A Resistência Térmica de Contato entre a ferramenta de forjamento e a peça é um parâmetro importante para a otimização, por simulação computacional, do comportamento do material forjado. Os procedimentos atuais destinados à determinação da Resistência Térmica de Contato apresentam discrepância significativa nos resultados. A falta de valores confiáveis deste parâmetro afeta a precisão da simulação. Visando a importância das ferramentas computacionais para a otimização do processo de forjamento, no presente trabalho foi desenvolvida uma nova técnica para determinar a Resistência Térmica de Contato. A técnica inovadora inclui o método de medição de temperaturas interfaciais desconhecido anteriormente, a montagem para realizá-lo e o sistema de medição de temperaturas volumétricas. Esta técnica é destinada ao uso sob condições de altas e moderadas temperatura e pressão muito grande, o que é característico da zona de contato material forjado–ferramenta. A inovação foi testada com sucesso para alguns materiais típicos (aço, liga de alumínio e liga de titânio) utilizados no forjamento a quente ou a morno. Os valores da Resistência Térmica de Contato, obtidos nos testes, são recomendados para uso em programas de simulação computacional. / The Thermal Contact Resistance between a die and a blank is an important parameter in the computer simulation used for the optimization of the blank plastic deformation. The known procedures intended for the determination of the Thermal Contact Resistance show significant discrepancy in results. The lack of reliable values of this parameter affects the precision of the simulation. Taking in account the importance of computer tools for the optimization of the forging process, a new technique for the determination of the Thermal Contact Resistance has been developed in the present study. The developed technique includes a method for the measurement of the interface temperatures, which was unknown before, and the equipment for the realization of this method as well as the system for the measurement of the volumetric temperatures. This technique is intended for use under moderate and high temperature / high pressure conditions at the die–workpiece interface. The innovation has been tested successfully on some typical materials (steel, aluminium alloy e titanium alloy) used in warm and hot forging. Values of the Thermal Contact Resistance obtained by these tests are recommended for use in computer simulations.

A Resistência Térmica de Contato entre a ferramenta de forjamento e a peça é um parâmetro importante para a otimização, por simulação computacional, do comportamento do material forjado. Os procedimentos atuais destinados à determinação da Resistência Térmica de Contato apresentam discrepância significativa nos resultados. A falta de valores confiáveis deste parâmetro afeta a precisão da simulação. Visando a importância das ferramentas computacionais para a otimização do processo de forjamento, no presente trabalho foi desenvolvida uma nova técnica para determinar a Resistência Térmica de Contato. A técnica inovadora inclui o método de medição de temperaturas interfaciais desconhecido anteriormente, a montagem para realizá-lo e o sistema de medição de temperaturas volumétricas. Esta técnica é destinada ao uso sob condições de altas e moderadas temperatura e pressão muito grande, o que é característico da zona de contato material forjado–ferramenta. A inovação foi testada com sucesso para alguns materiais típicos (aço, liga de alumínio e liga de titânio) utilizados no forjamento a quente ou a morno. Os valores da Resistência Térmica de Contato, obtidos nos testes, são recomendados para uso em programas de simulação computacional. / The Thermal Contact Resistance between a die and a blank is an important parameter in the computer simulation used for the optimization of the blank plastic deformation. The known procedures intended for the determination of the Thermal Contact Resistance show significant discrepancy in results. The lack of reliable values of this parameter affects the precision of the simulation. Taking in account the importance of computer tools for the optimization of the forging process, a new technique for the determination of the Thermal Contact Resistance has been developed in the present study. The developed technique includes a method for the measurement of the interface temperatures, which was unknown before, and the equipment for the realization of this method as well as the system for the measurement of the volumetric temperatures. This technique is intended for use under moderate and high temperature / high pressure conditions at the die–workpiece interface. The innovation has been tested successfully on some typical materials (steel, aluminium alloy e titanium alloy) used in warm and hot forging. Values of the Thermal Contact Resistance obtained by these tests are recommended for use in computer simulations.

A Resistência Térmica de Contato entre a ferramenta de forjamento e a peça é um parâmetro importante para a otimização, por simulação computacional, do comportamento do material forjado. Os procedimentos atuais destinados à determinação da Resistência Térmica de Contato apresentam discrepância significativa nos resultados. A falta de valores confiáveis deste parâmetro afeta a precisão da simulação. Visando a importância das ferramentas computacionais para a otimização do processo de forjamento, no presente trabalho foi desenvolvida uma nova técnica para determinar a Resistência Térmica de Contato. A técnica inovadora inclui o método de medição de temperaturas interfaciais desconhecido anteriormente, a montagem para realizá-lo e o sistema de medição de temperaturas volumétricas. Esta técnica é destinada ao uso sob condições de altas e moderadas temperatura e pressão muito grande, o que é característico da zona de contato material forjado–ferramenta. A inovação foi testada com sucesso para alguns materiais típicos (aço, liga de alumínio e liga de titânio) utilizados no forjamento a quente ou a morno. Os valores da Resistência Térmica de Contato, obtidos nos testes, são recomendados para uso em programas de simulação computacional. / The Thermal Contact Resistance between a die and a blank is an important parameter in the computer simulation used for the optimization of the blank plastic deformation. The known procedures intended for the determination of the Thermal Contact Resistance show significant discrepancy in results. The lack of reliable values of this parameter affects the precision of the simulation. Taking in account the importance of computer tools for the optimization of the forging process, a new technique for the determination of the Thermal Contact Resistance has been developed in the present study. The developed technique includes a method for the measurement of the interface temperatures, which was unknown before, and the equipment for the realization of this method as well as the system for the measurement of the volumetric temperatures. This technique is intended for use under moderate and high temperature / high pressure conditions at the die–workpiece interface. The innovation has been tested successfully on some typical materials (steel, aluminium alloy e titanium alloy) used in warm and hot forging. Values of the Thermal Contact Resistance obtained by these tests are recommended for use in computer simulations.

This thesis investigates the cooling behaviour of polymers during the microinjection moulding process. The work included bespoke experimental mould design and manufacturing, material characterisation, infra-red temperature measurements, cooling analysis and cooling prediction using commercial simulation software. To measure surface temperature of the polymers, compounding of polypropylene and polystyrene with carbon black masterbatch was performed to make materials opaque for the IR camera. The effects of addition of carbon black masterbatch were analysed using differential scanning calorimetry and Fourier transform infrared spectroscopy. Sapphire windows formed part of the mould wall and allowed thermal measurements using an IR camera. They were laser machined on their inside surfaces to generate a range of finishes and structures. Their topographies were analysed using laser confocal microscope. The surface energy of sapphire windows was measured and compared to typical mould steel, employing a contact angle measurement technique and calculated using Owens-Wendt theory. A heating chamber was designed and manufactured to study spreading of polymer melts on sapphire and steel substrates. A design of experiments approach was taken to investigate the influence of surface finish and the main processing parameters on polymer cooling during microinjection moulding. Cooling curves were obtained over an area of 1.92 by 1.92 mm of the sapphire window. These experiments were conducted on the Battenfeld Microsystem 50 microinjection moulding machine. A simulation study of polymer cooling during the microinjection moulding process was performed using Moldflow software. Particular interest was paid to the effect of the values of the interfacial heat transfer coefficient (HTC) on the simulated cooling predictions. Predicted temperature curves were compared to experimentally obtained temperature distributions, to obtain HTC values valid for the material and processing parameters.

No description available.

This thesis investigates the cooling behaviour of polymers during the microinjection moulding process. The work included bespoke experimental mould design and manufacturing, material characterisation, infra-red temperature measurements, cooling analysis and cooling prediction using commercial simulation software. To measure surface temperature of the polymers, compounding of polypropylene and polystyrene with carbon black masterbatch was performed to make materials opaque for the IR camera. The effects of addition of carbon black masterbatch were analysed using differential scanning calorimetry and Fourier transform infrared spectroscopy. Sapphire windows formed part of the mould wall and allowed thermal measurements using an IR camera. They were laser machined on their inside surfaces to generate a range of finishes and structures. Their topographies were analysed using laser confocal microscope. The surface energy of sapphire windows was measured and compared to typical mould steel, employing a contact angle measurement technique and calculated using Owens-Wendt theory. A heating chamber was designed and manufactured to study spreading of polymer melts on sapphire and steel substrates. A design of experiments approach was taken to investigate the influence of surface finish and the main processing parameters on polymer cooling during microinjection moulding. Cooling curves were obtained over an area of 1.92 by 1.92 mm of the sapphire window. These experiments were conducted on the Battenfeld Microsystem 50 microinjection moulding machine. A simulation study of polymer cooling during the microinjection moulding process was performed using Moldflow software. Particular interest was paid to the effect of the values of the interfacial heat transfer coefficient (HTC) on the simulated cooling predictions. Predicted temperature curves were compared to experimentally obtained temperature distributions, to obtain HTC values valid for the material and processing parameters.

Operating temperature range is one of the primary design considerations for developing effective disc brake system performance. Very high braking temperatures can introduce effects detrimental to performance such as brake fade, premature wear, brake fluid vaporization, bearing failure, thermal cracks, and thermally-excited vibration [2]. This project is concerned with investigating deficiencies and proposing improvements in brake system Finite Element (FE) models in order to provide high quality descriptions of thermal behaviour during braking events. The work focuses on brake disc/pad models and the degree of rotational freedom allowed for the pad. Conventional models [10] allow no motion/or free motion of the pad. The present work investigates the effect on disc/pad interface temperature and pressure distributions of limited relaxations of this rotational restriction. Models are proposed, developed and validated that facilitate different rotational degrees of freedom (DoF) of the pad. An important influencing factor in friction brake performance is the development of an interface tribo-layer (ITL). It is reasonable to assume that allowing limited rotational motion of the pad will impact the development of the ITL (e.g. due to different friction force distributions) and hence influence temperature. Here the ITL is modelled in the numerical simulations as a function of its thickness distribution and thermal conductivity. Different levels of ITL thermal conductivity are defined in this work and results show that conductivity significantly a1qwffects interface temperature and heat partition ratio. The work is based around a set of test-rig experiments and FE model developments and simulations. For the experimental work, a small-scale test rig is used to investigate the friction induced bending moment effect on the pad/disc temperature. Significant non-uniform wear is observed across the friction surface of the pad, and reasons for the different wear rates are proposed and analyzed together with their effect on surface temperature. Following on from experiment a suite of models is developed in order to evidence the importance of limited pad motion and ITL behaviours. A 2D coupled temperature-displacement FE model is used to quantify the influence of different pad rotational degrees of freedom and so provide evidence for proposing realistic pad boundary settings for 3D models. Normal and high interface thermal conductance is used in 2D models and results show that the ITL thermal conductivity is an important factor influencing the maximum temperature of contact surfaces and therefore brake performance. The interface heat partition ratio is calculated by using the heat flux results and it is confirmed that this value is neither constant nor uniform across the interface surfaces. Key conclusions from the work are (i) that ITL thermal conductivity is an important factor influencing the interface temperature/heat flux distribution and their maximum values, (ii) that allowed motion of the pad significantly affects the interface pressure distribution and subsequently the temperature distribution, (iii) that the transient heat partition in friction braking is clearly quite different to the conventional friction-pair steady heat partition (the heat partition ratio is not uniformly distributed along the interface) and (iv) that the thickness of the ITL increases through braking events, reducing the heat transfer to the disc, and so providing a possible explanation for increasing pad temperature observed over the life time of a brake pad.

Yes / A 2D coupled temperature-displacement FE model is developed for a pad-disc brake system based on a restricted rotational pad boundary condition. The evolution of pressure, heat flux, and temperature along the contact interface during braking applications is analysed with the FE model. Results indicate that different rotational pad boundary conditions significantly impact the interface pressure distribution, which in turn affects interface temperature and heat flux distributions, and suggest that a particular pad rotation condition is most appropriate for accurately modelling friction braking processes. The importance of the thermal contact conductance in the analysis of heat transfer in friction braking is established, and it is confirmed that the heat partition ratio is not uniformly distributed along the interface under normal and high interface thermal conductance conditions.

Contact resistance is the most important and universal characteristic of all types of electrical and thermal contacts. Accurate measurement of contact resistance is important, because it serves as a measure for judging the performance and operational life span of contacts. Rise in contact temperature is one of the major factors that pose a big threat to the stability of electrical contacts. Dissipation of heat by solid conduction through a contact interface is governed by its thermal contact conductance (TCC). This emphasizes the need to study the TCC of an electrical contact along with its electrical contact resistance (ECR). Simultaneous measurement of ECR and TCC is important for understanding the interconnection between these two quantities and the possible influence of one over another. Real time experimental data and analytical correlations can be extremely helpful in developing electrical contacts with improved thermal management capabilities. As a part of the experimental investigation, a test facility has been developed for making simultaneous measurement of ECR and TCC across flat contacts. The facility has the capability of measuring ECR and TCC over a wide range of operating parameters, such as contact pressure, contact temperature, interstitial gaseous media, ambient pressure, etc. It is also capable of determining the electrical resistivity and thermal conductivity of materials as a function of temperature, which is very helpful in analyzing the generated contact resistance data. Using this facility, simultaneous ECR and TCC measurements are made across bare and gold plated contacts of OFHC Cu (oxygen free high conductivity copper) and brass. Simultaneous ECR and TCC measurements are made on nominally flat contacts in the contact pressure range of 0 – 1 MPa and the interface temperature range of 20 – 120 °C. Effect of contact pressure and interface temperature on ECR and TCC is studied on bare and gold coated contacts in vacuum, N2, Ar, and SF6 environments. TCC strongly depends on the thermophysical properties of the interstitial media and shows a significant enhancement in gaseous media, because of the increased interfacial gap conductance compared to vacuum. The gas pressure is varied in the range of 1 – 2.6 bar to study its effect on the gap conductance at different contact pressures and interface temperatures. Minor increase in the ECR observed in gaseous media is found to be independent of the properties of the media. Experimental results indicated that ECR depends on the gas pressure as well as on the applied contact load. Effect of gold coating and its thickness on the ECR and TCC across OFHC Cu and brass contacts is studied. Measurements on electroplated gold specimens having different gold layer thicknesses (0.1, 0.3, and 0.5 µm) indicated that ECR decreases and TCC increases with increasing gold coating thickness. Effect of gold coating on the substrate properties, contact surface tomography, and microhardness is analyzed and correlated to the observed behavior of ECR and thermal gap conductance. An attempt is made to understand and quantify the changes in the contact surface characteristics due to contact loading and heating, by measuring various surface topography parameters before and after the experimentation. Effect of thermal stresses (generated due to temperature variations) on ECR and TCC is studied and inclusion of an experimentally measured temperature dependent load correction factor is suggested in the theoretical models to take into account the effect of thermal stresses in contact assemblies.

Nowadays numerical simulations are used to optimize manufacturing process. These numerical simulations need a large amount of input parameters and some of these parameters have not been sufficiently described. One of this parameter is thermal contact resistance, which is not sufficiently described for high temperatures and high contact pressure. This work describes experimental measuring of thermal contact resistance and how to determine thermal contact conductance which can be used as a boundary condition for numerical simulations. An Experimental device was built in Heat Transfer and Fluid Flow Laboratory, part of Brno University of Technology, and can be used for measuring thermal contact conductance in various conditions, such as contact pressure, initial temperatures of bodies in contact, type of material, surface roughness, presence of scales on the contact surface. Bodies in contact are marked as a sensor and a sample, both are embedded with thermocouples. The temperature history of bodies during an experiment is measured by thermocouples and then used to estimate time dependent values of thermal contact conductance by an inverse heat conduction calculation. Results are summarized and the dependence of thermal contact conductance in various conditions is described.