Sensitivity analysis for finite element modeling of humeral bone and cartilage

The objective of this work was to study the effectiveness of non -obstructive particle damping (NOPD) treatment in honeycomb (HC) structures. The NOPD approach entails development of a design and procedure for such a treatment, based on finite element modeling (FEM) analyses and tests. Laboratory tests were conducted to evaluate the performance of various particles u nder different vibration environments. Modeling and predictions were carried out simultaneously as tests were in progress and the model was correlated with the test data. This paper describes results of modal tests carried out at the Boeing RPP (Rocketdyne Propulsion a nd Power) Engineering Development Laboratory (EDL) on honeycomb panels and FEM analyses for the prediction of its modal characteristics. Introduction: Honeycomb structures are typically stiff. Therefore, flexural waves induced by loads, from such source s as turbulent boundary layers, have structural velocities that travel faster than the speed of sound in the surrounding air. The latter makes the honeycomb structures efficient radiators of noise at most frequencies, even down to the low end of the spect rum. Damping can help reduce the amplitudes of these waves at all frequencies. The higher the damping achieved, with a reasonably low weight penalty, the more beneficial it is in reducing the amplitude of vibration. It is relatively easy to absorb vibra tion energy in the high frequencies. Many damping treatment options exist, including viscoelastic materials. NOPD, on the other hand, could provide significant damping even at low frequencies, which could make its use very desirable 1,2,3 . To study the dam ping effectiveness of light particles placed inside the cells of stiff honeycomb structures a test and analysis program was carried out at RPP in the Fall of 2002: finite element analyses were carried out to predict the modal characteristics of HC panels, and to correlate those characteristics with laboratory modal test results. Tests were conducted with different particle materials filling the honeycomb cells. The panels were suspended with rubber bungee chords and structurally excited by shakers. The resp onse amplitudes and damping values, predicted using the test -data were compared under no particles with the ones with various particles filling the cells. Statistical Energy Analysis (SEA) was then carried out to predict the acoustic attenuation profile in the frequency range of interest. Analytical Design Developed and Correlated with Test Results: Square pieces of 2 ft. x 2 ft. x ½ in. HC were tested in the lab for modal characterization with different particle fillings. Several analyses were performed to estimate the passive damping material properties of the various NOPD materials based on test data obtained in earlier tests. These properties were then used to predict the damping of different panels with different particle treatments. The process requ ired several finite element models created using Abaqus (a commercially available FEM code with attractive non -linear analysis capabilities) composite laminate shells to represent the honeycomb structure with fiberglass face -sheets. The face -sheets were t reated as orthotropic since they were layered symmetrically across their thickness with respect to orientation angle of the fibers of individual layers. The honeycomb core itself was modeled as an orthotropic material with perturbations in density and dam ping to represent the assortment of NOPD materials tested. For correlation with tests and determination of particular modal damping, modal frequency dependent composite damping was used. Also, the quasi -analytical design sensitivity for frequency respons e in Abaqus was found to be useful during the correlation steps. The measured weight of the fiberglass panel was used in all of the analyses. Stiffness of the composite panel was correlated through the empty panel frequencies and mode shapes. The dampi ng values were then matched by test/analysis correlation. The values for the general modal characteristics of the various particles were then used in the acceleration response predictions, as is described below: The FEM analyses and test results indicated numerous modes starting at around 63 Hz. The FEM was used to predict the modal characteristics, with the cells modeled as individual solid elements, and with the face sheets modeled as separate solid elements. The FEM predictions showed a first bending mo de at 75 Hz with the uncorrelated model, and after correlation with test data at 63 Hz. The FEM was modified to reflect the mass and damping effects of each kind of particle on the honeycomb response and correlated with test data. Figure 1 shows the variou s FEM mode shapes of the baseline (empty) panel side -by -side with the measured mode shapes from the test results. The panels were analyzed and the results were correlated with the test data from previous tests as follows:

Bone geometry on the contact stress in the shoulder for evaluation of pressure ulcers: Finite element modeling and experimental validation

The effect of walking on inclined surfaces (uphill and downhill) on gait parameters of healthy subjects using self-paced treadmill in virtual environments

Masticatory overload on dental implants is one of the causes of marginal bone resorption. The implant–abutment connection (IAC) design plays a critical role in the quality of the stress distribution, and, over the years, different designs were proposed. This study aimed to assess the mechanical behavior of three different types of IAC using a finite element model (FEM) analysis. Three types of two-piece implants were designed: two internal conical connection designs (models A and B) and one internal flat-to-flat connection design (model C). This three-dimensional analysis evaluated the response to static forces on the three models. The strain map, stress analysis, and safety factor were assessed by means of the FEM examination. The FEM analysis indicated that forces are transmitted on the abutment and implant’s neck in model B. In models A and C, forces were distributed along the internal screw, abutment areas, and implant’s neck. The stress distribution in model B showed a more homogeneous pattern, such that the peak forces were reduced. The conical shape of the head of the internal screw in model B seems to have a keystone role in transferring the forces at the surrounding structures. Further experiments should be carried out in order to confirm the present suppositions.

Developing a subject-specific finite element (FE) model, especially with only high quality hexahedral solid elements and quadrilateral shell elements, is very time-consuming. Recently, template-based mesh morphing method has become popular to construct subject-specific FE models, in which a baseline FE mesh can be morphed into a FE model with subject-specific geometry. Because the mesh morphing algorithm could be programmed and run automatically, it is a very promising method for future applications of subject-specific FE models in injury biomechanics studies. Radial Basis Function (RBF) as a powerful spatial interpolation method has already been used as a mesh morphing method (1). The types of RBFs can affect the morphed mesh quality and geometry accuracy in the RBF method. However, to date, no previous study has tried to compare the differences generated by different RBFs. Therefore, in this study, different RBFs were used to morph a baseline infant head FE model into 10 different subject-specific infant head FE models based on CT images from 10 children aged from 0 to 3 months. The mesh quality and geometry accuracy of the subject-specific models generated by different RBFs were compared using statistic analysis.

A growing number of computational material science and computational mechanics research is currently devoted to the explicit modeling of microstructures at various length and time scales. The finite element models of grains and grain boundaries in polycrystals include discretization of the grain interior. In addition, grain boundaries are explicitly discretized as cohesive zones with appropriate damage properties to facilitate the simulation of intergranular cracking. Such finite element models may easily involve hundreds of grains and millions of finite elements. They may also be combined with advanced lattice orientation dependent constitutive models, such as for example anisotropic elasticity and crystal plasticity. The complexity of the model, including the random lattice orientations, may therefore represent a serious difficulty in detecting possible issues in the finite element model and the interpretation of the results. A number of self-consistency model-checks are therefore needed to verify the model. Two tests are proposed and demonstrated in the paper. The first is aiming at the assessment of the finite element mesh quality within the grains in terms of the results. The second is primarily aiming at the verification of the consistent modeling of the cohesive layer at the grain boundaries. In addition, some useful information about the finite element mesh quality in terms of results is also given.

Complex variable methods for shape sensitivity of finite element models

As the population ages, there is an increasing trend in patients with lumbar degenerative diseases (LDD) complicated by osteoporosis seeking lumbar fusion surgery. However, standardized strategies for minimally invasive surgical procedures among these populations still need improvement in clinical practice. This study was to integrate clinical and biomechanical approaches to investigate and demonstrate the effectiveness of oblique lateral interbody fusion combined with bone cement-augmented anterolateral screw (OLIF-BCAAS) in such patients. A single-center, retrospective case-controlled clinical study and finite element model (FEM) analysis. A single-center, retrospective case-controlled clinical study and finite element model (FEM) analysis were conducted. 48 cases were enrolled in the clinical study, then assigned to either OLIF-BCAAS or OLIF combined with posterior internal fixation with pedicle screws (OLIF-PIFPS). Clinical outcomes and radiological parameters were statistically analyzed. The FE models of intact lumbar spine, OLIF-BCAAS, and OLIF-PIFPS were constructed based on computed tomography (CT) scans of a healthy male. These FE models were analyzed under different loading conditions. There were significant differences in the surgical time, blood loss, and lower back score within 1year postoperatively between the two groups (p < 0.05). Moreover, both OLIF surgical techniques showed significant improvements in disc height (DH) postoperatively; however, the reduction in DH at postoperative 12months was more pronounced in the OLIF-PIFPS group than in the OLIF-BCAAS group (p < 0.05). Five cases (5/23, 21.74%) of cage subsidence (CS) were detected in the OLIF-BCAAS group, with 4 out of 23 cases (17.39%) considered as mild CS. In contrast, the amount of CS was 12 cases (12/25, 48%) in the OLIF-PIFPS group, which included 3 cases of severe CS. However, there was a trend towards statistical difference in CS between the two groups (p = 0.057). The FEM analysis showed significant reductions in the local range of motion and L3 maximum displacement with respect to L4 under six motion patterns in the two OLIF surgical models. Moreover, stress on the endplate and cage in the OLIF-BCAAS model was higher than that in the OLIF-PIFPS model; however, stress on the supplemental fixation devices was significantly lower than that observed in the OLIF-PIFPS model. Both OLIF surgical techniques for treating LDD with osteoporosis can achieve favorable clinical outcomes. However, OLIF-BCAAS exhibits more significant advantages over OLIF-PIFPS by maximizing the benefits of minimally invasive surgery. Moreover, OLIF-BCAAS is associated with lower postoperative back pain and a reduced incidence of postoperative CS.

The tensile response of three-dimensional angle-interlock woven composite (3DAWC) under quasi-static loading was investigated in experimental and finite element model (FEM) analysis. The FEM analysis was based on micro-structure at yarn level and connected with commercial FEM software ABAQUS/Explicit (ver. 6.10) to calculate the tensile property under quasi-static loading. The experimental and FEM stress-strain results were compared. Good agreement proved that the FEM method based on micro-structure was reasonable and effective and could be used to design 3-D woven structural composite.

Background and objective: population-based finite element analysis of hip joints allows us to understand the effect of inter-subject variability on simulation results. Developing large subject-specific population models is challenging and requires extensive manual effort. Thus, the anatomical representations are often subjected to simplification. The discretized geometries do not guarantee conformity in shared interfaces, leading to complications in setting up simulations. Additionally, these models are not openly accessible, challenging reproducibility. Our work provides multiple subject-specific hip joint finite element models and a novel semi-automated modeling workflow.Methods: we reconstruct 11 healthy subject-specific models, including the sacrum, the paired pelvic bones, the paired proximal femurs, the paired hip joints, the paired sacroiliac joints, and the pubic symphysis. The bones are derived from CT scans, and the cartilages are generated from the bone geometries. We generate the whole complex’s volume mesh with conforming interfaces. Our models are evaluated using both mesh quality metrics and simulation experiments.Results: the geometry of all the models are inspected by our clinical expert and show high-quality discretization with accurate geometries. The simulations produce smooth stress patterns, and the variance among the subjects highlights the effect of inter-subject variability and asymmetry in the predicted results.Conclusions: our work is one of the largest model repositories with respect to the number of subjects and regions of interest in the hip joint area. Our detailed research data, including the clinical images, the segmentation label maps, the finite element models, and software tools, are openly accessible on GitHub and the link is provided in Moshfeghifar et al.(2022)[1]. Our aim is to empower clinical researchers to have free access to verified and reproducible models. In future work, we aim to add additional structures to our models.

Background The incidence of cervical spondylosis is increasing, gradually affecting people’s normal lives. Establishing a finite element model of the cervical spine is one of the methods for studying cervical spondylosis. MRI (Magnetic Resonance Imaging) still has certain difficulties in transitioning from human imaging to establishing muscle models suitable for finite element analysis. Medical software provides specific morphologies and can generate muscle finite element models. Additionally, there is little research on the static analysis of cervical spine finite element models with solid muscle. Purpose A new method is proposed for establishing a finite element model of the cervical spine based on CT (Computed Tomography) data and medical software, and the model’s effectiveness is validated. Human movement characteristics based on the force distribution in various parts are analyzed and predicted. Methods The muscle model is reconstructed in medical software and a three-dimensional finite element model of the entire cervical spine (C0–C7) is established by combining muscle models with CT vertebral data models. 1.5 Nm of load is applied to the finite element model to simulate the cervical spine movement. Results The finite element model was successfully established, and effectiveness was verified. Stress variations in various parts under six movements were obtained. The effectiveness of the model was basically verified. Conclusion The finite element model of the cervical spine for mechanical analysis can be successfully established by using medical software and CT data. In daily life, the C2–3, C3–4, C4–C5 intervertebral discs, rectus capitis posterior major, longus colli, and obliquus capitis inferior are more prone to injury.

To construct a model for a controlled memory (CM) nickel-titanium (NiTi) file and another M-wire NiTi file with the same geometry by using finite element analysis. To evaluate the flexibility of a CM NiTi file by using three dimensional finite element method and to compare its mechanical responses with that M-wire NiTi. Based on the reverse engineering, the 21 mm long, 25#/08 taper Hyflex NT NiTi file and Hyflex CM NiTi file were fixed by the cantilever bending model at a distance of 9.5 mm from the tip of the file. The mechanical tester's indenter was loaded/unloaded at a distance of 3 mm from the tip of the file. The maximum displacement was 3 mm, the load displacement curve was obtained. Subsequently, by using a micro-CT to scan (layer spacing of 8 μm) NiTi files, and ABAQUS (6.10) was introduced to construct a geometric model. Hyflex NT was considered as a shapememory alloy constitutive model, Hyflex CM was considered as a power-hardening plastic constitutive model, respectively. Comparing the load-displacement curve of cantilever bending in the three-dimensional finite element model with the load-displacement curve in the experiment. Two tetrahedral element models were constructed, the total number of nodes was 99 353 and the total number of cells was 63 744. When the loading displacement was 1 mm, the stress distribution of the cross section at 6.1 mm from the tip of the file was observed. The upper and lower surfaces were subjected to the maximum bending stress and entered the phase transformation yield stage. The finite element simulation could clearly show the deformation of the file. Various information such as deformation characteristics and stress distribution in the process were well fitted to the actual experimental curve. The constitutive behavior of the material has a significant effect on the mechanical behavior of NiTi file. The finite element model established for the NiTi file of the CM wire can accurately capture the characteristics of various deformation processes of the NiTi root canal file, and it has a good fit with the actual experimental curve. The finite element model can be used for study on bending properties of CM wire.

Stress distribution remains unclear in early-stage osteonecrosis of the femoral head (ONFH). To clarify this issue, we generated patient-specific finite element models (FEMs) from 51 patients with ONFH. Patients' hips were classified into three groups: ONFH without a sclerotic boundary (Stage 1, n = 6), ONFH with a sclerotic boundary (Stage 2, n = 10), and ONFH with both a sclerotic boundary and <2 mm collapse (Stage 3, n = 35). Four hips without ONFH were used as controls. Stress distribution in each FEM was compared with magnetic resonance imaging (MRI) and computed tomography (CT) results. Fifteen wholly resected femoral heads in Stage 3 hips were assessed by micro-CT. Furthermore, we histologically examined three Stage 2 femoral heads that subsequently developed subchondral fractures after FEM analyses. In all FEMs of both control and Stage 1 hip, stress was equally distributed on the femoral head surface. However, in all FEMs of both Stages 2 and 3 hips, stress was concentrated at the lateral boundary of the femoral head surface, corresponding to both a low-intensity band on T1-weighted MRI images and sclerotic changes on CT. On micro-CT, subchondral fractures consistently began at the lateral boundary with sclerotic changes, in which bone volume fraction was increased. Histology showed breakage of subchondral plates at the junction between necrotic and reparative zones. In early-stage ONFH, sclerotic changes caused stress concentration, which can trigger subchondral fractures at the lateral boundary. Clinical Significance: Our results will clarify the pathogenic mechanism of collapse in ONFH. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3169-3177, 2018.

Prediction of crack coalescence of steam generator tubes in nuclear power plants

Introduction: AAA rupture occurs as a consequence of the imbalance between aortic wall's strength and the loading stress. FEM provides information on the regional distribution of stresses in the wall of AAA and proved to be a more accurate predictor of aneurysm rupture. The risk of rupture is expressed through peak wall stress (PWS) and rupture risk equivalent diameter (RRED) that includes wall strength in calculation. Aim: To determine the influence of FEM and subsequent biomechanical analysis of AAA on treatment decisions in common clinical practice. Material and methods: This prospective study included 48 patients with asymptomatic AAA. The specific anatomical and biomechanical parameters were determined by a FEM analysis: location of the PWS and diameter of the aorta, parietal thrombus in the level of PWS and the maximum value of the measured diameter (MD) as well as rupture risk equivalent diameter (RRED). Decision of treatment would change if maximal aneurysm diameter and RRED are on different sides of the 55 mm that is contemporary treatment threshold for AAA. Results: In 20 patients (41.67%) values of RRED could change treatment decisions. Four patients (20%) with aneurysm diameter (MD) less than 55 mm would be transferred to the group of patients with indications for surgical treatment because their RRED was higher than the limit of 55 mm. Sixteen patients (80%) would be transferred to the group of patients for further follow up without surgical treatment, because their RRED was less than the limit of 55 mm although their MD was higher than 55mm. Conclusion: Finite element model (FEM) of abdominal aortic aneurysm (AAA) and subsequent biomechanical analysis would lead to change of surgical indications for treatment of AAA in almost half of included patients.