Effect of post-fill pressure and nanoclay on void morphology in resin transfer molded composites.

Resin transfer molded (RTM) composites usually suffer from the formation of flow-induced defects such as voids. Detrimental effects of voids on performance of molded parts have been studied extensively. Yet, knowledge of effective void removal strategies, along with detailed morphological void distribution within molded composites is very limited. In this investigation, effects of post-fill pressure on void content is investigated for random-mat, E-glass/epoxy RTM disks. Measured void contents agree well with results obtained in other studies for similar ranges of modified capillary number values. Packing helped significantly reduce void contents in RTM parts. In addition, voids are found to concentrate primarily within or adjacent to the fibers. Three-dimensional features of the formed voids are included in more detailed analyses of morphology variations of voids within the composite from both through-the-thickness and planar surfaces.Effects of applying a packing pressure on void morphology are investigated for similar composites. Packing pressures of zero and 570 kPa are applied and voidage is evaluated from both through-the-thickness and planar views. The packed composite is found to contain almost 92% less void content than the unpacked composite, accompanied by a 40% drop in average void size. Along the flow direction, removal of voids seems to depend on their arrangement at the end of the filling stage.Finally, effect of nanoclay content on void morphology in RTM nanoclay/E-glass/epoxy composites are investigated. ClositeRTM25A nanoclay loads of 0, 2, 5, and 10 wt% are mixed with a low-viscosity epoxy resin prior to filling. Void occurrence is observed to increase considerably with increasing nanoclay content from 2.1% in the composite without nanoclay to 5.1 and 8.3% in 5%- and 10%-nanocomposites, respectively. However, the composite with 2 wt% nanoclay yields the lowest void content of 0.7%. Voids are observed to be smaller after the addition of nanoclay at all concentrations

Defect Modeling and Vibration-Based Bending Fatigue of Additively Manufactured Inconel 718

Additive manufacturing (AM) is convenient for building components with complex features. However, the long-term integrity of these components is uncertain, since AM parts have defects such as pores and rough surfaces. In this work, an analytical model was developed to determine the impact of defects, and a novel bending fatigue test was used to determine the fatigue life of channeled specimens. The analytical model, based off the theory of critical distances, investigates coupled pores and predicts their potential for fatigue failure. This resulted in a maximum allowable pore size and spacing recommendation for coupled defects. Additionally, specimens with through channels built using laser powder bed fusion were tested in high-cycle vibration-based bending fatigue. The resultant S-N curve and fractography studies revealed similar performance between the channeled specimens and the solid specimens. This research serves to increase understanding of additive defects and their influence on the fatigue life of AM components

Failure prediction of steel components under the coupled effect of excessive plastic deformations and pitting corrosion

publishedVersio

An Iberian Heritage: Hispano-Moresque architectural tiles in Portuguese and Spanish collections

This is the first archaeometric study comparing Hispano-Moresque tiles from different Portuguese and Spanish collections, no other published one being known at the time of writing. Despite the increasing interest in the Iberian ceramic cultural heritage, a specific study dedicated to architectural tiles was lacking. With this in mind, this thesis offers a first approach on the technological features of these impressive – although somehow undervalued – architectural tiles. With this work, important Portuguese and Spanish Hispano-Moresque tile collections are characterised, compared and studied: National Palace of Sintra (Portugal) (PNS), Monastery of Santa Clara-a-Velha (Coimbra, Portugal) (SCV), archaeological site of Santo António da Charneca (Barreiro, Portugal) (SAC), Instituto Valencia de Don Juan (Madrid, Spain) (IVDJ), Casa de Pilatos (Seville, Spain) (CPS) and Museo de Cerámica y Artes Sumtuarias “González Marti” (Valencia, Spain) (MCV). The aim is to provide a physicochemical characterisation of both the glazes and the ceramic bodies of the tiles to better understand the production technology. The methodology proposed for this study had the main purpose of developing a minimally invasive and essentially non-destructive approach with complementary analytical techniques that will allow for replication in future studies with other Hispano-Moresque tile collections. The techniques chosen were: Micro-Particle Induced X-Ray Emission (μ-PIXE), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), Scanning Electron Microscopy with X-ray Microanalysis (SEM-EDS), μ-Raman spectroscopy, Micro-X-ray diffraction (μ-XRD) and Synchrotron Radiation Micro-X-ray diffraction (SR-μ-XRD). The archaeometric study concluded that calcareous clays were the standard material used for the ceramic bodies of the tiles. Lime content is frequently higher than 20 wt.%, which is a high value among the typical calcareous clays analysed in the literature, although within the expected results for tinopacified ceramic bodies. The glaze technology employed in Hispano-Moresque tiles followed the Islamic tradition that was introduced in the Iberian Peninsula from the 8th century onwards. High-lead glazes (ca. 30-50 wt.% PbO) were identified in all analysed samples. Two types of high-lead glazes were identified: “transparent” and tin-opacified. Besides the disparity in tin contents, the two glaze types also evidence differences in sodium and lead values. A sodium compound (most likely NaCl) may have been added to compensate the lower PbO content in tin-opacified glazes. The pictorial layer is composed of five colours: white (SnO2), blue (SnO2 + CoO), green (CuO), amber (Fe2O3) and brown (MnO). These colours exhibit different shades depending on the glaze recipe, its thickness and the influence of the underlying ceramic body. White and blue are consistently tin-opacified, whereas most green, amber and brown glazes are transparent. The results of the archaeometric study identify a widespread ceramic technology. Nevertheless, it is still visible a higher proximity between the CPS, IVDJ-Seville, SCV and PNS collections – although with differences among them – whereas the MCV and IVDJ-Toledo groups display distinct features that attest for their different provenance

Book reviews

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45933/1/357_2005_Article_BF01195682.pd

Coarse geometry: a foundational and categorical approach with applications to groups and hyperspaces

The topic of the manuscript is coarse geometry, also known as large-scale geometry, which is the study of large-scale properties of spaces. It found applications in geometric group theory after the work of Gromov, and in Novikov and coarse Baum-Connes conjectures. The thesis is divided into three parts. In the first one, we provide a foundational and categorical approach to coarse geometry. Large-scale geometry was originally developed for metric spaces and then Roe introduced coarse structures as a large-scale counterpart of uniformities. However, coarse spaces are innerly symmetric objects, and thus are not suitable to parametrise asymmetric objects such as monoids and quasi-metric spaces. In order to fill the gap, we introduce quasi-coarse spaces. Moreover, we consider also semi-coarse spaces and entourage spaces. These objects induce para-bornologies, quasi-bornologies, semi-bornologies, pre-bornologies (also known as bounded structures) and bornologies, and this process is similar to the definition of uniform topology from a (quasi-)uniform space. We study all the notions introduced and recalled to find extensions of classical results proved for metric or coarse spaces, and similarities with notions and properties for general topology. Furthermore, we study the categories of those objects and the relations among them. In particular, since all of them are topological categories, we have a complete understanding of their epimorphisms and monomorphisms, and the description of many categorical constructions. Among them, of particular interest are quotients. We then focus our attention on Coarse, the category of coarse spaces and bornologous maps, discussing its closure operators and the cowellpoweredness of its epireflective subcategories, and its quotient category Coarse/~, which turns out to be balanced and cowellpowered. The second part is dedicated to study the large-scale geometry of algebraic objects, such as unitary magmas, monoids, loops and groups. In particular, we focus on coarse groups (groups endowed with suitable coarse structures) and we investigate their category. We study different choices, underlining advantages and drawbacks. With some restrictions on the coarse groups that we are considering, if we enlarge the class of morphisms to contain bornologous quasi-homomorphisms (and not just bornologous homomorphisms), every coarse inverse of a homomorphism which is a coarse equivalence is a quasi-homomorphism. This observation is connected to the notion of localisation of a category and could provide a categorical justification to the notion of quasi-homomorphism. Once the categories of coarse groups are fixed, inspired by the notion of functorial topologies, we can introduce functorial coarse structures on Grp, the category of groups and homomorphisms, and on TopGrp, the category of topological groups and continuous homomorphisms. Among them, we pay attention to the ones induced by cardinal invariants, and to those associated to the family of relatively compact subsets. As for the latter functorial coarse structure, we study the transformation of large-scale properties along Pontryagin and Bohr functors. The third part is devoted to coarse hyperspaces, which are suitable coarse structures on power sets of coarse spaces. This construction was introduced following the work of Protasov and Protasova and miming the classical notion of uniform hyperspace. We see how properties of the initial coarse space are reflected on the hyperspace. Since the coarse hyperspace is highly disconnected, it is convenient to consider some special subspaces of it. For example, if the base space is a coarse group, it is natural to consider the subspace structure induced on the lattice of subgroups, called subgroup exponential hyperballean. We show that both the subgroup exponential hyperballean and the subgroup logarithmic hyperballean, another coarse structure on the subgroup lattice, capture many properties of the group

Quantitative Methods for Similarity in Description Logics

Description Logics (DLs) are a family of logic-based knowledge representation languages used to describe the knowledge of an application domain and reason about it in formally well-defined way. They allow users to describe the important notions and classes of the knowledge domain as concepts, which formalize the necessary and sufficient conditions for individual objects to belong to that concept. A variety of different DLs exist, differing in the set of properties one can use to express concepts, the so-called concept constructors, as well as the set of axioms available to describe the relations between concepts or individuals. However, all classical DLs have in common that they can only express exact knowledge, and correspondingly only allow exact inferences. Either we can infer that some individual belongs to a concept, or we can't, there is no in-between. In practice though, knowledge is rarely exact. Many definitions have their exceptions or are vaguely formulated in the first place, and people might not only be interested in exact answers, but also in alternatives that are "close enough". This thesis is aimed at tackling how to express that something "close enough", and how to integrate this notion into the formalism of Description Logics. To this end, we will use the notion of similarity and dissimilarity measures as a way to quantify how close exactly two concepts are. We will look at how useful measures can be defined in the context of DLs, and how they can be incorporated into the formal framework in order to generalize it. In particular, we will look closer at two applications of thus measures to DLs: Relaxed instance queries will incorporate a similarity measure in order to not just give the exact answer to some query, but all answers that are reasonably similar. Prototypical definitions on the other hand use a measure of dissimilarity or distance between concepts in order to allow the definitions of and reasoning with concepts that capture not just those individuals that satisfy exactly the stated properties, but also those that are "close enough"

An evaluation of the structural integrity of HSLA steels exposed in simulated flue-gases under dynamic conditions for anthropogenic CO2 transport.

Carbon capture and storage (CCTS) is a transitional technology offering a nearterm method of mitigating climate change. Pipelines are considered to be the most suitable systems for CCTS; however, structural integrity of pipeline has to be guaranteed in order for this technology to become a practical technical solution. The investigation detailed here is based on a systematic experimental approach to investigate the structural integrity of API X100, X60 and X70 steels exposed in simulated flue-gas under dynamic conditions. A core of the structured experiments through some methods such as aging test, tensile properties, fracture toughness, residual stress and engineering critical assessment was accomplished in parent material and exposed samples on flue-gas. The temperature range of evaluation for tensile test covers -70C to 21C while fracture toughness was over the range -196C to 21C. Tensile properties of virgin material show that steels meet standard specification while aging samples do not show significant scatter compared with parent steels. Ovalisation of the fracture surface and splitting phenomenon was observed which is related with steel anisotropy. Fracture toughness obtained from experiment was compared with that calculate by two existing correlations. However both correlations did not predict the level of fracture toughness expected indicating the methods used in this work has limited applicability under the test conditions used here. Residual stress (RS) induced in API X100 steel by cold rolling method was characterised using two complementary techniques known as Neutron Diffraction (ND) and Incremental Hole Drilling (IHD). The RS distribution shows good agreement for both techniques used but reproducibility of them depends on their own inaccuracies. An Engineering Criticality Assessment (ECA) was performed based in Failure Assessment Diagram (FAD) approach using all the experimental data obtained by a leak-before-break method under three operational pressures. The results showed the effect on the integrity of material under the presence of a flaw length assessed. Overall, the thesis presents a combined engineering critical assessment which involved the examination of materials used to transport flue-gas and established a methodology to determine fracture toughness alongside with the FAD to assess the integrity of pipelines