Javier Echávarri Otero

Development of Personalized Annuloplasty Rings: Combination of CT Images and CAD-CAM Tools

Although the use of personalized annuloplasty rings manufactured for each patient according to the size and morphology of their valve complex could be beneficial for the treatment of mitral insufficiency, this possibility has been limited for reasons of timelines and costs as well as for design and manufacturing difficulties, as has been the case with other personalized implant and prosthetic developments. However, the present quality of medical image capture equipment together with the benefits to be had from computer-aided design and manufacturing technologies (CAD-CAM) and the capabilities furnished by rapid prototyping technologies, present new opportunities for a personalized response to the development of implants and prostheses, the social impact of which could turn out to be highly positive. This paper sets out a personalized development of an annuloplasty ring based on the combined use of information from medical imaging, from CAD-CAM design programs and prototype manufacture using rapid prototyping technologies.

A thermal resistances-based approach for thermal-elastohydrodynamic calculations in point contacts

This article presents a thermal resistances-based approach for solving the thermal-elastohydrodynamic lubrication problem in point contact, taking the lubricant rheology into account. The friction coefficient in the contact is estimated, along with the distribution of both film thickness and temperature. A commercial tribometer is used in order to measure the friction coefficient at a ball-on-disc point contact lubricated with a polyalphaolefin base. These data and other experimental results available in the bibliography are compared to those obtained by using the proposed methodology, and thermal effects are analysed. The new approach shows good accuracy for predicting the friction coefficient and requires less computational cost than full thermal-elastohydrodynamic simulations.This article presents a thermal resistances-based approach for solving the thermal-elastohydrodynamic lubrication problem in point contact, taking the lubricant rheology into account. The friction ...

Analysis of different multiaxial fatigue criteria in the prediction of pitting failure in spur gears

The aim of this article is to study the appearance of pitting in spur gears by taking account of different multiaxial fatigue criteria. The stress levels undergone by the teeth are considered in order to be able to predict their life and compare the fatigue strength of gear materials. The process begins calculating the stress field inside the teeth flanks due to the pressure and shear stress in the contact along the mesh. Once the stresses are known, the appearance of failure is studied by using different multiaxial fatigue criteria: Dang Van, Crossland and Liu-Mahadevan criteria. The accuracy of each criterion to predict pitting in gears is analysed using experimental data.

Royal Manufactures Promoted by the Spanish Crown during the 18th and 19th Centuries: An Approach to European Industrialisation

This work presents the Royal Factories promoted by the Spanish crown in the 18th and 19th centuries in the context of European industrialisation. They are classified together with the main types of factories and some specific examples are described. The article includes a discussion on the conditions that promoted their proliferation as the precursors of present-day state-owned industry, as well as the main causes that led to their decline.

The Machine Renaissance

The Renaissance in Western Europe in the fourteenth to sixteenth centuries marked strong activity of recovery and revitalisation in artistic, scientific, and literature frames that overcame the stagnation of the Middle Ages. Unlike during medieval times, the opening of society during the Renaissance promoted the spread of machines in many environments. Little by little, many existing machines were no longer considered simply as a means of carrying out civil or military engineering works.

Medieval Machines and Mechanisms

In medieval times the most creative mechanical developments took place in the Islamic world. Some of those engineering and technological achievements are little-known due to the fact that, at that time, knowledge passed from master to apprentice through direct experience without being recorded in any written form. In addition, few manuscripts were actually written and only a few of them have survived through time.

Industrial Archaeology: From the 17th to the 21st Century. Reconstruction of Herschel’s Telescope

Towards the end of 1997, the director of the National Astronomical Observatory, Jesus Gomez, commissioned the Machines and Mechanisms Laboratory of this School, to produce a viability study for the reconstruction of “Herschel’s Great Telescope”. This device was built in the 18th century as part of the fine set of instruments that on the orders of Charles IV, were to equip the Madrid Royal Observatory, which had been created by Charles III in 1790. Unfortunately, this great telescope was destroyed in the War of Independence. All that survived were a few remains, and the image of its structure, thanks to the magnificent illustrations executed by the hand of Mendoza (Fig. 1), the naval officer to whom the King had entrusted its construction.

Film Thickness Formula for Thermal EHL Line Contact Considering a New Reynolds–Carreau Equation

This article presents thermal EHL calculations for line contacts using a new analytical form of the Reynolds equation for lubricants whose rheological behaviour follows a modified Carreau model proposed by Bair. The isothermal calculation process was presented in: de la Guerra (Tribol Int 82:133–141, 2015). A new parametric formula is hereby developed using the aforementioned Reynolds–Carreau equation and adding the thermal effects to the solving process. The accuracy of this formula is discussed by comparing the estimates with the experimental and numerical results available. This analytical formula provides a fast and easy calculation methodology with good accuracy within a reasonably wide range of operating conditions.

Friction coefficient in mixed lubrication: A simplified analytical approach for highly loaded non-conformal contacts

This article presents an analytical model for predicting friction in mixed lubrication regime. The calculations consider load shared between roughness asperities and the lubricant film, as well as the appearance of thermal effects in the contact and the influence of the lubricant rheology. Tests using tribometers have been performed to measure the friction coefficient in non-conformal surfaces for both point and line contacts. This allows verifying the results of the model under a broad range of experimental conditions with an influence on the lubrication conditions. Reasonably good precision has been found in the results obtained, which combined with a simplicity of use confers the model a high practical utility for rough estimates of the friction coefficient under mixed lubrication.This article presents an analytical model for predicting friction in mixed lubrication regime. The calculations consider load shared between roughness asperities and the lubricant film, as well as ...

The Evolution and Development of Mechanical Engineering through large cultural areas

Mechanical Engineering is probably the forerunner of many branches of Engineering and has persistently been their companion up to the present. For this reason, the History of Machines embraces a very broad period of the History of Mankind, and can be studied from many perspectives. This paper attempts to link progress in Mechanical Engineering to the great cultures that have arisen throughout the History of Mankind.