Finite Element Model Predictions Research Articles

The role of electrical anisotropy and effective conducting thickness in understanding and interpreting static resistance measurements in CFRP composite laminates

This study is focused on (i) the experimental characterization of the anisotropic electrical resistivity of carbon fiber reinforced polymer (CFRP) composites and (ii) the development and experimental validation of predictive finite element (FE) models of the electrical response in CFRP laminates based on the concept of the effective conducting thickness. Two experimental methods have been developed to characterize the anisotropic electrical resistivities in three principle directions for the CFRP composite laminates using a direct current source. One method utilizes a traditional 6-probe resistance scheme and the alternative point-type 4-probe method is based on a handheld probe device similar to the JIS K7194 standard for homogenous plastics. An extensive experimental study has been conducted to characterize the anisotropic electrical resistivities of 16-ply unidirectional and 16-ply symmetric cross-ply IM7/977-2 and 32-ply unidirectional IM7/977-3 composites using the developed methods. Exploiting the concept of the effective conducting thickness, which describes the effective depth of current penetration through the thickness of an electrically anisotropic material, a unique methodology is developed for constructing FE models of these highly anisotropic CFRP materials. The concept of effective conducting thickness was identified as a critical component in achieving accuracy of the FE results as well as recovery of experimental resistivity from the alternative point-type 4-probe method. The FE models have been validated using the experimental results on the CFRP specimens of varying layup and thickness, and the techniques developed in this work may lead to advancements in non-destructive techniques in the areas of electrical characterization and damage sensing.

S15-02 SESSION 15: PLANNING/IMAGING - PART I DEVELOPMENT OF BONE CUTTING INSTRUMENTATION IN THE APPLICATION OF ROBOTIC ASSISTED CRANIOSYNOSTOSIS SURGERY USING THE DA VINCI PLATFORM.

Introduction: The aim of this project was to develop a bone cutting tool for the da Vinci robotic platform with application in craniofacial procedures for the correction of craniosynostosis with advantages of enhanced surgeon ergonomics, improved bone cutting precision, visualization and minimal access surgery. Methods: In order to assess the feasibility of a robotic-assisted approach, a custom ultrasonic tool was developed to address the unique challenges of accessing the required cut locations on the skull using the remote-center-of-motion configuration of the da Vinci Si system. To address these limitations, new blade geometry was developed to allow for cutting at any angle of attack using a genetic shape optimization algorithm in finite element software. The tool was also designed to maximize length and minimize diameter to be suitable for minimally invasive access. Over 200 iterations of blade design, with cutting up to 4 mm and a 0.5 mm kerf were assessed. The error between finite element model predictions and testing averaged 1% (for prediction of shape and location of modal shapes). Results: A custom ultrasonic tool was developed to address the unique challenges of accessing the required cut locations on the skull using the remote-center-of-motion configuration of the da Vinci Si system. A key advantage of the da Vinci system are the highly dexterous wristed instruments; however, it is infeasible to develop a wristed ultrasonic tool due to high cycles and stresses. To address these limitations, new blade geometry was developed to allow for cutting at any angle of attack using a genetic shape optimization algorithm in finite element software. The tool was also designed to maximize length and minimize diameter to be suitable for minimally invasive access. Over 200 iterations of blade design, with cutting up to 4 mm and a 0.5 mm kerf were assessed. The error between finite element model predictions and testing averaged 1% (for prediction of shape and location of modal shapes). Bone substitute and animal bone were used for testing. 6 cuts total each cut 40 mm in length, 3 mm in depth (3 cuts using Bonesaw sample PCF40, 3 cuts using Bonesaw sample PCF50, Bonesaw samples: PCF40 (0.64 g/cc) and PCF50 (0.80 g/cc) were made and analyzed for time per cut (cutting speed), forces on sample (ATI Gamma), cutting motion/method (video recorded) and soft tissue damage (silicon pad). Data to be presented. Conclusion: Preliminary work has demonstrated an effective blade design that is amenable to application in bone cutting using piezo-electric technology using the da Vinci Si platform. Application in a simulated model for endoscopic strip craniectomy will be presented.

Spontaneous cellular vibratory motions of osteocytes are regulated by ATP and spectrin network

Vibration at high frequency has been demonstrated to be anabolic for bone and embedded osteocytes. The response of osteocytes to vibration is frequency-dependent, but the mechanism remains unclear. Our previous computational study using an osteocyte finite element model has predicted a resonance effect involving in the frequency-dependent response of osteocytes to vibration. However, the cellular spontaneous vibratory motion of osteocytes has not been confirmed. In the present study, the cellular vibratory motions (CVM) of osteocytes were recorded by a custom-built digital holographic microscopy and quantitatively analyzed. The roles of ATP and spectrin network in the CVM of osteocytes were studied. Results showed the MLO-Y4 osteocytes displayed dynamic vibratory motions with an amplitude of ~80 nm, which is relied both on the ATP content and spectrin network. Spectrum analysis showed several frequency peaks in CVM of MLO-Y4 osteocytes at 30 Hz, 39 Hz, 83 Hz and 89 Hz. These peak frequencies are close to the commonly used effective frequencies in animal training and in-vitro cell experiments, and show a correlation with the computational predictions of the osteocyte finite element model. These results implicate that osteocytes are dynamic and the cellular dynamic motion is involved in the cellular mechanotransduction of vibration.

Thermal simulation and phase modeling of bulk metallic glass in the powder bed fusion process

One of the major challenges with the powder bed fusion process (PBF) and formation of bulk metallic glass (BMG) is the development of process parameters for a stable process and a defect-free component. The focus of this study is to predict formation of a crystalline phase in the glass forming alloy AMZ4 during PBF. The approach combines a thermal finite element model for prediction of the temperature field and a phase model for prediction of crystallization and devitrification. The challenge to simulate the complexity of the heat source has been addressed by utilizing temporal reduction in a layer-by-layer fashion by a simplified heat source model. The heat source model considers the laser power, penetration depth and hatch spacing and is represented by a volumetric heat density equation in one dimension. The phase model is developed and calibrated to DSC measurements at varying heating rates. It can predict the formation of crystalline phase during the non-isothermal process. Results indicate that a critical location for devitrification is located a few layers beneath the top surface. The peak is four layers down where the crystalline volume fraction reaches 4.8% when 50 layers are built.

Prediction of failure stages for double lap joints using finite element analysis and artificial neural networks

Abstract Prediction of failure stages of double lap bolted joints is an important task for design. Finite element (FE) and artificial neural networks (ANNs) methods are widely used in such tasks to reduce time, money, and efforts consumed in laboratory experiments. Three dimension elastic-plastic FE analysis was adopted to simulate the failure stages of double lap joint in the present work. After completing mesh sensitivity analysis for the present FE model, only nine experiments were conducted to verify the prediction of the present FE model. Taguchi technique was applied to reduce the number of loading cases (different joint geometry and tightening torque) from one hundred twenty five cases of loadings to only twenty seven cases of loadings. The FE results of twenty seven cases of loadings were accomplished to provide the training set of ANNs. Finally, a comparison between the results obtained from FE and ANNs was made. Results indicated that, either FE or ANNs can highly predict the failure stages of double lap bolted joints for different e/D, w/D, and tightening torque values. Therefore, FE and ANNs methods may be considered good candidates to predict the mechanical behavior and failure mode of such joint.

Optimization of corner micro end milling by finite element modelling for machining thin features

Manufacturing thin metal features at miniature scale with high precision milling represents some challenges for different applications such as micro moulds, micro channels, micro gears, surgical instruments, etc. In order to enhance the cutting mechanism understanding and optimize the machining of thin features, 3D finite element modeling (FEM) is applied for the micro end-milling process of thin features. In this study, FE model was used to investigate the minimum wall thickness machinable in order to optimize the experimental machining and enhance the quality of the machined features. Wall thickness uniformity and burr formation were evaluated to achieve the finest overall feature quality. Finally, the FEM prediction results were compared against the experimental tests.

Development and Validation of 3D Finite Element Models for Prediction of Orthodontic Tooth Movement.

Objectives The aim of this study was to develop and validate three-dimensional (3D) finite element modeling for prediction of orthodontic tooth movement. Materials and Methods Two orthodontic patients were enrolled in this study. Computed tomography (CT) was captured 2 times. The first time was at T0 immediately before canine retraction. The second time was at T4 precisely at 4 months after canine retraction. Alginate impressions were taken at 1 month intervals (T0–T4) and scanned using a digital scanner. CT data and scanned models were used to construct 3D models. The two measured parameters were clinical tooth movement and calculated stress at three points on the canine root. The calculated stress was determined by the finite element method (FEM). The clinical tooth movement was measured from the differences in the measurement points on the superimposed model. Data from the first patient were used to analyze the tooth movement pattern and develop a mathematical formula for the second patient. Calculated orthodontic tooth movement of the second patient was compared to the clinical outcome. Results Differences between the calculated tooth movement and clinical tooth movement ranged from 0.003 to 0.085 mm or 0.36 to 8.96%. The calculated tooth movement and clinical tooth movement at all reference points of all time periods appeared at a similar level. Differences between the calculated and clinical tooth movements were less than 0.1 mm. Conclusion Three-dimensional FEM simulation of orthodontic tooth movement was achieved by combining data from the CT and digital model. The outcome of the tooth movement obtained from FEM was found to be similar to the actual clinical tooth movement.

Energy dissipation characteristics of polyurea and polyurea/carbon black composites

The energy dissipation characteristics of polyurea and polyurea/carbon black composites are determined under cycling loading at different amplitudes and excitation frequencies. These characteristics are measured experimentally and validated against the predictions of finite element models (FEM). Further validation of the energy dissipated is carried out by comparisons with the product of the storage modulus and the loss factor of the polymer as obtained from the measurement of the complex moduli using the Dynamic Mechanical Thermal Analyzer (DMTA). The obtained results indicate an excellent agreement between the experiments and the predictions of the FEM. Furthermore, it is observed that the energy dissipated per unit volume of pristine polyurea is, on average, about 10% higher than that of polyurea/carbon black composites.

Numerical tools to investigate mechanical and fatigue properties of additively manufactured MS1-H13 hybrid steels

Additive manufacturing (AM) has been recently used to deposit metal powder on top of conventional metals. Of particular interest is hybrid additively manufactured steels which were found to be a suitable solution to benefit from features of each metal at different spots of a mechanical component. Due to its superior mechanical characteristics, maraging steel (MS1) has recently attracted tremendous attention for additive manufacturing applications mainly in aerospace, tool and die, and marine industries or to be 3D printed on top of other metals as a hybrid product using different techniques such as Direct Metal Laser Sintering (DMLS). In this paper a predictive finite element (FE) model and a combined analytical-numerical framework were developed to evaluate the mechanical performance of hybrid additively manufactured components and facilitate the prediction of hardness and fatigue life of these parts. The proposed tools were employed in two scopes: First to simulate the indentation hardness test of hybrid DMLS-MS1-H13 steels; and second to calculate fatigue crack nucleation life of maraging steel including defects (i.e. welding residual stresses). Parameters such as local and global displacements, changes in Young’s modulus, and hardness, high cycle fatigue life, welding temperature distribution, and residual stress were investigated. The hardness experiments were carried out to improve the reported data found in similar studies, which were used as the main resource to validate the proposed numerical framework. The capabilities of the presented frameworks enable this work to target existing ambiguities in additively manufactured mechanical components.

Numerical investigation of non-linear equivalent-frame models for regular masonry walls

The accuracy of the Equivalent Frame Method (EFM) in modelling the seismic non-linear behaviour of unreinforced masonry (URM) buildings is investigated for regular walls (i.e. walls with regular openings’ distribution) with different pier-to-spandrel geometrical relations. The developed EFM is composed of pier and spandrel elements with spread plasticity to simulate the flexural behaviour and lumped plasticity to simulate the shear behaviour. The investigation focuses on checking, by means of comparison with Finite Element Model (FEM) assumed as reference, the applicability of EFM to existing buildings. These structures are often characterized by geometrical schemes difficult to be represented by ideal frames. To point out the role of the geometrical configuration, the numerical results provided by the two modelling approaches are compared for different representative cases of regular walls characterized by pier-spandrel configurations rather typical in existing URM buildings. In addition to the innovative EFM approach, based on a fiber discretized beam element, also a more traditional approach, based on beam elements with lumped plasticity, is included in the comparative study. The two different EFM approaches were implemented in the software Midas GEN © [44], while an open source software was used to implement the FEM (Kratos Multiphysics [59–60]). All the models were used to perform static non-linear analyses under equivalent loading and boundary conditions.The evaluation of EFM and FEM is derived from a comparative simulation of a two-storey URM wall experimentally tested by other researchers. Two alternative approaches are assumed for the definition of piers’ effective heights in the EFM, i.e. the models proposed by Dolce [1] and Augenti [2]. The results demonstrate that remarkable differences may be detected in EFM and FEM predictions of the shear capacity and damage mechanisms as a function of pier-spandrel geometrical configurations. This result highlights the need for a cautious application of EFM to existing URM structures.

NiTi-Nb micro-trusses fabricated via extrusion-based 3D-printing of powders and transient-liquid-phase sintering

We present a novel additive manufacturing method for NiTi-Nb micro-trusses combining (i) extrusion-based 3D-printing of liquid inks containing NiTi and Nb powders, solvents, and a polymer binder into micro-trusses with 0/90° ABAB layers of parallel, ∼600 µm struts spaced 1 mm apart and (ii) subsequent heat-treatment to remove the binder and solvents, and then bond the NiTi powders using liquid phase sintering via the formation of a transient NiTi-Nb eutectic phase. We investigate the effects of Nb concentration (0, 1.5, 3.1, 6.7 at.% Nb) on the porosity, microstructure, and phase transformations of the printed NiTi-Nb micro-trusses. Micro-trusses with the highest Nb content exhibit long channels (from 3D-printing) and struts with smaller interconnected porosity (from partial sintering), resulting in overall porosities of ∼75% and low compressive stiffnesses of 1–1.6 GPa, similar to those of trabecular bone and in agreement with analytical and finite element modeling predictions. Diffusion of Nb into the NiTi particles from the bond regions results in a Ni-rich composition as the Nb replaces Ti atoms, leading to decreased martensite/austenite transformation temperatures. Adult human mesenchymal stem cells seeded on these micro-trusses showed excellent viability, proliferation, and extracellular matrix deposition over 14 days in culture. Statement of SignificanceNear-equiatomic NiTi micro-trusses are attractive for biomedical applications such as stents, actuators, and bone implants because of their combination of biocompatibility, low compressive stiffness, high surface area, and shape-memory or superelasticity. Extrusion-based 3D-printing of NiTi powder-based inks into micro-trusses is feasible, but the subsequent sintering of the powders into dense struts is unachievable due to low diffusivity, large particle size, and low packing density of the NiTi powders. We present a solution, whereby Nb powders are added to the NiTi inks, thus forming during sintering a eutectic NiTi-Nb liquid phase which bonds the solid NiTi powders and improves densification of the struts. This study investigates the microstructure, porosity, phase transformation behavior, compressive stiffness, and cytocompatibility of these printed NiTi-Nb micro-trusses.

Experimentally validated predictive finite element modeling of the V0-V100 probabilistic penetration response of a Kevlar fabric against a spherical projectile

This work presents the first fully validated and predictive finite element modeling framework to generate the probabilistic penetration response of an aramid woven fabric subjected to ballistic impact. This response is defined by a V0-V100 curve that describes the probability of complete fabric penetration as a function of projectile impact velocity. The exemplar case considered in this article comprises a single-layer, fully clamped, plain-weave Kevlar fabric impacted at the center by a 0.22 cal spherical steel projectile. The fabric finite element model comprises individually modeled three-dimensional warp and fill yarns and is validated against the experimental material microstructure. Sources of statistical variability including yarn strength and modulus, inter-yarn friction, and precise projectile impact location are mapped into the finite element model. A series of impact simulations at varying projectile impact velocities is executed using LS-DYNA on the fabric models, each comprising unique mappings. The impact velocities and outcomes (penetration, non-penetration) are used to generate the numerical V0-V100 curve which is then validated against the experimental V0-V100 curve obtained from ballistic impact testing and shown to be in excellent agreement. The experimental data and its statistical analysis used for model input and validation, namely, the Kevlar yarn tensile strengths and moduli, inter-yarn friction, and fabric ballistic impact testing, are also reported.

Outlier-Detection Methodology for Structural Identification Using Sparse Static Measurements.

The aim of structural identification is to provide accurate knowledge of the behaviour of existing structures. In most situations, finite-element models are updated using behaviour measurements and field observations. Error-domain model falsification (EDMF) is a multi-model approach that compares finite-element model predictions with sensor measurements while taking into account epistemic and stochastic uncertainties—including the systematic bias that is inherent in the assumptions behind structural models. Compared with alternative model-updating strategies such as residual minimization and traditional Bayesian methodologies, EDMF is easy-to-use for practising engineers and does not require precise knowledge of values for uncertainty correlations. However, wrong parameter identification and flawed extrapolation may result when undetected outliers occur in the dataset. Moreover, when datasets consist of a limited number of static measurements rather than continuous monitoring data, the existing signal-processing and statistics-based algorithms provide little support for outlier detection. This paper introduces a new model-population methodology for outlier detection that is based on the expected performance of the as-designed sensor network. Thus, suspicious measurements are identified even when few measurements, collected with a range of sensors, are available. The structural identification of a full-scale bridge in Exeter (UK) is used to demonstrate the applicability of the proposed methodology and to compare its performance with existing algorithms. The results show that outliers, capable of compromising EDMF accuracy, are detected. Moreover, a metric that separates the impact of powerful sensors from the effects of measurement outliers have been included in the framework. Finally, the impact of outlier occurrence on parameter identification and model extrapolation (for example, reserve capacity assessment) is evaluated.

Population-based structural identification for reserve-capacity assessment of existing bridges

Transportation networks provide an essential contribution to addressing the needs of reliable and safe mobility in urban environments. The core of these networks is made up of infrastructure such as roads and bridges that often, have not been designed to meet current needs. Optimal management requires an accurate knowledge of how existing structures behave. This helps avoid unnecessary replacement and expensive interventions when cheaper and more sustainable alternatives are available. Structural-model updating takes advantage of measurements and more qualitative observations to identify suitable behaviour model classes and values for parameters that influence real behaviour. Error domain model falsification (EDMF) has been proposed as a robust population-based methodology to identify sets of models by comparing finite-element model predictions with measurements at sensor locations. This paper introduces a methodology, which is compatible with EDMF, to assess the reserve capacity of bridges for serviceability and ultimate limit states. A case study—the structural identification of a reinforced-concrete bridge in Singapore—illustrates the framework developed for the estimation of reserve capacity. Several analyses with increasing levels of model detail using design and updated values of relevant parameters are presented. Traffic-load specifications of design-stage codes (British Code—1978) and current codes (Eurocodes) are compared. Results show that typical conservative practices carried out during design and construction have led to an as-built reserve capacity of 60%. A large proportion of the as-built reserve capacity has been exploited to accommodate dramatically increased values of traffic-load specifications that are provided by current Singapore codes which have caused a reduction in reserve capacity to 20%. Such a reduction may be less significant in countries where code specifications have not changed as much. Finally, it is shown that advanced methods of analysis and assessment are more suitable than design-stage approaches to quantify the reserve capacity.

Femoral fracture load and fracture pattern is accurately predicted using a gradient-enhanced quasi-brittle finite element model

Nonlinear finite element (FE) modeling can be a powerful tool for studying femoral fracture. However, there remains little consensus in the literature regarding the choice of material model and failure criterion. Quasi-brittle models recently have been used with some success, but spurious mesh sensitivity remains a concern. The purpose of this study was to implement and validate a new model using a custom finite element designed to mitigate mesh sensitivity problems. Six specimen-specific FE models of the proximal femur were generated from quantitative tomographic (qCT) scans of cadaveric specimens. Material properties were assigned a-priori based on average qCT intensities at element locations. Specimens were experimentally tested to failure in a stumbling load configuration, and the results were compared to FE model predictions. There was a strong linear relationship between FE predicted and experimentally measured fracture load (R2 = 0.79), and error was less than 14% over all cases. In all six specimens, surface damage was observed at sites predicted by the FE model. Comparison of qCT scans before and after experimental failure showed damage to underlying trabecular bone, also consistent with FE predictions. In summary, the model accurately predicted fracture load and pattern, and may be a powerful tool in future studies.

On the design of a MEMS piezoelectric accelerometer coupled to the middle ear as an implantable sensor for hearing devices

The presence of external elements is a major limitation of current hearing aids and cochlear implants, as they lead to discomfort and inconvenience. Totally implantable hearing devices have been proposed as a solution to mitigate these constraints, which has led to challenges in designing implantable sensors. This work presents a feasibility analysis of a MEMS piezoelectric accelerometer coupled to the ossicular chain as an alternative sensor. The main requirements of the sensor include small size, low internal noise, low power consumption, and large bandwidth. Different designs of MEMS piezoelectric accelerometers were modeled using Finite Element (FE) method, as well as optimized for high net charge sensitivity. The best design, a 2 × 2 mm2 annular configuration with a 500 nm thick Aluminum Nitride (AlN) layer was selected for fabrication. The prototype was characterized, and its charge sensitivity and spectral acceleration noise were found to be with good agreement to the FE model predictions. Weak coupling between a middle ear FE model and the prototype was considered, resulting in equivalent input noise (EIN) lower than 60 dB sound pressure level between 600 Hz and 10 kHz. These results are an encouraging proof of concept for the development of MEMS piezoelectric accelerometers as implantable sensors for hearing devices.

Analysis of the effect of different patologies on the sound transmission through the middle ear by means of a finite-element model

The middle ear is part of the human auditory system and its function is to transmit acoustical energy to the inner ear by means of mechanical vibrations. Finite-Element (FE) models of the human middle ear have been studied since 90s, making it possible to evaluate its dynamic behavior in different ways. In this work, an accurate FE model of the human middle ear is described and used for assessing the relationship between the reduction of sound transmission through the ossicular chain and hearing loss due to three different pathologies: tympanic membrane perforation, stapedial tendon ossification and stapes fracture. For these three pathologies, case studies from the literature with experimental hearing loss data are reviewed and clinical results are compared to the FE model predictions. In all cases a good relationship between sound transmission reduction predicted by the FE model and the hearing loss measured through audiometric tests were found. Results show that an accurate FE model of the human middle ear can be a powerful tool for clinical applications and research in otology, allowing to predict the effect of middle ear pathologies and to evaluate the results of corrective surgeries on hearing.

Battened Steel Columns with Semi-Continuous Base Plate Connections: Experimental Results vs. Theoretical Predictions

The paper describes a comparison of experimental results and theoretical predictions regarding the lateral force-displacement response of built-up battened steel columns including semi-rigid and partial-strength base plate connections. Two specimens, representing samples of columns extracted from an existing industrial building, were fabricated and tested. Different types of both the battens and the base-plate connections characterized the two specimens. Preliminary lateral-loading tests in a range of elastic response, under varying levels of the concomitant axial force, allowed both exploring initial (elastic) stiffness and estimating yield displacements. Subsequently, cyclic lateral-loading tests with a given value of the axial force allowed investigating the restoring force characteristics in case of seismic actions. First, the paper describes and comments on the experimental performance of the two specimens. Second, numerical finite-element model predictions are illustrated and compared with experimental results. Third, based on the experimental results, as well as on the FE model analysis, the study looks for possible extensions and adaptations to current Eurocode 3 prediction models.

The Effect of Muscle Direction on the Predictions of Finite Element Model of Human Lumbar Spine.

The normal physiological loads from muscles experienced by the spine are largely unknown due to a lack of data. The aim of this study is to investigate the effects of varying muscle directions on the outcomes predicted from finite element models of human lumbar spine. A nonlinear finite element model of L3–L5 was employed. The force of the erector spinae muscle, the force of the rectus abdominis muscle, follower loads, and upper body weight were applied. The model was fixed in a neural standing position and the direction of the force of the erector spinae muscle and rectus abdominis muscle was varied in three directions. The intradiscal pressure, reaction moments, and intervertebral rotations were calculated. The intradiscal pressure of L4-L5 was 0.56–0.57 MPa, which agrees with the in vivo pressure of 0.5 MPa from the literatures. The models with the erector spinae muscle loaded in anterior-oblique direction showed the smallest reaction moments (less than 0.6 Nm) and intervertebral rotations of L3-L4 and L4-L5 (less than 0.2 degrees). In comparison with loading in the vertical direction and posterior-oblique direction, the erector spinae muscle loaded in the anterior-oblique direction required lower external force or moment to keep the lumbar spine in the neutral position.

Intubation biomechanics: validation of a finite element model of cervical spine motion during endotracheal intubation in intact and injured conditions.

OBJECTIVE Because of limitations inherent to cadaver models of endotracheal intubation, the authors' group developed a finite element (FE) model of the human cervical spine and spinal cord. Their aims were to 1) compare FE model predictions of intervertebral motion during intubation with intervertebral motion measured in patients with intact cervical spines and in cadavers with spine injuries at C-2 and C3-4 and 2) estimate spinal cord strains during intubation under these conditions. METHODS The FE model was designed to replicate the properties of an intact (stable) spine in patients, C-2 injury (Type II odontoid fracture), and a severe C3-4 distractive-flexion injury from prior cadaver studies. The authors recorded the laryngoscope force values from 2 different laryngoscopes (Macintosh, high intubation force; Airtraq, low intubation force) used during the patient and cadaver intubation studies. FE-modeled motion was compared with experimentally measured motion, and corresponding cord strain values were calculated. RESULTS FE model predictions of intact intervertebral motions were comparable to motions measured in patients and in cadavers at occiput-C2. In intact subaxial segments, the FE model more closely predicted patient intervertebral motions than did cadavers. With C-2 injury, FE-predicted motions did not differ from cadaver measurements. With C3-4 injury, however, the FE model predicted greater motions than were measured in cadavers. FE model cord strains during intubation were greater for the Macintosh laryngoscope than the Airtraq laryngoscope but were comparable among the 3 conditions (intact, C-2 injury, and C3-4 injury). CONCLUSIONS The FE model is comparable to patients and cadaver models in estimating occiput-C2 motion during intubation in both intact and injured conditions. The FE model may be superior to cadavers in predicting motions of subaxial segments in intact and injured conditions.