Effect of Fe and Mn Content on the Microstructures and Tensile Behaviour of AlSi7Cu3 Alloy: Thermal Analysis and Tensile Tests

The present study was performed on two AlSi7Cu3 alloys with different Fe and Mn contents (standard alloy and high-Fe/Mn alloy). The evolution of microstructures during solidification of the standard AlSi7Cu3 alloy was investigated by thermal analysis and interrupted quenching test. The effect of Fe and Mn content on the solidification reaction and sequence were studied. The results show that increasing the Fe and Mn content changes the precipitation sequence of the iron-intermetallic α-Al15 (Fe,Mn)3Si2 and β-Al5FeSi, leading to the precipitation of α + β phases at a higher temperature. Microstructural characterizations were also performed on the fully solidified alloys to study the effect of Fe and Mn content on the microstructure of AlSi7Cu3 alloy. Fe and Mn were found to promote the formation of Fe-intermetallics. With the increase of Fe/Mn content, Fe-intermetallics increased in both size and amount, while more small pores (Feret diameter < 200 µm) were also introduced. 3D networks of α-Al15(Fe,Mn)3Si2 and β-Al5FeSi phases were revealed by Lab X-ray Computed Tomography, however, it is difficult to perform a quantitative analysis of the respective volume fraction of α-Al15(Fe,Mn)3Si2 and β-Al5FeSi phase from their 3D morphology. Monotonic tensile tests on both alloys show the mechanical properties of the studied alloys were not sensitive to the Fe/Mn content, while the fractography analysis reveals that cracks growth and final fracture under monotonic load are more prone to occur through the eutectic Si, Al2Cu phases and iron-intermetallics than through aluminium matrix.The authors wish to thank the ANR (Agence Nationale de la Recherche) MatetPro project INDiANA (ANR-12RMNP-0011) for funding the study on Al-Si alloys, Pierre Osmond from PSA Peugeot Citroën for providing the material of this study and the China Scholarship Council (CSC) for funding the PhD thesis of Zaidao Li. The ISIS4D X-Ray CT platform which has been funded by International Campus on Safety and Intermodality in Transportation (CISIT), the Nord-Pas-de-Calais Region, the European Community and the National Center for Scientific Research is also acknowledged for microtomographic acquisition, and thank the Common Center of Microscopy (CCM) of Lille University for the SEM and EDS. The authors also thank Dr. Dan Luo for her assistance with casting and SEM analysis. UK Research & Innovation (UKRI) [Engineering & Physical Sciences Research Council (EPSRC) EP/N007638/1]

Damage imaging post processing for delamination size assessment of CFRP aeronautic structures

Thanks to their high strength to mass ratio, composite materials are now widespread in the aerospace industry. Nevertheless, this type of material is sub- ject to internal damages like delamination. In order to detect and localize these damages, robust and precise Structural Health Monitoring algorithms exist for this purpose and have been validated experimentally. However, in order to avoid struc- tures catastrophic failures and to estimate their residual life, there is still a huge need of reliable damage size assessment methods. In this paper, a damage quanti cation method is proposed. This strategy is based on the extraction of a damage size sen- sitive feature computed from damage imaging results. Here damage imaging stands for methods that use ultrasonic Lamb waves-based map of damage localization like- lihood index. This feature is extracted from each labelled example of a training set in order to infer a mathematical model used to predict the area of a delamination of unknown damages. The proposed method is successfully validated on experimental data carried out on CFRP plate samples equipped with a piezoelectric transducers network.This work has received funding from the European Union's Horizon 2020 research and innovation program under the REMAP project (grant agreement number 769288). https://h2020-remap.eu

Matrix metalloproteinase-9 activity and a downregulated Hedgehog pathway impair blood-brain barrier function in an <i>in vitro</i> model of CNS tuberculosis

Central nervous system tuberculosis (CNS TB) has a high mortality and morbidity associated with severe inflammation. The blood-brain barrier (BBB) protects the brain from inflammation but the mechanisms causing BBB damage in CNS TB are uncharacterized. We demonstrate that Mycobacterium tuberculosis (Mtb) causes breakdown of type IV collagen and decreases tight junction protein (TJP) expression in a co-culture model of the BBB. This increases permeability, surface expression of endothelial adhesion molecules and leukocyte transmigration. TJP breakdown was driven by Mtb-dependent secretion of matrix metalloproteinase (MMP)-9. TJP expression is regulated by Sonic hedgehog (Shh) through transcription factor Gli-1. In our model, the hedgehog pathway was downregulated by Mtb-stimulation, but Shh levels in astrocytes were unchanged. However, Scube2, a glycoprotein regulating astrocyte Shh release was decreased, inhibiting Shh delivery to brain endothelial cells. Activation of the hedgehog pathway by addition of a Smoothened agonist or by addition of exogenous Shh, or neutralizing MMP-9 activity, decreased permeability and increased TJP expression in the Mtb-stimulated BBB co-cultures. In summary, the BBB is disrupted by downregulation of the Shh pathway and breakdown of TJPs, secondary to increased MMP-9 activity which suggests that these pathways are potential novel targets for host directed therapy in CNS TB

Are children with developmental dyslexia all the same? A cluster analysis with more than 300 cases

Reading is vital to every aspect of modern life, exacerbated by reliance of the internet, email, and social media on the written medium. Developmental dyslexia (DD) characterizes a disorder in which the core deficit involves reading. Traditionally, DD is thought to be associated with a phonological impairment. However, recent evidence has begun to suggest that the reading impairment in some individuals is provoked by a visual processing deficit. In this paper, we present WISC‐IV data from more than 300 Italian children with a diagnosis of DD to investigate the manifestation of phonological and visual subtypes. Our results indicate the existence of two clusters of children with DD. In one cluster, the deficit was more pronounced in the phonological component, while both clusters were impaired in visual processing. These data indicate that DD may be an umbrella term that encompasses different profiles. From a theoretical perspective, our results demonstrate that dyslexia cannot be explained in terms of an isolated phonological deficit alone; visual impairment plays a crucial role. Moreover, general rather than specific accounts of DD are discussed

Benchmarking of Methods for the Identification of Flexural Wavenumbers in Wooden Plates

laminated wood panels. Laboratory measurements are performed on a plywood panel, an inhomogeneous and orthotropic plate, and the propagation characteristics of flexural waves are characterized along five radial directions. The methods considered for the analysis are the inhomogeneous wave correlation method, the Prony method and the Time-of-Flight (ToF) method. The first two methods are implemented using the same data: a dense line of points obtained with a scanning Laser Doppler Vibrometer (LDV) and a piezoelectric transducer as an exciter. The ToF method uses a different data set, gathered using four accelerometers and an instrumented impact hammer. The results show a remarkable match between the first two methods, while the third method requires a precise time-domain filtering operation to provide accurate results. Nevertheless, the third method provides a simple and low-cost alternative to the use of the LDV that can be more suited to in situ measurements. The accuracy limits of each method, especially in terms of targeted frequency bandwidth are discussed