Prediction of the effect of temperature on impact damage in carbon/epoxy laminates

6 pages, 10 figures.-- Issue title: "EURODYMAT 2003 - 7th International Conference on Mechanical and Physical Behaviour of Materials under Dynamic Loading" (Porto, Portugal, Sep 8-10, 2003).The effect of temperature on impact damage in Carbon Fiber Reinforced Plastic (CFRP) tape laminates produced by low velocity impact was studied by numerical simulations made to model drop weight tower impact tests on carbon/epoxy laminate composites. The damage model was implemented into a user subroutine of the finite element code ABAQUS. The model takes into account the thermal stresses resulting form the different thermal expansion coefficients in each ply of the laminate. The tests and simulations show how temperature affects the propagation of each damage mode. Matrix cracking and delamination are greatly affected by low temperature, white matrix crushing and fibre failure appear only in a small region at all the impact energies and test temperatures.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnologia (Project MAT-98/0273) for the financial support of this work.Publicad

Damage in CFRPs due to low velocity impact at low temperature

10 pages, 21 figures.This work examines the response of carbon fibre-reinforced epoxy matrix (CFRP) laminates at low impact velocity and in low temperature conditions. Square specimens of carbon fibre/epoxy laminates with different stacking sequences (unidirectional, cross-ply, quasi-isotropic and woven laminates) were tested using a Drop Weight Tower device. The test temperature ranged from 20 down to −150 °C. After the impact tests, the damage extension was measured by C-Scan ultrasonic inspection and the damage mechanisms were studied by optical and scanning electron microscopy. Results showed the influence of temperature, of ply reinforcement architecture and of stacking sequence on the mechanical behaviour of the CFRP laminates subjected to low velocity impulsive loads.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT 98/0273) for the financial support of this work, and to the Department of Engineering Science of the University of Oxford for their assistance in the C Scan inspection tests.Publicad

Dynamic tensile behaviour at low temperature of CFRP using a split Hopkinson pressure bar

11 pages, 17 figures.This paper deals with the effect of temperature (room and low temperatures) on the tensile properties at high strain rates of CFRP laminates. Dynamic tests were performed on different carbon/epoxy laminates configurations: unidirectional, [0]10 and [90]10, and quasi-isotropic [±45/0/90]S. All these tests were carried out at two temperatures: 20 and −60 °C. Validation of Hopkinson bar theory using one-dimensional wave propagation theory was performed by analysing the effect of low temperature on elastic wave propagation along the bars of the experimental device, and the subsequent wave dispersion phenomena. The value of the strain on the specimen derived from the signals recorded at the bar gauges was compared with that obtained from a gauge glued on the specimen. All the experimental results of the response of CFRPs at high strain rates and low temperature are analysed and discussed.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT-98/0273) for the financial support of this work.Publicad

Is the Fast Evolution Scenario for Virialized Compact Groups Really Compelling? The Role of a Dark Massive Group Halo

We report on results of N-body simulations aimed at testing the hypothesis that galaxies in X-ray emitting (i.e., virialized) Compact Groups are not tidally stripped when they are embedded in a common, massive, quiescent dark matter halo. To disentangle the effects of interactions from spurious effects due to an incorrect choice of the initial galaxy model configurations, these have been chosen to be tidally-limited King spheres, representing systems in quasi-equilibrium within the tidal field of the halo. The potential of the halo has been assumed to be frozen and the braking due to dynamical friction neglected. Our results confirm the hypothesis of low rates of tidal stripping and suggest a scenario for virialized Compact Group evolution in their quiescent phases with only very moderate tidally induced galaxy evolution can be generally expected. This implies the group stability, provided that the dynamical friction timescales in these systems are not much shorter than the Hubble time. We discuss briefly this possibility, in particular taking account of the similarity between the velocity dispersions of a typical virialized Compact Groups and the internal velocity dispersion of typical member galaxies. A number of puzzling observational data on Compact Groups can be easily explained in this framework. Other observations would be better understood as the result of enhanced merging activity in the proto-group environment, leading to virialized Compact Group formation through mergers of lower mass halos, as predicted by hierarchical scenarios of structure formation.Comment: 18 pages, 1 postscript file, 2 tables, to be published in ApJLet

The building stone of the Roman city of Lixus (NW Morocco): provenance, petrography and petrophysical characterization

The characterization of building materials is a key tool to assess deterioration processes and improve potential restoration works of archaeological sites. The aim of this paper is to identify and characterize the most important building stones used in the construction of the Roman city of Lixus (Larache, Morocco) by means of petrographic and petrophysical techniques. Based on the visual analysis of the monuments, three major building stones (i.e. lithotypes) have been identified: i) Oligocene sandstones, ii) Quaternary sandstones and iii) Quaternary conglomerates. Based on the analysis of the regional geology and exploitation marks, these three lithotypes have been recognised to crop out in the surroundings of Lixus and the quarries, presumably Roman in origin, recognized. The Oligocene sandstone is the primary building stone in Lixus as it forms and crops out extensively in the Tchemmis hill, at the top of which the city is settled. The Quaternary sandstones and conglomerates, which represent nearshore deposits and eolianites, crop out along the Atlantic coast where they form part of the cliffs next to Larache. Petrographic results indicate that lithotypes differ notably in grain size, ratio of detrital to allochemical components, and the configuration of their porous system. Mechanical analysis shows that the Oligocene sandstones are more resistant to compression than the Quaternary sandstones and conglomerates, the latter exhibiting relatively low compressive strength. The Oligocene sandstones, which display scarce porosity and permeability, show a hydric behaviour characterized by a very low degree of absorption and desorption water, likely resulting from a poor connectivity of the pore network. Contrary to the latter lithotype, the Quaternary sandstones, which exhibit very high porosity and permeability, display a hydric behaviour characterized by high degree of both absorption and desorption of water. This is attributed to the low degree of cementation compared to porosity of this lithotype and the excellent connectivity of the porous network. Finally, Oligocene and Quaternary sandstones do not show a significant weight loss after the accelerated artificial aging test, indicating that both are slightly affected by salt crystallization and presumably ice formation. Results indicate that the relatively fine state of conservation of the building rocks of Lixus is linked to intrinsic factors such as mineralogy and petrophysical characteristics together with the favourable effect of the climatic condition of the study area

Taxonomic identification of different species of the genus aeromonas by whole-genome sequencing and use of their species-specific Β-lactamases as phylogenetic markers

Altres ajuts: Departament de Microbobiologia de l'Hospital de la Santa Creu i Sant Pau, i l'Institut de Recerca de l'Hospital de la Santa Creu i Sant PauSome Aeromonas species, potentially pathogenic for humans, are known to express up to three different classes of chromosomal Β-lactamases, which may become hyperproduced and cause treatment failure. The aim of this study was to assess the utility of these species-specific Β-lactamase genes as phylogenetic markers using whole-genome sequencing data. Core-genome alignments were generated for 36 Aeromonas genomes from seven different species and scanned for antimicrobial resistance genes. Core-genome alignment confirmed the MALDI-TOF identification of most of the isolates and re-identified an A. hydrophila isolate as A. dhakensis. Three (B, C and D) of the four Ambler classes of Β-lactamase genes were found in A. sobria, A. allosacharophila, A. hydrophila and A. dhakensis (bla, bla and bla). A. veronii only showed class-B- and class-D-like matches (bla and bla), whereas those for A. media, A. rivipollensis and A. caviae were class C and D (bla, bla and bla). The phylogenetic tree derived from concatenated sequences of Β-lactamase genes successfully clustered each species. Some isolates also had resistance to sulfonamides, quinolones and aminoglycosides. Whole-genome sequencing proved to be a useful method to identify Aeromonas at the species level, which led to the unexpected identification of A. dhakensis and A.rivipollensis and revealed the resistome of each isolate

Static behavior of CFRPs at low temperatures

8 pages, 11 figures.This paper summarizes the results of the tests to determine the effect of the low temperature on the mechanical behavior of carbon fiber reinforced epoxy laminates. Tensile and bending static tests were carried out on two laminate lay-ups (quasi-isotropic and cross-ply laminates), determining properties such as the mechanical strength, stiffness and strain to failure. The results show the changes in the mechanical behavior of this material at different test temperatures (20, −60 and −150 °C).The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT 98/0273) for the financial support of this work.Publicad

The building stone of the Roman city of Lixus (NW Morocco) : provenance, petrography and petrophysical characterization

Characterization of building material is a key tool to assess deterioration processes and improve potential restoration works of archaeological sites. The aim of this paper is to identify and characterize the building stone used in the construction of the Phoenician-Roman city of Lixus (Larache, Morocco) by means of petrographic and petrophysical technics. Based on the visual analysis of the monuments, three major building stones (i.e., lithotypes) have been identified: (1) Oligocene sandstones, (2) Quaternary sandstones, and (3) Quaternary conglomerates. Based on the analysis of the regional geology and exploitation marks, these three lithotypes have been identified to crop out in the surroundings of Lixus and the quarries, presumably Roman in origin, recognized. The Oligocene sandstone is the primary building stone in Lixus as form and crop out extensively in the Tchemmis hill, at top of which the city is settled. The Quaternary sandstones and conglomerates, which represent nearshore deposits and eolianites, are less abundant as building rocks in Lixus and crop out along the Atlantic coast where form part pf the cliffs close to Larache. Petrographic results indicate that lithotypes differ notably in grain size, ratio of detrital to allochemical components, and the configuration of their porous system. Mechanical analysis show that the Oligocene sandstones are more resistant to compression than the Quaternary sandstones and conglomerates, the latter exhibiting low compressive strength. The Oligocene sandstones, which display scarce porosity and permeability, show a hydric behaviour characterized by a very low degree of absorbing and desorbing water, likely resulting from a poor connectivity of the pore network. Contrary to later lithotype, the Quaternary sandstones and conglomerates, which exhibit very high porosity and permeability, display a hydric behaviour characterized by high degree of both absorbing and desorbing water. This behaviour is attributed to both the low degree of cementation and excellent connectivity of the porous network of the lithotype typical of coastal deposists. Finally, the accelerated artificial aging test they do not show a significant weight loss after twelve cycles of salt crystallization, indicating that the three lithotypes are not vulnerable to sodium sulphate attacks. Results of this study indicate that the good state of conservation of the building rocks of Lixus is linked to intrinsic factors as mineralogy and petrophysical characteristics together with the favourable effect of the climatic condition of the study area