A Case Report: Is the Lack of Sufficient Radial Force Unfreezing the “Frozen Elephant Trunk”?

The “frozen elephant trunk” is a hybrid technique to treat aortic arch and proximal descending aortic pathologies in a single step. Despite its encouraging early and long-term results, some stent-graft-related adverse events have been reported. Here, we describe a possible treatment option to “re-freeze” the FET in case of loss of landing zone. We report a patient who developed significant kinking of the FET over the course of the first 2 postoperative years. The 1-year follow-up computed tomography angiography (CTA) showed significant kinking and proximal migration of the endograft portion of the FET, resulting in new thrombus formation. Due to kinking and thrombus progression in subsequent CTA follow-ups (2 years and 2½ years) with risk for peripheral embolization, a secondary endovascular repair was indicated. Transfemoral relining of the stent component with a thoracic aortic endovascular repair (Zenith®TX2®30142) stent-graft was performed. In the context of postoperative aneurysm sac shrinkage, the low radial force and lack of longitudinal stiffness of the hybrid graft may lead to proximal migration, thus secondary kinking, emphasizing the importance of an adequate degree of oversizing of the primary graft and an appropriate follow-up. Selection of a suitable graft for a particular pathology concerning the radial force and longitudinal stiffness is furthermore important.

Finite Element Structure Analysis of Automobile Suspension Control Arm Based on Neural Network Control

The control arm is an important transmission and guidance device in the Macpherson suspension system, which has an important impact on the ride comfort, operation stability, and safety of the vehicle, so it is necessary to study the structural performance of the control arm. In this paper, based on neural network control model, finite element analysis, and fatigue analysis theory, the strength, stiffness, and dynamic and fatigue performance of the control arm are studied and analyzed. Taking the ground contact force of the tire as the input condition, the static analysis of the front suspension is carried out, and the boundary condition of the load of the control arm is extracted. The finite element strength of the control arm is calculated in the OptiStruct solver under the conditions of uneven road, braking, and turning. At the same time, the longitudinal stiffness and lateral stiffness of the control arm are analyzed. The simulation results show that the control arm has better strength and stiffness performance.

Spontaneous Extension Wave for In Vivo Assessment of Arterial Wall Anisotropy

Another type of natural wave, traced from longitudinal wall motion and propagation along the artery, is unprecedentedly observed in our in vivo human carotid artery experiments. We coin it as extension wave (EW) and hypothesize that EW velocity (EWV) is associated with arterial longitudinal stiffness. The EW is thus assumed to complement the PW, whose velocity (PWV) is tracked from the radial wall displacement and linked to arterial circumferential stiffness through the Moens-Korteweg equation, as indicators for arterial mechanical anisotropy quantification by noninvasive high-frame-rate ultrasound. The relationship between directional arterial stiffnesses and the two natural wave speeds was investigated in wave theory, finite-element simulations based on isotropic and anisotropic arterial models, and in vivo human common carotid artery (N=10) experiments. Excellent agreement between the theory and simulations showed that EWV was 2.57 and 1.03 times higher than PWV in an isotropic and an anisotropic carotid artery model, respectively, while in vivo EWV was consistently lower than PWV in all 10 healthy human subjects. A strong linear correlation was substantiated in vivo between EWV and arterial longitudinal stiffness quantified by a well-validated vascular guided wave imaging technique (VGWI). We thereby proposed a novel index calculated as EWV2/PWV2 as an alternative to assess arterial mechanical anisotropy. Simulations and in vivo results corroborated the effect of mechanical anisotropy on the propagation of spontaneous waves along the arterial wall. The proposed anisotropy index demonstrated the feasibility of the concurrent EW and PW imaged by high frame-rate ultrasound in grading of arterial wall anisotropy.

Experimental characterization and numerical determination of the rigidity of a Binder Magnetic synchronous belt transmission type AT10

Given the important role of synchronous belts in the functioning of mechanisms, they are the subject of numerous studies and researches in order to define them more and more finely. Their mechanical characteristics influence the behavior in operation of the mechanisms that they entail. Also, the measurement of the characteristics of the longitudinal stiffness of the belt and the stiffness of the teeth is necessary to better control their behavior. In addition, these parameters constitute input data for models of lifetime and dynamic behavior of synchronous transmissions. An approach for the determination of longitudinal stiffness is presented. We have demonstrated a study comparing the measurement of the rigidity of a toothed belt by two methods. This is to qualify the first method of measurement through experimentation. And the second measurement method using the simulation of this toothed belt by SOLIDWORKS software.

Diaphragm muscle fibrosis involves changes in collagen organization with mechanical implications in Duchenne Muscular Dystrophy

In Duchenne muscular dystrophy (DMD), diaphragm muscle dysfunction results in respiratory insufficiency, a leading cause of death in patients. Increased muscle stiffness occurs with buildup of fibrotic tissue, characterized by excessive accumulation of extracellular matrix (ECM) components such as collagen. However, changes in mechanical properties are not explained by collagen amount alone and we must consider the complex structure and mechanics of fibrotic tissue. The goals of our study were to (1) determine if and how collagen organization changes with the progression of DMD in diaphragm muscle tissue, and (2) predict how collagen organization influences the mechanical properties of ECM. We first visualized collagen structure with scanning electron microscopy (SEM) images and then developed an analysis framework to quantify collagen organization and generate image-based finite-element models. The image analysis revealed significant age- and disease-dependent increases in collagen fiber straightness and alignment, ranging from 4.7 to 13.4%, but collagen fibers retained a transverse orientation relative to muscle fibers. The mechanical models predicted significant age- and disease-dependent increases in transverse effective stiffness and average stress, ranging from 8.8 to 12.4%. Additionally, both healthy and diseased models revealed an increase in transverse stiffness relative to longitudinal stiffness, with significant age- and disease-dependent increases in the ratio of transverse to longitudinal stiffness, ranging from 19.7 to 24.5%. This study revealed changes in diaphragm ECM structure and mechanics during the progression of disease in the mdx muscular dystrophy mouse phenotype, highlighting the need to consider the role of collagen organization on diaphragm muscle function.

A comparative study of static and dynamic properties of honeycomb non-pneumatic wheels and a pneumatic wheel

Three-dimensional finite element (FE) models of the honeycomb NPWs with three different spokes’ configurations, realized by varying the cell angle, were formulated. The validity of the proposed NPW FE models was demonstrated by comparing the predicted wheel responses with the reported data. A FE model of the pneumatic wheel of identical size was also formulated and verified on the basis of the measured vertical force-deflection and cornering properties. The verified NPW models were subsequently employed to study their feasibility through comparisons of in-plane as well as out-of-plane properties with those of the pneumatic wheel. The influences of the cell angle and normal wheel load on the static and dynamic properties of the NPWs were also investigated. The results showed load-dependent longitudinal stiffness of the wheel due to strong coupling between radial and longitudinal deformations of the honeycomb spokes. The lateral stiffness, however, was observed to be load-independent due to negligible coupling between radial and lateral deformations of the spokes. The spokes of the honeycomb NPWs could thus be easily tuned to achieve vertical and longitudinal stiffness comparable to those of the reference pneumatic wheel. The lateral and cornering stiffness of the NPWs with the planar spokes, however, were substantially higher, irrespective of the spokes’ configuration considered. The significantly higher cornering stiffness resulted in rapid saturation of the cornering force of the NPWs at side-slip angles about 1.1°, which is likely to cause lateral sliding of the wheels and potential loss of directional control under higher side slip conditions.

Investigation on the Rotational Dynamics of a Timing Belt Drive Including an Oval Driving Pulley

Recent developments in timing belt drive for the automotive engine have seen the use of non-circular pulleys. This study presents an experimental and numerical investigation on this type of transmission including an oval pulley. A specific test rig has been designed to enable the identification of the proper effect of an oval pulley on the transmission dynamics. The belt tensions, the speeds, and torques of the driving and driven pulleys were measured and analyzed for three different transmission configurations: (1) circular driving pulley and oval driving pulley without (2) and/or with (3) load torque applied. Analyses were carried out in the time and frequency domains by considering the driving pulley rotation angle as a reference. In parallel a numerical model has been developed, it accounts for the specific motions of the belt seating/unseating points on the oval pulley and its neighboring pulleys. The model considers the variation of lengths for the belt spans adjacent to the oval pulley. This induces variable longitudinal stiffness and influences the transmission dynamics that is predicted versus time and compared with experiments. The phasing angle of the oval driving pulley was adjustable in order to study its influence. With no resistant torque applied, it was found that, for low-speeds, the oval pulley has a pure kinematic effect on the transmission dynamics. When a load torque is applied, the effectiveness of the oval pulley regarding the belt tensions and transmission error fluctuations is verified experimentally for some specific intervals of the phasing angle.

Research on the longitudinal mechanical behaviours of subway turnouts of large slope under train braking force

To study subway turnouts’ adaptability to steep gradients, a finite element model of a metro No. 9 simple turnout was established. The main works include: (1) The train’s most unfavourable loading condition was modelled. (2) The turnout’s longitudinal displacement and stress were analysed with different gradients under the train braking load, temperature change load and a combination of the two, to determine the structure’s safety and stability under the most unfavourable working conditions. (3) The turnout structure’s cumulative longitudinal deformation under reciprocating load was studied. Both a fastener longitudinal resistance-displacement experiment under reciprocating load and a numerical simulation of No. 9 turnout modelled by the finite element modelling software, ANSYS, were carried out to study the gradient’s influence on the turnout’s longitudinal mechanical characteristics. (1) The turnout’s longitudinal displacement and stress increase linearly with an increase in gradient and temperature change, both of which are unfavourable to the turnout structure. As the gradient increases from 0‰ to 30‰, the longitudinal stress and displacement increase by more than 10%. (2) The turnout’s rail strength and displacement on a 30‰ slope under the most unfavourable load conditions are within the specification limitations. (3) Under reciprocating load, the fastener longitudinal stiffness decreases and the maximum and residual longitudinal displacement of the switch rail increase; an increased gradient intensifies these effects on the turnout.

3D Models Reveal the Influence of Achilles Subtendon Twist on Strain and Energy Storage

The Achilles tendon (AT) has complex function in walking, exchanging energy due to loading by the triceps surae muscles. AT structure comprises three subtendons which exhibit variable twist among themselves and between individuals. Our goal was to create 3D finite element (FE) models to explore AT structure-function relationships. By simulating subtendon loading in FE models with different twisted geometries, we investigated how anatomical variation in twisted tendon geometry impacts fascicle lengths, strains, and energy storage. Three tendon FE models, built with elliptical cross sections based on average cadaver measurements, were divided into subtendons with varied geometric twist (low, medium, and high) and equal proportions. Tendon was modeled as transversely isotropic with fascicle directions defined using Laplacian flow simulations, producing fascicle twist. Prescribed forces, representing AT loading during walking, were applied to proximal subtendon ends, with distal ends fixed, and tuned to produce equal tendon elongation in each case, consistent with ultrasound measurements. Subtendon fascicle lengths were greater than free tendon lengths in all models by 1–3.2 mm, and were longer with greater subtendon twist with differences of 1.2–1.9 mm from low to high twist. Subtendon along-fiber strains were lower with greater twist with differences of 1.4–2.6%, and all were less than free tendon longitudinal strain by 2–5.5%. Energy stored in the AT was also lower with greater twist with differences of 1.8–2.4 J. With greater subtendon twist, similar elongation of the AT results in lower tissue strains and forces, so that longitudinal stiffness of the AT is effectively decreased, demonstrating how tendon structure influences mechanical behavior.

The use of a new slab track system in the renovation of the Vierendeel railway bridges in Mechelen

<p>The existing ballastless track with wooden sleepers on the Vierendeel bridges in Mechelen will be replaced by a new slab track system with continuously welded rails across the bridge. Additionally, the rails will be positioned eccentrically on the stringers due to track optimization. This paper describes the design and implementation of this new modular track system that consists of prefabricated fully welded steel frames that are bolted onto the existing superstructure. During the design stage, focus was on the required load transfer via the steel frame to the bridge superstructure, on the large difference in steel characteristics between the old and new material and on the position of joints and fastenings. Lateral and longitudinal stiffness of the track was tested on a prototype and the final solution was already installed and successfully implemented on one bridge. In addition, field tests in relation to rail-bridge interaction have started.</p>