genghis Khan
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Natural Frequencies ◽  
Turbine Blades ◽  
Computation Time ◽  
Shell Element ◽  
Element Model ◽  
Shell Elements ◽  
Barrier Coating ◽  
Order Of Magnitude

A fast finite element model based tool has been developed to calculate the natural frequencies of fundamental modes of cooled gas turbine bladed disk assemblies during conceptual design. The tool uses shell elements to model the airfoil, shank, and disk, and achieves order of magnitude reduction in computation time allowing exploration of a wide design space at the preliminary design stages. The analysis includes prestress effects due to centrifugal loading and approximate temperature loading on the parts. Sensitivity studies are performed to understand the relative impact of design features such as airfoil internal geometry, bond coat, and thermal barrier coating on the system natural frequencies. Critical features are selected which need to be modeled to get an accurate natural frequency estimate. The results obtained are shown to be within 5% of the frequencies obtained from a full-fidelity finite element model. A case study performed on seven blade designs illustrates the use of this tool for quick aeromechanical assessment of a large number of designs.

The Role of Fluid Dynamics in Distributing Ankle Stresses in Anatomic and Injured States

2016 ◽  
Vol 37 (12) ◽  
pp. 1343-1349 ◽  
Author(s):  
Kamran S. Hamid ◽  
Aaron T. Scott ◽  
Benedict U. Nwachukwu ◽  
Kerry A. Danelson
Keyword(s):  
Finite Element ◽  
Synovial Fluid ◽  
Principal Stress ◽  
Maximum Stress ◽  
High Stress ◽  
Distal Tibia ◽  
Element Model ◽  
Maximum Principal Stress ◽  
Ankle Injuries ◽  
Element Analysis

Background: In 1976, Ramsey and Hamilton published a landmark cadaveric study demonstrating a dramatic 42% decrease in tibiotalar contact area with only 1 mm of lateral talar shift. An increase in maximum principal stress of at least 72% is predicted based on these findings though the delayed development of arthritis in minimally misaligned ankles does not appear to be commensurate with the results found in dry cadaveric models. We hypothesized that synovial fluid could be a previously unrecognized factor that contributes significantly to stress distribution in the tibiotalar joint in anatomic and injured states. Methods: As it is not possible to directly measure contact stresses with and without fluid in a cadaveric model, finite element analysis (FEA) was employed for this study. FEA is a modeling technique used to calculate stresses in complex geometric structures by dividing them into small, simple components called elements. Four test configurations were investigated using a finite element model (FEM): baseline ankle alignment, 1 mm laterally translated talus and fibula, and the previous 2 bone orientations with fluid added. The FEM selected for this study was the Global Human Body Models Consortium–owned GHBMC model, M50 version 4.2, a model of an average-sized male (distributed by Elemance, LLC, Winston-Salem, NC). The ankle was loaded at the proximal tibia with a distributed load equal to the GHBMC body weight, and the maximum principal stress was computed. Results: All numerical simulations were stable and completed with no errors. In the baseline anatomic configuration, the addition of fluid between the tibia, fibula, and talus reduced the maximum principal stress computed in the distal tibia at maximum load from 31.3 N/mm2 to 11.5 N/mm2. Following 1 mm lateral translation of the talus and fibula, there was a modest 30% increase in the maximum stress in fluid cases. Qualitatively, translation created less high stress locations on the tibial plafond when fluid was incorporated into the model. Conclusions: The findings in this study demonstrate a meaningful role for synovial fluid in distributing stresses within the ankle that has not been considered in historical dry cadaveric studies. The increase in maximum stress predicted by simulation of an ankle with fluid was less than half that projected by cadaveric data, indicating a protective effect of fluid in the injured state. The trends demonstrated by these simulations suggest that bony alignment and fluid in the ankle joint change loading patterns on the tibia and should be accounted for in future experiments. Clinical Relevance: Synovial fluid may play a protective role in ankle injuries, thus delaying the onset of arthritis. Reactive joint effusions may also function to additionally redistribute stresses with higher volumes of viscous fluid.

Transient Thermal Analysis and Viscoplastic Damage Model for Life Prediction of Turbine Components

2014 ◽  
Vol 137 (4) ◽  
Author(s):  
A. Staroselsky ◽  
T. J. Martin ◽  
B. Cassenti
Keyword(s):  
Finite Element ◽  
Life Prediction ◽  
Failure Modes ◽  
Damage Model ◽  
High Stress ◽  
Three Dimensional ◽  
Element Model ◽  
Dissipated Energy ◽  
Transient Thermal ◽  
Turbine Airfoils

This paper reports the process and computer methodology for a physics-based prediction of overall deformation and local failure modes in cooled turbine airfoils, blade outer air seals, and other turbomachinery parts operating in severe high temperature and high stress environments. The computational analysis work incorporated time-accurate, coupled aerothermal computational fluid dynamics (CFD) with nonlinear deformation thermal-structural finite element model (FEM) with a slip-based constitutive model, evaluated at real engine characteristic mission times, and flight points for part life prediction. The methodology utilizes a fully coupled elastic-viscoplastic model that was based on crystal morphology, and a semi-empirical life prediction model introduced the use of dissipated energy to estimate the remaining part life in terms of cycles to failure. The method was effective for use with three-dimensional FEMs of realistic turbine airfoils using commercial finite element applications. The computationally predicted part life was calibrated and verified against test data for deformation and crack growth.

scholarly journals Effectiveness of Selected Fitness Exercises on Stress of Femoral Neck using Musculoskeletal Dynamics Simulations and Finite Element Model

2014 ◽  
Vol 41 (1) ◽  
pp. 59-70 ◽  
Author(s):  
Jing-Guang Qian ◽  
Zhaoxia Li ◽  
Hong Zhang ◽  
Rong Bian ◽  
Songning Zhang
Keyword(s):  
Finite Element ◽  
Femoral Neck ◽  
Finite Element Model ◽  
High Stress ◽  
Gluteus Maximus ◽  
Neck Region ◽  
Peak Stress ◽  
Element Model ◽  
Dynamics Model ◽  
Simple Method

AbstractThe purpose of the study was to establish a dynamics model and a three-dimensional (3D) finite element model to analyze loading characteristics of femoral neck during walking, squat, single-leg standing, and forward and lateral lunges. One male volunteer performed three trials of the five movements. The 3D kinematic data were captured and imported into the LifeMOD to establish a musculoskeletal dynamics model to obtain joint reaction and muscle forces of iliacus, gluteus medius, gluteus maximus, psoas major and adductor magnus. The loading data LfeMOD were imported and transformed into a hip finite-element model. The results of the finite element femur model showed that stress was localized along the compression arc and the tension arc. In addition, the trabecular bone and tension lines of the Ward's triangle also demonstrated high stress. The compact bone received the greatest peak stress in the forward lunge and the least stress in the squat. However, the spongy bone in the femoral neck region had the greatest stress during the walk and the least stress in the squat. The results from this study indicate that the forward lunge may be an effective method to prevent femoral neck fractures. Walking is another effective and simple method that may improve bone mass of the Ward's triangle and prevent osteoporosis and femoral neck fracture.

scholarly journals Models for strain localization in Law Dome, Antarctica

1996 ◽  
Vol 23 ◽  
pp. 396-401 ◽  
Author(s):  
R. J. M. Rowden-Rich ◽  
C. J. L. Wilson
Keyword(s):  
Finite Element ◽  
Shear Stress ◽  
Strain Localization ◽  
High Stress ◽  
Element Model ◽  
Ice Flow ◽  
Progressive Development ◽  
Bedrock Topography ◽  
Ice Cap ◽  
Marked Oscillation

A finite-element model was implemented that relates the computed flow to some field and fabric observations recorded on the Law Dome ice cap, East Antarctica. The results of the model suggest that the general ice flow is markedly affected by the bedrock topography. The zones of measured anomalous flow correlate with significant changes in the modelled stress within the ice mass. Stress increases of up to 50% above the reduced model shear stress were obtained in the models where the ice moved over a bedrock rise. Stress relaxation also occurs in the ice mass as the ice moves downward to a lee depression. There is a marked oscillation in the direction of principal stress and this is responsible for the progressive development of a set of high stress zones that are superimposed on the down-slope ice movement.

Fatigue Life Investigation of a High Pressure Inner Casing Under In-Service Conditions

2016 ◽  
Author(s):  
Hui Hong ◽  
Weizhe Wang ◽  
Zhenwei Cai
Keyword(s):  
Finite Element ◽  
High Pressure ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
High Stress ◽  
Element Model ◽  
Steam Pressure ◽  
Strain Behavior ◽  
Service Conditions ◽  
High Stress Level

The fatigue life of a specific inner casing of an ultra-supercritical steam turbine was investigated under a half year in-service conditions. The Ramberg-Osgood model and Manson-Coffin-Basquin strain-life equation were used to describe the stress-strain behavior and calculate the fatigue damage. A temperature comparison was performed to validate the reliability of finite element model. The results showed that fluctuating steam pressure rather than temperature had more significant effect on the variation of stress in the casing. Locations with high stress level were prone to cause larger fatigue damage. Statistical analysis was carried out to reveal that over half fluctuations of steam pressure could cause damage.

scholarly journals Finite Element Model for Analysis of the Spatial Interfacial Debonding of FRP from Concrete

2017 ◽  
Vol 26 (3) ◽  
pp. 096369351702600
Author(s):  
Feng Zhang ◽  
Lei Gao
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Finite Element Model ◽  
Plate Thickness ◽  
High Stress ◽  
Element Model ◽  
Horizontal Stress ◽  
Interfacial Debonding ◽  
Plate Edge ◽  
Free Region

The debonding of the FRP plate from concrete and crack-propagation processes are complex and the current research studies regarding this debonding mechanism are insufficient and not comprehensive. This work proposes a plane stress model along with equal width and different width FRP to concrete models to simulate the debonding and crack-propagation processes are presented. The longitudinal and horizontal stress distributions were analysed and the FRP to concrete width effect and FRP thickness parameters were also studied by means of the proposed three-dimensional finite element model. The results show that the different width 3D model is optimal for analysing the spatial interfacial debonding of FRP from concrete. The concrete surface horizontal stress distribution along the length of the concrete substrate could judge the effective bond length. Both the normal stress and shear stress are mainly divided into the following two small central stress regions under the PRP plate: a high stress gradient region near the FRP plate edge and a stress-free region near the concrete edge. The debonding strength and the stiffness of the bonding interface increase with the width of the FRP plate and the FRP plate thickness. The stress range and magnitude are strongly dependent on the width of the FRP plate. Debonding begins at the FRP plate edge; the thicker FRP plate more easily exhibits debonding.

Finite element analysis of stress around a sternum screw used to prevent sternal dehiscence after heart surgery

2002 ◽  
Vol 216 (5) ◽  
pp. 315-321 ◽  
Author(s):  
R S Jutley ◽  
M A Watson ◽  
D E T Shepherd ◽  
D W L Hukins
Keyword(s):  
Finite Element ◽  
Contact Stress ◽  
Heart Surgery ◽  
High Stress ◽  
Median Sternotomy ◽  
Element Model ◽  
Element Analysis ◽  
Sternal Dehiscence ◽  
Cortical Shell ◽  
The Wire

The sternum screw has been proposed as a means of preventing sternal dehiscence, following heart surgery, by increasing the contact area between the wire used to close the median sternotomy and the surrounding bone; as a result, the contact stress is reduced. A finite element model was constructed of a cylindrical wire or screw passing through a block of sternum which consisted of cancellous bone sandwiched within a cortical shell. The thickness of the cortical shell and the material properties of bone were varied between reasonable values. The stress distribution in the sternum was calculated for each model when the wire was subjected to a tension (250 N) which would be required for six wires to withstand a strong cough (40kPa). Results were validated by comparison with a simple analytical model in which the bone and wire were considered incompressible. They show that the screw reduces the contact stress to almost one-seventh of its value when wire is used alone. Contact stresses are especially high if the cortical shell is thin. The high stress in the bone around a screw falls off within a few millimetres. As a result, no problems are anticipated in placing six screws in each half-sternum so that the sternotomy may be closed with the usual six wires.

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