A thorough understanding of esophageal biomechanics is essential for predicting tissue failure and preventing iatrogenic tearing during surgical procedures, such as esophageal atresia repair. This knowledge is also crucial for the engineering design of mechanically compatible tissue replacements. Melatonin, known for its regenerative properties, could improve the mechanical integrity of esophageal tissue and minimize post-surgical complications, including anastomotic leakage. This study characterizes the passive hyperelastic and damage behavior of the neonatal lamb esophagus and evaluates the effect of melatonin treatment.In-vitro monotonic uniaxial tensile tests were performed on esophageal samples from newborn lambs, which were divided into control (n=4) and melatonin-treated (n=4) groups. The samples were separated into internal (mucosa/submucosa), external (muscularis), or integrated (intact wall) layers, and tested in both longitudinal and circumferential directions. A hyperelastic-damage constitutive model was calibrated to the experimental data to quantify the anisotropic and softening response of the tissues.The esophageal tissue exhibited significant anisotropy, with greater stiffness in the longitudinal direction. No statistically significant differences were observed between the control and melatonin-treated groups, in the Cauchy stress versus stretch response or in an analysis of characteristic curve descriptors computed in nominal stress (q>0.05). However, the small sample sizes left the study underpowered to detect the moderate-to-large effect sizes (Hedges’ g = 0.5-0.9) observed in several comparisons, which therefore warrant confirmation in adequately powered cohorts. The proposed constitutive model accurately captured the non-linear hyperelastic and damage behavior, including the softening up to rupture, across all tissue layers (R2>0.86).This study provides experimentally calibrated material parameters for an anisotropic hyperelastic-damage model of the neonatal lamb esophagus, extending prior hyperelastic descriptions to include softening behavior. Although a 30-day low-dose melatonin treatment did not produce robust alterations in passive mechanical properties, the established constitutive framework provides valuable baseline data to inform computational simulations of surgical procedures and optimize tissue-engineered esophageal grafts.

This work introduces a deep neural network (DNN) surrogate model designed to accelerate mechanical parameter identification using the ring tensile test. The surrogate is trained on finite element simulations of the ring tensile test using an anisotropic constitutive model, serving as an efficient approximation of the forward problem. Its main application is the batch characterization of small aortic tissue samples, where specimen availability and computational cost limit traditional inverse analyses. Validation against experimental data from thoracic aorta samples of Wistar rats shows strong predictive capability, with initial correlation coefficients of 0.73 or higher across all identified parameters. The DNN surrogate provides accurate initial estimates that can be refined through finite element-based inverse analysis, allowing to include the residual stress effects in vessel mechanics. While training requires a substantial computational cost, the framework enables rapid, high-throughput characterization and can be generalized to other non-standard mechanical tests involving complex stress–strain states.

Arterial response emerges from interactions among collagen, elastin, smooth muscle cells, and ground matrix, but macroscopic models resolve these mechanisms only indirectly. We propose a first-order computational homogenization framework based on a solid-embedded-fiber representative volume element (RVE) coupled to a macroscopic finite element problem. Four configurations combine two fiber-tracing strategies with linear boundary displacement or periodic microscale constraints. All four produce comparable homogenized responses and reveal phase-specific behavior unavailable from effective curves alone. Collagen dominates homogenized stress, while local fields show heterogeneous and asymmetric load transfer between fibers and matrix. Periodic constraints slightly reduce peak stresses, broaden local stress and strain distributions, and increase solution times. Recruitment-window parameters most strongly influence nonlinear stiffening, followed by collagen stiffness and volume fraction. Similar homogenized responses can hide local-field differences caused by fiber topology and boundary conditions. The nested FE2 framework links each macroscopic point to an embedded-fiber RVE during equilibrium. This coupling supports complex problems and constituent viscoelasticity, damage, fiber failure, or rupture because the local deformation path need not be known beforehand. Microscale boundary conditions must be selected in advance to produce a representative RVE response. Constituent-specific data remain necessary for validation.

This research reports on numerical simulations of the multi-pass laser forming process aimed at obtaining cylindrical surfaces from planar AISI 304 stainless-steel sheets. The effect of laser power, scanning speed, and distance between irradiation lines on the thermomechanical material response is assessed, with particular emphasis on the final curvature radius, maximum temperature, and final plastic deformation. To this end, a coupled thermomechanical finite element formulation is applied to the analysis of different experimental tests reported in the literature. The predictive capabilities of this model are demonstrated in the analysis of bent parts exhibiting a wide range of curvature radii, whose values were found in this work to inversely correlate with the total line energy input to the workpiece. In such situations, it was found that both the thermal response and the effective plastic strain values obtained in each test correlate directly with the line energy value. Furthermore, the distance between irradiation lines was identified as a key parameter in the formation of cylindrical surfaces, as it significantly influences the displacement and induced deformation. However, no significant impact of this parameter on the effective plastic strain was observed.

One of the purposes of tissue engineering is to offer therapeutic alternatives to treat various esophagus-related diseases. To develop viable esophageal replacements that are both mechanically and biologically compatible and to assess the impact of pharmacological treatments on esophageal tissue at the macro- and micro-structural levels, it is crucial to understand the biomechanical properties of the esophagus. In this study, we analyzed esophageal tissue samples from nine newborn lambs. Subjects were randomly separated into a control group (n = 5) and a melatonin-treated group (n = 4). The passive mechanical response of the esophagus was studied by performing in-vitro uniaxial tensile tests along longitudinal and circumferential directions. Samples were classified into three types: internal tissue (mucosa and submucosa layers), external tissue (external muscular layer), and integrated tissue (comprising all layers). Uniaxial stress versus stretch curves of each classification were used to determine mechanical properties that were statistically analyzed. Moreover, average experimental results were used to calibrate an anisotropic hyperelastic model. Stress-stretch curves from uniaxial tests showed a highly anisotropic behavior, with a higher stiffness along the longitudinal direction and internal tissue exhibiting the highest stiffness. To contrast the results obtained from mechanical testing, histological analysis of esophagus samples was carried out. Microstructural components were quantified and morphological measurements of the main zones were performed. No significant differences were found at the macro- and microstructural levels of the tissue, indicating that the supply of low doses of melatonin does not alter the biomechanical properties of the esophagus.

A comprehensive study of the post-necking response of materials is a relevant aspect in many metal-forming applications. For this purpose, the proposal of a suitable constitutive model to describe the elastoplastic response, an adequate material characterization, and the rise of numerical simulation as a feasible tool in the control and design of parts subjected to plastic deformation are key aspects that have to be addressed. In this context, to characterize the elastoplastic behavior of rolled C11000-H2 99.90% pure copper sheets, a constitutive model accounting for appropriate yield criterion function (Cazacu-Plunket-Barlat 06, named CPB06) and hardening law (modified Voce) is presented. In this material, the necking formation is produced at low levels of strain (5% approximately in a tensile test). The 3D stress state that develops afterward is a critical aspect that must be considered when developing an adequate characterization of this material. Therefore, there is a need to formulate an effective and robust strategy to determine the model parameters. In this regard, a coupled calibration procedure is proposed, using a combined experimental-analytical-computational approach. To calibrate the model parameters, this methodology is used with experimental results of proportional loading paths corresponding to uniaxial tensile tests carried out in seven in-plane directions, along with the equibiaxial condition via hydraulic bulge tests. Then, uniaxial tensile tests under non-proportional loading paths, with specimens previously pre-strained along the rolling direction of the sheets to two levels, both beyond the ultimate tensile strength (UTS) zone: 0.07 and 0.14, are used subsequently to evaluate the performance of the model previously calibrated. The reasonably good experimental-numerical agreement in the material response for these last cases successfully validated the proposed characterization methodology.

Este trabajo presenta la simulación de estanques de sección circular sometidos a condiciones de sloshing. El modelo se construye en el marco del método de partículas combinado con elementos finitos PFEM. La evolución de la superficie libre ante distintas condiciones de llenado y de agitación impuesta externa se compara con reportes analíticos y experimentales de la literatura con la finalidad de validar la metodología para el análisis de este tipo de estanques contenedores. Los autores agradecen el soporte brindado por el proyecto de cooperación de la VII Comisión Mixta AGCID-WBI RI07 y el proyecto DICYT 052516CSSA_Ayudante.

AIMS:The long-term effect of high altitude hypoxia (HAH) exposure is a relevant problem in cardiovascular biomechanics, that has not yet been fully assessed. Regarding this, the study examined the passive viscoelastic response of the descending thoracic aorta of individuals exposed to HAH. MAIN METHODS:Through a guinea-pig animal model, subjected to either normoxic-normobaric or HAH conditions (groups N and H, respectively), biaxial tensile and uniaxial stress relaxation tests were performed on artery samples. The experimental data obtained from these biomechanical tests allowed us to characterize an anisotropic quasi-linear viscoelastic model based on the Gasser-Holzapfel-Ogden (GHO) hyperelastic material. KEY FINDINGS:Among the main results, biaxial tensile tests exhibited a trend towards a higher stiffness (at high stretch levels) in the hypoxic group. Results of stress relaxation tests revealed a similar behavior between groups, at both the initial, more pronounced stress-relaxation stage, attributed to the effect of elastin fibers, and at the second stage, with a less pronounced decrease in stress due to the role of collagen fibers. SIGNIFICANCE:Our study suggests that although HAH does not alter significantly the passive elastic and viscous properties of aortic tissue under ex-vivo conditions, there is a tendency to material stiffening to supra-physiological levels. Assessment of the biomechanical response is crucial to determine the pathophysiological effects in the cardiovascular system derived from exposure to HAH.

This study aims to assess the efficacy of melatonin in mitigating the adverse effects of hypobaric hypoxia on the cardiovascular system of neonatal lambs (30 days old). Two groups were considered for this purpose: (i) Melatonin-treated group (N = 5) and (ii) Control group (N = 6) without treatment. All subjects were exposed to hypobaric hypoxia during gestation and perinatal periods, with melatonin administered after birth. The study focused on the carotid artery, a known predictor of cardiovascular risk. Biomechanical tests, morphometric, and histological measurements were conducted, and a numerical model was developed based on the biomechanical data. Key findings showed remodeling effects: Firstly, a realignment of collagen fibers towards a longitudinal direction was observed with melatonin treatment, similar to non-hypoxic arteries. Second, changes in residual stress and ex-vivo luminal radius were noted, aiming to reduce wall stress and increase vascular resistance. These changes indicate an antihypertensive response, reducing the effects of increased blood pressure and flow due to hypobaric hypoxia. This study demonstrates that biomechanical and histomorphometric methodologies effectively assess the beneficial effects of melatonin treatment under hypobaric hypoxia exposure.

In the finite element method framework, a fluid-structure formulation is developed by coupling an Eulerian fixed-mesh fluid approach with a Lagrangian deforming-mesh description for a flexible solid. The coupled formulation is solved using a staggered scheme during time. For the fluid solution stage, the solid walls are considered as a time-variable internal boundary. The velocity and pressure fields are obtained by solving the weak form of the fluid dynamic equations in which the solid velocity is imposed on the internal boundary via a penalization term. For the solid solution stage, the displacement field is obtained by solving the discrete solid dynamic equations which consider traction forces computed by integrating pressures and viscous stresses on the nodes belonging to the solid walls. This novel technique is firstly applied to analyze a flexible splitter under the shedding of a flow past square cylinder due to this problem is considered as a benchmark in the literature. The present solutions agree with those computed using body-fitted techniques, thus validating the proposal. Secondly, flexible splitter motions under the shedding of flow past cylinders with different cross-sections and splitter lengths are comprehensively studied. Overall, the computed results confirmed that the hydrodynamic coefficients on the cylinders were reduced because of the presence of the splitter.

The effect of triaxiality on the evolution of damage in Al-2024 aluminum cylindrical specimens is studied in this work. Uncoupled and coupled damage models, all of them explicitly dependent on triaxiality, are assessed and compared. These models are characterized by tensile tests on cylindrical specimens without notches, to obtain the material parameters for each model. The capability of each model to predict fracture when different positive triaxial conditions evolve is then evaluated through tensile tests on notched cylindrical specimens. In particular, the damage index, evaluated at the fracture strain level, is compared with the experimental results validating the models. Moreover, the triaxiality evolution in the different specimens is studied in order to assess its effect on damage, demonstrating that the fracture strain decreases at greater triaxiality values. Observations through scanning electron microscopy confirm this pattern; i.e., an increase in triaxiality reveals a shift in the fracture mechanism from a more ductile condition in the original specimens to a more brittle one as the notch radius decreases. In addition, bilinear damage evolution is proposed to describe the physical behavior of the material when the Lemaitre coupled model is considered. In such a case, special attention must be devoted to the material characterization since coupling between hardening material parameters and damage affects the results.

La pared arterial es un tejido capaz de modificar su forma, estructura y propiedades ante perturbaciones externas como el envejecimiento, enfermedades cardiovasculares e intervenciones quirúrgicas. Estas alteraciones se definen dentro de los fenómenos de crecimiento y remodelación (C&R), que se desencadenan con el objetivo de mantener un estado de homeostasis mecánica. Con el fin de indagar en estos efectos, se presenta un estudio de carácter numérico-computacional asociado a la implementación y caracterización de un modelo de naturaleza mecanobiológica: el modelo de mezclas restringidas con enfoque al crecimiento y remodelación (C&R-MMR). Respecto a la caracterización, se utiliza información experimental disponible de ensayos biomecánicos en arterias sometidas a la condición de hipoxia hipobárica (HH). Los principales resultados dan cuenta de la determinación de los parámetros del C&R-MMR, los cuales se correlacionan con la información experimental, describiendo la evolución desde una condición sin HH hasta cuando se desarrolla efecto de la hipoxia.

Solid oxide fuel cells (SOFC) are a viable alternative for environmentally-friendly conversion of hydrogen into energy and multiphysics simulation can be used to diminish the experimental effort to improve their efficiency. However, an appropriate model of the involved processes and their parameters must be chosen. This paper studies the effects of choice between Maxwell-Stefan and Fick's law models, and uncertainty of electrode ionic conductivity sigma(ion) ion and anodic reference exchange current density i(0,ref,f), on cell performance as implemented in the COMSOL Multiphysics (R) software. In the case of Maxwell-Stefan, peak average power output increased by 21.9% as sigma(ion) varies from 10(-3) to 10(-1) S/cm, while the model based on Fick's law shows an increase of 55.2%. The Maxwell-Stefan model exhibits an increase in peak power of 6% as i(0,ref,f) ranges from 0.4 to 0.8 A/cm(2), and the Fick's law model an increase of 8.2%. The dependence of the Maxwell-Stefan model on sigma(ion) is characterized as logarithmic in the studied range. The Maxwell-Stefan model is deemed preferable because its lower sensitivity to the studied parameters helps mitigate uncertainty. It is concluded that despite its limitations, multiphysics modeling is a useful tool for directing research on SOFC materials owing to its descriptive potential.

Total hip replacement is one of the most successful orthopedic operations in modern times. Osteolysis of the femur bone results in implant loosening and failure due to improper loading. To reduce induced stress, enhance load transfer, and minimize stress, the use of Ti-6Al-4V alloy in bone implants was investigated. The objective of this study was to perform a three-dimensional finite element analysis (FEA) of the femoral stem to optimize its shape and analyze the developed deformations and stresses under operational loads. In addition, the challenges associated with the manufacturing optimization of the femoral stem using large strain-based finite element modeling were addressed. The numerical findings showed that the optimized femoral stem using Ti-6Al-4V alloy under the normal daily activities of a person presented a strains distribution that promote uniform load transfer from the proximal to the distal area, and provided a mass reduction of 26%. The stress distribution was found to range from 700 to 0.2 MPa in the critical neck area of the implant. The developed computational tool allows for improved customized designs that lower the risk of prosthesis loss due to stress shielding.

A constant effort is made in the physical metallurgy of transformation induced plasticity (TRIP) steels. These are multiphase steels, whose mechanical behavior depends on the different phases present, the intrinsic strength of each phase, the work hardening of each constituent and the austenite to martensite transformation, among others. Hard and soft phases can be distinguished in these steels and both stress and strain are distributed between them. The objective of this work was to simulate the stress-strain behavior for two TRIP steels. Bouquerel’s model was modified to account for the initial martensite, a moderate hard austenite and adjustable strain hardening parameters. The austenite fraction that transforms into martensite was computed through an Olson and Cohen model. The Mecking-Kocks model was used to evaluate the increment in the dislocation density and the Rodriguez-Gutierrez model, to compute the hardening of martensite. Ferrite is considered a soft phase, martensite and bainite, hard phases and austenite, a phase with a moderate hardness. The routine was implemented in MATLAB, and results were compared with those obtained experimentally in a tension test of two TRIP steels of the same composition but different heat treatments, obtaining in both cases a good agreement for the stress-strain-curves.

El estudio del comportamiento mecánico de materiales a través de ensayos de tracción biaxial plana ha sido un objetivo relevante durante los últimos años. Si bien, numerosos autores han descrito diferentes técnicas y protocolos para la caracterización mecánica con este método, no existe un acuerdo relacionado con cómo poder estimar parámetros de un modelo constitutivo hiperelástico a través de este ensayo. En el contexto de muestras de pequeña dimensión, comúnmente algunos tejidos biológicos, es necesario utilizar un montaje de tipo garras. Este montaje impone un estado de deformaciones altamente concentradas en la zona de punzonado de la muestra, dificultando así el análisis de tensiones del material. En este estudio, se analiza el comportamiento mecánico del ensayo de tracción biaxial plano utilizando garras en un elastómero, con un enfoque numérico-experimental que utiliza el método de elementos finitos y análisis de contacto en altas deformaciones. Finalmente, se propone una estrategia de optimización de parámetros mecánicos que considera el efecto sobre las zonas de concentración de tensión.

We performed first-principles density functional theory (DFT) calculations to numerically investigate the electronic band structures of penta-graphene (PG), a novel two-dimensional carbon material with a pentagonal lattice structure, and its chemically functionalized forms. Specifically, we studied hydrogenated PG (h-PG), fluorinated PG (f-PG), and chlorinated PG (Cl-PG). We used the generalized gradient approximation (GGA) and the hybrid Heyd–Scuseria–Ernzerhof (HSE06) exchange-correlation functional in the DFT-based software VASP to capture electronic properties accurately. Our results indicate that hydrogenation and fluorination increased the indirect bandgap of PG from 3.05 eV to 4.97 eV and 4.81 eV, respectively, thereby effectively transforming PG from a semiconductor to an insulator. In contrast, we found that chlorination closed the bandgap, thus indicating the metallic behavior of Cl-PG. These results highlight the feasibility of tuning the electronic properties of PG through functionalization, offering insight into designing new materials for nanoelectronic applications.

In this study, the prediction of damage in the wire drawing process of 2011 aluminum alloy was investigated through both experimental and numerical methods. A comprehensive experimental setup was designed involving 20 cases of wire drawing with varying die angles (10°, 15°, 21°, 27°, and 34°) and reductions (21%, 29%, 31%, and 38%). Each case was tested three times, and the drawing forces, as well as occurrences of wire breakage, were recorded. The mechanical behavior of the material was firstly characterized using uniaxial tensile tests, whose results were used to determine the material parameters of both the hardening Voce law and those of uncoupled and coupled damage models. Then, the numerical simulations of the wire drawing process were performed using a finite element model, accounting for axisymmetric conditions and mesh convergence analysis to ensure accuracy. The previously characterized damage models were applied to evaluate their fracture prediction capabilities. A novel presentation method using three-dimensional graphs was employed to indicate the level of damage for each angle and reduction, providing greater sensitivity and insight into the damage values. Good agreement between the experimental and numerical data was demonstrated for the bilinear coupled damage model, validating its effectiveness. This study contributes to a better understanding of damage prediction in the wire drawing process, with implications for improving industrial practices and material performance evaluations.

The Constrained Mixture Model (CMM) is a novel approach to describe arterial wall mechanics, whose formulation is based on a referential physiological state. The CMM considers the arterial wall as a mixture of load-bearing constituents, each of them with characteristic mass fraction, material properties, and deposition stretch levels from its stress-free state to the in-vivo configuration. Although some reports of this model successfully assess its capabilities, they barely explore experimental approaches to model patient-specific scenarios. In this sense, we propose an iterative fitting procedure of numerical-experimental nature to determine material parameters and deposition stretch values. To this end, the model has been implemented in a finite element framework, and it is calibrated using reported experimental data of descending thoracic aorta. The main results obtained from the proposed procedure consist of a set of material parameters for each constituent. Moreover, a relationship between deposition stretches and residual strain measurements (opening angle and axial stretch) has been numerically proved, establishing a strong consistency between the model and experimental data.

The concept of mechanobiological equilibrium (MBE) is incorporated into the finite kinematic growth (KG) model for growth and remodelling (G&R), in order to propose an alternative, rate-independent formulation (MBE-KG).The method proposed yields non-transient solutions to G&R problems and quasi-equilibrated evolutions when imposed perturbations are slow relative to the adaptive process.We perform a finite element implementation of the method and show its performance on some illustrative problems involving the simulation of aneurysms on a single-layered artery model.