Materials Science Forum Vols. 514-516

Abstract: This work presents a methodology to improve the final thickness distribution of thermoformed parts. The conventional plug is replaced by a new version containing concentric layers with independent displacements. The results show that thickness gradients can be significantly reduced, with a simultaneous increase of the minimum values. Varying the relative displacement of the inner layers can bring about significant differences in the final thickness distribution, thus enabling the production of parts with prescribed thickness profiles that maximise their mechanical performance.

Abstract: Depth sensing indentation equipment allows the mechanical properties of thin films to be easily determined, particularly the hardness and Young’s modulus. In order to minimize the influence of the substrate on the measured properties, the indentation depth must be limited to a small fraction of the film’s thickness. However, for very thin films, the determination of the contribution of the substrate and the film to the measured mechanical properties becomes a hard task, because both deform plastically. The numerical simulation of ultramicrohardness tests can be a helpful tool towards better understanding of the influence of the parameters involved in the mechanical characterization of thin films. For this purpose, a three-dimensional numerical simulation home code, HAFILM, was used to simulate ultramicrohardness tests on coated substrates. Materials with different Young’s modulus film/substrate ratios were tested. Analyses of strain and stress distributions for several indentation depth values were performed, in order to clarify the composite behaviour.

Abstract: Microporosity is the major processing defect in pressure die cast AZ91 magnesium alloy. There is a big difference in the arrangement of pores in different regions of the castings. The present work explains the pore arrangement in pore bands and other regions. Quantification and characterization of pores in pore bands is expected to be useful to understand the process-propertymicrostructure correlation. A computational microstructural (image) analyzing technique has been developed by a programming language to quantify and analyze the micropores in pore bands. The pore band regions and the rest were separated and quantified. In addition, image analyzing technique was used to measure the clustering tendency of porosity in pore bands and it was compared with other regions.

Abstract: A model based on steric hindrance mechanisms [1] is used to determine the pore sizes of two ultrafiltration (UF) membranes. The lysozyme rejection coefficients of those membranes are predicted through the same model after modification of the pore size and solute radius by taking into account the development of electric double layers. Two asymmetric cellulose acetate membranes M1 and M2 were prepared and characterized. Membrane M1 has an hydraulic permeability of 2.1x10-6 m/s/bar, a molecular weight cut-off (MWCO) of 30,000 Da and an average pore radius of 2.6 nm. Membrane M2 has an hydraulic permeability of 5.9x10-6 m/s/bar, a molecular weight cut-off (MWCO) of 60,000 Da and an average pore radius of 5.3 nm. Aqueous solutions of lysozyme containing a NaCl concentration of 0.1M were ultrafiltrated through membranes M1 and M2. The predicted lysozyme rejections considering the development of electric double layers on the protein and membrane pore surfaces, are in good agreement with the experimental results.

Abstract: A new algorithm to determine Voronoi partitions of space using periodic boundary conditions has been implemented in GAMGI free software package. This algorithm was used to study the topological and geometric properties of Voronoi polyhedra obtained for Poisson and Laguerre seeding distributions. The Random Sequential Adsorption (RSA) method was used to generate a Laguerre seeding distribution with a volume fraction of spheres φ ≈ 0.36. The resulting normalised cell volume distributions were compared with the gamma and lognormal density functions using χ2 goodness of fit testing, and in both cases the gamma function provides a better description. The Lewis and Aboav empirical relations approximately apply to both partitions, with least square correlation factors R2 equal to 0.98 for the Lewis law and 0.95 for the Aboav law.

Abstract: In new car production, an innovative method to produce strong and light panels consists in applying Tailor Welded Blanks (TWBs) in the body-in-white base structure. Since the fusion welding processes can induce significant changes in the material properties of the base materials, an important question is whether the weld bead has a significant influence on the overall behaviour of the welded blanks. In this work, some preliminary conclusions on this subject were achieved based on results of the numerical simulation of simple mechanical tests: tensile, shear and simple bending. The numerical simulations were performed with a fully implicit finite element program (DD3IMP). The results obtained show that for a slight mismatch of properties between the weld and the base materials, no important influence of the weld in the TWBs behaviour is noticed. However, a significant strength reduction can be observed for strong undermatch conditions (lower mechanical properties in the weld) even when the weld bead is very narrow.

Abstract: In this study, the as-moulded shrinkage and pressure data are obtained experimentally and compared with numerical simulations. The mouldings were produced in polypropylene (PP). The effect of pressure on viscosity in the predicted pressure evolution was analyzed and also its influence on the shrinkage. The results show that the rise of holding pressure determines the reduction of the shrinkage. Also, it was observed that the pressure predictions are qualitatively in good agreement with the experimental data. However noticeable quantitative discrepancies can be observed when the effect of pressure on viscosity is not considered. If the effect of pressure on the melt viscosity is considered the deviation between predicted and the experimental pressure evolution is substantially reduced.

Abstract: The Direct Metal Laser Sintering (DMLS) technology uses a mixture of metal powders with different melting points to build objects layer by layer, directly from the geometric digitalised information. This process allows the manufacturing of prototype and production tools. In this study, the M3/2 high speed steel powder blended with 20 wt.% Cu3P and 0.25 wt.% graphite was laser-sintered, using two scan speeds (100 and 200 mm/s), keeping constant both hatching (0.30mm between two consecutive lines) and laser power (180W). The powder was spread in uniform layers of about 20m over a steel plate (100x60x6mm). The laser beam scanned small areas (12x15mm) in a single direction (OX). The surface morphology of the laser-sintered material shows that all material melted, but for 200mm/s scan speed, strings are well defined. This is probably due to a lower level of energy supplied to the material. The microstructure of the sintered material was studied in the longitudinal and transverse sections, to evaluate the consolidation process and layer growth. The material showed porosity and cracks formed during the process.

Abstract: The corrosion resistance under mechanical stress can be one of the most concerning types of localized corrosion for the application of stainless steel reinforcements in concrete. This paper will assess the stress corrosion cracking susceptibility, by the slow strain rate test method (SSRT), of three austenitic stainless steel alloys: one conventional Fe-Cr-Ni base alloy and two new composition Fe-Cr-Mn base alloys adequate to the manufacturing of ribbed bars for reinforcing concrete. The SSRT results show that only one of the austenitic Fe-Cr-Mn alloys is susceptible to stress corrosion cracking while the other shows a performance similar to that of the AISI 304 stainless steel alloy.

Abstract: The market is changing very quickly, demanding the companies the capability of producing better and/or more performing products. This changing market leads the companies to be more flexible and agile. In particular, for the tool makers and the stamping companies, they are requested to participate in the design phase of the product and process, as well as to produce prototypes and small series in very short time and with low costs. To answer to these demands in the stamping steps design and consequently in the tool design, several finite elements packages are widely used, allowing the tool designers to foresee the results of their options/decisions without the need to manufacture and test tools, with the inherent excessive cost of money and time. Following this methodology, CAE analysis, the final phase of tool try out, always necessary, will be certainly shorter and less expensive, once they start with a solution quite more worked and, for sure, closer to the final solution. In this industrial context, appeared the great motivation for the development of competences on the rapid manufacturing of stamping tools (active elements: punch, die and blankholder), on the numerical simulation of the process and, on the development of the modular tool concept. In this paper the main results of the development of these areas of research, are presented. In particular, the use of the numerical simulation, using PAM-STAMP 2G software, for the validation of the stamping phases, the realisation of laboratorial stamping tests using tools produced by the several techniques available on Portugal for rapid prototyping. At the same time, it was developed the modular tool concept, i.e., a tool in which by fast and easy change of the active elements, different parts can be formed. The active elements of the tool have been manufactured by several rapid tooling techniques, like DMLS - Direct Metal Laser Sintering, LOM - Laminate Object Manufacturing, HSM – High Speed Milling and also the machining of non-traditional materials such as nylon, ureol and aluminium. Some inserts have been produced by indirect techniques such as reinforced resins (polyurethane, epoxy and urethane) using shells produced by SLstereolithography. Finally some conclusions are drawn.