Disc Stress Research Articles

Biomechanical evaluation of the thoracolumbar spine comparing healthy and irregular thoracic and lumbar curvatures

BackgroundThe geometric alignment of the spine plays an integral role in stability, biomechanical loading, and consequently, pain, and a range of healthy sagittal curvatures has been identified. Spinal biomechanics when sagittal curvature is outside the optimal range remains a debate and may provide insight into the load distribution throughout the spinal column. MethodA thoracolumbar spine model (Healthy) was developed. Thoracic and lumbar curvatures were adjusted by 50% to create models with varying sagittal profiles: hypolordotic (HypoL), hyperlordotic (HyperL), hypokyphotic (HypoK), and hyperkyphotic (HyperK). In addition, lumbar spine models were constructed for the former three profiles. The models were subjected to loading conditions simulating flexion and extension. Following validation, intervertebral disc stresses, vertebral body stresses, disc heights, and intersegmental rotations were compared across all models. ResultsOverall trends demonstrated that HyperL and HyperK models had a noticeable reduction in disc height and greater vertebral body stresses compared to the Healthy model. In comparison, the HypoL and HypoK models displayed opposite trends. Considering the lumbar models, the HypoL model had reduced disc stresses and flexibility, while the contrary was observed in the HyperL model. Results indicate that the models with excessive curvature may be subjected to greater stress magnitudes, while the straighter spine models may reduce these stresses. ConclusionsFinite element modeling of spine biomechanics demonstrated that variations in sagittal profiles influence the load distribution and range of motion of the spine. Considering patient-specific sagittal profiles in finite element modeling may provide valuable insight for biomechanical analyses and targeted treatments.

Biomechanical Effects of a Novel Pedicle Screw W-Type Rod Fixation for Lumbar Spondylolysis: A Finite Element Analysis.

Lumbar spondylolysis involves anatomical defects of the pars interarticularis, which causes instability during motion. The instability can be addressed through instrumentation with posterolateral fusion (PLF). We developed a novel pedicle screw W-type rod fixation system and evaluated its biomechanical effects in comparison with PLF and Dynesys stabilization for lumbar spondylolysis via finite element (FE) analysis. A validated lumbar spine model was built using ANSYS 14.5 software. Five FE models were established simulating the intact L1-L5 lumbar spine (INT), bilateral pars defect (Bipars), bilateral pars defect with PLF (Bipars_PLF), Dynesys stabilization (Bipars_Dyn), and W-type rod fixation (Bipars_Wtyp). The range of motion (ROM) of the affected segment, the disc stress (DS), and the facet contact force (FCF) of the cranial segment were compared. In the Bipars model, ROM increased in extension and rotation. Compared with the INT model, Bipars_PLF and Bipars_Dyn exhibited remarkably lower ROMs for the affected segment and imposed greater DS and FCF in the cranial segment. Bipars_Wtyp preserved more ROM and generated lower stress at the cranial segment than Bipars_PLF or Bipars_Dyn. The injury model indicates that this novel pedicle screw W-type rod for spondylolysis fixation could return ROM, DS, and FCF to levels similar to preinjury.

Effect of muscle activation on dynamic responses of neck of pilot during emergency ejection: a finite element study.

To determine the effect of muscle activation on the dynamic responses of the neck of a pilot during simulated emergency ejections. A complete finite element model of the pilot's head and neck was developed and dynamically validated. Three muscle activation curves were designed to simulate different activation times and levels of muscles during pilot ejection: A is the unconscious activation curve of the neck muscles, B is the pre-activation curve, and C is the continuous activation curve. The acceleration-time curves obtained during ejection were applied to the model, and the influence of the muscles on the dynamic responses of the neck was investigated by analyzing both angles of rotation of the neck segments and disc stresses. Muscle pre-activation reduced fluctuations in the angle of rotation in each phase of the neck. Continuous muscle activation caused a 20% increase in the angle of rotation compared to pre-activation. Moreover, it resulted in a 35% increase in the load on the intervertebral disc. The maximum stress on the disc occurred in the C4-C5 phase. Continuous muscle activation increased both the axial load on the neck and the posterior extension angle of rotation of the neck. Muscle pre-activation during emergency ejection has a protective effect on the neck. However, continuous muscle activation increases the axial load and rotation angle of the neck. A complete finite element model of the pilot's head and neck was established and three neck muscle activation curves were designed to investigate the effects of muscle activation time and level on the dynamic response of the pilot's neck during ejection. This increased insights into the protection mechanism of neck muscles on the axial impact injury of the pilot's head and neck.

Influence of braking sequence on railway brake disc's radial crack propagation behavior

AbstractThe influence of braking sequence on railway brake disc's radial crack propagation behavior is analyzed considering the effect of crack geometry features, material elastoplasticity, and crack closure. The results show that when the residual stress generated in the initial braking is low, the peak stress in the subsequent braking will be low, and the average response state is more inclined to compression. The influences of the braking sequence are mainly reflected in the mid‐late stage of crack growth. In the early stage, the radial cracks almost synchronously expand inward and outward. While in the mid‐late stage, the cracks mainly expand inward. When the initial braking is relatively mild, the brake disc's stress–strain response and crack propagation behavior can be improved. It is beneficial to extend the brake disc's service life by designing a suitable prefabricated working condition or introducing an appropriate residual stress field through surface treatment.

Microtubule stabilization promotes the synthesis of type 2 collagen in nucleus pulposus cell by activating hippo-yap pathway.

Intervertebral disc degeneration (IDD) is the cardinal pathological mechanism that underlies low back pain. Mechanical stress of the intervertebral disc may result in a change in nucleus pulposus cells state, matrix degradation, and degeneration of the disc. Microtubules, which are components of the cytoskeleton, are involved in driving or regulating signal pathways, which sense and transmit mechano-transduction. Microtubule and the related proteins play an important role in the development of many diseases, while little is known about the role of microtubules in nucleus pulposus cells. Researchers have found that type II collagen (COL2) expression is promoted by microtubule stabilization in synovial mesenchymal stem cells. In this study, we demonstrated that microtubule stabilization promotes the expression of COL2 in nucleus pulposus cells. Stabilized microtubules stimulating Hippo signaling pathway, inhibiting YAP protein expression and activity. In addition, microtubules stabilization promotes the expression of COL2 and alleviates disc degeneration in rats. In summary, our study for the first time, identifies microtubule as a promising therapeutic target for IDD, up-regulating the synthesis of COL2 via Hippo-Yap pathway. Our findings may provide new insights into the etiologies and pathology for IDD, further, targeting of microtubule acetylation may be an effective strategy for the treatment of IDD.

Biomechanical responses of the human lumbar spine to vertical whole-body vibration in normal and osteoporotic conditions

BackgroundThe prevalence of osteoporosis is continuing to escalate with an aging population. However, it remains unclear how biomechanical behavior of the lumbar spine is affected by osteoporosis under whole-body vibration, which is considered a significant risk factor for degenerative spinal disease and is typically present when driving a car. Accordingly, the objective of this study was to compare the spine biomechanical responses to vertical whole-body vibration between normal and osteoporotic conditions. MethodsA three-dimensional finite-element model of the normal human lumbar spine-pelvis segment was developed using computed tomographic scans and was validated against experimental data. Osteoporotic condition was simulated by modifying material properties of bone tissues in the normal model. Transient dynamic analyses were conducted on the normal and osteoporotic models to compute deformation and stress in all lumbar motion segments. FindingsWhen osteoporosis occurred, vibration amplitudes of the vertebral axial displacement, disc bulge, and disc stress were increased by 32.1–45.4%, 25.7–47.1% and 23.0–42.7%, respectively. In addition, it was found that for both the normal and osteoporotic models, the response values (disc bugle and disc stress) were higher in L4–L5 and L5–S1 intervertebral discs than in other discs. InterpretationOsteoporosis deteriorates the effect of whole-body vibration on lumbar spine, and the lower lumbar segments might have a higher likelihood of disc degeneration under whole-body vibration.

Effect of a Double Helical Spring Decompression Structure Backpack on the Lumbar Spine Biomechanics of School-Age Children: A Finite Element Study

<b>Background:</b> A children’s backpack is one of the important school supplies for school-age children. Long-term excessive weight can cause spinal deformity that cannot be reversed. This study compared a double helical spring decompression structure backpack (DHSB) with a traditional backpack (TB) to explore the optimization of decompression devices on upper body pressure. The finite element (FE) method was then used to explore the simulation of lumbar stress with different backpacks, in order to prove that DHSB can reduce the influence of backpack weight on lumbar vertebrae, avoid the occurrence of muscle discomfort and spinal deformity in children; <b>Methods:</b> 18 male children subjects (age: 12.5 ± 0.6 years; height: 145.5 ± 1.9 cm; bodyweight: 40.8 ± 3.1 kg) ran with DHSB and TB at a speed of 3.3 ± 0.2 m/s. Flexible pressure sensors were used to measure the pressure on the shoulder, back, and waist during running. The pressure data was then inputted into the FE model to simulate the effect of carrying different backpacks on the stress of the lumbar intervertebral disc (IVD); <b>Result:</b> There was a significant difference in shoulder and waist peak pressure between the DHSB and TB during the running posture. At a speed of 3.3 ± 0.2 m/s, the peak pressure of the shoulder and waist decreased. After finite element analysis, it was found that carrying DHSB on the back could effectively reduce the intervertebral disc pressure between L4-5 and L5-S1 by 27.9% and 34.1%, respectively; <b>Conclusion:</b> DHSB can effectively reduce the pressure on the shoulder and waist when children are running and can reduce the influence of backpacks on children’s posture to a certain extent. By finite element analysis, it is found that carrying DHSB can effectively reduce the stress of the lumbar intervertebral disc, and the damage to lumbar vertebrae is lower than with a TB.

Disk Stress in the Wave Generator of a Large Wave Gear

Disk Stress in the Wave Generator of a Large Wave Gear

Evaluation possibility of the turbine disks using of converted aircraft engines of the NK family

The article examines the possibility of using converted aircraft engines for gas pumping units using the example of the main parts of the GTE - the disks of the NK-8-2U aircraft engine and the NK-16ST and NK-16-18ST ground engines. For all disks of the second stage of low-pressure turbines of three engines, the stress-strain state calculation was performed using the boundary integral equations method (BEM) and using the FEM in the Ansys program. For three disk stress concentrators, the theoretical stress concentration coefficient was determined and the maximum equivalent stresses were calculated. During long-term operation, the main parameters of engine operation change due to degradation changes (wear, erosion and corrosion, development of seals, contamination and resizing of flow parts). As a result, the main parameters of engine operation change, in particular, the rotation speed of the rotors and the gas temperature in the turbine, which determine the stress-strain state, which must be taken into account when predicting durability. The compliance of the results of the calculated study of the stress-strain state of turbine disks with their real load was confirmed by the data of their metallurgical study after prolonged operation. Using the Manson formula for the disks of three engines, their cyclic durability was determined before the formation of a crack of low-cycle fatigue. Using the linear damage summation hypothesis, the total damage rates (under static loading and under fatigue loading) for the disks of three engines were calculated. It is established that after the conversion of aircraft engines that have spent their life in flight operation, it is advisable to continue the use of turbine disks on ground-based GTU.

Aeromechanical Optimization of Scalloping in Mixed Flow Turbines

Abstract Scalloping of radial and mixed-flow turbocharger turbine rotors has been commonplace for many years as a means of inertia reduction and stress relief. The interest in turbine rotor inertia reduction is driven by transient loading requirements of turbocharged internal combustion engines, as this is a key factor in the time taken to meet transient engine torque requirements. Due to the high-density materials used in turbine rotors, any material removal from the turbine wheel has a significant impact on turbocharger inertia, and thus the transient response of the engine. It is well known that scalloping reduces not only inertia, but also efficiency. This study aimed to identify if it was possible to produce a new scallop design which reduced the scalloping efficiency penalty without increasing inertia or compromising mechanical constraints. This was carried out with the aim of developing design recommendations for scalloping where a complete minimization of inertia is not the design goal. A multipoint, multi-physics numerical optimization, with constraints on inertia and back disc stress, was carried out to determine what efficiency benefit could be realized by aerodynamically designing mixed-flow turbine scalloping. An efficiency benefit was identified across the entire turbocharger operating line, with increased benefit at low engine load, whilst not exceeding the design constraints. Scalloping losses for the baseline design were found to be greatest at low engine load, where the turbine experienced a low expansion ratio, mass flow, and speed. This explains why an aerodynamic redesign yields the greatest benefit under those operating conditions. These performance predictions were experimentally validated on the cold flow test rig at Queen's University Belfast, with good agreement between simulated and measured data. To conclude the study, a detailed loss audit was carried out to identify key loss generating flow structures and to understand how changes in geometry affected the formation and development of these flow structures throughout the passage. A large vortex which entered the passage from the scalloped region and interacted with the tip leakage vortex along the suction surface of the blade was identified as the main source of loss due to scalloping. The optimized design was found to better control the location of entry of this vortex into the blade passage, thus reducing the associated loss and facilitating a performance improvement. Geometric design guidelines were then proposed based on these findings.

Comparison of the Optimal Design of Spinal Hybrid Elastic Rod for Dynamic Stabilization: A Finite Element Analysis

The spinal hybrid elastic (SHE) rod is a semi-rigid pedicle screw-based rod for spinal dynamic stabilization. This study investigated the biomechanical effects of different ratios of SHE rod using finite element analysis (FEA). A three-dimensional nonlinear FEA of an intact lumbar spine model (INT) was constructed. The SHE rod was composed of an inner nitinol stick (NS) and an outer polycarbonate urethane shell (PS). Four groups implanted at L3–L4 had the same outer diameter (5.5 mm) but different NS diameter/PS thickness ratios: Nt45, Nt35, Nt25, and Nt15. The resultant intervertebral range of motion (ROM), disc stress, facet joint contact force, screw stress, NS stress, and PCU stress were analyzed. The results indicated that ROM, disc stress, and facet force decreased moderately in the implanted L3–L4 levels and increased slightly in the adjacent L2–L3 levels. The NS stress and NS diameter trended towards inverse proportionality. Changing the ratio did not markedly influence screw or PS stress. The SHE rod system with elastic NS and insulated PS has a 5.5 mm diameter for universal pedicle screws. The SHE rod system provides sufficient spinal support and increases gentle adjacent segment stress. Considering the durability, the optimal NS diameter/PS thickness ratio of the SHE rod system is 3.5/2.0 mm.

Biomechanical Performances of an Oblique Lateral Interbody Fusion Cage in Models with Different Bone Densities: A Finite Element Analysis.

Finite element models of the L3-S1 vertebrae were reconstructed using computed tomography scans. We compared the biomechanical performances of an oblique lateral interbody fusion (OLIF) cage in different bone density mode. Low bone density is an els.key factor limiting the use of stand-alone OLIF cage. Four models-intact (M0), normal bone density with OLIF (M1), bone mass loss with OLIF (M2), and osteoporotic with OLIF (M3)-were created based on 3-dimensional scans. Flexion, extension, and lateral bending movements (each lasting 10N·m) were performed on the superior surface of the L3 vertebra with a compressive preload of 500N. Range of motion (ROM), peak stresses in the L4-5 cortical endplates, cage stress, and adjacent intervertebral disk stress were evaluated. ROMs during different physiological movements were similar to those reported by previous researchers. Compared with that in M0, L4-5 ROMs of all movements decreased in M1, M2 and M3, most evidently in M3. Stress distribution in the cortical endplates rose to 7.8% in M1 and M2, even 16.2% in M3. Cage stress increased by less than 8.1% in M1 and M2, but by 25.3% in M3, especially in the movements of extension and right rotation. Compared with that in M0, L3-4 and L5-S1 intervertebral disk stress increased with bone density in all the other models, by up to 69.8% and 98.3%, respectively. As osteoporosis worsened, stress in the adjacent intervertebral disk also increased. Stand-alone OLIF in M3 is not recommended because of the risk of cage subsidence. OLIF in M1 and M2 achieved similar results in various lumbar spine movements. In M1 and M2 model (T > - 2.5), the L4-L5 showed reduced mobility in all directions, increased rigidity, limited cage displacement, lessened deformation, and better stability.

Biomechanical evaluation of lumbar spondylolysis repair with various fixation options: A finite element analysis.

Objective: This study was designed to compare the biomechanical properties of lumbar spondylolysis repairs using different fixation methods by using three-dimensional finite element analysis. Methods: Five finite element models (A, B, C, D, and E) of L4-S1 vertebral body were reconstructed by CT images of a male patient (A: intact model; B: spondylolysis model; C: spondylolysis model with intrasegmental direct fixation by Buck screw; D: spondylolysis model with intersegmental indirect fixation by pedicle screw system; E: spondylolysis model with hybrid internal fixation). L5-S1 level was defined as the operative level. After the intact model was verified, six physiological motion states were simulated by applying 500N concentrated force and 10Nm torque on the upper surface of L4. The biomechanical properties of the three different internal fixation methods were evaluated by comparing the range of motion (ROM), maximum stress, and maximum displacement. Results: Compared with Model B, the ROM and maximum displacement of Model C, D, and E decreased. The maximum stress on L5/S1 disc in models A, B, and C was much higher than that in Model D and E under extension and lateral bending conditions. Under axial rotation and lateral bending conditions, the maximum stress of interarticular muscle and internal fixation system in Model B and Model C was significantly higher than that in Model D and Model E. In contrast to Model D, the stress in Model E was distributed in two internal fixation systems. Conclusion: In several mechanical comparisons, hybrid fixation had better biomechanical properties than other fixation methods. The experimental results show that hybrid fixation can stabilize the isthmus and reduce intervertebral disc stress, which making it the preferred treatment for lumbar spondylolysis.

Non-Axisymmetric Modelling of Moving Heat Source for Spatial and Temporal Investigation of Temperature in Railway Vehicles Disc Brake

Railway disc brake is vulnerable to surface damages including fade, wear, squeal, thermal cracks and fatigue being just few of them. To counteract these negative consequences, reliable thermal model that can accommodate space and time variables is essential. The aim of this study is to develop new non-axisymmetric moving heat source and compare its efficiency with pre-existing traditional models. Factors responsible for temperature spatial and temporal variation are identified first and then programmed in ANSYS APDL similar capability to a FORTRAN. Heat flux and convection coefficients are calculated by empirical equations and stored in parameters and arrays for later use, based on small time and pad angular increment. The modelling is to successfully solve the problems in traditional models by estimating surface temperature difference as high as 49 °C, within acceptable computation time. Besides, its consideration of radial distance reported variations from traditional models as high as 10% and 60% in moving heat source and axisymmetric, respectively. And, it is also verified with the literature within acceptable variation. Finally, it is suggested that the model can be applied in conducting pad geometry optimization, thermal stress and fatigue life of disc brake.

Re-imagining Brake Disc Thermal Fatigue Testing to Relate to Field Use

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The validation of brake discs has remained, to this day, heavily reliant on “Thermal Abuse” or “Thermal Cracking” type testing, with many procedures so dated that most engineers active in the industry today cannot even recall the origin of the test. These procedures - of which there are many variants - all share the trait of greatly accelerating durability testing by performing repeated high power (high speed and high deceleration) brake applies to drive huge temperature gradients and internal stress, and often allowing the disc to get very hot, to where the strength of the material from which the disc is constructed is significantly degraded. There is little debate about whether these procedures work; by and large disc durability issues in the field are extremely rare. However, without the connection to the duty cycle in the field, it is extremely difficult to interpret results (especially since many standards allow significant cracking before a failure is declared), and this can lead to significant re-testing and design modifications that not necessarily needed. The publication of SAE J2995 (based heavily on VDA 311) provided a versatile and powerful means of relating simple lab-based test duty cycles to severe field use. There is not a straightforward interpretation of J2995 for brake discs; however, in combination with simple models relating braking power to disc stresses, a potential path emerges to connect disc thermal abuse to field use. The present study explores this path, with a series of inertia dynamometer-based studies designed to see if an S-N curve (relating braking power to disc life) could be developed for disc thermal abuse, and if this could then be used to relate the results to customer use. Initial results are promising, giving hope that disc durability validation can transition eventually to a less empirical, and more engineered approach.&lt;/div&gt;&lt;/div&gt;

The effect of tooth cusp morphology and grinding direction on TMJ loading during bruxism

Increased mechanical loading of the temporomandibular joint (TMJ) is often connected with the onset and progression of temporomandibular joint disorders (TMD). The potential role of occlusal factors and sleep bruxism in the onset of TMD are a highly debated topic in literature, but ethical considerations limit in vivo examinations of this problem. The study aims to use an innovative in silico modeling approach to thoroughly investigate the connection between morphological parameters, bruxing direction and TMJ stress. A forward-dynamics tracking approach was used to simulate laterotrusive and mediotrusive tooth grinding for 3 tooth positions, 5 lateral inclination angles, 5 sagittal tilt angles and 3 force levels, giving a total of 450 simulations. Muscle activation patterns, TMJ disc von Mises stress as well as correlations between mean muscle activations and TMJ disc stress are reported. Computed muscle activation patterns agree well with previous literature. The results suggest that tooth inclination and grinding position, to a smaller degree, have an effect on TMJ loading. Mediotrusive bruxing computed higher loads compared to laterotrusive simulations. The strongest correlation was found for TMJ stress and mean activation of the superficial masseter. Overall, our results provide in silico evidence that TMJ disc stress is related to tooth morphology.

Biomechanical comparison between unilateral and bilateral percutaneous vertebroplasty for osteoporotic vertebral compression fractures: A finite element analysis.

Background and objective: The osteoporotic vertebral compression fracture (OVCF) has an incidence of 7.8/1000 person-years at 55–65 years. At 75 years or older, the incidence increases to 19.6/1000 person-years in females and 5.2–9.3/1000 person-years in males. To solve this problem, percutaneous vertebroplasty (PVP) was developed in recent years and has been widely used in clinical practice to treat OVCF. Are the clinical effects of unilateral percutaneous vertebroplasty (UPVP) and bilateral percutaneous vertebroplasty (BPVP) the same? The purpose of this study was to compare biomechanical differences between UPVP and BPVP using finite element analysis. Materials and methods: The heterogeneous assignment finite element (FE) model of T11-L1 was constructed and validated. A compression fracture of the vertebral body was performed at T12. UPVP and BPVP were simulated by the difference in the distribution of bone cement in T12. Stress distributions and maximum von Mises stresses of vertebrae and intervertebral discs were compared. The rate of change of maximum displacement between UPVP and BPVP was evaluated. Results: There were no obvious high-stress concentration regions on the anterior and middle columns of the T12 vertebral body in BPVP. Compared with UPVP, the maximum stress on T11 in BPVP was lower under left/right lateral bending, and the maximum stress on L1 was lower under all loading conditions. For the T12-L1 intervertebral disc, the maximum stress of BPVP was less than that of UPVP. The maximum displacement of T12 after BPVP was less than that after UPVP under the six loading conditions. Conclusion: BPVP could balance the stress of the vertebral body, reduce the maximum stress of the intervertebral disc, and offer advantages in terms of stability compared with UPVP. In summary, BPVP could reduce the incidence of postoperative complications and provide promising clinical effects for patients.

Effects of Occlusal Plane Inclination on the Temporomandibular Joint Stress Distribution: A Three-Dimensional Finite Element Analysis.

Background Sudden changes in masticatory loads and occlusal conditions contribute to temporomandibular disorders. Clockwise (CW) or counterclockwise (CCW) rotation of the occlusal plane is one of the factors that alter the direction of the occlusal forces transmitted to the temporomandibular joint structures. Finite element analysis was used to identify possible regions of high stress in the temporomandibular joint. Materials and Methods A computer-aided design model of a symmetrical edentulous maxillomandibular bony complex with a temporomandibular joint was manually generated using Rhinoceros 4.0 freeform modeling software. Three-dimensional discrete mesh generation was performed using VRMesh Studio. The reference occlusal plane angle was accepted as 8° in the sagittal plane, and by modifying 4° in the CW and CCW directions, CW and CCW models were obtained, respectively. The present study aimed to evaluate the changes in stress distribution in the condylar cartilage and temporomandibular disc using the von Mises and maximum-minimum principal stress evaluations of three different occlusal plane inclinations. The null hypothesis of this three-dimensional finite element analysis was that “occlusal plane inclination does not change the stress distribution on the temporomandibular joint structures.” Results The compressive stress on the condyle increased with CW rotation of the occlusal plane. The von Mises equivalent stress of the temporomandibular disc shifted to the medial, posterior, and superior directions after CW and CCW rotations of the occlusal plane. The CW rotation of the occlusal plane increased the von Mises equivalent.

Finite element analysis after rod fracture of the spinal hybrid elastic rod system

BackgroundThe spinal hybrid elastic (SHE) rod dynamic stabilization system can provide sufficient spine support and less adjacent segment stress. This study aimed to investigate the biomechanical effects after the internal fracture of SHE rods using finite element analysis.MethodsA three-dimensional nonlinear finite element model was developed. The SHE rod comprises an inner nitinol stick (NS) and an outer polycarbonate urethane (PCU) shell (PS). The fracture was set at the caudal third portion of the NS, where the maximum stress occurred. The resultant intervertebral range of motion (ROM), intervertebral disc stress, facet joint contact force, screw stress, NS stress, and PCU stress were analyzed.ResultsWhen compared with the intact spine model, the overall trend was that the ROM, intervertebral disc stress, and facet joint force decreased in the implanted level and increased in the adjacent level. When compared with the Ns-I, the trend in the Ns-F decreased and remained nearly half effect. Except for torsion, the PS stress of the Ns-F increased because of the sharing of NS stress after the NS fracture.ConclusionsThe study concluded the biomechanical effects still afford nearly sufficient spine support and gentle adjacent segment stress after rod fracture in a worst-case scenario of the thinnest PS of the SHE rod system.

Steady-State Thermal Analysis of Functionally Graded Rotating Disks Using Finite Element and Analytical Methods

A steady-state thermal analysis for a hollow and axisymmetric functionally graded (FG) rotating disk with a uniform thickness was performed in this study. In the studied FG disk, metal and ceramic materials were considered for the inner and outer surfaces, respectively, when the material properties varied along the radial direction but not through material thickness variations. A power law distribution was employed to represent the material properties. Three different methods were used to present the temperature distribution along the radial direction of the FG disk, namely (1) an in-house finite element (FE) program, (2) the ANSYS parametric design language (APDL), and (3) an analytical solution. Furthermore, the in-house FE program presented the thermal stress and thermal strain of the FG disk. The weighted residual method in the FEM was used to present the temperature distribution when the material properties along an element are varying in contrast with using a commercial finite element software when the material properties are constant within an element to simulate FGMs. The accuracy of the in-house FE program was tested, and it was shown that the temperature distributions obtained by using the abovementioned methods were exactly the same. A parametric material gradation study was performed to understand the effects on the temperature, thermal strain, and stress. The material gradation was found to have a significant effect in this regard. The in-house finite element program enables one to perform a post-processing analysis in a more efficient and convenient manner than that through simulations in a finite element software program such as ANSYS. Lastly, this in-house code can be used to perform an optimization analysis to minimize the thermal strain and stress while the stiffness of the plate is maintained when the material properties within an element vary.