Materials Science Forum Vols. 636-637

Abstract: The environment is a prominent issue today. Designing environmentally sustainable products is an attempt to address this question. In many cases, natural materials are environmentally friendly for product design manufacturing. The goal of this work is to study the mechanical behaviour of NL10 and NL30 cork agglomerates. Compression, shear and bending tests in sandwich specimens made of glass or jute fiber in facings and cork agglomerates as core were carried out. The sandwich specimens were manufactured by Resin Transfer Moulding (RTM) process. Results show that NL30 has a higher compression strength and shear resistance than NL10 agglomerate due to its manufacturing process, which originates superior density, but the NL30 agglomerate superior density is undesirable. Sandwich test specimens that presented failure by rupture of the core in both types of tests, core shear tests and three point bending tests, showed that the failure is mainly adhesive occurring between the adhesively joined cork grains. Since grains are unaffected and remain intact, it is possible to improve these materials by using better agglutinants and new bonding techniques with the intent of getting cork agglomerates with higher shear and flexural strength.

Abstract: The cross section variation, mechanical properties and moisture absorption of vegetable sisal fibres compressed at temperatures of 120, 160 and 200 °C were determined and compared with values obtained in non-compressed fibres. The thermo-mechanical treatment carried out resulted in a relevant increasing of fibre stiffness (elastic modulus) and decreasing of fibre moisture absorption.

Abstract: Aerospace components are characterized by having high strength to weight ratios in order to obtain lightweight structures. Recently, different types of sandwich components using composite materials have been developed with the purpose of combining the effect of reinforced face-sheets with low weight core materials, such as honeycombs and foams. However, these materials must combine damage tolerance characteristics with high resistance under both static and dynamic loads. Cork composites can be considered as an alternative material for sandwich components since cork is a natural material with some remarkable properties, such as high damage tolerance to impact loads, good thermal and acoustic insulation capacities and excellent damping characteristics for the suppression of vibrations. The experiments carried out in this investigation were oriented in order to optimize the specific strength of cork based composites for sandwich components. Static bending tests were performed in order to characterize the mechanical strength of different types of cork agglomerates which were obtained considering distinct production variables. The ability to withstand dynamic loads was also evaluated from a set of impact tests using carbon-cork sandwich specimens. The results from experimental tests showed that cork agglomerates performance depends on the cork granulate size, the type of reinforcing elements and the bonding procedure used for the cohesion with the matrix material.

Abstract: The increasing use of biofuels, namely blends of gasoline with ethanol, requires the identification of its impact on the fuel admission components of internal combustion engines that have not been specially design to work with high levels of ethanol. This paper provides a discussion on performance testing of corkrubber gaskets from a commercial company (ACC – Amorim Cork Composites) to seal these engines using gasoline and gasoline-ethanol blends. In order to evaluate the chemical compatibility of four corkrubber composites, several samples were immersed in different blends of gasoline with ethanol to determine the changes of hardness, volume, thickness and weight. The results of these tests differed between materials, but all of them showed less damage tolerance to blends with low and medium percentages of ethanol (e.g., E5, E10, E25, E50) when compared to gasoline or blends with higher percentages of ethanol (E85).An aggressiveness factor is proposed to compile results from the immersion tests. Validation tests were carried out in conditions as close as possible to the service and accordingly to similar test standards. This study allows concluding on which of these corkrubber composites have adequate sealing properties for gasoline as well as blends of gasoline with ethanol.

Abstract: Bitumen ageing stands for a number of physico-chemical modifications that occur in bitumen as a response to environmental conditions. Several tests have been proposed to simulate bitumen ageing. Two of the most common ones are: a) the Rolling Thin Film Oven Test (RTFOT), which simulates short term ageing; b) the Pressure Ageing Vessel (PAV) test, which accounts for long-term ageing and it is usually performed on the RTFOT residue. A study of the physico-chemical modifications of a 50/70 pavement grade bitumen caused by ageing is presented. Both RTFOT and PAV tests were used. A follow-up of bitumen modifications due to ageing was done by several methods. In particular: 1) Fourier transform infrared spectroscopy (FTIR), to follow bitumen oxidation by the increase of oxygenated functional groups, which were quantified by taking appropriate structural indices; 2) Iatroscan thin layer chromatography (TLC), to follow bitumen composition expressed by the generic SARA fractions (saturates, aromatics, resins and asphaltenes); 3) Gel permeation chromatography (GPC), under “ultra-fast” conditions, to follow the colloidal structure of bitumen; and 4) Differential scanning calorimetry (DSC), to evaluate the changes of the crystallized fractions (%FC) and the glass relaxation temperature (Tg). The results show that the PAV test causes more severe changes in bitumen than the RTFOT test. In particular, the evolution of the oxidation processes could be quantified by taking carbonyl and sulfoxide structural indices. Ageing also modified the SARA profile, namely, the relative contribution of aromatics, resins and asphaltenes fractions. On the other hand, DSC data remained almost unaffected after ageing tests, which may be indicative of the survival of most of the phases of the bitumen after these tests. Finally, a comparative analysis of the sensitivity and performance of all these methods is presented.

Abstract: Low-density sheet moulding compounds incorporating hollow glass micro-spheres are being increasing used namely in automotive industry, boats and deep-water submarines and core materials. This paper presents the results obtained in a current study of the viscous properties on hybrid short fibre/hollow glass microspheres composites fabricated with epoxy binder. Dynamic mechanical analysis (DMA) was used to study the effect of the filler volume fraction and of the addition of glass fibre reinforcement on the dynamic stiffness modulus, damping coefficient and glass transition temperature in tensile mode. The specimens were cut from plates produced by resin transfer moulding in vacuum with microspheres weight contents up to 13%. Elastic modulus decreases significantly with the increasing of filler volume fraction. In contrary, it increases significantly with the glass fibre reinforcement content. Glass transition temperature apparently tends to decrease with microspheres and of glass fibre reinforcement’s content. Tmax temperatures tend to increase slightly with the addition of fibre reinforcements and the microsphere filler. Maximum damping coefficient is much lower for the foams when compared with net resin.

Abstract: Bench-scale and industrial expanded polystyrene formworks (EPSFWs) were prepared and tested in terms of shock resistance and compression analyses. The composition of the EPSFWs was varied and the influence of the substitution of calcium carbonate by granite, kaolin or slate on the mechanical properties of the EPSFWs was analyzed. Bench-scale samples were subjected to a previous selection based on the optimal mechanical behavior. Samples containing large grain sand and slate were chosen for the subsequent industrial scale preparation. The real EPSFWs were also tested from the shock resistance and compression standpoints. The results obtained suggest that the samples showing the best performance among all the tested EPSFWs are those in which calcium carbonate was substituted by slate. This fact is of special interest since large amounts of slate dust are obtained in the area of Spanish Extremadura from local mines. Thus, the preparation of formworks represents a good alternative for the valorization of this by-product.

Abstract: Interests in finding new rare-earth doped oxide materials able to remotely sense high temperature have been intensifying in recent years. If applied, advanced combinatorial strategy for materials science should be efficient in finding a suitable host material, and in optimizing a rare earth ion’s doping concentration, luminescence intensity, emission lifetime, etc. This research demonstrates our preliminary effort to apply the advanced combinatorial material strategy to this new area of finding materials for sensing high temperatures.

Abstract: Rare-earth (RE) doped oxide materials are one of the interesting sensor materials potentially able to remote-sense strain inside an object under high temperature. In contrast to commonly investigated temperature-sensing methods of monitoring temperature-dependent luminescent characteristics of those doped RE ions, sensing strain under high temperatures, however, will be much difficult. This research develops a new strained superlattice that has the potential to sense strain under the high temperature environment, via monitoring the superlattice’s period-dependent luminescence.

Abstract: This paper reports the study of the humidity-sensitive electrical properties of TiO2:WO3 thick films. Prototype sensors have been prepared by depositing an emulsion of TiO2 and WO3 powders in acetone with cellulous glue onto an alumina substrate, by a spin coating technique using a low spreading speed (125 r.p.m.). Films were prepared with five different atoms proportions of Ti and W: 100:0, 100:1, 100:6, 100:18 and 100:36. The oxides thick films were successively fired at the temperatures of 600, 700, 900, 1100, and 1300 °C, during 2 hours at each of these temperatures. Measurements were obtained at a constant temperature of 25 °C and at various relative humidities (RHs) in the frequency range of 0.01 Hz – 40 MHz. It was thought that the humidity sensing of the TiO2 matrix would be influenced by the substitution of the Ti4+ ions for higher valence ions, W6+ in the present study. In the measuring frequency range, samples impedance varies of three-four orders of magnitude over the RH range of 10-100 %. It is found to be the sensitivity highly dependent on both the measuring frequency and the sintering temperature. A parameter called characteristic humidity is defined to represent the sensitive response of sensors. This parameter is used to evaluate the influence of the W6+ ions on the sensitivity behaviour of the sensors.