Multi-criteria selection of structural adhesives to bond ABS parts obtained by rapid prototyping

One of the most used methods in rapidprototyping is Fused Deposition Modeling (FDM), which provides components with a reasonable strength in plastic materials such as ABS and has a low environmental impact. However, the FDM process exhibits low levels of surface finishing, difficulty in getting complex and/or small geometries and low consistency in “slim” elements of the parts. Furthermore, “cantilever” elements need large material structures to be supported. The solution of these deficiencies requires a comprehensive review of the three-dimensional part design to enhance advantages and performances of FDM and reduce their constraints. As a key feature of this redesign a novel method of construction by assembling parts with structuraladhesive joints is proposed. These adhesive joints should be designed specifically to fit the plastic substrate and the FDM manufacturing technology. To achieve this, the most suitable structuraladhesiveselection is firstly required. Therefore, the present work analyzes five different families of adhesives (cyanoacrylate, polyurethane, epoxy, acrylic and silicone), and, by means of the application of technical multi-criteria decision analysis based on the analytic hierarchy process (AHP), to select the structuraladhesive that better conjugates mechanical benefits and adaptation to the FDM manufacturing proces

Aplicación de la programación en Autolisp en la enseñanza de la geometría. Curvas trocoidales

En este artículo presentamos las posibilidades que, desde un punto de vista didáctico, ofrece la programación en AutoLISP en la enseñanza de la geometría, en particular en el trazado y aplicación de curvas trocoidales. La idea original consistía en realizar un programa que crease un nuevo comando de AutoCAD capaz de trazar cualquier curva trocoidal –tanto particulares (evolventes y cicloides) como no particulares (epitrocoides, hipotrocoides o peritrocoides)–, con independencia de la situación del punto generador (alargadas, acortadas o normales). La elaboración del programa es relativamente simple. Para obtener todos los puntos de la curva es necesario aplicar siempre las mismas propiedades, lo que hace especialmente aconsejable la automatización del proceso. El programa realizado permite seleccionar sobre la pantalla generatriz y directriz, así como el punto que genera la curva. Se nos ofrece, asimismo, establecer el sentido de giro de la ruleta, la precisión de puntos hallados en cada ciclo (tantos como deseemos o como nuestro ordenador sea capaz de soportar), el número de vueltas y, por último, la posibilidad de apreciar, o no, la generación de la trocoide. Esta última opción permite observar, en la pantalla del ordenador, el giro de la generatriz sobre la directriz y la generación progresiva de la curva. Esta pequeña animación –contenida en un comando de AutoCAD– ha convertido un programa originalmente concebido para el trazado de curvas trocoidales, en una herramienta didáctica

Development of a smart splint to monitor different parameters during the treatment process

[ES]Para determinadas lesiones musculoesqueléticas por rotura compleja, el único tratamiento disponible es el uso de férulas de inmovilización. Este tipo de tratamiento suele provocar molestias y ciertos contratiempos en los pacientes. Además, suelen generarse otras complicaciones a nivel vascular, muscular o articular. Actualmente, existe una alternativa realmente posible que solucionaría estos problemas e incluso permitiría una recuperación más rápida y mejor. Esto es posible gracias a la aplicación de la ingeniería en técnicas de fabricación aditiva y al uso de materiales biocompatibles disponibles en el mercado. Este estudio propone el uso de estos materiales y técnicas, incluyendo la integración de sensores en el interior de las férulas.Los principales parámetros considerados a estudiar son la presión, la humedad y la temperatura. Estos aspectos se combinan y analizan para determinar cualquier tipo de evolución inesperada del tratamiento. De esta forma, será posible monitorizar algunas señales que se estudiarían para detectar problemas asociados a la propia fase inicial del tratamiento. El objetivo de este estudio es generar una férula inteligente mediante el uso de biomateriales y técnicas de ingeniería basadas en la fabricación avanzada y el sistema de sensores, con fines clínicos. Los resultados muestran que el prototipo de la férula inteligente permite obtener datos cuando se coloca sobre el brazo de un paciente. Durante el tratamiento se leen dos temperaturas: en contacto con la piel y entre la piel y la férula. Las variaciones de humedad debidas al sudor dentro de la férula también se leen mediante un sensor de humedad. Un sensor de presión detecta ligeros cambios de presión en el interior de la férula. Además, se ha incluido un sensor de infrarrojos como detector de presencia.[EN]For certain musculoskeletal complex rupture injuries, the only treatment available is the use of immobilization splints. This type of treatment usually causes discomfort and certain setbacks in patients. In addition, other complications are usually generated at the vascular, muscular, or articular level. Currently, there is a really possible alternative that would solve these problems and even allows a faster and better recovery. This is possible thanks to the application of engineering on additive manufacturing techniques and the use of biocompatible materials available in the market. This study proposes the use of these materials and techniques, including sensor integration inside the splints. The main parameters considered to be studied are pressure, humidity, and temperature. These aspects are combined and analyzed to determine any kind of unexpected evolution of the treatment. This way, it will be possible to monitor some signals that would be studied to detect problems that are associated to the very initial stage of the treatment. The goal of this study is to generate a smart splint by using biomaterials and engineering techniques based on the advanced manufacturing and sensor system, for clinical purposes. The results show that the prototype of the smart splint allows to get data when it is placed over the arm of a patient. Two temperatures are read during the treatment: in contact with the skin and between skin and splint. The humidity variations due to sweat inside the splint are also read by a humidity sensor. A pressure sensor detects slight changes of pressure inside the splint. In addition, an infrared sensor has been included as a presence detector

Mechanical Model and FEM Simulations for Efforts on Biceps and Triceps Muscles under Vertical Load: Mathematical Formulation of Results

[ES]Aunque las contracciones isométricas en los músculos humanos se han analizado varias veces, no existen modelos de elementos finitos que nos permitan utilizar la misma articulación modelada (el codo en nuestro caso) en diferentes condiciones. La mayoría de las articulaciones del codo utilizan elementos 3D para el mallado. Representar los músculos de la articulación es bastante útil cuando el estudio se centra en el propio músculo, para conocer la distribución de tensiones en el músculo y comprobar en detalle las lesiones musculares (inserción tendón-músculo, por ejemplo). Sin embargo, esta técnica no es útil para estudiar el comportamiento del músculo en diferentes posiciones de la articulación. Este estudio, basado en el modelo mecánico de la articulación del codo, propone una metodología para modelar los músculos a estudiar en diferentes posiciones modelándolos con elementos 1D. Además, la metodología permite calcular las tensiones del bíceps y tríceps bajo carga para diferentes ángulos de apertura de la articulación del codo. Los resultados de la simulación se han modelado matemáticamente para obtener formulaciones generales de estas tensiones en función de la carga y del ángulo de apertura.[EN]Although isometric contractions in human muscles have been analyzed several times, there are no FEA models that allow us to use the same modeled joint (the elbow under our case) in different conditions. Most elbow joints use 3D elements for meshing. Representing the muscles in the joint is quite useful when the study is focused on the muscle itself, knowing stress distribution on muscle, and checking damage in muscle in a detailed manner (tendon–muscle insertion, for example). However, this technique is not useful for studying muscle behavior at different positions of the joint. This study, based on the mechanical model of the elbow joint, proposes a methodology for modelling muscles that will be studied in different positions by meshing them with 1D elements. Furthermore, the methodology allows us to calculate biceps and triceps efforts under load for different angles of elbow joint aperture. The simulation results have been mathematically modelled to obtain general formulations for these efforts, depending on the load and the aperture angle

Filament Advance Detection Sensor for Fused Deposition Modelling 3D Printers

The main purpose of this paper is to present a system to detect extrusion failures in fused deposition modelling (FDM) 3D printers by sensing that the filament is moving forward properly. After several years using these kind of machines, authors detected that there is not any system to detect the main problem in FDM machines. Authors thought in different sensors and used the weighted objectives method, one of the most common evaluation methods, for comparing design concepts based on an overall value per design concept. Taking into account the obtained scores of each specification, the best choice for this work is the optical encoder. Once the sensor is chosen, it is necessary to design de part where it will be installed without interfering with the normal function of the machine. To do it, photogrammetry scanning methodology was employed. The developed device perfectly detects the advance of the filament without affecting the normal operation of the machine. Also, it is achieved the primary objective of the system, avoiding loss of material, energy, and mechanical wear, keeping the premise of making a low-cost product that does not significantly increase the cost of the machine. This development has made it possible to use the printer with remains of coil filaments, which were not spent because they were not sufficient to complete an impression. Also, printing models in two colours with only one extruder has been enabled by this development

Behavior under Load of A Human Shoulder: Finite Element Simulation and Analysis

[EN]Most musculoskeletal injuries occur during the work routines in different areas, due to repetitive and sustained movements, they are often located in the shoulder. For workers in the building sector, the repetitive movements and displacements occur under load and unnatural postures of the shoulder joint. For this reason, this study aims to model in 3D the biological components which form the shoulder joint for the later finite element analysis. Three cases with different loads have been considered for this study. Due to a linear and isotropic joint approach it has been possible to evaluate the tensions in the main components of the shoulders: muscles, tendons and ligaments

Fabricación aditiva de piezas anatómicas con fines docentes para diferentes titulaciones de ciencias de la salud

Memoria ID-109. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2018-2019

Modelo biomecánico de normalidad de la columna lumbar: Repercusión del deporte de élite en el raquis lumbar

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Medicina, Departamento de Cirugía. Fecha de lectura: 28-11-2019Esta tesis tiene embargado el acceso al texto completo hasta el 28-05-2021Título: Modelo biomecánico de normalidad de la columna lumbar. Repercusión del deporte de élite en el raquis lumbar. Introducción: La columna lumbar es una estructura tridimensional perfectamente definida anatómica y funcionalmente que juega un papel determinante en la biomecánica de la toda columna vertebral y en el análisis postural de los individuos. Su conocimiento es fundamental porque permite el estudio de su tipo de apoyo, de su estabilidad, de su movilidad y de todas sus características cinemáticas y dinámicas. El estudio del raquis lumbar requiere disponer del modelo biomecánico de un grupo control que sea la referencia de normalidad para el resto de los individuos. El modelo planteado debe basarse en funciones de distribución normal que caractericen el raquis lumbar con el objeto de determinar las funciones de relación entre ellas. La práctica deportiva profesional o de alto nivel requiere una intensidad y exigencia física del aparato musculoesquelético que plantea el estudio de su repercusión en el raquis lumbar Objetivos: Se propone desarrollar una metodología para la caracterización del modelo biomecánico del raquis lumbar de un grupo control y de cuatro grupos de deportistas de alto nivel en disciplinas con técnica de ejecución, condiciones de contorno y biomecánica de la columna lumbar diferentes: piragüismo, natación, baloncesto halterofilia. El objetivo planteado es realizar el análisis comparativo de cada modelo biomecánico de deporte frente al modelo del grupo control para valorar la repercusión del deporte de élite en la postura y la biomecánica de su raquis lumbar. Resultados: Los resultados obtenidos permiten determinar la independencia del sexo, edad e índice de masa corporal con las variables morfológicas que definen el raquis lumbar del grupo control, y obtener las ecuaciones de distribución normal que las relacionan y que caracterizan su comportamiento biomecánico del raquis lumbar. La comparación realizada entre el modelo biomecánico del raquis lumbar del grupo control y los de los grupos de deportistas de élite permiten evaluar el tipo y grado de repercusión que pueden padecer debido a la práctica deportiva.Title: Normal biomechanical model of the lumbar spine. Elite sport impact on the lumbar spine. Introduction: The lumbar spine is a three‐dimensional structure that plays a decisive role in the biomechanics of the entire spine and in the postural analysis of individuals. It is perfectly defined both anatomically and in a functional way. Its knowledge is fundamental because it allows the study of its support type, its stability, its mobility and all its kinematic and dynamic characteristics. For the study of the lumbar spine it is required a control biomechanical model that will serve as a reference for the rest of individuals. The proposed model should be based on normal distribution functions that characterize the lumbar spine in order to determine the relationship functions between them. Professional or high‐level sports practice requires an intensity and physical requirement of the musculoskeletal system that the study of its impact on the lumbar spine raises. Goals: The development of a methodology for the characterization of the biomechanical model of the lumbar spine of a control group is proposed as well as four groups of high‐level athletes. These four athlete disciplines have execution technique, boundary conditions and different lumbar spine biomechanics: canoeing, swimming, weightlifting and basketball. The objective is to carry out the comparative analysis of each biomechanical sport model with the model of the control group to assess the impact of elite sport on the posture and biomechanics of its lumbar spine. Results: The results obtained allow determining the independence of sex, age and body mass index with the morphological variables that define the lumbar spine of the control group. It is also possible to obtain the equations of normal distribution relate to them and that characterize their biomechanical behaviour of the lumbar spine. The comparison made between the lumbar spine biomechanical model of the control group and those of the elite athlete groups allows us to evaluate the type and degree of impact they may suffer due to sports

A Finite Element Model for the Analysis of Squeaking Hips

The hip is the second largest articulation of the human body, with its primary role in locomotion. It is exposed to a high number of risks first of all the wear which causes its correct functioning. In some cases, the damages suffered by this articulation can be such as to require its total replacement (Total Hip Replacement -THR-). In recent years with the growing of ceramics materials both for femoral head and for acetabular cup (hard on hard bearings), it has been observed a dynamical phenomenon known as squeaking which should cause a premature failure of the implant. Aim of this paper is to present a Finite Element Model in order to investigate the influence of main prostheses geometrical parameters on its first ten modes of vibration. The obtained results are a good agreement with the available literature data showing a general decreasing of the first six natural frequencies with the increasing of the implants

On the Dental BioTribology: Comparison of Zirconia/Zirconia and Zirconia/Natural Tooth Friction Coefficients by Using a Reciprocating Tribometer

In recent years the interest of tribology applied to dentistry is taking on a large scale due to its rapid expansion and growth. Intensive experimental research conducted on dental tribology allows to develop a more detailed understanding of all the phenomena that take part in the phenomenon of tooth wear. The purpose of this work is to investigate tribological performances in the tooth-to-tooth contact and material-to-natural tooth contact (zirconia vs. zirconia and natural tooth vs. zirconia). The tribological tests were carried out by using a reciprocating tribometer under lubricated conditions (artificial saliva). The normal force in these tests was 20 N, and the duration was of 60 min. The stroke length was 2 mm, according to the range of displacement used in scientific literature. The wear mass loss evaluation was evaluated by using a gravimetric method. A topographic analysis was carried with a 3D non-contact optical profiler in order to characterize the wear mechanisms present in the worn surfaces after each of tribo-tests. The results show that the minimum value of the COF is obtained in the case of Zirconia vs. Zirconia tribo-couple, corresponding to 0.49±0.03. In the case of the tooth-tooth couple this value is 0.52 ±0.03. The results on the wear mass loss show a very low wear rate when coupling in tribological condition natural tooth with a ceramic restoration (a mean value of 0.5 mg was found). This rate is even lower when the contact is between two artificial zirconia teeth