Materials Science Forum Vols. 636-637

Abstract: Great interest is dedicated to the wheel/rail contact problem, in particular as a result of some accidents worldwide and also in Portugal. In the present work a three dimensional finite element analysis of the wheel/ rail contact problem was performed using the software ABAQUS. A preliminary study on simpler geometries was carried out, in order to identify the solution strategies giving more accurate solutions. The influence of mesh refinement, friction coefficient, and numerical techniques as Lagrange and penalty functions were analysed in the simpler cases of contact of two cylinders along a generatrix, and the contact of a cylinder and a rigid plane. The corresponding Hertz solutions were programmed using MATLAB in order to compare with the finite element analyses. The numerical procedures giving better results were later applied to the wheel/rail contact problem, using standard rail and wheels profiles used by the Portuguese Railways company (CP). The influence of small geometry variations on the stress analysis results was then studied, and the study of initiation of defects using the Dang Van fatigue criterion was performed.

Abstract: Instrumented indentation testing is a technique widely used in different materials to evaluate the penetration depth in function of the indenter load. Considering Berkovich indenter, this methodology has been used to determine mechanical properties such as hardness, Young modulus and a stress versus strain curve of the elastic-plastic behaviour under compression of the tested materials. However, the implementation of this technique to evaluate mechanical properties and also its results have still brought doubts on research areas. Nowadays, the use of a numerical methodology able to evaluate the stress and strain fields during indentation cycle can lead to a more secure interpretation. The aim of this work was to simulate the Berkovich indentation testing and to propose a methodology to extract the stress-strain curve through experimental and numerical analyses. The obtained numerical results for the load-displacement curve were quite similar to the experimental curve presented in the literature.

Abstract: In the present study, numerical simulations of nanohardness tests of titanium aluminium nitride (TiAlN) hard coatings with titanium and aluminium ductile interlayers were performed in order to determine the influence of interlayers of ductile metals on the overall mechanical properties of multilayer coatings. The investigation was designed to determine the role of ductile interlayers in altering the hardness value and the Young´s modulus of the multilayer coating as a whole, in comparison with a monolayer TiAlN hard coating, for the cases of composites with different numbers and thicknesses of interlayers.

Abstract: This study presents an experimental characterization of cork storage modulus used to model the vibration response of bars built using alternate layers of cork and steel. In the experimental setup, the specimen was suspended from a fixed support by two thin lines while a shaker was suspended from a mobile support by metallic chains. The shaker was connected to the bar specimen through a force transducer imposing a dynamical deformation that propagates through the specimen. An accelerometer in the opposite extremity of the bar measures the corresponding vibration response and the cork storage modulus is then obtained from the first peak of this frequency response. The proposed methodology successfully characterized the storage modulus of the cork material used in the multilaminated periodic bars. The results obtained illustrate a satisfactory correlation between

Abstract: Most piezoelectric gravimetric biosensors are based on quartz crystal microbalances or surface acoustic wave devices. In this paper we describe a polymer film system, made of piezoelectric polyvinylidene difluoride (PVDF) and the Immobilon-P membrane (porous PVDF), for biosensing applications. In operation a film is accommodated in a flow cell and connected to an electronic circuit, constituting an oscillatory resonant device; the output signal is its resonance frequency. This device successfully detected the binding between bovine IgG and bovine anti-IgG. Work on the modelling of this film system is presented. Two different approaches are being considered: the finite element method (FEM) and the ABCD matrices. Results comparing theoretical and experimental data are presented.

Abstract: This work examines the elastic work and fracture energy of a mortar and two concretes using the wedge splitting method to attain stable crack propagation. A comparison was made of the fracture energy in mortar and concrete using two different aggregates: crushed stone and pebbles, both with sizes between 4.8 and 9.5 mm. The mortar was made of sand, Portland cement and water, using a cement: sand ratio of 1:2. The water content was 0.46 of the cement mass. The samples were molded and then cured for seven days at 25oC in 100% relative humidity. After curing, the samples were dried at 55oC for 48 hours. The concretes were produced using the same procedure, but with the addition of the aggregates. The amount of aggregate was 10 wt.% of the total weight of cement plus sand. After curing and drying, the samples were subjected to the wedge splitting procedure. The tests were carried out at a constant displacement rate of 0.030 mm/min. The following results were obtained: elastic work: 80.4 ± 0.6, 114 ± 9 and 110 ± 12 mJ, and fracture energy: 30.3 ± 0.6, 40 ± 1, and 40 ± 5 J.m-2, respectively, for the mortar and for the concretes containing crushed stone and pebbles. These results allow us to conclude that the aggregates improved the elastic work and the fracture energy of the concretes. However, the type of aggregate did not make any difference to the properties. These findings contradict what is generally known, i.e., “that concrete produced with pebbles is inferior to concrete made with crushed stone”, at least insofar as it concerns the energies associated with the fracture process.

Abstract: This paper shows the possibility of reutilize paper sludge waste as supplementary cementing material for the cement manufacture. This industrial waste consists essentially of a mixture of organic matter (30%) and inorganic compound, such as calcite and clay minerals. The raw paper sludge does not present pozolanic properties, but once calcined at 650°C during 2 hours, exhibits a good pozolanic activity. Calcined paper sludge was used as partial Portland cement replacements of 0 and 10%. It was a sligth increment in compressive strength for 10 % of substitution from 7 days on. Furthermore, calcined paper sludge reduces the initial and final setting times of cement paste.

Abstract: The building materials used as a coating on the walls are exposed at different conditions of the weather for long periods of time, reason why is very important to determine the effects of sunlight, heat, humidity and other effects of climate change in the colour and the properties of these materials. In this work was carried out a study on the behaviour of colour and gloss of white cement with some different industrial waste additions submitted to ultra-violet light exposure. The addition of the different materials employed in this work does not modify lightness or chromatic coordinates after the exposure at ultraviolet light, however reduces significantly the gloss of the samples, including white Portland cement.

Abstract: A very early stage of cement paste hydration is studied at microscopic level of description. Within context of nucleation theory the critical (and, thus, growable) size of clusters of calcium hydroxide (so-called portlandite) is estimated for chosen water to cement ratios at given temperature. Furthermore, also the barrier of portlandite nulceation is determined. It is shown that these static characteristics of process are practically unchanged contrary to number density of portlandite critical clusters formed in unit volume of mixture per unit time.

Abstract: A novel method that allows determining instantaneous concentration of calcium ions, Ca2+, in hydrated cement paste (HCP) is suggested. EDTA solution (belonging to a group of carboxylic acids/carboxylates and borates) seems to be very effective retarder altering nucleation and subsequent growth of newly forming clusters of calcium minerals. Concentrations of Ca2+ have been determined for various water to cement ratios, at different times and for given temperature.