Rui F. Martins

X-ray tomographic imaging of Al/SiCp functionally graded composites fabricated by centrifugal casting

Abstract The present work refers to an X-ray microtomography experiment aiming at the elucidation of some aspects regarding particle distribution in SiC-particle-reinforced functionally graded aluminium composites. Precursor composites were produced by rheocasting. These were then molten and centrifugally cast to obtain the functionally graded composites. From these, cylindrical samples, around 1 mm in diameter, were extracted, which were then irradiated with a X-ray beam produced at the European Synchrotron Radiation Facility. The 3-D images were obtained in edge-detection mode. A segmentation procedure has been adapted in order to separate the pores and SiC particles from the Al matrix. Preliminary results on the particle and pore distributions are presented.

Structural characterisation of NiTi thin film shape memory alloys

Currently, microactuators are being developed using shape memory alloys (SMAs), which allow simple design geometries and provide large work outputs in restricted space. Several techniques have been used to produce NiTi shape memory alloy thin films, but from the practical point of view, only the sputter deposition method has succeeded so far. Vacuum evaporation of NiTi binary alloy entails the potential problem of the evaporation rates of each component not being the same due to differences in vapour pressure. Aiming to study the possible applications of SMAs to microfabrication, NiTi thin films were produced at CENIMAT by sputter and vacuum evaporation using raw materials from different sources. The films were analysed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) at room temperature, as well as in situ high temperature, in order to characterise the temperature ranges at which the different structural transformations occur.

A failure analysis study of wet liners in maritime diesel engines

Abstract This paper presents the results of a study regarding the failure mechanisms detected in alloyed cast iron liners of marine engines. The liners have shown cracks and extensive corrosion after about 1200 service hours, located in the adjustment flange between the liners in the cylinder block. This study includes the material characterisation using chemical, microstructural, hardness and fractographic analysis. The metallurgical results have shown that the material was acceptable concerning the composition and microstructure. The paper also presents the results obtained for the distribution of stresses and temperatures in the critical areas of the cylinder liner. A 2D finite element code was used for this study, using axisymmetric elements with reduced integration. The results have shown that the thermal stresses are significantly more important than the mechanical stresses, the latter being due exclusively to the effect of the combustion gases in the cylinder. For the two geometries which were analysed, the peak stresses were slightly above 100 MPa in tension. This value of stress is high for the cast iron of the liners, and leads to a great potential risk of initiation and propagation of the tiny surface corrosion defects found in these zones. The detailed geometric changes introduced in the second design of the liner gave a little improvement in the stress distribution in the critical areas, although this may not be enough to avoid cracking conditions in the critical areas.

Assessment of drug delivery devices.

Abstract For critical drug delivery, it is important to have a constant and well-known infusion rate delivered by the complete infusion set-up (pump, tubing, and accessories). Therefore, various drug delivery devices and accessories were tested in this article in terms of their infusion accuracy, start-up delay, response time, and dependency on the viscosity. These measurements were performed as part of the European funded research project MeDD. The obtained results show that the infusion accuracy of the devices is flow rate and accessory depended, especially for low flow rates. Viscosity does not have a significant impact on the flow rate accuracy.

Redesign of Exhaust Systems for Naval Gas Turbines: Usage of a New Cr-Mn Austenitic Stainless Steel

Studies performed earlier show that the thermal shock loading has influence, together with the normal service loadings, in the fatigue life of some critical welded joints present in the exhaust systems of naval gas turbines [1-2]. In order to prevent the fatigue crack propagation that was verified in service [3], a recently developed ultrahigh-strength austenitic stainless steel was selected (Cr-Mn steel - number 1.4376) and its mechanical properties and the fatigue resistance are under study. This new material could replace, locally, the current material used in the main structure of the exhaust system (AISI 316L). Experimental data are shown. The temperature measured at the critical locations was about 350°C and the pressure applied in the system was calculated through a Computational Fluid Dynamics simulation (CFD), whose results are presented in the paper. The stresses induced by the loadings will be important to estimate the lifetime from the fatigue resistance tests (S-N curves) that will be performed, at 350°C, in butt and T-welded joints of AISI 316L stainless steel with Cr-Mn austenitic stainless steel.

Primary standards for measuring flow rates from 100 nl/min to 1 ml/min - gravimetric principle.

Abstract Microflow and nanoflow rate calibrations are important in several applications such as liquid chromatography, (scaled-down) process technology, and special health-care applications. However, traceability in the microflow and nanoflow range does not go below 16 μl/min in Europe. Furthermore, the European metrology organization EURAMET did not yet validate this traceability by means of an intercomparison between different National Metrology Institutes (NMIs). The NMIs METAS, Centre Technique des Industries Aérauliques et Thermiques, IPQ, Danish Technological Institute, and VSL have therefore developed and validated primary standards to cover the flow rate range from 0.1 μl/min to at least 1 ml/min. In this article, we describe the different designs and methods of the primary standards of the gravimetric principle and the results obtained at the intercomparison for the upper flow rate range for the various NMIs and Bronkhorst High-Tech, the manufacturer of the transfer standards used.

Failure Mechanisms on Exhaust Systems of Naval Gas Turbines

Some exhaust systems of naval gas turbines have been periodically repaired due to thermal-fatigue crack propagation after entering into service. Those structures were made of austenitic stainless steel grade AISI 316L in thin wall plates, which were bent in rolling machines and welded with longitudinal and circumferential joints by means of shielded metal arc, TIG or MIG/MAG welding processes. The plate thickness is about 3.7 mm and the temperature on the exhaust system is approximately 500°C and 350°C in the critical zones, which are located in the lower and intermediate regions of the exhaust system.Several cracks were detected at the critical regions, near the weld toe of butt and T-welded joints. The stress concentration factors induced by the weld angle, toe radius and rolled surface finishing diminishes the fatigue life strength. Some cracked material samples were taken out from the exhaust system structure and were analysed with a Scanning Electron Microscope (SEM/EDS), in order to determine the failure mechanisms involved in the crack propagation process. Those results are presented in the paper. Several high temperature fatigue and creep tests were performed with CT specimens. The mechanisms of crack propagation on the CT specimens were studied by SEM and compared with the fracture surfaces obtained from the samples taken out from the structure. The carbide precipitation on the grain boundaries was also studied.

Metallurgical Study of a AISI 316L Stainless Steel Used in a Gas Turbine Exhaust System

Several high temperature fatigue and possibly creep-fatigue cracks have nucleated and propagated through the 3.7 mm wall thickness of a gas turbine exhaust system of a navy combat ship made of a grade type AISI 316L annealed stainless steel. The main cracks propagated near some welded joints, where the measured working temperature was approximately equal to 350°C (Fig.1). The paper presents tensile, fatigue and creep data obtained from experimental tests that were performed in several test specimens obtained from steel plates used in-service. Results of optical microscopy for the microstructure of the material and analysis of the fracture surfaces carried out with the SEM have identified the failure mechanisms at test temperatures. The paper also presents microhardness and grain size measurements carried out together with microstructural observations in the SEM. A research work to investigate carbide precipitation in virgin thin sheet specimens, as used in these exhaust tubes, was also performed and it is presented. The influence of stages time (100, 200, 100+100 and 4x50 hours) and of thermal exposure temperatures (500 and 550°C) was assessed to compare the metallurgical properties of the material. Finally, the paper shortly analyses other materials that could replace the used one.

Simulation of a three-dimensional craniofacial structure under the application of orthodontic loads

The aim of this study was to develop a three-dimensional model of a patient’s craniofacial structure to be analysed using the finite element method in order to estimate the forces required to carry out a dental positioning’s correction. The three-dimensional model was composed by several anatomical structures, namely the teeth, the periodontal ligaments, and the trabecular and cortical bones, which were modelled with the aid of computed tomography cone beam images. The tomographic images were analysed and reconstructed using the 3D Slicer software, while the assembly of the anatomical structures modelled, as well as the contact surfaces between contiguous parts, was defined in computer-aided design software. Bone remodelling and the occurrence of tissue’s injuries were considered during the numerical simulations carried out. By imposing displacements to each tooth, it was possible to calculate the orthodontic loads needed to carry out dental correction (reaction forces), as well as the distributions of stresses and deformations inherent to the clinical treatment, allowing to obtain a craniofacial structure capable of simulating the dental movements of upper and lower arches with anatomical realism. In addition, this methodology constitutes a personalised dental medicine that could lead to the development of highly customised orthodontic appliances where different mechanical loads could be applied individually to each tooth to achieve the foreseen dental correction.

Fatigue resistance of rotary endodontic files subjected to planar and non-planar curvatures induced by in vitro tooth canals

Purpose The purpose of this paper is to assess the fatigue life of different sizes of HyFlex CM™ endodontic files when submitted to planar or to non-planar curvatures, and to two different rotational speeds, namely 500 rpm or 250 rpm. The influence of superimposing back and forth motion to rotational bending of endodontic files was also assessed. Design/methodology/approach In all, 64 HyFlex CM™ files of different sizes, namely ref. 0.04/20, 0.06/20, 0.04/35 and 0.06/35, were submitted to rotational bending tests at two different rotational speeds. The planar radius of curvature imposed to the endodontic files was about 4.5 mm, along an angle of 45°, in order to simulate an apical canal that would induce severe loading to the files during clinical treatment. Additionally, 11 Hyflex CM™ files ref. 0.04/20 were submitted to rotational bending tests at 500 rpm inside a mandible first molar manufactured through selective laser melting (SLM), aiming to simulate non-planar curvatures of a real tooth canal. Findings When considering planar curvature, the endodontic file ref. 0.06/20, tested at 250 rpm, has shown the highest fatigue resistance (4,185 revolutions, 1,004 seconds), while the lowest fatigue resistance was registered for instrument ref. 0.04/35 submitted to 500 rpm (747 revolutions, 89 seconds). Hence, depending on the rotational speed, surface finish and the size of the endodontic files tested (taper and tip’s diameter), significant differences in fatigue resistance were noticed. If non-planar curvatures were considered, the minimum fatigue resistance was equal to 107 seconds, and back and forth motion allowed extending the minimum fatigue lifetime to 140 seconds. Originality/value The fatigue resistance of endodontic files is frequently determined through in vitro fatigue tests carried out under single planar curvature or eventually under double planar curvatures. However, non-planar loadings are frequently induced on endodontic instruments when treating root canals with severe multiplanar curvatures. In the research herein presented, a mandible first molar was 3D printed by using the SLM technique in an AISI 316 L stainless steel and more realistic experimental fatigue tests were carried out.