Interface fails and Young's module approximation of multilayer flexible devices through finite element method.

Electronic flexible devices are prone to degrade their electrical performance or lose functionality when subjected to deformations. Brittle fracture is a common damaging effect observed in devices composed of low-thickness layered materials stacked onto a flexible substrate by dissimilar mechanical properties interaction. This work studies the mechanical behavior of Organic Flexible Solar Cells (OFSC) with a heterostructure PET/ITO/P3HT:PCBM/Ag subjected to uniaxial displacements through an experimental and numeric point of view. Experimental showed that damage proceeds in two ways. First, the formation of a grid crack pattern begins at the ITO layer, and second, the delamination in the ITO/P3HT:PCBM interface. The numerical model analyzed the force and displacements and the absorption/dissipation of strain energy on layers and interfaces of the device. The comparison of the global Young's module for experimental and numeric studies validated the numeric analysis, with results of 4.16 ± 0.05 GPa for experimental and 4.36 ± 0.15 GPa for numeric. Additionally, the model associates the ITO layer with the highest strain energy dissipation or the most prone to failure, which agrees with the experiments. Then, the model successfully predicts the mechanical behavior of OFSC and represents a valuable tool for studying flexible devices and predicting the appearance of mechanical damage when subjected to uniaxial deformations, even being able to avoid potential damage changing parameters such as the thickness of the layers.

Type of Feet in a Mexican Population: Analysis of the Footprint Morphology and Literature Review / Tipos de pies en una Población Mexicana: Análisis de la Morfología de la Huella Plantar y Revisión de la Literatura

ABSTRACT There is no specific age when the vault of the feet is completely formed. The objective of this study was to analyze the footprint morphology and obtain the Chippaux-Smirak Index in a Mexican population to identify the type of feet and its prevalence. A database of images of the soles of both feet was analyzed. The database contained images of 1,014 persons between 2 and 73 years old from Guanajuato state, Mexico. Moreover, a literature review was performed to identify the type of feet in the Mexican population. It was observed that less than 17 % of the population have cavus foot (p= 0.018). Furthermore, less than 25 % of the population between 17 and 73 years have flatfoot 3 (p= 0.0079) in the left foot. Also, only nine articles related to the type of foot in the Mexican population were found, but most of them were performed on young population. The formation of the medial arc could be beyond the first decade of life and the relatively high prevalence of flatfoot in adult life should be studied. Finally, the results found can be useful for orthopedists, physiotherapists, clinicians, and parents who are concerned about the foot health of their children.

RESUMEN No hay una edad específica en la que la bóveda de los pies esté completamente formada. El objetivo de este estudio fue analizar la morfología de la huella de los pies y obtener el Índice de Chippaux-Smirak en una población mexicana para identificar el tipo de pie y su prevalencia. Se analizó una base de datos de imágenes de las plantas de ambos pies. La base de datos contenía imágenes de 1,014 personas de entre 2 y 73 años del estado de Guanajuato, México. Además, se realizó una revisión bibliográfica para identificar el tipo de pie en la población mexicana. Se observó que menos del 17 % de la población tiene pie cavo (p= 0,018). Además, menos del 25 % de la población entre 17 y 73 años tiene pie plano 3 (p= 0,0079) en el pie izquierdo. Además, se encontraron 9 artículos relacionados con el tipo de pie en población mexicana, pero la mayoría de ellos fueron desarrollados en población joven. La formación del arco medial podría estar más allá de la primera década de vida. Se encontró una prevalencia relativamente alta de pie plano en la vida adulta que debe ser estudiada. Finalmente, los resultados encontrados pueden ser útiles para ortopedistas, fisioterapeutas, médicos y padres preocupados por la salud de los pies de sus hijos.

A detailed analysis in thoracic aorta by means of the entropy generation rate: Prediction of the atherosclerotic lesion.

A detailed numerical analysis is carried out in a real human thoracic aorta by means of the Computational Fluid Dynamics (CFD) for the prediction of the atherosclerosis lesion. Common hemodynamics parameters, such as, the oscillatory shear index (OSI) and the time average wall shear stress (TAWSS) are used for the prediction of the atherosclerosis lesion. Furthermore, the entropy generation rate is considered to obtain the main irreversibilities that occurs inside the thoracic aorta for the prediction of the atherosclerosis lesion. The model considers the blood flow inside the thoracic aorta in an unsteady state. The results show contours of velocity, streams lines, velocity profiles and the comparison of the hemodynamics parameters OSI versus TAWSS. Moreover, contours of the entropy generation rate are showed inside the aorta. The time averaged entropy generation rate (TAEGR) is obtained as a result of the entropy generation analysis. Finally, TAEGR index is compared and discussed with the common hemodynamics parameters, OSI and TAWSS. The accuracy to detect prone locations to atherosclerotic development in the real aorta using the TAEGR in comparison to the OSI and the TAWSS is in good agreement.

Structural assessment of pre-flexion in silicone implants for arthroplasty of the first metatarsophalangeal joint.

The development of numerical models to analyze pathologies and implants related to the first metatarsophalangeal joint of the foot remains an issue for attention. The structural effects of implants pre-flexion have been discarded in several finite elements analyses due to complexities to achieve these positions. This work aims to evaluate if the pre-flexion stress state should be included or could be discarded when only flexion is applied in two different silicone commercial implants, Swanson and Tornier, during a gait cycle. Finite element models were created for silicone implants. Both models were discretized using high-order finite elements. The hyperelasticity constitutive material model of Arruda-Boyce was used, based on experimental data; its behavior was compared with linear elastic models reported and used frequently assuming small and large deformations and applying to the Swanson and Tornier implants a flexion angle of 64°, which corresponds to in vivo measurements reported after implantation. Comparison between models, regarding hyperelastic model, showed mean variations of up to 32.5% for stresses and 14.01% for bending moment in Swanson implant, while for Tornier implant mean variations of 29.73% and 632.55% was obtained for stress and bending moment respectively. The maximum stress value obtained for the hyperelastic model in the Swanson implant reached a value of 22.82% of the tensile strength of the implant material while in the Tornier implant reached a value of 25.92%, the above values were evaluated at a flexion angle of 64°. The results suggest considering in finite element analyses not only the stress state generated to achieve critical flexion position in pleflexed implants models but also the hyperelastic material behavior of silicone for implants to avoid dismissing the non-linear structural behavior of hyperelastic materials.

A Novel Kinematic Model of the Tibiofemoral Joint Based on a Parallel Mechanism.

This paper presents a complete kinematic model of the tibiofemoral joint (TFJ) based on a RRPP + 4-SPS parallel mechanism, where R, P, and S stand for revolute, prismatic, and spherical joints, respectively. The model accounts for the contact between tibia and femur, and the four major ligaments: anterior cruciate, posterior cruciate, medial collateral, and lateral collateral, with anatomical significance in their length variations. An experimental flexion passive motion task is performed, and the kinematic model is tested to determine its capability to reproduce the workspace of the motion task. In addition, an optimization process is performed to simulate prescribed ligament length variations during the motion task. The proposed kinematic model is capable to reproduce with high accuracy an experimental three-dimensional workspace, and at the same time, to simulate prescribed ligament length variation during the spatial flexion task. Prescribed ligament length variations are achieved through an optimization process of the ligament insertion points. This model can be used to improve the multibody kinematic optimization (MKO) process during gait analysis, and also in the design of rehabilitation devices as well as trajectories to accelerate the recovery of injured ligaments. The model shows potential to predict ligament length variations during different motion tasks, and can serve as a basis to develop complex models for kinetostatic and dynamic analyses without dealing with computationally expensive models.