Materials Science Forum Vols. 730-732

Abstract: Today, the cost, excellence and availability of raw materials are of principal importance. Due to environmental concerns, a very large number of companies are currently developing manufacturing processes using alternative materials for their crop and in search of new markets for the sub-products of their first-line production. Textile industry is an example of the reality that the industry is living these days. With a significant production of waste fibrous materials, textile companies are now looking for applications where waste materials could be an added-value material. Composites reinforced by fibres are being considered for several uses when high performance is essential. The corrosion resistance, potentially high overall durability, light weight, tailor ability and high specific performance attributes enable the use of composite materials in areas in which the use of conventional material might be constrain due to durability, weight or lack of design flexibility. This paper describes the work that is being done at University of Minho concerning the development of waste fibers reinforced composite materials. Different waste fibers reinforced composite materials have been produced varying the density and the variation in ratio of resin and waste fibers. Waste fibers have been collected within some textile companies and processed in order to individualize the fibers and to allow subsequent processing. Composite panels have been produced by compression moulding technique, through the application of heat and pressure. Panel thicknesses of 5 mm using resin aminoplastic for urea-formaldehyde have been produced. Materials thus obtained have been tested in tensile, bending, compression test. The results obtained are presented and discussed.

Abstract: Marble processing activities generates a significant amount of waste in dust form. This waste, which is nowadays one of the environmental problems worldwide, presents great potential of being used as mineral addition in blended cements production. This paper shows preliminary results of an ongoing project which ultimate goal is to investigate the viability of using waste marble dust (WMD), produced by marble Portuguese industry, as cement replacement material. In order to evaluate the effects of the WMD on mechanical behaviour, different mortar blended cement mixtures were tested. These mixtures were prepared with different partial substitution level of cement with WMD. Strength results of WMD blended cements were compared to control cements with same level of incorporation of natural limestone used to produce commercial Portland-limestone cements. The results obtained show that WMD blended cements perform better than limestone blended cements for same replacement level up to 20% w/w. Therefore, WMD reveals promising attributes for blended cements production.

Abstract: The analysis of Cu ETP of a component of electric motors manufactured by WEG is presented. The work included three main tasks: metallographic analyses at the micro and macro levels; mechanical testing; scanning electron microscopy observations. The objective was the evaluation of the state of bars material before and after service. It was found that material in both conditions presents similar microstructures. This indicates that, despite the rotor working at temperatures above 300°C, no grain recrystallization can be identified. It was verified that the copper bar base material presents higher hardness values of than the copper ring. A decrease of yield and rupture stresses as the temperature increases was observed during tensile tests at different temperatures. During testing, a fatigue life of 10⁷ cycles for a remote stress of approximately 134MPa is estimated. It can be concluded that the material after and before service presents different properties, the first one presenting lower strength. This behavior is reflected in lower hardness, yield and rupture stress of the material taken from the fractured rotor bars. This observation can be a result of the high temperature (above 300°C) that is present in the rotor during each start.

Abstract: The stop-drilling technique is a simple and economic way to delay crack propagationby drilling a hole on the crack tip and reducing stress concentration. This paper presents thepropagation of cracks and investigates how the increasing of the stop-drill diameter improvescrack initiation life in specimens of 2024-T3 aluminium alloy of C-130 aircraft skin. A numericalmethod was applied to simulate an automatic crack propagation by interacting ANSYSr andMATLABr, and several experimental fatigue tests were done to support the computationalresults. A Morrow equation was used to predict the fatigue life of the stop-drill. Good agreementof stress intensity factor along crack length was obtained between numerical and experimentalresults. All results show that fatigue life increases when the stop-drill diameter is larger. Whencompared to the 2mm diameter stop-drill, the experimental results show an improvement of189% and 464% to 4mm and 6mm diameter stop-drill fatigue life, and the numerical results of333% and 952%, respectively.

Abstract: Presented in this paper is an explicit full-range stress-strain relation for stainlesssteel alloys applicable at normal and elevated temperatures. The relation utilizes an approxima-tion of the closed form inversion of a highly accurate three-stage stress-strain relation recentlyobtained from the Ramberg-Osgood equation. The three stage inversion is formulated using anappropriate rational function assumption to approximate the fractional deviation of the actualstress-strain relation from an idealized linear elastic behaviour. The temperature dependenceon the stress-strain relation is then introduced by modifying the basic mechanical propertiesof stainless steel to account for the temperature e ects. The proposed approximate inversionis applicable over the full-range of the stress well beyond the elastic region up to the ultimatestress. Moreover, the inversion can be applied to both tensile and compressive stresses. Theproposed approximate inversion is tested over a wide range of material parameters as well as awide range of temperatures. It is shown that the new expression results in stress-strain curveswhich are both qualitatively and quantitatively in excellent agreement with experimental re-sults and the fully iterated numerical solution of the full-range stress-strain relation for normalas well as elevated temperatures

Abstract: Melting TiAl based alloys in ceramic crucibles often leads to chemical contamination, alloy heterogeneity and non-metallic inclusions. The severity of such phenomena usually depends on the nature of crucible materials, the melting stock composition and the melting parameters, namely superheating time and temperature and melting pressure. Among the referred drawbacks, Al loss during melting is a critical aspect, as its concentration in TiAl based alloys has a very strong effect in their mechanical properties. Although a few studies of critical factors affecting the evaporation behaviour of Al during electron beam and induction skull melting of Ti-Al alloys had been carried out, until now no information was released on this subject for the ceramic crucible induction melting process. In this work a Ti-48Al alloy was induction melted in a zircon crucible with Y₂O₃ inner layer, using 50 and 100 °C superheating temperatures and 0, 60 and 90 second holding times, and poured into a graphite mould. The effect of different temperature/time combinations in the alloy composition, Al loss by evaporation and extent of the metal/crucible interaction was studied for different melting pressures. Al loss was found to increase significantly for melting pressures below around 10^-1 mbar, at a rate that increases as melting pressure decreases, until a maximum rate is reached, remaining constant for lower pressure levels. Metal/crucible interaction increased directly with the melting pressure and superheating time, leading to alloy contamination with yttrium and oxygen. For the experimental set-up and conditions used on this work, optimal superheating time/pressure combinations that lead to acceptable alloy composition and sanity have been identified.

Abstract: A phase-field model is proposed for the simulation of microstructure and solute concentration during the solidification of Fe-C-P-Mn quaternary alloys. In this paper, a study is presented to analyze both the effects of partition coefficient and solute diffusivity on the microstructural evolution during solidification simulation. Partition coefficient and diffusivity are very important from a practical standpoint, because both parameters exert a strong influence on the dendrite morphology. Additionally, the proposed model is applied for quaternary alloys to the analysis of the time-dependent solidified fraction. Simulations permit to conclude that the solidified fraction is proportional to the square root of time, as expected for any diffusion-controlled growth process. Phase-field simulations on non-isothermal dendrite growth are also examined. Two-dimensional simulation results exhibit different dendrites in multicomponent alloys for different solute concentrations. Changes in the carbon concentration seem to affect the dendrite morphology, due to its higher concentration and its lower equilibrium partition coefficient. Changes in the phosphorus concentration affect the dendrite morphology and the interface velocity, when its content is increased from 10^-3mol%P. Higher manganese content slows down the solidification kinetic, while the dendrite morphology remains unchanged.

Abstract: It is widely acknowledged within the textile engineering community that Shape Memory Alloys (SMA), exhibit great potential for several applications. This paper presents the research undertaken at the University of Minho aiming to study the behaviour of weft-knitted fabrics produced with SMA nitinol^® wires. SMA nitinol^® wires of type B (which shows shape memory effect at body temperature) of 50, 127 and 210 µm diameters have been used to produce weft-knitted fabrics with different loop types, e.g. stitch, tuck and miss. The influence of the loop type on the performance of the weft-knitted fabric, in terms of energy absorption, has been analyzed. Tensile tests were carried out according to ISO1462 standard, using a H100KS Hounsfield universal testing instrument. The results aim to help future applications of SMA in the development of new textile materials.

Abstract: Eddy currents are based on electromagnetic induction and analysis of electrical currents on conductive materials. This method is used for thickness measurements, corrosion and defects detection, electrical conductivity and magnetic permeability measurements. Recently, it has been exploited as a materials characterization technique, namely in solid state welding, since, compared to hardness, it is based in distinct physical phenomena. Electrical conductivity is controlled by electronic mobility, while hardness depends on crystal defects and thus a scale factor exists. This paper presents results of this characterization technique applied to multipass solid state friction stir processing (FSP) of AA1100 alloy. These results were compared to microstructural analysis and hardness measurements and show that eddy current is a feasibly, reliable and expedite technique to characterize processed materials. The electrical conductivity measured by eddy currents, maps more precisely structural features, while hardness does not. Measurement of electrical conductivity field suggests having potential to constitute an alternative and/or complement to hardness evaluation with the further advantage of being a non-destructive method.

Abstract: In this study, an experimental investigation into the shear strength behaviour of aluminium alloy single-lap adhesive joints was carried out in order to understand the effect of temperature on the strength of adhesively bonding joints. Single lap joints (SLJs) were fabricated and tested at RT and high temperatures (100°C, 125°C, 150°C, 175°C and 200°C). Results showed that the failure loads of the single-lap joint test specimens vary with temperature and this needs to be considered in any design procedure. It is shown that, although the tensile stress decreased with temperature, the lap-shear strength of the adhesive increased with increasing of temperature up to the glass transition of the adhesive (T_g) and decreased for tests above the T_g.