F. Macedo

Thermal contact resistance evaluation in polymer-based carbon fiber composites

The thermal contact resistance of polymer-based carbon fiber composites was calculated from experimental thermal conductivity values. Thermal conductivity of the composites increases as the fiber content increases. In order to explain the variation with size and volume fraction of the conductive inclusions in the composite, an effective medium model, which includes the effect of interfacial thermal resistance, was applied. Two different geometries for the fiber distribution in the matrix were considered. The calculated thermal contact resistance obtained from the effective medium models is in good agreement with the theoretical predictions. Once tested and validated, these models can also contribute to evaluate the best choice of materials for composite production, as maximum values for the thermal conductivity can be estimated.

Photothermal characterization of amorphous thin films

Thin amorphous films deposited on steel substrates by physical vapour deposition, chemical vapour deposition and sputtering with thicknesses between 2 and 4 μm have been analysed with respect to their thermal properties by non-destructive evaluation based on infrared detection of thermal waves. Samples with and without exposure to friction wear have been compared. The main results are that the friction effects can be characterized by their effects on the thermal properties, the thermal diffusivity and effusivity of the coating. It has been found that it is mainly the thermal conductivity of the coating that is affected by friction wear and the induced stresses.

Analysis of multifunctional oxycarbide and oxynitride thin films by modulated IR radiometry

Multifunctional coatings consisting of transition metal oxycarbides and oxynitrides deposited by physical vapour deposition techniques on tool steel are analysed in this work by means of modulated IR radiometry (MIRR), a non-contact non-destructive thermal wave measurement technique, with respect to the thermal transport properties relevant for time-dependent surface heating processes of coating–substrate systems. In order to interpret the measured data quantitatively, an inverse solution of the two-layer thermal wave problem is applied, which relies on the thermal wave phase lag data measured as a function of modulation frequency of the periodically modulated laser beam heating intensity. Based on these measurements and their quantitative interpretation, correlations between the thermal transport properties of the coatings and their deposition conditions have been found, which can be used to monitor deposition processes. For a second objective of this work, namely to determine the film thickness by means of MIRR, different sets of thin films of approximately constant thermal transport properties, but differing film thickness, have been measured. To discuss the limitations and error limits of these non-contact non-destructive measurements of the coating thickness, the results obtained by MIRR are compared with the coating thickness determined by destructive measurements.

Photothermal characterization of sputtered thin films and substrate treatment

Photothermal radiometry has been applied to relatively thin TiN-based hard coatings on high speed steel. The main results are that the photothermal depth profiles of the samples are strongly influenced by the substrate preparation, that an empirical correlation between the measured photothermal depth profile and different coatings can easily be established, that however a quantitative determination of the thermal properties (thermal diffusivity, effusivity) based on unique solutions of the heat diffusion equation is difficult. This is due to three reasons: the coatings are relatively thin and transparent, and the substrates alone already exhibit strong gradients of the thermal properties.

Modulated IR radiometry for determining thermal properties and basic characteristics of titanium thin films

Titanium thin films of different thicknesses were prepared by direct current magnetron sputtering to study modulated infrared (IR) radiometry as a tool for analyzing film thickness. Thickness was varied by regularly increasing the deposition time, keeping all the other deposition parameters constant. The influence of film thickness on morphological, structural, and electrical properties of the titanium coatings also was investigated. The experimental results revealed a systematic grain growth with increasing film thickness, along with enhanced film crystallinity, which led to increased electrical conductivity. Using the results obtained by modulated IR radiometry, the thickness of each thin film was calculated. These thickness values were then compared with the coating thickness measurements obtained by scanning electron microscopy. The values confirmed the reliability of modulated IR radiometry as an analysis tool for thin films and coatings, and for determining thicknesses in the micrometer range, in particular.

Contact angle measurement of SAC 305 solder: numerical and experimental approach

The solder process comprises the ability of a melted alloy to flow or spread on a substrate for the formation of a metallic bond driven by the physical–chemical properties of the system. Thus, the study of wetting behaviour is an important step in the characterisation of solder alloys and requires the discussion of different parameters that affect the solder junctions. The main objective of this work is to use a CFD study to determine the influence of several parameters in the melting shape obtained with a solder, of the SAC 305 type and compare the numerical results with experimental data. The computational model was implemented in ANSYS Fluent® and the simulations were carried out involving the melting of a material using the volume of fluid method to capture the solidification/melting interfaces based on an enthalpy-porosity approach. The results show that shape of the melted solder is greatly influenced by the contact angle and, to a smaller extent, by the surface tension. It was also concluded that it is possible to accurately predict the shape of the melted solder using computational fluid dynamic tools in complement to the experimental validation.

Laser modulated optical reflectance of thin semiconductor films on glass

Semiconductor films, deposited by reactive magnetron sputtering on glass substrates, have been analyzed with the help of laser modulated optical reflectance. The results are discussed with respect to the thermal and charge carrier transport properties. Charge carrier surface recombination at the front surface and at the interface between semiconductor film and glass substrate have been identified both for microcrystalline and amorphous films.

Influence of Copper Layer Content in the Elastic and Damping Behavior of Glass-Fiber/Epoxy-Resin Composites

The impact in the elastic behavior and internal friction, caused by the introduction of Copper layers in Glass-Fiber/Epoxy Resin composites and temperature effects, were studied and evaluated recurring to Dynamic Mechanical Analysis. It is shown that the introduction of Copper layers increases the storage modulus of the composites and delays their glass transition temperature, however, it allows a faster transformation. Additionally, it is concluded that the introduction of Copper layers elevates the internal friction during the glass transition phase by the inversion of the deformation mechanism due to thermal expansion and increase in the Poisson’s ratio of the epoxy resin to a value near 0.5 where its deformation is approximately isochoric. This increase in damping capacity is relevant in application with cyclic fatigue and mechanical vibration.

Synthesis of polymer-based triglycine sulfate nanofibres by electrospinning

In this work we present the synthesis and characterization of polyethylene oxide (PEO) based triglycine sulfate (NH2(CH2OOH)3H2S04, TGS) nanofibres obtained by electrospinning. The fibres, with typical diameters of about 190?750?nm and above several hundred micrometres in length, present the nanocrystals of TGS embedded in a polymer matrix. The obtained nanofibres were characterized by FT-IR spectroscopy and the domain structure was examined by piezoforce microscopy. Dielectric permittivity measurements on the TGS?PEO nanofibres exhibit the characteristic ferroelectric?paraelectric phase transition at around 50??C.

Modeling the Reflow Soldering Process in PCB’s

In the present work two different types of case studies are modelled, carried out involving the fusing of a material using the CFD (Computational Fluid Dynamics) software Ansys Fluent, using the VOF method (Volume of Fluid) to capture the position of the existing interfaces and the Solidification/melting method which uses an enthalpy-porosity approach to simulate the fusion of the material.The first case focus itself in the analysis of fusing process and dropping behavior of the melted plate in the presence of a thermal source. The validation is made using a study found in the bibliography and then using water as the melting material given that its behavior is well known. Then tin is used as the melting material followed by the use of SAC 405 as the melting plate. This study compares various materials properties and verifies the influence of some of these particular properties by changing them (surface tension and heat of fusion).The second case focus on the simulation of a geometry obtained at balance at a constant temperature by the SAC 405 soldering alloy in the presence of a component and the copper substrate on top of a PCB.Copyright