CDRsp - Comunicações em conferências internacionais
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- Ask not what additive manufacturing can do for youPublication . Gibson, I.The paraphrase of John F Kennedy’s famous words is for 2 purposes. Firstly it is to acknowledge that there are some people who have considered that it is a major part of their life’s work to promote Additive Manufacturing (AM) technology as primarily a selfless act. AM comprises an outstanding range of technology that should be brought to public attention as a true revolution in how we design and manufacture products. The second purpose is to show that technology development is only one part of this promotion process and that there are other ways in which we can get involved. This paper describes the author’s journey over the (approximately) 20 years since he was introduced to what was then called Rapid Prototyping (RP). It is not a catalogue of research and development projects but rather a list of activities that he has been involved in to help promote and support AM technology over these years. It will describe the conferences, activities, associations and publications that have been created to allow academics and professionals to describe and discuss their work amongst themselves and to the larger society.
- Comparison by computer fluid dynamics of the drag force acting upon two helmets for wheelchair racersPublication . Forte, P; Marinho, D. A.; Morouço, P; Pascoal-Faria, P.; Barbosa, T. M.The aim of this study was to compare the drag force created by two helmets (time trial and road)used by a wheelchair racer. The head and helmet of the racer were scanned to obtain the3D models. Numerical simulation was run on Fluent, having as output the drag force for both helmets (road and time trial) in two different positions (0º and 90º) and increasing velocities (from 2.0 to 6.5 m/s). The greatest aerodynamic drag was noted wearing a time trial helmet in 90º ranging from 0.1025N to 0.8475N; this was also the position with the highest drag. The velocity with higher drag for booth helmets was at 6.5 m/s. The time trial helmet at 0º had the lower aerodynamic drag, compared with the same position of road helmet. The drag force seems to be lower wearing the time trial helmet and keeping the 0º position and, thus, should be considered for sprinting events.
- Cyclic plastic behaviour of 7075 aluminium alloyPublication . Nogueira, F.; Cunha, J.; Mateus, A.; Malça, C.; Costa, J. D.; Branco, R.This paper aims at studying the cyclic plastic behaviour of the 7075-T651 aluminium alloy under fully-reversed strain-controlled conditions. Tests are conducted under strain-control mode, at room temperature, in a conventional servo-hydraulic machine, from smooth samples, using the single step method, with strain amplitudes (∆ε/2) in the range ±0.5 to ±2.75%. This material has exhibited a mixed behaviour, i.e. cyclic strain-hardens at higher strain amplitudes (∆ε/2/>1.1%) and cyclic strain-softens at lower strain amplitudes (∆ε/2<1.1%). A linear relationship between the degree of cyclic strain-hardening and the strain amplitude has been established for higher strain amplitudes. Fatigue-ductility and fatigue-strength properties agree with those found in the open literature for the same loading conditions.
- A finite element method to study multimaterial wind towersPublication . Pascoal-Faria, P.; Dias, C.; Oliveira, M; Alves, N.Wind towers are used to produce electrical energy from the wind. A significant number of towers is manufactured using tubular separately steel or concrete, having limitations such as maximum diameter and height imposed essentially by transportation limitations. Developed computational studies on structural design of towers have been mainly focused on a single material. This investigation aims to develop a finite element method able to study structural design of wind towers combining different materials. The finite element model combines solid and shell elements encompassing different geometries. Several case studies are considered to validate the proposed method and accurate results are obtained.
- Maximizing the placement of congruent polyhedrain a parallelepiped containerPublication . Gaspar, M. Belbut; Martins-Ferreira, N.Given multiple identical polyhedral objects and a parallelepiped container, how should one place the objects so that the largest number fits inside the container? This simple question is important in many applications, yet the answer is elusive. In fact, we know of no published solution for this very general formulation. Still, in many circumstances, further restrictions apply, resulting in a large number of variations requiring different algorithmic strategies. In this presentation we will further formalize the problem, present some of its many variations, and in particular one that applies to the stereolithographic rapid prototyping technology.
- Mechanical properties assessment for TPMS based scaffolds using homogenization methodsPublication . Pinheiro, J.; Castro, A. P. G.; Ruben, R. B.; Guedes, J. M.; Fernandes, P. R.The combination of computational methods with recent 3D printing technologies allows for the control of scaffolds microstructure, in order to obtain application-driven mechanical properties. Lately, geometries obtained using triply periodic minimal surfaces (TPMS) have been used to design porosity-controlled scaffolds for bone tissue engineering. The objective for this work is to assess the properties of TPMS scaffolds obtained using Schwartz P, Schwartz D and Gyroid, with different porosity levels. These properties are computed by an asymptotic homogenization method to obtain the effective permeability and stiffness. Results show that the obtained properties compare well with the properties of bone scaffolds presented in literature and obtained using different means.
- Numerical Calculations in Tissue EngineeringPublication . Almeida, Henrique de Amorim; Bártolo, Paulo J.The design of optimized scaffolds for tissue engineering is a key topic of research, as the complex macro- and micro- architectures required for a scaffold depends not only on the mechanical properties, but also on the physical and molecular queues of the surrounding tissue within the defect site. Thus, the prediction of optimal features for tissue engineering scaffolds is very important for its mechanical, vascular or topological properties. The relationship between high scaffold porosity and high mechanical properties is contradictory, as it becomes even more complex due to the scaffold degradation process. A scaffold design strategy was developed, based on the finite element method, to optimise the scaffold design regarding the mechanical and vascular properties as a function of porosity. Scaffolds can be considered as a LEGO structure formed by an association of small elementary units or blocks. In this research work, two types of family elementary scaffold units were considered: non-triple periodic minimal surfaces and triple periodic minimal surfaces that describe natural existing surfaces. The main objective of this work is to present the undergoing research based on numerical simulations for the evaluation and prediction of the scaffold's behaviour under structural and vascular loading, and its topological optimisation.
- Numerical study on injection parameters optimization of thin wall and biodegradable polymers partsPublication . Santos, Cyril; Mendes, A; Carreira, P.; Mateus, Artur; Malça, C.Nowadays, the molds industry searches new markets, with diversified and added value products. The concept associated to the production of thin walled and biodegradable parts mostly manufactured by injection process has assumed a relevant importance due to environmental and economic factors. The growth of a global consciousness about the harmful effects of the conventional polymers in our life quality associated with the legislation imposed, become key factors for the choice of a particular product by the consumer. The target of this work is to provide an integrated solution for the injection of parts with thin walls and manufactured using biodegradable materials. This integrated solution includes the design and manufacture processes of the mold as well as to find the optimum values for the injection parameters in order to become the process effective and competitive. For this, the Moldflow software was used. It was demonstrated that this computational tool provides an effective responsiveness and it can constitute an important tool in supporting the injection molding of thin-walled and biodegradable parts.
- Optimalmould - part II: Global optimization of the injection moulding cycle timePublication . Ramos, Carina; Carreira, Pedro; Bartolo, Paulo; Alves, NunoThe time required to produce a plastic part is a key issue in injection moulding process as it strongly determine the cost per part. Several approaches have been proposed to address this problem. However they do not cover all aspects related to the complete cycle time of the injection moulding process, only focusing on steps such as filling time, cooling time and packing time. This paper presents a global optimisation strategy for the injection moulding cycle time, covering all time steps related to the injection moulding process, including a novel mathematical model to predict the ejection time. An industrial case study was considered to validate the proposed approach. The obtained results are very close to the experimental ones. © 2012 American Institute of Physics.
- Optimalmould-part I: Multi-objective optimization to moulds design for injection of polymersPublication . Ramos, Carina; Carreira, P.; Bártolo, Paulo; Alves, NunoThe problem of mould design optimisation for polymer injection is a key issue for both mouldmaking and polymer injection industries. Several computational tools have proposed to address this problem. However they do not cover all aspects related to both mould design and injection moulding process, usually requiring the geometrical configuration of the initial mould solution. This paper presents a novel multi-objective optimisation tool, integrating CAD and CAE tools to optimise mould design parameters and injection moulding process parameters. No initial geometric definition of the mould is required. An industrial case study was considered to validate the proposed approach and the performance of several optimisation algorithms evaluated.