173 research outputs found
SWE bridge: software interface for plug & work instrument integration into marine observation platforms
The integration of sensor systems into marine
observation platforms such as gliders, cabled observatories
and smart buoys requires a great deal of effort due to the
diversity of architectures present in the marine acquisition
systems. In the past years important steps have been taken in
order to improve both standardization and interoperability,
i.e. the Open Geospatial Consortium’s Sensor Web
Enablement. This set of standards and protocols provide a
well
-defined framework to achieve standardized data chains.
However a significant gap is still present in the lower
-end of
the data chain, between the sensor systems and the
acquisition platforms. In this work a standard
s
-based
architecture to bridge this gap is proposed in order to achieve
plug & work, standardized and interoperable acquisition
systems.Award-winningPostprint (published version
The Economic Cost of A Hurricane: A Case Study of Puerto Rico and Hurricane Georges 1998 Using Synthetic Control Method
The aim of this study is to evaluate the long–term effect of a hurricane in the output of a country. The study estimates the effects of Hurricane Georges on Puerto Rico in 1998 using aggregated level data. To do so, this research uses a suitable method for comparative studies, the synthetic control method. Hurricane Georges caused an estimate of US $4.3 billion in direct damages. The results give validity to recent studies on natural disasters providing negative effects on growth. It was found that the Purchasing Power Parity over GDP could have been 9 percent higher by 2010 if the hurricane would have never affected Puerto Rico. Moreover, it shows that Puerto Rico’s economy has yet to recover after 12 years of the event. The case of Georges brings an insight into the long–term impacts of a natural disaster as a singular event. A difference in time and country is conducted as an alternative method with also negative effects on the dependable variable
Sensor metadata for automated integration of sensor resources into research data infrastructures
Peer ReviewedPostprint (published version
Sensor web enablement implementations in marine observation platforms
The study of global phenomena requires the integration of scientific data coming from multiple sources. Data is usually acquired by a wide variety of observation platforms, managed by different institutions and often using non-standardized data and metadata formats. In order to address these issues a generic solution to integrate sensor data into spatial data infrastructures based on the Sensor Web Enablement framework is proposed.Peer Reviewe
Applying OGC sensor web enablement to ocean observing systems
The complexity of marine installations
for ocean observing systems has grown significantly in
recent years. In a network consisting of tens, hundreds
or thousands of marine instruments, manual
configuration and integration becomes very
challenging. Simplifying the integration process in
existing or newly established observing systems would
benefit system operators and is important for the
broader application of different sensors. This article
presents an approach for the automatic configuration
and integration of sensors into an interoperable
Sensor Web infrastructure. First, the sensor
communication model, based on OGC's SensorML
standard, is utilized. It serves as a generic driver
mechanism since it enables the declarative and
detailed description of a sensor's protocol. Finally, we
present a data acquisition architecture based on the
OGC PUCK protocol that enables storage and
retrieval of the SensorML document from the sensor
itself, and automatic integration of sensors into an
interoperable Sensor Web infrastructure. Our
approach adopts Efficient XML Interchange (EXI) as
alternative serialization form of XML or JSON. It
solves the bandwidth problem of XML and JSON.Peer ReviewedPostprint (author's final draft
R-Curve approach to describe the fracture resistance of tool steels
This work addresses the events involved in the fracture of tool steels, aiming to understand the effect of primary carbides, inclusions, and the metallic matrix on their effective fracture toughness and strength. Microstructurally different steels were investigated. It is found that cracks nucleate on carbides or inclusions at stress values lower than the fracture resistance. It is experimentally evidenced that such cracks exhibit an increasing growth resistance as they progressively extend, i.e., R-curve behavior. Ingot cast steels present a rising R-curve, which implies that the effective toughness developed by small cracks is lower than that determined with long artificial cracks. On the other hand, cracks grow steadily in the powder metallurgy tool steel, yielding as a result a flat R-curve. Accordingly, effective toughness for this material is mostly independent of the crack size. Thus, differences in fracture toughness values measured using short and long cracks must be considered when assessing fracture resistance of tool steels, especially when tool performance is controlled by short cracks. Hence, material selection for tools or development of new steel grades should take into consideration R-curve concepts, in order to avoid unexpected tool failures or to optimize microstructural design of tool steels, respectively.Peer ReviewedPostprint (author's final draft
The role of adhesive forces and mechanical interaction on material transfer in hot forming of aluminium
In this work, the mechanisms resulting in transfer of aluminium on hot forming tools have been analysed by means of two separate laboratory tests. The influence of chemical affinity in aluminium adhesion has been studied in contact tests, measuring the force used in pulling at low velocity an aluminium ball pressed against a tool surface. The role of mechanical interaction has been investigated through ball-on-disc sliding tests at high temperature, using tool steel discs with different surface finish against an aluminium counterpart. These tests have been used for the evaluation of different strategies in adhesive wear reduction, including different tool steels and surface modification, and to study the effect of surface finish on the material transfer mechanisms observed.Peer ReviewedPostprint (author’s final draft
Journal of Physics: Conference Series
Lightweight designs and demanding safety requirements in automotive industry are increasingly promoting the use of Advanced High Strength Steel (AHSS) sheets. Such steels present higher strength (above 800 MPa) but lower ductility than conventional steels. Their great properties allow the reduction of the thickness of automobile structural components without compromising the safety, but also introduce new challenges to parts manufacturers. The fabrication of most cold formed components starts from shear cut blanks and, due to the lower ductility of AHSS, edge cracking problems can appear during forming operations, forcing the stop of the production and slowing down the industrial process.
Forming Limit Diagrams (FLD) and FEM simulations are very useful tools to predict fracture problems in zones with high localized strain, but they are not able to predict edge cracking. It has been observed that the fracture toughness, measured through the Essential Work of Fracture (EWF) methodology, is a good indicator of the stretch flangeability in AHSS and can help to foresee this type of fractures.
In this work, a serial production automotive component has been studied. The component showed cracks in some flanged edges when using a dual phase steel. It is shown that the conventional approach to explain formability, based on tensile tests and FLD, fails in the prediction of edge cracking. A new approach, based on fracture mechanics, help to solve the problem by selecting steel grades with higher fracture toughness, measured by means of EWF. Results confirmed that fracture toughness, in terms of EWF, can be readily used as a material parameter to rationalize cracking related problems and select AHSS with improved edge cracking resistance.Peer ReviewedPostprint (published version
Fatigue resistance evaluation of high Mn-TWIP steel through damage mechanics: A new method based on stiffness evolution
The work presented here deals with the implementation of a new methodology that allows fast and reliable determination of the fatigue strength. It is based on monitoring the specimen stiffness changes at different stress levels, as an indicator of the evolution of fatigue damage. This new rapid fatigue test uses techniques available in many laboratories, as the DIC (Digital Image Correlation) technique and common extensometers. Moreover, the obtained data are easier to handle than infrared cameras or acoustic emission systems data, and the experimental procedure to determine the fatigue limit is more evident than in the self-heating method.
Experiments have been conducted in TWIP (Twinning Induced Plasticity) steel, a material used for lightweighting the structural parts of vehicles. With their excellent energy absorption capacity, TWIP steels can satisfy the part requirements in terms of crash performance, while their high tensile strength can deal with the cyclic loads acting on chassis parts. Therefore, many efforts focus on improving the fatigue strength of TWIP steels through pre-straining and/or surface treatments. However, finding the best way to improve the fatigue resistance requires time and resources that often hinder the development of the material. For this reason, a TWIP steel has been selected to check the new rapid fatigue test. The prediction made using the proposed approach is validated by comparison with conventional staircase results and fatigue crack growth standardised tests. The good agreement allows proposing the new method as a fast and efficient way to determine the fatigue resistance in metals.Peer ReviewedPostprint (published version
Analysis of fracture resistance of tool steels by means of acoustic emission.
The usage of advanced high strength steels (AHSS) in structural automotive components has
been broadened in the past few years to satisfy the strict specifications of the automotive industry.
Besides showing excellent strength to weight rations, AHSS have several limitations due to the high loads required in cold forming and cutting tools, which decrease considerably the tooling performances. Therefore, these important forces of impact provoke unforeseen breakage of the dies. The aim of this research is to study the micromechanical behaviour and fracture mechanisms (nucleation and crack propagation) during fracture of tool steels using the acoustic emission (EA) technique. To do that, bending testing specimens of different tool steels were monitored in order to establish a relationship between AE signals and their mechanical behavior (carbide breakage, cracks emanating from them and crack propagation through the metallic matrix).Postprint (published version
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