Machinability And Surface Quality Of Hybrid Composite CFRP/Al2024

oai:myjas.www.journal.unisza.edu.my:article/1The use of hybrid composite has increased due to their special mechanical and physical properties. However, machining of composite materials is extremely difficult due to non-homogeneous, anisotropic and highly abrasive characteristics. The performance of machined surface quality of CFRP/Al2024 was described using two level full factorial methodology. Trimming test was performed under dry conditions using 6mm diameter of burr tools end mills. The factors investigated were spindle speed(N), feed rate(fr) and depth of cut(dc), furthermore Ra CFRP and Ra Al2024 were the response variables. This work aims to minimize the machined surface quality of CFRP/Al2024 between 1μm to 2μm. The finding of this empirical study has shown that, the best estimated value of fr should be 500 mm/min to 530 mm/min, N is between and 2313.870 rpm to 2336.042 rpm. For both response spindle speed is the most significant effect followed by Feed rate and Depth of Cut

Splitting Arabic Texts into Elementary Discourse Units

International audienceIn this article, we propose the first work that investigates the feasibility of Arabic discourse segmentation into elementary discourse units within the segmented discourse representation theory framework. We first describe our annotation scheme that defines a set of principles to guide the segmentation process. Two corpora have been annotated according to this scheme: elementary school textbooks and newspaper documents extracted from the syntactically annotated Arabic Treebank. Then, we propose a multiclass supervised learning approach that predicts nested units. Our approach uses a combination of punctuation, morphological, lexical, and shallow syntactic features. We investigate how each feature contributes to the learning process. We show that an extensive morphological analysis is crucial to achieve good results in both corpora. In addition, we show that adding chunks does not boost the performance of our system

Evaluation of the performance of coated and uncoated carbide tools in drilling thick CFRP/aluminium alloy stacks

This paper aims to establish the wear mechanisms of coated and uncoated tungsten carbide drills when drilling carbon fibre reinforced plastics (CFRP)/aluminium alloy (Al) stacks. During the drilling experiments, thrust forces were measured. A scanning electron microscope (SEM) and a numerical microscope, provided with a scanning device, were periodically used to analyse tool wear mechanisms and to measure wear progression of the tool cutting edges. For both coated and uncoated drills, abrasion was the dominant tool wear mechanism, affecting the entire cutting edges. Higher wear was observed on uncoated tools which caused a significant increase in thrust force during drilling both Al and CFRP materials. The influence of these phenomena on the quality of the holes and on the generated roughness was also discussed.FUI-Usinage de Multi-Matériaux et Innovation (U2MI

Experimental study on thermal and morphological analyses of green composite sandwich made of flax and agglomerated cork

International audienceThe building sector has been showing great interest in incorporating technologically advanced materials with lightweight, ecofriendly, high strength, and stiffness properties in flooring, roofing, and partition walls, etc. In addition to the mechanical properties, these materials should have good thermal properties as well. In response to these requirements, an attempt has been made to study the thermal behavior of green composite sandwich made of flax and agglomerated cork. Composite sandwiches were fabricated by using flax as skin reinforcement and agglomerated cork as core with different densities as 240, 280, and 340 kg m−3 using vacuum bagging method. Glass was also used as skin reinforcement for manufacturing composite sandwiches for comparison purpose. Experiments were conducted to predict thermal properties, viz. thermal conductivity, thermal expansion, flammability, and thermal stability. The experimental results show that the lowest thermal conductivity of 0.03 W m−1 K−1 was observed in flax-based composite sandwich having core density of 240 kg m−3; the lowest thermal expansion of 29.2 × 10−5 °C−1 was observed in glass-based composite sandwich having core density of 340 kg m−3; the highest value of time to ignition was 12 s, and minimum propagation rate was 0.25 mm s−1 in flax-based composite sandwich having core density of 340 kg m−3; The highest initial degradation temperature was 362 °C for glass-based skin and 263 °C for cork having density of 240 kg m−3

Compressive behaviour of concrete elements confined with GFRP-prefabricated bonded shells

International audienceIn this paper, a new technique is proposed to confine concrete columns using GFRP-prefabricated bonded shells and a shrinkage-compensating cement mortar. The confinement is performed with three identical shells, each of which contains two stepped lap joints at their ends. The main advantage of this technique is that the shells can be directly assembled on site by structural bonding to cover any column shape. The gap between the shells and the column is filled with shrinkage-compensating cement mortar. To evaluate the efficiency of this technique, several concrete specimens were confined, instrumented and tested under monotonic compression. To simulate the actual strengthening conditions, the load was directly applied on the concrete cross-section. The results show clearly the benefits of an efficient confinement in terms of a noticeable increase in the axial strength and ductility where the stress\textendashstrain curves are characterised by a third softening phase and the failure mode which spread over the whole length of the shells

Experimental and numerical investigations of the damages induced while drilling flax/epoxy composite

International audienceThe influence of the drilling parameters and the stacking sequence of flax/epoxy composite laminate on the cutting force and the damage induced were studied experimentally and numerically. Drilling tests were carried out based on full experimental design and the delamination at the entry and exit of the hole were quantified using an optical microscopy. Moreover, the damages at the wall of the hole were analyzed using scanning electron microscopy. Based on the experimental results, it was observed that the drilling forces and the machining quality are influenced on the one side by the spindle speed and feed and on the other side by the stacking sequence composite plate. In fact, the cutting forces recorded when drilling a composite plate with [90/0/90/0] 2s is 30% higher to the one recorded when drilling a composite made with quasi-isotropic stacking sequence. A numerical model was developed in ABAQUS/Explicit using Hashin’s failure criteria in order to predict the cutting forces and the defects induced by the interaction of the drill and composite as a function of the machining parameters. The developed model has been validated at the macro-scale (thrust force) and the meso-scale (delamination at the entry and exit of the hole)