Materials Science Forum Vols. 730-732

Abstract: This paper studies the resistance of two high-density polyethylene geonets (manufactured with or without the additive Tinuvin 783) against thermo-oxidation. The materials were exposed to thermo-oxidation by two methods: oven-ageing tests at 100 °C and a new method developed by our research team. The damages suffered by the geonets were evaluated by tensile tests (determination of tensile strength, elongation at maximum load and toughness). Finally, the results obtained in the oven-ageing tests were compared with the results obtained by the new method.

Abstract: Nowadays, composite structures based on wood are frequently used. In civil engineering, mostly timber-concrete composite structures are used, particularly in reconstruction of old timber girder floor structures or manufacture of new ones at the reconstruction of old buildings in areas exposed to frequent earthquakes. In new buildings it is mainly glued laminated timber or lumber, while in reconstruction square timber is used. A timber beam is coupled with a concrete slab made either of conventional or a lightweight concrete. Best results are achieved by coupling timber with lightweight aggregate concrete that has all the properties similar to the timber except for its strength that is much higher and comparable to that of conventional concrete. This paper analyzes a composite timber-lightweight aggregate concrete structure. The basic girder is a T-cross section, with the web made of glulam, and flange made of lightweight concrete with expanded clay aggregate (Liapor). The two materials are coupled by means of mechanical fasteners, allowing joint action of the composite section. Quality of coupling has been determined by experimental tests carried out at the Laboratory of the Technical Mechanics Institute, Faculty of Civil Engineering in Zagreb. Finite element method was used for modelling of composite structures using ABAQUS software. The aim of this study was to determine the advantages of using timber-lightweight aggregate concrete composite structure, compared to solutions in which timber-conventional concrete composite structure or reinforced concrete slab are used.

Abstract: The inherent design freedom promoted by the employment of thermoplastic profiles is one of the major reasons for their attractiveness. Theoretically, thermoplastic profiles can be produced with any cross section suited for a specific application. The design of the corresponding extrusion dies usually employ a methodology based on experimental trial-and-error approaches, being highly dependent on the experience of the designer and highly demanding in terms of resources. These difficulties are obviously more evident when the plastic profile has a complex geometry. This research team is involved since the mid-nineties on the development of computational tools to aid the design of thermoplastic profile extrusion dies. Initially, the numerical code employed was based on structured meshes that limited its use to simple geometries. In this work, a numerical modelling code developed to work with unstructured meshes is described and employed in a case study involving the design of a extrusion die for the production of complex cross section profile. The results obtained show that the developed code can be a useful tool to aid the design of complex profile extrusion dies.

Abstract: As other ceramic materials, glass presents a brittle behaviour and a broad scatter of strength results, due to the random distribution of micro-cracks on its surface. On the other hand, the specific properties of glass and Polyvinyl Butyral (PVB) are combined in laminated glass, resulting in a viscoelastic behaviour for the whole assembly. In this paper, a probabilistic design model is proposed for laminated glass plates of annealed and tempered glass, taking into account the time-dependent properties of the PVB interlayer and the glass characterization by means of a three-parameter Weibull cumulative distribution function of critical stresses. To validate the model proposed, an experimental programme was carried out using laminated glazing of 1.4 m x 1.4 m, varying the kind of glass, thickness and boundary conditions.

Abstract: The acceleration of industrial machines mobile parts has been increasing over the last few years, due to the need of higher production in a short period of time. The machines were dimensioned for a lower value of acceleration, which means there is not enough rigidity for the correct operation at much higher accelerations. Nowadays, the accelerations can be near 12 times the acceleration of gravity. There is the need of improving rigidity to make possible the correct machine operation without undesired vibrations that can ultimately lead to failure. The main applications of this work are plotters and laser cutting machines. To improve rigidity, one must improve the relevant material properties, and the relevant geometric variables of the model.[1] A novel Finite Element Model Updating methodology is presented in this paper. The considered models were : a ribbed plate and a tubular beam. The models were built by means of the Finite Element Method (FEM), and MATLAB was used to control the optimization process, using a programming code. Both material properties and geometric parameters were optimized. The main aim of the materials modeling is to know how the value of the objective function changes with the value of the material properties. Materials selection was performed, using material selection charts, to select the best material for the application. The value of these properties was not in the catalogue, and the properties used to perform the material selection were related to a material sub-class, Eg. Steel. The final material selection determined the best specific material for the application, and that material was mechanically tested. The mechanical tests performed were: Tensile Test and Extensometry Test, to obtain the relevant material properties, mainly Young Modulus, Poisson Coefficient and Yield Stress. The deflection of the optimized models reduced strongly in comparison to the initial models.

Abstract: Adhesive-bonding for the unions in multi-component structures is gaining momentum over welding, riveting and fastening. It is vital for the design of bonded structures the availability of accurate damage models, to minimize design costs and time to market. Cohesive Zone Models (CZM’s) have been used for fracture prediction in structures. The eXtended Finite Element Method (XFEM) is a recent improvement of the Finite Element Method (FEM) that relies on traction-separation laws similar to those of CZM’s but it allows the growth of discontinuities within bulk solids along an arbitrary path, by enriching degrees of freedom. This work proposes and validates a damage law to model crack propagation in a thin layer of a structural epoxy adhesive using the XFEM. The fracture toughness in pure mode I (G_Ic) and tensile cohesive strength (s_n⁰) were defined by Double-Cantilever Beam (DCB) and bulk tensile tests, respectively, which permitted to build the damage law. The XFEM simulations of the DCB tests accurately matched the experimental load-displacement (P-d) curves, which validated the analysis procedure.

Abstract: This work presents 3-D Finite Element Model of the heat transfer inside granite during pulsed laser ablation with the aim of achieving laser cleaning treatment without damaging the stone surface. The model is focused on biotite, the most affected granite-forming mineral, owing to its low melting temperature. The model predicts sizes of the molten region that are consistent with experimental results. Moreover, the effects of different irradiation parameters; i.e., fluence, laser repetition frequency, and speed of scan have been investigated through the size of the biotite molten region. This model may be considered as the first stage of a comprehensive model of the laser ablation process in granite.

Abstract: Microinjection moulding is one of the key technologies for the mass production of plastics microcomponents. Recently, significant effort has been made to test the limits of applicability of existent numerical codes for simulating the polymer flow at the microscale. However, the modelling precision in what concerns polymer flow in microimpressions depends on factors which may not be properly accounted for in the process simulation. In this study, a micropart with variable thickness was designed, and the moulding block fabricated and instrumented. Short shots and complete filling of the cavity were carried out and the flow front progress was subsequently evaluated. These data were also assessed numerically by 3D-finite element modelling. A flow simulation considering the polymer as incompressible was carried out to investigate how the mesh size and density affected the prediction of the flow field in the microimpression, using the same processing conditions of the experimental study. The reduction of the mesh size as well as the increase of the mesh density are consistent with better representativeness of the experimental flow front progress in the microimpression. Moreover, the weld line prediction also tends to be improved. This study suggests that the mesh adaption and domain discretization is important in numerical studies of the polymer flow at the microscale.

Abstract: This paper discusses the integrated use of rapid prototyping commercial technology and finite element method to support design of engineering components. The study was carried out on PolyJet RP technology. The resin properties were investigated by standard tests (ASTM) and used as input data on Abaqus software application. The results of the physical test were used to calibrate and validate the finite element model. Experimental tests were executed capturing critical loads and main forces acting on the geometric model and compared with the virtual model. The results showed small percentage differences between the physical and virtual models. Viscoelasticity of the resin was also detected in the analyzed physical model. Initial results have shown that the integration of these two technologies can assist in developing functional products, considering the technical limitations of the current prototype materials.

Abstract: Thermoplastics have very low thermal diffusivity, which is advantageous for some applications but create difficulties for their processing. In fact, in continuous processes, such as extrusion, it can limit the production rate, which is dependent on the installed cooling capability of the extrusion line, originates the development of considerable thermal gradients during the cooling stage and, consequently, the development of stresses that can be frozen in the product (generally referred as residual thermal stresses) that will affect negatively its mechanical performance in use. Therefore, the conditions in which the cooling stage takes place not only determine the production rate, but also the final properties of extruded products. Due to the large number of parameters influencing the cooling stage, its optimization requires the use of proper modelling codes. The work here presented is intended to improve the scope of application of an existing 3D non-isothermal multi-domain numerical code based on the finite volume method (FVM), through the implementation of unstructured meshes enabling, therefore, to predict the evolution of the thermal field during the cooling stage of the extrusion of complex profiles.