Abstract: 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.
Abstract: The present work shows the microstructural and mechanical results obtained in joints
WC-Co / steel 90MnCrV8 (high strength steel). The joints were carried out using diffusion welding
processes and soft interlayers Cu-Ni. The binary Cu-Ni alloys were obtained by electrochemical
deposition techniques. The microstructural and mechanical changes provoked in the steel, due to
heat treatments, were studied in order to know plastic deformation during the joints. The diffusion
welds were obtained in an Edwards vacuum furnace (10-3 - 10-4 Pa), three welding temperatures
were used, (825 °C, 850 °C and 875 °C) and 30, 45 and 60 minutes, as welding times. The constant
pressure was 5 MPa. The welding interface microstructure was studied by scanning electron
microscopy (SEM-EDX). In order to determine the mechanical behaviour of all joints were carried
out shear tests. The optimum results were obtained at 850 °C / 45 min and 850 °C / 60 min.
Nevertheless, the diffusion welding conditions allowed attaining high quality welding interfaces in
all joints of WC-Co / 90MnCrV8
Abstract: In this work, two different consolidation techniques were used to obtain AlN samples:
slip casting and dry pressing of granules obtained from aqueous suspensions by freeze granulation.
The green samples were sintered at a temperature (1750°C) lower than those usually used
(>1800°C), using CaF2 and YF3 as sintering aids. The microstructural features were analysed by
scanning electron microscopy (SEM) and the crystalline phases formed were identified by X-ray
(XRD). Full dense AlN-based ceramics were obtained from both consolidation techniques; however
the thermal conductivity values were quite different. The presence of carbon in the samples derived
from the freeze granulated powder containing organic processing additives de-waxed in an inert
atmosphere revealed to be helpful in the cleaning of oxygen present at the grain boundaries and
consequently, for enhancing the thermal conductivity.
Abstract: Aluminosilicates represent the major group of solid inorganic matter of the terrestrial
crust. In specific conditions of temperature and pressure, the aluminosilicates may, in strong
alkaline environment, react among themselves, giving place to the formation of stable materials of
high mechanical strength, able to support high levels of temperature and resistant to acid action.
They also have the ability for the immobilisation of heavy metals and radionuclides.
When subject to a previous thermal treatment, certain aluminosilicates like kaolin, can be directly
activated at room temperature and normal pressure.
In this work, the conditions of preparation of metakaolin (a meta-phase of kaolin) are optimised.
Temperatures of kaolin dehydration and exposition time to temperature are studied by the use of
XRD, FTIR and NMR-MAS, and so far by the application of Murat-Bachiorrini Criterion. The
results obtained show that energy savings are considerable.
Abstract: PXRD (powder x-ray diffraction), FT-IR (Fourier Transform infrared), N2 adsorption at -
196 °C and TG/DTA (thermogravimetric and differential thermal analyses) techniques have been
used for characterisation of MgAl- and ZnAl-CrO4 LDHs, which had been prepared by the ion
exchange method from the corresponding chloride LDH (layered double hydroxides) precursors.
The results indicates that the oxometalate intercalation in both systems produces interlayer
microporosity and a basal spacing of 8.7 Å; This gallery height decreases when the samples are
calcined in the temperature range 100-300 °C, due to a grafting process. A larger thermal stability is
detected for MgAl-CrO4 sample than for the zinc-containing one.
Abstract: This work aims at characterising an alumina powder obtained by combustion synthesis,
and at evaluating the technical properties of sintered bodies. Particle size distribution and XRD
were used to characterise the alumina powder; electrophoresis and rheological measurements were
used to select the most suitable processing conditions. Sintered density, flexural strength, Vickers
hardness and SEM analysis were used to characterise the bodies sintered at 1600°C. The
experimental results showed that a density of 3.60 g/cm3 could be obtained in absence of sintering
aids and that the sintered bodies exhibited a flexural strength of 220 MPa and a Vickers hardness of
Abstract: In the present work, glass fibre polypropylene (GF/PP) woven fabrics were manufactured from cost-effective flexible thermoplastic towpregs produced by a developed dry coating process. The paper describes the modifications made on the developed coating line to allow producing thermoplastic towpregs able to be woven in textile equipments. The produced fabrics were observed under optical microscopy and submitted to tests in order to evaluate their textile-like properties, glass fibre content and flexibility. Composites processed from those fabrics by compression moulding were also submitted to mechanical testing in order to assess their performance. The obtained experimental results have shown that the woven fabrics produced are cost-effective and present properties good enough to be applied in large-scale commercial markets (e.g. automotive). Future research efforts will be carried to try decreasing the towpreg frictional properties and the amount of polymer lost during the textile processing and improving the feeding technology to warp yarns directly from a creel.
Abstract: This paper describes the work that is being done at the University of Minho concerning
the development of braided rods for concrete reinforcement. A preliminary research study has been
conducted to understand the mechanical behaviour of braided fabrics. Various samples have been
produced varying the type of fiber (glass, polyester and aramid), the type of braided fabric (simple,
hybrid and core reinforced) and in the latter case, the number of core reinforcing yarns. The tensile
properties of these samples have been evaluated and the results presented. The influence of each
factor on the tensile properties of braided fabrics has also been analysed and discussed. In order to
produce braided reinforced composite rods to use as a concrete reinforcement, a special technique
has been developed using a standard vertical braiding machine. The braided reinforced composite
materials have been produced in rib structure to improve adhesion between them and the concrete.
Special samples have been prepared and tested to evaluate the adherence between both materials
involved. The tensile and bending properties of braided reinforced composite rods have been
evaluated and the results obtained presented and discussed.
Abstract: The theoretical treatment of a cavity resonator consists of solving the Maxwell equations
in that cavity, respecting the boundary conditions. The resonance frequencies appear as conditions
in the solutions of the differential equation involved and are not significantly affected by the fact
that the cavity walls have a finite conductivity. Solutions for rectangular cavities and for the lowest
resonant mode, where the probability of mistaking one mode from another is slight, are readily
The measurement of the complex permittivity, ε* = ε´-iε´´, can be made using the small
perturbation theory. In this method, the resonance peak frequency and the quality factor of the
cavity, with and without a sample, can be used to obtain the complex dielectric permittivity of the
material. We measure the shift in the resonant frequency of the cavity, f, caused by the insertion of
the sample, which can be related to the real part of the complex permitivitty, ε´, while the change in
the inverse of the quality factor of the cavity, (1/Q), gives the imaginary part, ε´´.
In this work we report the construction details, the performance tests of the cavity to confirm the
possibility of the use of the small perturbation theory, and the application of the technique to
measure the complex permittivity of a reinforced plastic.
Abstract: In this paper the influence of tribophysical activation on non-isothermal sintering of
barium titanate has been investigated. BaTiO3 powders were tribophysically activated in a planetary
ball mill for 0, 60 and 120 min., pressed and non-isothermally sintered up to 1380oC. Dilatometric
analysis was performed in air in the temperature range from room temperature to 1380oC with
heating rates of 10, 20 and 30oC/min. The samples were analyzed by the X-ray powder diffraction
method. Investigation of the morphology of microstructure constituents was performed using the
scanning electron microsocopy method. With the purpose of optimizing technological parameters
the results obtained by microstructure analysis were correlated with the results of quantitative