In the present work, several mechanisms of four bars for knee prosthesis were studied and evaluated. We compared and defined the design parameters as well as an optimization method in terms of their stability and voluntary control to get a new mechanism. Few methods have been published to compare the performance and design parameters of the wide variety of polycentric knee mechanisms. In this work, we developed a method for performance comparison of polycentric knee mechanisms and designing a stable and novel four-bar mechanism with a voluntary control configuration. We defined design parameters for the optimization of a stable knee mechanism with voluntary control, presented a new dimensional design that can be functional for transfemoral users with different anthropometric characteristics and contributed with a simple method to obtain a mechanism with optimal sizing. A comparison of dimensional parameters of several mechanisms of knee prosthesis was obtained. There is the proposal of a new optimized mechanical configuration for assuring the voluntary control and a stable trajectory of the knee mechanism. With this method, it is possible to compare and design personalized mechanisms. Clinical relevance This method proposes a simple way to evaluate polycentric knees, and it is easy to use to compare and design stable mechanisms with voluntary control for transfemoral users with personal design parameters, if required.

Este es un artículo publicado en acceso (Open Access) abierto bajo la licencia Creative Commons Attribution NonCommercial, que permite su uso, distribución y reproducción en cualquier medio, sin restricciones siempre que sin fines comerciales y que el trabajo original sea debidamente citado. Resumen: Las aleaciones para el relleno superficial Fe-Mn-C (Hadfield) han demostrado una excelente resistencia al desgaste bajo altas cargas dinámicas. En los últimos años se han realizado numerosos estudios para aumentar la resistencia al desgaste y mejorar su desempeño, a través de la introducción de otros elementos de aleación. En el presente trabajo se investiga la microestructura y dureza de los depósitos de relleno con alto contenido de Mn y adiciones de 1.2% de V y 2.4% de Si. Los depósitos estudiados se realizaron utilizando electrodos tubulares revestidos fabricados a escala de laboratorio. Las fases y microconstituyentes en el metal depositado se identificaron mediante microscopía óptica (MO), electrónica de barrido (MEB), difracción de rayos X (DRX), dureza y microdureza. De acuerdo a los resultados obtenidos, la adición de V al sistema aleante originó que la fase predominante fuera la austenita. Además, contribuyó a la formación de carburos de vanadio (VC) en la microestructura de la capa de relleno, sin observarse la presencia de carburos complejos. Por otra parte, la presencia de Si favoreció la formación de una red de ferrita interdendrítica. La adición de estos elementos de aleación mejoró las propiedades de estos depósitos, potencializando su uso en aplicaciones que requieren alta resistencia al desgaste bajo altas cargas. Palabras-clave:Hadfield; Microestructura; Relleno; Vanadio; Silicio. Effect of V and Si on the Microstructure of Deposits Welded Using Tubular Coated Electrodes with High Mn Content (Hadfield)Abstract: Fe-Mn-C (Hadfield) alloys for surfacing weld deposits have demonstrated excellent wear resistance under high dynamic loads. In recent years, numerous studies have been conducted to improve their wear resistance and performance through the introduction of others alloying elements. In the present work, microstructure and hardness of high Mn surfacing welds with 1.2% V and 2.4% Si additions were investigated. The surfacing welds were deposited using experimental tubular coated electrodes. Phases and micro constituents in the resulting deposits were identified using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness and micro hardness. Based on the obtained results, V additions to the alloy led to the formation of austenite as predominant phase. Besides, contributed to the formation of vanadium carbides (VC), without the presence of complex carbides. Otherwise, Si addition favored the formation of an interdendritical ferrite network. The addition of these elements favored the increase in the properties of the weld deposits, potentializing their use in applications that require high wear resistance under high loads.

RESUMEN:Las aleaciones utilizadas para el revestimiento de superficies sometidas a baja o moderada abrasión son altamente complejas. Con la finalidad de buscar una alternativa más simple, en el presente trabajo se estudian tres revestimientos, aplicados utilizando electrodos con diferentes composiciones basadas en fundiciones hipoeutéticas Fe-Si-V-C con 3,2 % de C, V entre 0,47 y 1,57 %, y Si entre 2,30 y 3,82 %. Los revestimientos resultantes fueron estudiados utilizando técnicas de microscopía óptica (MO), microscopía electrónica de barrido (MEB), difracción de rayos X (DRX) y dureza. Los resultados mostraron que para contenidos de Si y V bajos, se obtuvo la dureza más elevada (64 HRC), derivada de una microestructura donde predominan la martensita y la austenita. Al aumentar las cantidades de estos elementos en la aleación, se obtuvo mayoritariamente perlita, con zonas eutécticas y carburos de V distribuidos en ellas, originando una disminución de la dureza hasta 57 HRC. Por lo tanto, utilizando contenidos de Si y V bajos (cercanos a 2,30 % de Si y 0,47 % de V), los electrodos basados en el sistema aleante Fe-Si-V-C pueden ser una alternativa para revestir superficies sometidas a desgaste abrasivo bajo o moderado. ABSTRACT: Microstructural analysis of hypoeutectic white cast iron coatings with Si and V additions.Alloy systems used as coatings in surfaces under low or moderate abrasion are highly complex. In order to search for a simpler system, in this work three coatings were studied, applied using electrodes with different compositions, based on hypoeutectic white cast irons, with 3.2% C, V from 0.47 to 1.57%, and Si from 2.30 to 3.82%. Resulting coatings were studied using Optical (OM) and Scanning Electron Microscopies (SEM), X-ray diffraction (XRD) and hardness measurements. Results showed that maximum hardness (64 HRC) was obtained for low Si and V contents, due to a microstructure mainly composed by martensite and austenite. The increase in Si and V contents led to significant modifications in the microstructures, being perlite the main phase, with the presence of eutectic zones and V carbides. These modifications originated lower hardness for these coatings (57 HRC). This study allowed to define that using low Si and V contents (close to 2.30% Si and 0.47% V), electrodes of the Fe-Si-V-C system can be an alternative for coating surfaces under low or moderate abrasive wear.