Do high frequency acoustic emission events always represent fibre failure in CFRP laminates?

© 2017 Elsevier Ltd When damage in carbon fibre reinforced composites (CFRP) is monitored by acoustic emission (AE), it is a common belief that high frequency AE events originate from fibre failure. This shows that this statement may not correspond to the reality, and matrix cracks can emit high frequency AE signals. Quasi-static tension of [−45 2 /0 2 /+45 2 /90 2 ] s laminates was monitored by AE, Digital Image Correlation (DIC) on the surface of the sample and in-situ optical microscopy on the sample's polished edge. Unsupervised k-means clustering algorithm was applied to the AE results. By comparison with the direct DIC and microscopic observations, the AE cluster with high frequency and low amplitude was found to correspond to directly observed matrix cracks

Urgent applications in French administrative justice

The institute of urgent judicial decisions is a special procedure for administrative justice bodies in France, which allows to prescribe effectively and quickly a wide range of necessary measures (from the appointment of expert examinations to the suspension of normative administrative acts) and to protect the legitimate interests of individuals and organizations. There are two main categories of urgent judicial decisions, accordingly their functional purpose. The procedural features of urgent judicial decisions are related to the obligation of the French administrative courts to establish conditions for urgency and the need to prescribe certain measures as a matter of urgency. These criteria, being evaluative, are specified by the jurisprudence of the French administrative courts, according to which the judge determines whether there is a threat of causing immediate and sufficiently serious harm to the interests of the applicant and whether there is a need to take urgent measures, taking into account the circumstances of the case. At the same time, the urgent applications judge does not consider the case, but sets temporary measures that can be changed in the course of further proceedings. The article suggests creating mechanisms in Russian law that are similar to those existing in the French legal regulation of urgent judicial decisions in administrative cases. In particular, the author suggests expanding the powers of Russian courts to suspend normative administrative acts and individual decisions when courts take measures of preliminary protection in administrative claims

Multi-instrument in-situ damage monitoring in quasi-isotropic CFRP laminates under tension

© 2018 Digital Image Correlation monitoring of the surface strains, microscopic in-situ observations of the micro-damage on the specimen edge and Acoustic Emission (AE) are utilized simultaneously during tension tests of quasi-isotropic carbon fibre reinforced polymer composites. It is found that the cluster analysis for characteristic parameters of AE events (the main being the signal amplitude and frequency) does not unambiguously identify the type of damage which causes the event. With optical instruments, it is observed that the signatures of AE events depend on the position of the ply where damage happens and on the ply orientation (90° vs 45°). Robust evidences for the variations in AE characteristics of damage modes in different lay-ups are presented. AE events, originated from surface cracks, have high amplitude and low frequency, whereas AE events, originated from transverse cracks in the inner plies, have low amplitude and high frequency characteristics. Any conclusion for fibre breaks are not reached in this study. Therefore, measurements in this study rather point out that the AE events, which could be interpreted as fibre breaks because of their high frequency characteristics, as optical observations prove, correspond to other damage types in quasi-isotropic laminates

Multilevel modelling of mechanical properties of textile composites: ITOOL Project

The paper presents an overview of the multi-level modelling of textile composites in the ITOOL project, focusing on the models of textile reinforcements, which serve as a basis for micromechanical models of textile composites on the unit cell level. The modelling is performed using finite element analysis (FEA) or approximate methods (method of inclusions), which provide local stiffness and damage information to FEA of composite part on the macro-level