Materials Science Forum Vols. 587-588

Abstract: Polycrystalline ingots of Co70-xNixGa30 (22 ≤ x ≤ 25) alloys were prepared by a sequence of arc melting high purity Co, Ni and Ga in argon atmosphere, followed by homogenization at 1150°C under a pressure of 10-3 Pa, and quenching in ice water. Structural characterisation of the quenched alloys was carried out to verify the presence of the martensite phase at room temperature. The martensite start (Ms), martensite finish (Mf), austenite start (As) and austenite finish (Af) temperatures for the alloys were determined using a differential scanning calorimeter. The ferromagnetic to paramagnetic phase transition temperature (TC) of the alloys was determined using an indigenously developed ac susceptometer. All the alloys are FSMAs with Ms, Af and TC above room temperature. The composition dependence of the properties of these alloys could be understood on the basis of the e/a (electrons to atom) ratio and the Co/Ni ratio. Presence of γ-phase precipitates along with the β-phase in these alloys enhances the ductility as well as influences the physical properties of these alloys.

Abstract: This study deals with the analysis and characterization of wood polychromes by means of Laser-Induced Breakdown Spectroscopy (LIBS). Specimens from a Baroque altarpiece have been analyzed by using a Q-switched Nd:YAG laser source at the wavelength of 355 nm. Previously, a library of characteristic LIBS spectra of the most commonly used pigments and other materials involved was obtained. The knowledge of these spectra allowed us to identify the main constituents of the different layers in polychromes and to obtain compositional depth profiles.

Abstract: The aim of this research is to find a feasible method for the estimation of the tensile behaviour of woven membrane construction materials under bi-axial loading. During the model development, the woven membrane materials are treated as orthotropic, elastic and linear. Based on the constitutive relationships for orthotropic and elastic materials, two equations sets are deduced for the estimation of modulus in the warp and the fill direction respectively when suffering from the bi-axial loading. To checkout the validity of the estimation, seven groups of biaxial tensile tests with stress ratios of 1:0, 1:1, 2:1, 5:1, 1:2, 1:5 and 0:1 have been carried out on two kinds of PVCcoated woven membrane materials. From the comparison of the experiments and the prediction, it can be noticed that the model can achieve ideal results when it comes to the estimation of modulus in the leading direction, which is the direction with a higher stress than the other one. Therefore, based on the hypothesis of orthotropic, elastic and linear materials, there is an easy way to estimate the bi-axial tensile properties of woven membrane materials in the leading direction only through the uni-axial tensile tests.

Abstract: Inverse gas chromatography (IGC) has been applied to observe the interactions in filled polymer/organic solvent as well as modified filler/polymer systems under conditions approaching infinite dilution of the volatile component. In our study we will show that the Flory-Huggins theory is useful in the characterization of the interaction in polymer-filler systems. Authors propose to express the magnitude of modified filler/polymer interactions by Flory–Huggins ' 23 χ parameter. We examined the series of compositions of polyethylene (M= 35000) with different amount of modified silica filler (5, 10, 20 % wt).

Abstract: Ni-Ti SMA are smart materials undergoing first order martensitic transformations driven by temperature and/or stress. In the form of film they are very attractive candidates for microelectro- mechanical system (MEMS) applications. Future directions include the production of functionally graded films by changing deliberately the ratio Ti/Ni across their thickness. However, for the successful development of this type of films, it is important to characterize, model and control the variations in composition, crystalline structure and transformation temperatures. Our approach is in-situ XRD study of the actual growth of the films of varying composition along the thickness carried out using a deposition chamber installed at a synchrotron radiation beamline. These studies were complemented with ex-situ analysis techniques. The results achieved on a Ni-Ti film co-sputtered from Ni-Ti and Ti targets on a TiN buffer layer are presented in this paper. The deposition started by using optimised parameters for a near equiatomic composition. After 1 h (≈330 nm thick film), the Ti power was increased from 20 to 25 W, leading to the precipitation of Ti2Ni. The evolution of the lattice parameter values of the B2 phase, calculated from the corresponding XRD data, is clearly linked with the increase of the Ti power. The depth profile of the atomic concentrations determined by Auger Electron Spectroscopy (AES) is in agreement with the in situ XRD results. The temperature dependence of the electrical resistivity was used to monitor phase transformations, Scanning Electron Microscopy (SEM) has shown the presence of twinned martensite on the film’s surface at room temperature.

Abstract: In this work the performance of two surface treatments and the efficiency of a corrosion inhibitor were evaluated, in the control of steel corrosion in concrete induced by chlorides, through measurements of galvanic current and polarization resistance applied to embedded sensors fixed in existing concrete using different methodologies. From the results obtained the use of the different embedded sensors in the measurement of corrosion rate is discussed aiming the development of new systems for permanent evaluation of the on site performance of products for repairing reinforced concrete structures affected by reinforcement corrosion.

Abstract: The objective of this study was to develop new adhesive formulations based on 2,2-bis[4-(2- methacryloxyprop-1-oxy) phenyl] propane (CH3-BisGMA) aiming to obtain high double bond conversion (DC) even in the presence of radical scavengers and monomers with acidic groups. NMR, EPR spectroscopy and spatially-resolved 1H Stray-Field MRI observations enabled to study the influence of the composition in DC, free radical concentration, reactivity of the monomers and volumetric contraction.

Abstract: The orientational order generated in a cross-linked elastomer by uniaxial stress is probed with deuterium NMR spectroscopy. Spectra of technical unfilled natural rubber (NR) vulcanisates (cis-1,4-polyisoprene), locally swelled with o-dichlorobenzene-d4, exhibits quadrupolar doublets under elongation, which have an explicit dependence on the extension ratio and cross-link density. A new mechanical device was designed to fit into an NMR probe-head to permit the elongation of the networks in the interior of the magnet without removal of the sample thus avoiding the effect of the relaxation of the network chains after each step of uniaxial elongation and the observation of always the same section of the stretched sample. A molecular model of rubber elasticity was applied to describe the behavior of rubber network in mechanical and NMR experiments.

Abstract: The main objective of the present work is to present and discuss the effects of the residual stresses generated in the matrix. Both, elastic and elastic-plastic models using explicit finite element code Abaqus were developed to investigate the thermal residual stresses generated around a diamond particle embedded in a metal matrix (a binder) during the sintering process for obtaining a diamond tool. The first part of the work consists in examining the thermal residual stress field generated by using three sintering temperatures from which the bodies are cooled from (T1=800°C, T2=700°C and T3=600°C) and two diamond shapes modelled with 2D axisymmetric elements, one from a circle the other from an octagon, respectively. In this case only one type of binder showing typical elastic behaviour is considered. The second part of this work consists in comparing the finite element solutions using binders with different tensile behaviour (elastic vs. elastic-plastic behaviour). This last study has used a particle shape generated from the octagon, since this shape allows, in a great number of real situations, the simulation of a particle with a larger number of facets, in line with what it is observed when looking at a conventional diamond tool.

Abstract: The CPGC – Cork-Polyurethane Gel Composite is a material that is mechanically characterized by non-linear elastic behaviour at large deformations. The non-linear behaviour can be modelled by hyperelastic constitutive models based on strain energy functions enabling a structured phenomenological framework for CPGC material modelling. The CPGC is a promising material for human comfort enhancement and dynamic damping/control applications. This paper presents the experimental methodology used for the CPGC evaluation of material parameters used in the hyperelastic models and the finite element model build-up. A 3D foot FEA model is presented in order to evaluate the performance of the hyperelastic model in a real case situation and the mechanical performance of shoe insoles, namely, trough the monitoring of the contact pressure values at the insole/foot interface.