Finite Element Model Study Research Articles

Lumbar stability following graded unilateral and bilateral graded facetectomy—a finite element model study

Lumbar stability following graded unilateral and bilateral graded facetectomy—a finite element model study

Finite element modeling study of the suppression effect of external high magnetic field on the heat transfer of tungsten melt

Finite element modeling analysis has been employed to simulate the melt layer motion of tungsten and tungsten-based materials under high magnetic field. High heat flux of 2 GW m−2 was loaded for 3 ms at 1000 K and provided a molten bath. Meanwhile, high magnetic field from 0 to 8 T was loaded during the simulation. Both positive and negative surface tension temperature coefficient was tested. The result shows that the convention forced by the surface tension is suppressed by the magnetic field. The high magnetic field performs as a resistance of the heat transfer, leading to a reduced molten bath. The magnetic field mitigates the melting behaviur of the tungsten materials.

Biomechanical Prediction of Crack Angle Effect on Local Tensile Stress of Articular Cartilage

Purpose: Articular cartilage is an important load-bearing structure in synovial joint. Posttraumatic osteoarthritis may occur after cracking insult to cartilage, while not all insult to cartilage could progress into osteoarthritis. The initiating mechanism of osteoarthritis is still not well understood. Tensile stress is considered to have strong relationships with cartilage degradation. We hypothesize that cracks on articular cartilage under compression will induce tensile stress around the crack region, which may lead to chondrocytes change and cartilage degeneration. Methods: In this study, using a 2D finite element model and animal validation study, the relationship between crack angle and local tensile stress was investigated. Results: Under pure compressive load, 45 degrees oblique crack on cartilage could induce the highest peak tensile stress (3.9 times to compressive pressure) while no tensile stress was found in perpendicular crack cartilage. Animal study also confirmed finite element prediction that oblique crack may produce type I collagen around crack tip region. Conclusions: This finding implies that crack angle could be an important factor contributing to initiate osteoarthritis after a traumatic injury. New strategies for prevention and early treatment of osteoarthritis might benefit from this study.

Finite element modeling and experimental studies on mixed mode-I/III fracture specimens

In this study, finite element modeling and experimental studies on a mode-I/III specimen similar to the compact tension specimen are presented. By using bolts, the specimen is attached to two loading apparatus that allow different levels of mode-I/III loading by changing the loading holes. Specimens having two different thicknesses are analyzed and tested. Modeling, meshing and the solution of the problem involving the whole assembly, i.e., loading devices, bolts and the specimen, with contact mechanics are performed using ANSYSTM. Then, the mode-I/III specimen is analyzed separately using a submodeling approach, in which threedimensional enriched finite elements are used in FRAC3D solver to calculate the resulting stress intensity factors along the crack front. In all of the analyses, it is clearly shown that although the loading is in the mode-I and III directions, mode-II stress intensity factors coupled with mode-III are also generated due to rotational relative deformations of crack surfaces. The results show that the mode-II stress intensity factors change sign along the crack front and their magnitudes are close to the mode-III stress intensity factors. It is also seen that magnitudes of the mode-III stress intensity factors do not vary much along the crack front. Fracture experiments also performed and, using the stress intensity factors from the analyses and crack paths and surfaces are shown.

Microbubble oscillating in a microvessel filled with viscous fluid: A finite element modeling study

Understanding the dynamics of coated-microbubble oscillating in an elastic microvessel is important for effective and safe applications of ultrasound contrast agents (UCAs) in imaging and therapy. Numerical simulations are performed based on a two-dimensional (2D) asymmetric finite element model to investigate the influences of both acoustic driving parameters (e.g., pressure and frequency) and material properties (vessel size, microbubble shell visco-elastic parameters and fluid viscosity) on the dynamic interactions in the bubble–blood–vessel system. The results show that, the constrained effect of the blood vessel along the radial direction will induce the asymmetric bubble oscillation and vessel deformation, as well as shifting the bubble resonance frequency toward the higher frequency range. For a bubble (1.5-μm radius) activated by 1-MHz ultrasound pulses in a microvessel with a radius varying between 2 and 6.5μm, up to 26.95kPa shear stress could be generated on the vessel wall at a driving pressure of 0.2MPa, which should be high enough to damage the vascular endothelial cells. The asymmetrical oscillation ratio of the bubble can be aggravated from 0.12% to 79.94% with the increasing acoustic driving pressure and blood viscosity, or the decreasing vessel size and microbubble shell visco-elastic properties. The maximum compression velocity on the bubble shell will be enhanced from 0.19 to 22.79m/s by the increasing vessel size and acoustic pressure, or the decreasing microbubble shell visco-elasticity and blood viscosity. As the results, the peak values of microstreaming-induced shear stress on the vessel wall increases from 0.003 to 26.95kPa and the deformation degree of vessel is raised from 1.01 to 1.49, due to the enhanced acoustic amplitude, or the decreasing vessel size, blood viscosity and microbubble shell visco-elasticity. Moreover, it also suggests that, among above impact parameters, microbubble resonance frequency and UCA shell elasticity might play more dominant roles in dynamic interactions of the bubble–blood–vessel system.

The role of sclerotic changes in the starting mechanisms of collapse: A histomorphometric and FEM study on the femoral head of osteonecrosis

PurposeTo assess the distributions of stress, strain, and fractured areas using a finite element model (FEM), and examine the osteoclastic activity histopathologically in osteonecrosis of the femoral head. MethodsThree femoral heads were obtained during hip arthroplasty for femoral head osteonecrosis. One sample with a normal area, two samples with a non-sclerotic boundary without collapse (Type 1), two samples with a non-collapsed sclerotic boundary (Type 2), and two samples with a collapsed sclerotic boundary (Type 3) were collected from each femoral head for the FEM and histopathological analyses. FEM was performed using CT data, and the distributions of von Mises equivalent stress, octahedral shear stress, octahedral shear strain, and simulated fractured area were evaluated. Furthermore, the osteoclast count at the boundary was compared for each type. ResultsIn normal and Type 1 samples, the distributions of von Mises equivalent stress, octahedral shear stress, octahedral shear strain, and the fractured area were equally concentrated along the whole analytical range; however, in the Type 2 and 3 samples, they were concentrated along the thickened bone trabeculae at the boundary, which corresponded to the fractured area. Histopathologically, a significantly increased osteoclast number was observed only at the collapsed sclerotic boundary. ConclusionThese results demonstrated that both shear stress and shear strain tend to be concentrated on thickened bone trabeculae at the boundary. Fracture analyses revealed that the boundary of sclerotic changes, which results from the repair process, may be the starting point of the fracture. Additionally, the osteoclastic activity increases after collapse.

Nonlinear finite element modelling and parametric study of curved steel–concrete–steel double skin composite panels infilled with ultra-lightweight cement composite

Curved steel–concrete–steel (SCS) double skin composite structure with shear connectors has been developed and exhibits versatile potential applications in building and offshore constructions. A novel ultra-lightweight cement composite is used as core material and headed shear studs are welded on steel face plate to achieve the composite action. This paper demonstrates a comprehensive 3D nonlinear finite element (FE) analysis of curved double skin composite panels infilled with ultra-lightweight cement composite (ULCC) under patch load. Nonlinear FE analyses are performed using ABAQUS to study the load deflection behaviour up to the maximum load resistance. A constitutive model for ultra-lightweight cement composite is generated from standard test data and assigned to the concrete materials. A simplified connector element incorporated tension–elongation behaviour is proposed for the shear studs in the curved double skin composite panels. The accuracy of the FE model is validated using experimental results from the literature in terms of load displacement curves, failure modes and maximum load resistance. An extensive parametric study is carried out to identify the effect of the rise-to-span ratio, span-to-thickness ratio, concrete compressive strength and steel yield strength and loading type on the ultimate resistance.

A numerical study on the compressive and rotational behavior of fiber reinforced elastomeric isolators (FREI)

Fiber reinforced elastomeric isolators (FREI) possess unique characteristics relative to traditional steel reinforced elastomeric isolators (SREI). FREI can be classified as either bonded or unbonded according to the connection type employed. An understanding of the behavior of FREI under these loading configurations is needed in order to extend the application of FREI to bridges. The objective of this study is to investigate the response of FREI when vertical and rotational deformations are applied separately as well as in combination. Finite element modeling is carried out on five FREI having the same material properties but possessing different geometrical properties. The mean vertical pressure values employed in this studied are 1, 4.5, 7 and 10MPa, which represent the specified upper and lower limits presented in CAN/CSA-S6 and AASHTO-LRFD. The behavior of the isolators under different angles of rotation is investigated up to a maximum value of 0.05 radians. Results obtained from the finite element model study and values obtained from available closed-form analytical solutions are found to be in excellent agreement. In addition, results show that U-FREI experience lower normal stresses and shear strains in the elastomer and lower strains in the reinforcement relative to B-FREI.

Computational analyses of different intervertebral cages for lumbar spinal fusion

Lumbar spinal fusion is the most common approach for treating spinal disorders such as degeneration or instability. Although this procedure has been performed for many years, there are still important challenges that must be overcome and questions that need to be addressed regarding the high rates of non-union. The present finite element model study aimed to investigate the influence of different cage designs on the fusion process.An axisymmetric finite element model of a spinal segment with an interbody fusion cage was used. The fusion process was based on an existing mechano-regulation algorithm for tissue formation. With this model, the following principal concepts of cage design were investigated: (1) different cage geometries with constant compressive stiffness and (2) cage designs optimized to provide the ideal mechanical stimulus for bone formation, first at the beginning of fusion and then throughout the entire fusion process.The cage geometry substantially influenced the fusion outcome. A cage that created an optimized initial mechanical stimulus did not necessarily lead to accelerated fusion, but rather resulted in delayed fusion or non-union. In contrast, a cage made of a degradable material produced a significantly higher amount of bone and resulted in higher segmental stiffness. However, different compressive loads (250, 500 and 1000N) substantially affected the amount of newly formed bone tissue.The results of the present study suggest that aiming for an optimal initial mechanical stimulus may be misleading because the initial mechanical environment is not preserved throughout the bone modeling process.

Individual and combined effects of OA-related subchondral bone alterations on proximal tibial surface stiffness: a parametric finite element modeling study

The role of subchondral bone in OA pathogenesis is unclear. While some OA-related changes to morphology and material properties in different bone regions have been described, the effect of these alterations on subchondral bone surface stiffness has not been investigated. The objectives of this study were to characterize the individual (Objective 1) and combined (Objective 2) effects of OA-related morphological and mechanical alterations to subchondral and epiphyseal bone on surface stiffness of the proximal tibia. We developed and validated a parametric FE model of the proximal tibia using quantitative CT images of 10 fresh-frozen cadaveric specimens and in situ macro-indentation testing. Using this validated FE model, we estimated the individual and combined roles of OA-related alterations in subchondral cortical thickness and elastic modulus, and subchondral trabecular and epiphyseal trabecular elastic moduli on local surface stiffness. A 20% increase in subchondral cortical or subchondral trabecular elastic moduli resulted in little change in stiffness (1% increase). A 20% reduction in epiphyseal trabecular elastic modulus, however, resulted in an 11% reduction in stiffness. Our parametric analysis suggests that subchondral bone stiffness is affected primarily by epiphyseal trabecular bone elastic modulus rather than subchondral cortical and trabecular morphology or mechanical properties. Our results suggest that observed OA-related alterations to epiphyseal trabecular bone (e.g., lower mineralization, bone volume fraction, density and elastic modulus) may contribute to OA proximal tibiae being less stiff than normal.

Finite element modeling and parametric study of an automotive V-belt pulley for durability improvement

This paper presents an analysis of the geometric configuration and loading conditions influencing the durability of an automotive Vbelt pulley. Following the analysis steps specified in a previous studies [Proc. IMechE Part D. Vol. 223, 1301–1309 (2009), Int. J. Auto. Tech..Vol. 10, 73–77 (2009)], the fatigue life of a V-belt pulley was predicted under various conditions. The stress history of the pulley during operation was determined by performing consecutive static analyses on the pulley as it rotated. Using the stress history data calculated from finite element (FE) analysis, the damage over one pulley rotation was calculated, and the fatigue life and number of rotations to failure were estimated. A durability test was performed to compare with the analysis results for a reference analysis case. To determine the design factors affecting the durability, four parameters were evaluated: the contact angle between the pulley and belt, the contact depth of the belt, the distance between the bolt fastening face and the grooved rim area, and the bolt fastening load. The results revealed that a decrease in these parameters increased the durability of the pulley.

Biomechanical studies of the zygoma: A review of in vivo (italic) and FEM studies of the lateral orbital wall and zygomatic arch

The zygomatic region and lateral orbital wall are important structural components of the primate craniofacial skeleton, providing attachment for muscles, housing and protecting the eye, and resisting and transmitting forces incurred during feeding and fighting. The design of this region must therefore meet the needs of a number of different functional systems. The relative importance of these different systems in driving zygomatic morphology across different primate lineages remains to be elucidated. The role of this region in resisting, transmitting and dissipating feeding forces is amenable to study using in vivo bone strain and finite element modeling techniques. Based on these techniques Ross et al. (2011) suggested that there is a common pattern of deformation of the catarrhine facial skeleton, namely bending in frontal/coronal planes. Following Endo (1966) and Rak (1983), this bending was hypothesized to be due to inferiorly directed muscle forces acting on the zygomatic arches, producing torsion and sagittal bending of the arches. The highest strains and stresses associated with this deformation regime are experienced by the anterior root of the zygoma. The bone in this area is hypothesized to experience high shear stresses resulting from inferiorly directed muscle forces laterally and superiorly directed bite forces medially. This model was based on in vivo bone strain data from Macaca, Papio, and Chlorocebus, frame‐modeling of Gorilla and Homo, and finite element modeling (FEM) data from Macaca. Review of the available bone strain and/or FEM data for Cebus,Pan, and several fossil hominins reveals common patterns of strain across taxa with a range of morphologies and diets. Bone strain magnitudes in the arch and anterior root are high relative to strain magnitudes elsewhere in the cranium, suggesting an important role for structural strength in the design of this region. The notion of a fundamental framework of the catarrhine face receives some support from these data.

Design and Structural Analysis of Robot Arm for High Performance Packaging Robots

Current packaging robots cannot achieve the required speed due to the use of heavy parts. Magnesium alloys with appropriate surface treatment may be used to replace the traditional steel or aluminum parts and therefore to reduce robot arm weight. In this work, different prototype designs were made to examine the feasibility of the application of light alloys for robot arm, in comparison to conventional materials. Finite element modelling (FEM) studies were performed for structural analysis. The results demonstrated that magnesium alloys has advantages over steel or aluminum alloys in terms of the ratio of modulus over density, and the stress and elastic deformation experienced during operation due to arm weight.

Finite Element Modelling To Evaluate the Cross-plane Thermal conductivity and Seebeck Coefficient of Ge/SiGe Heterostructure

Finite element modelling (FEM) is used to evaluate a new experimental procedure for extracting the thermal conductivity and Seebeck coefficients from micro-fabricated structures with integrated heaters, thermometers and Ohmic contacts. This experimental technique was designed to simultaneously produce and measure the differential temperature and voltage output for the determination of both thermoelectric properties of Ge/SiGeheterostructures.This study demonstrates the reliability of the FEM modelling by comparing the simulation results with experiment. It demonstrates how FEM can be implemented to complement the experiments: it can be used to observe the heat distribution in the heterostructure. Therefore all the mechanisms of parasitic heat loss in the devices can be evaluated in order to improve the accuracy of the extraction of thermal coefficients and especially the thermal conductivity. This will allow for further analysis to be taken to optimize the ZT and power factor for the Ge/SiGeheterostructures.The micro-fabricated structures consisted of an etched mesa of the Ge/SiGeheterostructure with Ohmic contacts, for measuring the voltages, at the top and bottom. On the top of the mesa, a 30nm thick Si3N4 insulator was applied followed by a Ti/Pt thermometer, another 70nm of Si3N4 and then a NiCr heater. A second thermometer was micro-fabricated at the bottom of the mesa to allow the ▵T across the material to be measured as a function of the heater power [1]. The results obtained from the FEM studies closely matches the experimental results in [1].

Nonlinear finite element modelling and parametric study of CFRP shear-strengthened prestressed concrete girders

This paper presents a three-dimensional nonlinear finite element (FE) model for prestressed concrete girders strengthened in shear with externally bonded carbon fibre reinforced polymer (CFRP) reinforcement. A total strain rotating crack model, where the crack direction changes with the change in the direction of the principal tensile stress, was used for the concrete. In this model, explicit modelling of the concrete shear behaviour after cracking, e.g. via a shear retention parameter, is not required as the crack plane is always a principal plane with no shear stresses. The FE model was validated using experimental results from the literature. An extensive parametric study was carried out to identify the effect of the concrete compressive strength, CFRP width-to-spacing ratio, CFRP thickness, girder effective depth, shear span to effective depth ratio, level of prestress, tendon profile, pre-cracking and CFRP-to-concrete interface model on the predicted shear force capacity. The results suggested that the predicted shear strength enhancement can be significant and increases with the increase in concrete compressive strength, CFRP width-to-spacing ratio, and CFRP thickness but decreases with the increase in girder effective depth and shear span to effective depth ratio.

CLSM bridge abutments – Finite element modeling and parametric study

Controlled low strength materials (CLSMs) are increasingly gaining importance in the construction industry. Among many applications, CLSMs can be used for rapid and sustainable construction of bridge abutments. This paper describes the finite element analysis of a full-scale loading test of a bridge abutment backfilled with the CLSM referred to as “CLSM bridge abutment”. The finite element analysis will help with the understanding of the behavior of CLSM bridge abutments, in terms of bearing capacity, displacements and the developed axial force in anchors. The accuracy of the finite element results for the response and failure behavior of a CLSM mass was evaluated by a comparison with the experimental results. The experimental program included both standard compressive strength testing on CLSM cylinders and a laboratory full-scale testing on a CLSM bridge abutment. The analysis shows that the performance of a CLSM abutment while subject to a service load or a limiting failure load from a bridge superstructure can be simulated in a reasonably accurate manner.In addition, a parametric study was conducted to better understand the performance of the CLSM bridge abutments in terms of bearing capacity and overall behavior. This study investigated the performance of the CLSM bridge abutments as they are affected by material curing age, environment temperature and construction details. The results indicated that the CLSM bridge abutment is capable of carrying typical bridge loads with relatively after only one day from the placement. It was observed that the bearing capacity increased with further curing of the CLSM material.

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.

Finite element modelling and vibration control study of active plate with debonded piezoelectric actuators

A finite element model for a piezoelectric plate with edge debonded actuators is presented. This model is employed to investigate the effect of edge debonding on actuation authority, natural frequencies and vibration control performance. The regions of the plate with the piezoelectric patches are modelled such that each layer undergoes rotation due to shear deformation independently. The necessary constraints for continuity of displacements at the interfaces of the layers are imposed. The plate with edge debonded actuators is idealized by dividing it into debonded regions and healthy regions. A finite element procedure for imposing the constraints regarding continuity of displacements at the interfaces of the adjacent regions is developed and is implemented using MATLAB. Experiments are conducted for finding the actuation authority and natural frequencies of the plate with debonded actuators. It has been found that the developed model has predicted the mechanics of actuator debonding properly. The investigations have revealed the fact that the edge debonding of actuators will result in considerable degradation in actuation authority and vibration control performance.

Biomechanical analysis of various footprints of transforaminal lumbar interbody fusion devices.

A biomechanical finite element modeling study of the human lumbar spine. To evaluate the effects of a transforaminal interbody device's footprint on lumbar spine biomechanics to further examine the potential subtle biomechanical differences not captured in previous studies. In recent years, the evolution of interbody fusion devices has provided the surgeons with a multitude of options. An articulating transforaminal lumbar interbody fusion (TLIF) device is developed to overcome the surgical challenges associated with insertion of a large footprint interbody device through a small incision. A finite element model of the L3-S1 lumbar segment was modified to simulate replacement of various TLIF constructs with different cage designs including an articulating vertebral interbody (AVID) TLIF device and a generic TLIF device placed in different configurations. The instrumented models were subjected to a 400 N follower load along with a 10 N m bending moment at different physiological planes. The kinematics, loads, and stresses were compared among various models. Simulated cage designs provided similar kinematical stability within the treated segments. However, the articulating and double TLIF implants allowed for better load sharing through the anterior column. These implants resulted in lower endplate and pedicle screw stresses and in more homogenous stress distribution across the peripheral region of the endplate. An articulating, large footprint, peripherally placed TLIF device affords substantial biomechanical advantages. This device may be able to reduce the incidence of subsidence because of its ability to reduce and distribute the endplate stresses in the stronger peripheral region. It may also reduce the posterior hardware failure incidence owing to its ability to reduce the screw stresses as compared with traditional TLIF. Although double TLIF has been demonstrated to have similar biomechanical advantages as the AVID, complications associated with double TLIF (ie, larger surgical incision, longer surgical procedure, placement and alignment challenges) support AVID as a better optimized alternative.

Characteristic loosening of the distally straight cylindrical femoral stem

BackgroundThe cemented femoral stem with a distally straight cylindrical shape was designed to fill the distal femoral canal to facilitate higher cement pressurization and stability. We examined the mid-term outcomes of a stem made of titanium alloy and the efficacy of this shape. MethodsFour hundred and twenty-nine consecutive patients (505 hips), who underwent a total hip arthroplasty with the distally straight cylindrical stem made of titanium alloy as their primary hip arthroplasty at two institutes, were followed for a minimum 2 years. Loosening was defined as subsidence of over 3 mm, tilting of the femoral component, or fracture of the cement or the stem. A continuous radiolucent line along the entire interface was considered to indicate loosening, too. We examined the interface stresses on the distally straight cylindrical stem compared with a newly manufactured femoral prosthesis with a double-taper design using a finite element model study. ResultsThe mean follow-up was 101.3 months after surgery. Thirty patients (30 hips) had aseptic loosening of the stems. Of these 30 hips, 18 had osteolysis, 17 showed subsidence, and 11 had cement fractures at the tip of the stem. These 11 hips had osteolysis and ectasia in the same place: the stem tip. The stem survival rate with stem loosening as the end-point was 94.4 % at 10 years and 66.9 % at 15 years. A finite element model study revealed higher stress around the tip of the cylindrical stem compared with that in the double-taper stem. ConclusionsThe straight cylindrical stem is potentially subject to early failure because of high stress around the tip of the stem, and showed a characteristic loosening with osteolysis and ectasia at the tip of the stem.