Porto, Portugal
Porto, Portugal
Time filter
Source Type

Martinez X.,International Center for Numerical Methods in Engineering | Martinez X.,Polytechnic University of Catalonia | Oller S.,International Center for Numerical Methods in Engineering | Oller S.,Polytechnic University of Catalonia | And 6 more authors.
International Journal of Fatigue | Year: 2015

This paper presents a plastic-damage formulation and a new isotropic hardening law, based on the Barcelona plastic damage model initially proposed by Lubliner et al. (1989) [1], which is capable of predicting steel failure due to Ultra Low Cycle Fatigue (ULCF). This failure mechanism is obtained when the material is subjected to cyclic loads and breaks after applying a very low number of cycles, usually less than hundreds. The failure is driven by the plastic response of the material, and it is often predicted based on the plastic strains applied to it. The model proposed in this work has been formulated with the objective of predicting accurately the plastic behavior of the material, as well as its failure due to ULCF. This is achieved taking into account the fracture energy dissipated during the whole loading process. This approach allows the simulation of ULCF when it takes place due to regular cyclic loads or non-regular cyclic loads, as it is the case of seismic loads. Several simulations are conducted in order to show the capabilities of the formulation to reproduce the mechanical response of steel when it is subjected to regular and non-regular cyclic loads. The formulation is validated comparing the numerical results with several experimental tests made on X52 steel specimens. The agreement between the numerical and experimental results asses the validity of the proposed model to predict the plastic behavior of steel and its failure due to Ultra Low Cycle Fatigue. © 2014 Elsevier Ltd.

Laia R.,IDMEC | Pousinho H.M.I.,IDMEC | Melicio R.,IDMEC | Mendes V.M.F.,Polytechnic Institute of Lisbon
Proceedings - EUROCON 2015 | Year: 2015

Energy conversion from renewable energy has been possible due to extra-market supporting policies. The extra-market approach survives for low penetration levels, but as energy from wind penetration increases the extra-market policies are expected to become untenable. A wind power producer (WPP) should expect full competition in deregulated electricity market, i.e., has to have an offer strategy to be competitive. A WPP has to face uncertainties on available wind energy and market prices. Uncertainties have to be conveniently addressed; otherwise a decrease on the financial results is expected. A stochastic programming approach is presented to suitable address those uncertainties. The problem formulation is approached in the way of writing equations in order to benefit from the well-established mixed integer linear program (MILP) solvers in order to compute an offering strategy. A case study with data from the Iberian Electricity Market is used to illustrate the effectiveness of the proposed approach. © 2015 IEEE.

Varella R.A.,University of Lisbon | Goncalves G.,IDMEC | Duarte G.,IDMEC | Farias T.,University of Lisbon
SAE Technical Papers | Year: 2016

Internal combustion engine (ICE) cold-start is an issue that occurs either in conventional and hybrid powertrains before the ICE reaches its normal operation temperature, affecting both fuel consumption due to higher heat losses, and pollutant emissions due to low catalytic converter temperatures. The study of cold start emissions on conventional powertrains has been extensively addressed, although typically under laboratorial conditions, however studies addressing the impact of this phenomenon on hybrid powertrains is still reduced. Hybrid electric (HEV) and plug-in hybrid electric (PHEV) vehicles usually incorporate technologies to manage the battery and ICE power supply leading to ICE on/off operation under regular driving, which can result in a decrease on catalytic converter efficiency (due to cooling). This work suggest a new approach for the analysis of cold-start NOx emissions on conventional and hybrid powertrains, providing an insight on cold-start effects, namely in terms of emissions, under on-road conditions, by using a Portable Emission Measurement System (PEMS) to collect 1 Hz data on vehicle dynamics, road topography and exhaust gas composition. Data collected on different powertrain configurations is compared and analyzed in order to observe the impact of the cold-start phenomena in the normal day-to-day usage of vehicles. Since it was not possible to collect catalyst temperature, engine coolant temperature was used as proxy to define hot and cold running fuel use and emissions. Engine data, vehicle dynamics and exhaust gas composition were analyzed using the Vehicle Specific Power methodology to compare similar power conditions. Results indicate that powertrain configuration affect differently the NOx emission index (EI) over the power demand, however, on average, the ratio between cold and hot NOx EI is 1.61±0.20. © Copyright 2016 SAE International.

Nabais J.L.,IDMEC | Mendonca L.,D. Henrique Nautical Higher School Infante | Botto M.A.,University of Lisbon
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2012

Irrigation is one of the most consuming water resources in human activity. As water conveyance systems are commonly spatially distributed and crossing large regions it is important to guarantee their best efficiency A fault diagnosis architecture is an important tool to increase efficiency in water conveyance systems. In the presence of leaks, unauthorized water extractions or water level sensor faults, the service level can be severely compromised. Recent literature deal with these situations as a unique fault of water extraction type. Isolating correctly each fault is important to access the real current state of the irrigation canals and proceed in accordance to restore its nominal conditions. This paper proposes a fault diagnosis architecture to distinguish common faults in water canals, considering either unexpected water extractions, gate faults and downstream water level sensor errors. The architecture is based on geometric and hydraulic parameters and therefore can be extended to existent irrigation canals. The proposed fault isolation architecture is an important tool to support maintenance services and be extended to fault tolerant controllers. © 2012 IFAC.

Ribeiro I.,IDMEC | Pecas P.,IDMEC | Henriques E.,IDMEC
Leveraging Technology for a Sustainable World - Proceedings of the 19th CIRP Conference on Life Cycle Engineering | Year: 2012

The design and production of dedicated tools is usually a technically complex and demanding activity, as it highly influences the manufacturing process in which they are used, from material and energy consumption to reliability and cycle time parameters. However, despite being acknowledged by the industry, it is still lacking the quantification of these impacts due to the "one of a kind" nature of these tools. The model proposed in this paper overviews the research work under development, aiming to quantify the tool life cycle impacts. By using process-based models the costs and environmental impacts are assessed and modelled to be sensitive to part and tool design changes.

Pereira J.C.R.,IDMEC | de Jesus A.M.P.,IDMEC | de Jesus A.M.P.,University of Trás os Montes e Alto Douro | Xavier J.,University of Trás os Montes e Alto Douro | And 2 more authors.
Engineering Structures | Year: 2014

Steel structures subjected to extreme loading conditions (e.g. earthquakes, support settlements, industrial plant shutdown) undergo large deformations leading to fracture, either due to monotonic loading or ultra-low-cycle fatigue (ULCF) (Nf<100 cycles). Although developments have been made to understand and to model monotonic ductile damage and low-cycle fatigue (LCF), so far ULCF is neither sufficiently investigated nor understood. This paper presents the results of an investigation concerning the ULCF behaviour of the S185 structural steel. An experimental program was performed to derive ULCF data for notched specimens. LCF and monotonic damage data was also derived for the material under investigation, since ULCF exhibits damage features from both cases. While LCF data was derived for smooth specimens, monotonic tensile tests coupled with image-based methods were carried out on both smooth and notched specimens. Nonlinear finite element models were used to compute the history of relevant parameters of the investigated models for ULCF life prediction. Three existing alternative modelling approaches for ULCF were assessed using available experimental data, and important remarks for further enhancements proposed. © 2014 Elsevier Ltd.

Barbosa A.Q.,IDMEC | Da Silva L.F.M.,University of Porto | Ochsner A.,University of Technology Malaysia
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications | Year: 2014

The inclusion of particles (micro or nano) is a method to improve the mechanical properties, such as toughness, of structural adhesives. Structural adhesives are known for their high strength and stiffness but also for their low ductility and toughness. There are many processes described in the literature to increase the toughness, the use of rubber particles being one of the most common processes. In the present study, natural micro particles of cork were used with the objective to increase the ductility of a brittle epoxy adhesive. The idea is for the cork particles to act like a crack stopper. The influence of the amount of cork particles was studied. Particles of cork ranging in size from 125 to 250 mm were mixed in the epoxy adhesive Araldite 2020 from Huntsman. The amount of cork in the adhesive was varied between 0.5% and 5% in weight. This evaluation was made using tensile tests and it was evident that the failure strain was related to the amount of cork particles in the resin. The results concerning the single lap joints and the glass transition temperature confirm the increased ductility obtained in the tensile tests. © IMechE 2013.

Barbosa A.Q.,IDMEC | Da Silva L.F.M.,University of Porto | Ochsner A.,University of Technology Malaysia | Abenojar J.,Charles III University of Madrid | Del Real J.C.,Comillas Pontifical University
Ciencia e Tecnologia dos Materiais | Year: 2013

The inclusion of particles (nano or micro) is a method to improve the mechanical properties, such as toughness, of structural adhesives. Structural adhesives are known for their high strength and stiffness but also for their low ductility and toughness. There are many processes described in the literature to increase the toughness, such as rubber particles. In the present study, natural micro particles of cork were used with the objective to increase the mechanical properties of a brittle epoxy adhesive. The cork particles act like as a crack stopper leading to higher displacement of the specimen. The influence of the inclusion of cork particle was studied. Particles of cork ranging from 125 to 250 μm were mixed in the epoxy adhesive Araldite 2020 from Huntsman. This evaluation was made using tensile and impact tests and it was evident that mechanical properties were related to amount of cork particles in the resin, considering a uniform particle distribution. © 2013 Sociedade Portuguesa de Materiais (SPM).

Carmona Benitez R.B.,Anahuac University of North Mexico | Carmona Paredes R.B.,National Autonomous University of Mexico | Lodewijks G.,Technical University of Delft | Nabais J.L.,IDMEC
Expert Systems with Applications | Year: 2013

This paper presents a modification of the Grey Model (GM) to forecast routes passenger demand growth in the air transportation industry. Forecast methods like Holt-Winters, autoreg ressive models, exponen- tia smoothing, neural network, fuzzy logic, GM model calculate very high airlines routes pax growth. For this reason, a modification has been done to the GM model to damp trend calculations as time grows. The simulation results show that the modified GM model reduces the model exponential estimations grow. It allows the GM model to forecast reasonable routes passenger demand for long lead-times forecasts. It makes this model an option to calculate airlines routes pax flow when few data points are available. The United States domestic air transport market data are used to compare the performance of the GM model wit hthe proposed model. © 2013 Elsevier Ltd. All rights reserved.

De Jesus A.M.P.,IDMEC | De Jesus A.M.P.,University of Trás os Montes e Alto Douro | Da Silva A.L.L.,IDMEC | Da Silva A.L.L.,University of Porto | And 2 more authors.
Journal of Constructional Steel Research | Year: 2014

Fatigue damage is a concern for riveted metallic bridges due to the long operational period they have been subjected along with increasing traffic intensity. The usual fatigue assessment approach for riveted joints consists on using the global S-N curves with nominal or net stresses. Existing practice is based on the adoption of a unique S-N curve (e.g. the Eurocode 3, Class 71 S-N curve). However, this approach may lead to excessive conservative predictions since it is applied indistinctly of the riveted detail geometries (e.g. does not recognize the need for detail categorization) and materials (e.g. not specifically developed for puddle irons). Alternatively, local approaches to fatigue may be applied to any type of joints, made of any material, providing that material fatigue properties are available as well as accurate numerical models of the joints. This paper presents a numerical study concerning the fatigue modelling of riveted and bolted joints made of puddle iron from the centenary Portuguese Fão Bridge. Fatigue is assumed a process of crack initiation and propagation, both processes modelled using respectively the local strain and the Fracture Mechanics based fatigue approaches. A finite element model of the joints is proposed using solid and contact finite elements. The effects of the clamping stresses as well as the friction are taking into account with the proposed model. Numerical S-N curves are predicted and compared with the experimental data available for the investigated joints, a good agreement being observed. © 2014 Elsevier Ltd.

Loading IDMEC collaborators
Loading IDMEC collaborators