Maximum Stress Difference Research Articles

A comparative study of storage solutions on the biomechanical preservation of human saphenous veins

Storage solutions have a significant impact on the physiological properties of saphenous veins (SV), yet their effects on the biomechanics remained unclear. This study investigated how different storage solutions affect the biomechanical properties of SV. The goal was to find a solution that minimally impacts SV biomechanics, providing an effective method for SV preservation. A total of 108 SV samples (54 axial, 54 circumferential) were randomly divided into four groups: Baseline (tested within 24 h after surgical removal), and three stored for 72 h—sodium lactated ringer’s solution (SLR), physiological saline (PS), and Air. Uniaxial tensile experiments were performed, and differences in elastic modulus, maximum stress, and average stress–strain curves were evaluated. In the axial direction, the elastic modulus of SVs stored in SLR was significantly higher than in PS (7.21 ± 2.78 MPa vs. 3.90 ± 1.54 MPa, p = 0.009) and similar to Baseline (vs. 8.52 ± 3.43 MPa), while the PS group did not differ significantly from the Air group (3.90 ± 1.54 MPa vs. 2.50 ± 1.34 MPa, p > 0.99). The maximum stress in SLR was similar to Baseline (1.92 ± 0.82 MPa vs. 1.91 ± 0.58 MPa) and significantly higher than in PS (vs. 1.05 ± 0.56 MPa, p = 0.002). Similar trends could also be observed in the circumferential direction. PS significantly impairs the mechanical performance of SVs, while short-term storage in SLR can effectively preserve the biomechanical characteristics of SVs. SLR may be considered as an effective short-term storage solution for SV.

Effect of biomechanical load factors on the stress-strain state of teeth and underlying bone tissue

Background: The biomechanical conditions under which teeth, implants, and bone tissue function clearly determine their resistance to overloading and subsequent destruction. However, mathematical modeling has not previously been used to compare functional stress in teeth across a wide range of sensitive biomechanical load conditions. Aim: To compare the stress-strain state parameters of tooth and socket tissues under various biomechanical load conditions. Materials and methods: A mathematical model was used to assess the stress-strain state parameters of dental tissue and sockets under vertical and oblique load (150N) with various modeling settings, compared to reference model parameters. The following parameters were assessed: enamel attrition, bone density reduction, bone resorption by 30% and 50%, supra-occlusion, tooth cavity, composite restoration, and ceramic inlay. Results: Enamel attrition significantly increases stress under vertical and oblique loads: 1.9 and 1.6 times for enamel, and 1.5 and 1.2 times for dentin, respectively. Tooth cavities increase stress by 1.2 and 1.8 times (enamel; vertical and oblique loads, respectively), and 1.3 times (dentin; vertical load). Increased functional load causes a proportional increase in stress in hard tooth tissues and adjacent bone tissues. Supra-occlusion causes a sharp increase in stress in the enamel, with a point stress concentration. When a tooth cavity is filled with a composite or ceramic material, the stress-strain state parameters are similar to those in intact teeth (however, the enamel still experiences a 1.5-fold increase in stress under vertical pressure). Conclusion: 3D mathematical modeling revealed a significant difference in maximum stress in tooth and socket tissues compared to normal biomechanical conditions, as well as when comparing various sensitive load conditions. Stress in tooth and bone tissues increased in all cases of abnormal biomechanical conditions, especially when oblique load was applied.

A Systematic Study of CSTD-Generated Stress on Different Biomolecular Modalities

Although Closed System Transfer Devices (CSTDs) are used in oncology for dose preparation and administration, the impact of CSTDs on biologics and other non-small molecular modalities are not fully understood. We investigated particle formation when preparing and mock administering three experimental biologics (mAb, ADC, and fusion protein) using seven models of CSTDs. A wide range of visible and subvisible particle formation was observed among CSTD models. Particles were found to consist of silicone oil and protein. X-ray micro-computed tomographic images of the fluid paths of the CSTDs showed that most have highly tortuous fluid paths. Computational fluid dynamics analysis of dose preparation using the CSTDs that produced the highest and lowest amounts of particles demonstrated a 154-fold difference in maximum shear stress as well as a significant difference in solution residence time. Control experiments with silicone oil spiking showed that exposing the proteins to silicone oil does not account for the majority of visible and subvisible particle formation. These results demonstrate that the geometry of the fluid paths of CSTDs can have a detrimental effect on protein stability.

Biomechanical characterization of cadaveric brachial plexus microstructure

IntroductionPeripheral nerves consist of axons and connective tissue. The amount of connective tissue in peripheral nerves such as the brachial plexus varies proximally to distally. The proximal regions of the brachial plexus are more susceptible to stretch injuries than the distal regions. A description of the mechanical behavior of the peripheral nerve components is necessary to better understand the deformation mechanisms during stretch injuries.The purpose of this study was to model the biomechanical behavior of each component of the peripheral nerves (fascicles, connective tissue) in a cadaveric model and report differences in elastic modulus, maximum stress and maximum strain. MethodsForty-six specimens of fascicles and epi-perineurium were subjected to cyclical uniaxial tensile tests to obtain the stress and strain histories of each specimen, using a BOSE® Electroforce® 3330 and INSTRON® 5969 materials testing machines.Maximum stress, maximum strain and elastic modulus were extracted from the load–displacement and stress–strain curves, and analyzed using Mann-Whitney tests. ResultsMean elastic modulus was 6.34 MPa for fascicles, and 32.1 MPa for connective tissue. The differences in elastic modulus and maximum stress between fascicles and connective tissue were statistically significant (p < 0.001). ConclusionsPeripheral nerve connective tissue showed significantly higher elastic modulus and maximum stress than fascicles. These data confirm the greater fragility of axons compared to connective tissue, suggesting that the greater susceptibility to stretch injury in proximal regions of the brachial plexus might be related to the smaller amount of connective tissue.

Effect of variability of mechanical properties on the predictive capabilities of vulnerable coronary plaques

Background and Objective:Coronary plaque rupture is a precipitating event responsible for two thirds of myocardial infarctions. Currently, the risk of plaque rupture is computed based on demographic, clinical, and image-based adverse features. However, using these features the absolute event rate per single higher-risk lesion remains low. This work studies the power of a novel framework based on biomechanical markers accounting for material uncertainty to stratify vulnerable and non-vulnerable coronary plaques. Methods:Virtual histology intravascular ultrasounds from 55 patients, 29 affected by acute coronary syndrome and 26 affected by stable angina pectoris, were included in this study. Two-dimensional vessel cross-sections for finite element modeling (10 sections per plaque) incorporating plaque structure (medial tissue, loose matrix, lipid core and calcification) were reconstructed. A Montecarlo finite element analysis was performed on each section to account for material variability on three biomechanical markers: peak plaque structural stress at diastolic and systolic pressure, and peak plaque stress difference between systolic and diastolic pressures, together with the luminal pressure. Machine learning decision tree classifiers were trained on 75% of the dataset and tested on the remaining 25% with a combination of feature selection techniques. Performance against classification trees based on geometric markers (i.e., luminal, external elastic membrane and plaque areas) was also performed. Results:Our results indicate that the plaque structural stress outperforms the classification capacity of the combined geometric markers only (0.82 vs 0.51 area under curve) when accounting for uncertainty in material parameters. Furthermore, the results suggest that the combination of the peak plaque structural stress at diastolic and systolic pressures with the maximum plaque structural stress difference between systolic and diastolic pressures together with the systolic pressure and the diastolic to systolic pressure gradient is a robust classifier for coronary plaques when the intrinsic variability in material parameters is considered (area under curve equal to [0.91–0.93]). Conclusion:In summary, our results emphasize that peak plaque structural stress in combination with the patient’s luminal pressure is a potential classifier of plaque vulnerability as it independently considers stress in all directions and incorporates total geometric and compositional features of atherosclerotic plaques.

Biomechanical characterization of cadaveric brachial plexus regions using uniaxial tensile tests

IntroductionThe proximal regions of the brachial plexus (roots, trunks) are more susceptible to permanent damage due to stretch injuries than the distal regions (cords, terminal branches). A better description of brachial plexus mechanical behavior is necessary to better understand deformation mechanisms in stretch injury.The purpose of this study was to model the biomechanical behavior of each portion of the brachial plexus (roots, trunks, cords, peripheral nerves) in a cadaveric model and report differences in elastic modulus, maximum stress and maximum strain. MethodsEight cadaveric plexi, divided into 47 segments according to regions of interest, underwent cyclical uniaxial tensile tests, using a BOSE® Electroforce® 3330 and INSTRON® 5969 material testing machines, to obtain the stress and strain histories of each specimen.Maximum stress, maximum strain and elastic modulus were extracted from the load–displacement and stress–strain curves.Statistical analyses used 1-way ANOVA with post-hoc Tukey HSD (Honestly Significant Difference) and Mann-Whitney tests. ResultsMean elastic modulus was 8.65 MPa for roots, 8.82 MPa for trunks, 22.44 MPa for cords, and 26.43 MPa for peripheral nerves. Differences in elastic modulus and in maximum stress were statistically significant (p < 0.001) between proximal (roots, trunks) and distal (cords, peripheral nerves) specimens. ConclusionsProximal structures demonstrated significantly smaller elastic modulus and maximum stress than distal structures. These data confirm the greater fragility of proximal regions of the brachial plexus.

Simulation and Experimental Study of Nanosecond Pulse Laser Removal of Epoxy Paint on 6061 Aluminum Alloy Surface

Laser paint removal is a new cleaning technology that mainly removes paint through thermal ablation and mechanical stripping mechanisms. This paper established a thermal-mechanical coupling laser removal model of paint based on the heat conduction equation, Newton’s second law, and Fabbro’s theory. The removal process of epoxy resin paint film on an aluminum alloy surface via a nanosecond pulsed laser was studied using finite element simulations and experimental measurements. The simulation and experimental results show that the nanosecond pulse laser’s primary paint removal mechanism is the mechanical stripping caused by thermal stress and plasma shock. The laser paint removal threshold is 1.4 J/cm2. In addition, due to the different generation times of plasma shock and thermal stress, the mutual superposition of stress waves occurs in the material. This results in a discrepancy between the actual and thermal stress differences. Moreover, the thermal stress difference causes the maximum actual stress difference to fluctuate. The simulation model established in this paper can provide a reference for studying the thermal-mechanical coupling process of laser paint removal.

Advective gas flow in bentonite: Development and comparison of enhanced multi-phase numerical approaches

Understanding the impact of repository gas, generated from degradation of waste and its interaction with the host rock, is essential when assessing the performance and safety function of long-term disposal systems for radioactive waste. Numerical models based on conventional multi-phase flow theory have historically been applied to predict the outcome and impact of gas flow on different repository components. However, they remain unable to describe the full complexity of the physical processes observed in water-saturated experiments (e.g., creation of dilatant pathways) and thus, the development of novel representations for their description is required when assessing fully saturated clay-based systems. This was the primary focus of Task A within the international cooperative project DECOVALEX-2019 (D-2019) and refinement of these approaches is the primary focus of this study (Task B in the current phase of DECOVALEX-2023).This paper summarises development of enhanced numerical representations of key processes and compares the performance of each model against high-quality laboratory test data. Experimental data reveals that gas percolation in water-saturated compacted bentonite is characterised by four key features: (i) a quiescence phase, followed by (ii) the gas breakthrough, which leads to a (iii) peak value, which is then followed by (iv) a negative decay. Three models based on the multiphase flow theory have been developed. These models can provide good initial values and reasonable responses for gas breakthrough (although some of them still predict a too-smooth response). Peak gas pressure values are in general reasonably well captured, although maximum radial stress differences are observed at 48 mm from the base of the sample. Here, numerical peak values of 12.8 MPa are predicted, whereas experimental values are about 11 MPa. These models are also capable of providing a reasonable representation of the negative pressure decay following peak pressure. However, other key specific features (such as the timing of gas breakthrough) still require a better representation. The model simulations and their comparison with experimental data show that these models need to be further improved with respect to model parameter calibration, the numerical representation of spatial heterogeneities in material properties and flow localisation, and the upscaling of the related physical processes and parameters. To further understand gas flow localisation, a new conceptual model has been developed, which shows that discrete channels can possibly be induced through the instability of gas-bentonite interface during gas injection, thus providing a new perspective for modeling gas percolation in low-permeability deformable media.

Differences in the microstructural and mechanical qualities of semitendinosus tendon grafts between skeletally immature and mature patients in anterior cruciate ligament reconstruction

BackgroundThis study aimed to investigate the microstructural and mechanical properties of semitendinosus tendon graft tissues during anterior cruciate ligament reconstruction and the clinical outcomes in skeletally immature and mature patients. MethodsTwenty-two patients who underwent primary anterior cruciate ligament reconstruction using a hamstring tendon graft were analyzed and divided into skeletally immature (n = 7) and mature groups (n = 15) based on magnetic resonance imaging findings of the epiphyseal plate of the distal femur. Tissue samples were collected from the mid-portion of the semitendinosus tendon. The collagen fibril diameter, maximum stress, and strain at maximum stress point in the semitendinosus tendon tissues were calculated for comparison of the microstructural and mechanical properties between the two groups. Postoperative outcomes were also assessed between the two groups. ResultsThe mean and 60th and 80th percentiles of fibril diameters in the skeletally immature group were significantly smaller than those in the mature group (65.9 ± 13.0, 73.5 ± 19.3, and 91.3 ± 27.4 nm in the skeletally immature group; and 90.3 ± 14.7, 94.0 ± 18.4, and 125.3 ± 19.9 nm in the skeletally immature group; p = 0.001, 0.024, and 0.004, respectively). Additionally, the strain at maximum stress was higher in the skeletally immature group (237.2 ± 102.4% vs. 121.5 ± 51.9%, p = 0.024). However, there was no difference in maximum stress between the skeletally immature and mature groups (19.9 ± 14.3 MPa vs. 24.5 ± 23.4 MPa, p = 0.578). Strain was negatively correlated with the mean fibril diameter and the 60th and 80th percentiles of fibril diameters, whereas stress was positively correlated with the mean fibril diameter. The skeletally immature group had a higher pivot shift test-positive rate than the mature group at the last follow-up (p = 0.023). ConclusionSemitendinosus tendon graft tissues differed microstructurally and mechanically between skeletally immature and mature patients. Level of evidenceLevel Ⅳ

Experimental and numerical simulation of pull-out response in textile-reinforced concrete

Textile-reinforced concrete (TRC) is a construction material that uses continuous fibres such as carbon to create a lightweight and durable structural system. Even though TRC possesses vast possibilities in terms of its usage, identification of bond-slip behaviour at the material interface is one of the limitations that need to be addressed. Based on the literature, there are difficulties in determining the bond-slip relationship both experimentally and numerically, creating inconsistency in the results. This study aims to determine the bond-slip relation of TRC through pullout tests and validated through finite element analysis to replicate the actual bond-slip behaviour at the interface. The bond characteristics of TRC were assessed using a double-sided pullout test setup with different bond lengths of textile, namely 20 mm, 30 mm, 40 mm, 50 mm, and 60 mm. It was noticed that in short bond specimens (20 mm, 30 mm, and 40 mm), the phenomena of pullout failure were due to weakened bond at the interface until pre-peak, followed by complete loss of adhesive bond due to debonding of fibre. However, for the specimens with longer bond lengths (50 mm and 60 mm), rupture of the textile leading to a sudden loss of bond capacity was observed. Additionally, the general fibre pullout phenomenon curve was used to explain the debonding process. Using a calibrated tri-linear bond-slip interface relation, the numerical model was developed to simulate the pull-out response of fibre. The numerical model was able to reproduce experimental results, including maximum load, post-peak behaviour, and interfacial slip. The difference of maximum shear stress between pull-out tests and numerical modelling was within 2 % while the slip difference was between 4 and 31 % for different bond lengths. However, for longer bond lengths, the fibre failure mode was due to pullout instead of rupture, unlike the experimental results.

Experimental investigation of factors affecting the characterisation of soil strength properties using a Bevameter in-situ plate sinkage and shear test apparatus

The Bekker-Wong soil-wheel interaction model has been widely adopted in the terramechanics field. This model requires the soil to be characterised using a Bevameter, which entails performing in situ plate sinkage and shear stress tests. Bevameter soil characterisation is not a standardised test procedure, and the test setup may influence the identified soil model parameters. This study investigates the influence of the following five factors for partially saturated sandy soil: I) soil preparation method on pressure-sinkage, II) soil preparation method on shear stress, III) torsional vs. translational shear mechanism, IV) shear contact area, and V) the influence of shear velocity. The results indicate that the influence of soil preparation on pressure-sinkage response is substantial, exhibiting an order-of-magnitude difference. The influence of soil preparation on shear tests is notable, but less significant. The shear mechanism, shear contact area and shear velocity exhibited a maximum absolute shear stress difference of 18%, 20% and 10%, respectively. Moreover, depending on the test setup configuration and data processing decisions, the estimated internal soil friction angles ranged from 16.5 to 37.5° for the same soil. The findings are expected to have significant implications for the prediction of vehicle drawbar pull using the Bekker-Wong model.

Mechanical property analysis and structure optimisation of worm gear reducer

ABSTRACT In the process of lightweight design, there will be problems such as stress concentration and structural weakening. In order to improve the design defect of serious insufficient life caused by the bending failure of worm gear, the bending stress of worm gear tooth root was analyzed by solution method and finite element simulation method. The main research contents include: firstly, the bending stress of worm gear is calculated by analytical solution method; Secondly, CAD is used to reconstruct the model; Finally, HyperMesh is used for analysis of the structure. The maximum bending stress obtained from theoretical calculation is 34.56Mpa, and the maximum stress from simulation is 39.3Mpa, 29.6Mpa and 26.3Mpa respectively in the three areas of gear root A, B and C (figure 7). Compared with the finite element, the maximum stress difference between them is 4.74Mpa. The stress concentration point is determined, and the structure optimization is carried out; CAE analysis of the optimized model shows that stresses in A, B and C regions of the worm gear root are 33.4 MPa, 22.5 MPa and 5.9 MPa, respectively. After optimization, the maximum stress difference between the two is 1.16Mpa.The above analysis results provide theoretical support for the design of worm gear reducer.

Comparison of different plating systems in bilateral para symphysis fractures

Aim: The purpose of the present research was to evaluate the comparison of various plating systems used in treatment of bilateral para-symphysis fracture. Methodology: Fractures were generated in 3-dimensional finite element models, and were fixed with a single miniplate, parallel double miniplates, or perpendicular double miniplates. A 300 N perpendicular load was then applied on the left molar region, and a finite element analysis was performed. Vertical gaps between the fractured surfaces of bilateral para-symphyseal areas, maximum stress within the screw/plating system, and maximum stress around screw holes in the bone. Results: Compared to the single miniplate, both the parallel and perpendicular double miniplates demonstrated significantly less stress in the screw/plating system and screw holes in the bone. In addition, the perpendicular double miniplates had significantly smaller vertical gaps between fracture surfaces when compared to the single miniplate. Comparing parallel and perpendicular double miniplate fixations, less stress was found around the screw holes of the perpendicular miniplate models than those of the parallel miniplate models. There were no differences in vertical gaps or maximum stress within the screw/plating systems between the 2 double miniplate fixations.

Biomechanical study of anterior and posterior pelvic rings using pedicle screw fixation for Tile C1 pelvic fractures: Finite element analysis.

The purpose of this study was to analyse the biomechanical characteristics of pedicle screws with different placement methods and diameters in the treatment of Tile C1 pelvic fractures by finite element simulation technology and to compare them with the plate fixation model to verify the effectiveness of pedicle screw fixation. A three-dimensional digital model of a normal pelvis was obtained using computed tomography images. A finite element model of a normal pelvis containing major ligaments was built and validated (Model 1). Based on the verified normal pelvis finite element model, a Tile C1 pelvic fracture model was established (Model 2), and then a plate fixation model (Model 3) and a pedicle screw fixation model with different screw placement methods and diameters were established (Models 4-15). For all pelvic fracture fixation models, a vertical load of 500 N was applied on the upper surface of the sacrum to test the displacement and stress distribution of the pelvis in the standing state with both legs. The finite element simulation results showed the maximum displacement of Model 1 and Models 3-15 to be less than 1 mm. The overall maximum displacement of Models 4-15 was slightly larger than that of Model 3 (the maximum difference was 177.91×10-3 mm), but the maximum displacement of iliac bone and internal fixation in Models 4-15 was smaller than that of Model 3. The overall maximum stress (maximum stress of the ilium) and maximum stress of internal fixation in Models 4-15 were less than those in Model 3. The maximum displacement difference and maximum stress difference at the fracture of the pubic ramus between each fixed model were less than 0.01 mm and 1 MPa, respectively. The greater the diameter and number of pedicle screws were, the smaller the maximum displacement and stress of the pelvic fracture models were.The maximum displacement and stress of the pelvic fracture models of the screws placed on the injured side of the pubic region were smaller than the screws on the healthy side. Both the anterior and posterior pelvic rings are fixed with a pedicle screw rod system for treatment of Tile C1 pelvic fractures, which can obtain sufficient biomechanical stability and can be used as a suitable alternative to other implants.The greater the diameter and number of pedicle screws were, the greater the pelvic stability was, and the greater was the stability of the screws placed on the injured side of the pubic region than the screws on the healthy side.

THERMAL-DEFORMATION MODEL OF A Sr-MODIFIED A356 ALUMINUM ALLOY

The hot-deformation behavior of A356 aluminum alloy with a Sr modification was investigated using a Gleeble 1500 thermal simulator. The true stress-strain curves with a deformation temperature of 300–500 °C and a strain rate of 0.01–5 s–1 were clarified. The activation energy of the A356 aluminum alloy with Sr modification was 221.474 kJ/mol. The influences of friction and temperature on the curves were investigated, and then the constitutive equation was established. The results show that the flow stress is obviously affected by temperature and strain rate. The experimental stress is lower than the theoretical stress, and the stress difference between the experimental and theoretical stress increases with the increasing strain. The maximum stress difference reaches 17.8 MPa when the sample deformed at 300 °C/5 s–1 with a reduction of 16 %. For all the deformation conditions the correlation coefficient is 0.99 and the average relative error is 4.8 %, which shows the good predictability of the current model. The developed constitutive equation can provide guidance for the study of the hot-deformation behavior of similar aluminum alloys.

Measuring the density and viscosity of culture media for optimized computational fluid dynamics analysis of in vitro devices

Culture medium is frequently modelled as water in computational fluid dynamics (CFD) analysis of in vitro culture systems involving flow, such as bioreactors and organ-on-chips. However, culture medium can be expected to have different properties to water due to its higher solute content. Furthermore, cellular activities such as metabolism and secretion of ECM proteins alter the composition of culture medium and therefore its properties during culture. As these properties directly determine the hydromechanical stimuli exerted on cells in vitro, these, along with any changes during culture must be known for CFD modelling accuracy and meaningful interpretation of cellular responses. In this study, the density and dynamic viscosity of DMEM and RPMI-1640 media supplemented with typical concentrations of foetal bovine serum (0, 5, 10 and 20% v/v) were measured to serve as a reference for computational design analysis. Any changes in the properties of medium during culture were also investigated with NCI–H460 and HN6 cell lines. The density and dynamic viscosity of the media increased proportional to the % volume of added foetal bovine serum (FBS). Importantly, the viscosity of 5% FBS-supplemented RPMI-1640 was found to increase significantly after 3 days of culture of NCI–H460 and HN6 cell lines, with distinct differences between magnitude of change for each cell line. Finally, these experimentally-derived values were applied in CFD analysis of a simple microfluidic device, which demonstrated clear differences in maximum wall shear stress and pressure between fluid models. Overall, these results highlight the importance of characterizing model-specific properties for CFD design analysis of cell culture systems.

Comparison of Manual versus Semi-Automatic Segmentations of the Stenotic Carotid Artery Bifurcation

Background: The image reconstruction of stenotic carotid bifurcation can be managed by medical practitioners and non-medical investigators with semi-automatic or manual segmentation. The outcome of blood flow simulations may vary because of a single mean voxel difference along the examined section, possibly more in the stenotic lesions, which can lead to conflicting results regarding other research findings. The aim of our project is computational geometry reconstruction for blood flow simulations to make it suitable for comparison with plaque image analysis performed by commercially available software. In this paper, a comparison is made between the manual and semi-automatic segmentations performed by non-medical and medical investigators, respectively. Methods: 30 patients were classified into three homogeneous groups. Our group classification was based on the following parameters: plaque calcification score, thickness, extent, remodeling and plaque localization. The images in the first group were segmented individually by medical practitioners and experienced non-medical investigators, the second group was segmented collectively, and the last group was segmented individually again. Cross-sections along the centerline were extracted, then geometrical and statistical analyses were performed. Exploratory flow simulations were carried out on two patients to showcase the effect of geometrical differences on the hemodynamic flow field. Results: The largest centerline-averaged voxel difference between the medical and non-medical investigators occurred in the first group with a positive difference of 1.16 voxels. In the second and third groups, the average voxel difference decreased to 0.65 and 0.75, respectively. The example case from the first group showed that the difference in maximum wall shear stress in the middle of the stenosis is 30% with an average voxel difference of 1.73. Meanwhile, it can decrease to 4% when the average voxel difference is 0.64 for the example case from the third group. Conclusions: A collective review of the medical images should preceded the manual segmentations before applying them in computational simulations in order to ensure a proper comparison with plaque image analysis. Especially complex pathology such as calcifications should be segmented under medical supervision or after specific training. Non-significant differences in the segmentation can lead to significant differences in the computed flow field.

Structural Design Optimization and Prestress Simulation of the Laminate-Containment Launcher

The laminate-containment launcher is a high-efficiency electromagnetic railgun launcher (EMRL), which uses a laminate structure to reduce eddy current loss. However, the research on the design optimization of the laminate-containment launcher with prestress and mass as the goal is rarely mentioned. In this article, some key parameters of the laminate-containment launcher—the magnitude of interference $s$ , the axial thickness of the steel laminate $t_{s}$ and insulation laminate $t_{i}$ , the thickness of inner glass fiber $r_{g}$ , and the radial thickness of the laminate $r_{l}$ —are studied. On this basis, the influence of the five parameters on the hoop stress of the rail is fitted as a function by using the multiple nonlinear regression method. Then, the maximum hoop stress $f_{\mathrm {1max}}$ and the maximum hoop stress difference $f_{\mathrm {2max}}$ of the rail are calculated by using a nonlinear programming algorithm. Finally, the maximum hoop stress $f_{\mathrm {1max}}$ , the maximum hoop stress difference $f_{\mathrm {2max}}$ , and the maximum mass $f_{\mathrm {3max}}$ are taken as the reference values, and the optimal solution of the multiobjective function is obtained by using the weighted nonlinear programming algorithm. The results can be described as follows: the hoop stress of the rail changes linearly with the increase of the magnitude of interference, while the hoop stress changes approximately quadratic with the change of other parameters. Through the optimization of nonlinear programming algorithm with weighted form, the optimal design under different weighted values is obtained, which has a small error compared with the calculation results of ANSYS. The important characteristic that the hoop stress of the laminate-containment launcher presents wavy variation along the axial direction is obtained by numerical simulation. These results can provide theoretical guidance for the structural design of the laminate-containment launcher.

An Analysis of the Impact of Deviatoric Stress and Spherical Stress on the Stability of Surrounding Rocks in Roadway

In this study, a detailed analysis was conducted to evaluate the impacts of the deviatoric stress component and spherical stress component on the stability of surrounding rocks in the roadway via the theoretical analysis and calculation and numerical simulation. Based on the analysis, the distribution laws guiding the main stress differences, plastic zone, convergence of surrounding rocks, and third invariant of stress under various conditions (such as equal spherical stress and unequal deviatoric stress and equal deviatoric stress and unequal spherical stress) were developed, providing an optimization scheme for roadway support misunderstanding under the conditions of high spherical stress field and high deviator stress field. The study further reveals that under the circumstance of the constant spherical stress, the greater the deviatoric stress, the plastic zone range of the surrounding rock of the roadway, the range of tensile deformation of the surrounding rock, the amount of convergence of the surrounding rock, the probability of separation of the roof and floor of the roadway, and the principal stress difference and the main stress, the greater the concentration range of the maximum stress difference is, and the maximum principal stress difference is mainly concentrated in the roof and floor rocks of the roadway, and the greater the deviatoric stress, the greater the probability that the roof and floor rocks of the roadway will be separated, and the maximum principal stress difference is mainly concentrated in the roof and floor rocks of the roadway, the greater the deviator stress, the greater the concentration range of the maximum value of the principal stress difference and the principal stress difference; when the deviator stress is constant, the range of the plastic zone and the maximum principal stress difference concentration range of the surrounding rock of the roadway decrease with the increase of the ball stress, and the principal stress difference, the amount of convergence of the surrounding rock, and the range of tensile deformation increase with the increase of the ball stress. The maximum principal stress difference is mainly concentrated in the roof and floor rocks of the roadway. The principal stress difference increases with the increase of the spherical stress, and the maximum concentration range of the principal stress difference decreases with the increase of the spherical stress. After the method proposed in this paper optimizes the actual roadway support on site, the surrounding rock deformation of the roadway is small and the control is relatively ideal, which basically meets the engineering needs.

Influence of cracks and voids on the responses of composites

In this paper, numerical study on influence of parameters related to cracks and voids on the responses of the composites under tension, compression, and shear deformation is conducted by extended finite element method (XFEM). Under tension, the maximum stress of composites changes less than 5% when crack orientation, fiber orientation, and void distance change. The maximum averaged stress could differ by 10% when the crack location and crack length change. In the multi-crack composites, there is difference by 10% in maximum stress due to relative crack location. Under shear deformation, crack orientation affects the maximum averaged shear stress significantly when compared to the same composites under tension. The difference of maximum averaged shear stress is more than 15% when fiber orientation changes. The void distance results in 5% difference on the maximum stress of composites. In the multi-crack composites, the relative crack location could result in 10% difference in maximum averaged shear stress. Crack length also could result in significant difference in maximum stress of composites under shear deformation. Under tension and shear deformation, one crack is always the dominant crack and its propagation path determines the strength of the multi-crack composites. Unlike in tension and shear deformation, single crack in the composites under compression doesn’t result in the failure of composites even when the strain is 0.03. That is, no geometric buckling occurs for the single crack composite under compression. Noticeable crack propagation starts in multi-crack composites under geometric buckling, which result from the existence of multi-cracks and their interaction in the composites.