Milling/routing of carbon fibre reinforced plastic (CFRP) composites

The research relates to a study on the routing/slotting of CFRP composites of the type used in aerospace applications. Following a literature review, 3 phases of experimental work were undertaken to evaluate the effects of key process variables on the machinability of CFRP. The influence of varying operating parameters, tool material and cutting environment were initially investigated in Phase 1 work. The results showed that use of PCD was critical and highlighted the importance of chilled air in maintaining adequate tool life and acceptable workpiece integrity. Delivery of chilled air through a single-nozzle arrangement generally led to an increase in forces and delamination with the twin-nozzle configuration showing superior workpiece surface roughness. Phase 2 work detailed the effect of workpiece lay-up configuration on cutting forces, temperature and surface integrity following slotting and routing. Plies in the 45 direction generally exhibited the highest level of surface damage following machining. Experiments in Phase 3 showed that relatively small helix angles (± 3) had a negligible effect on tool life, forces and temperature. In addition, cutters with a single relief angle were found to have lower stability in operation compared to tools with a secondary clearance angle, with detrimental effects on surface roughness

Machining of Carbon Fibre: Optical Surface Damage Characterisation and Tool Wear Study

Better control of fibre composites machining requires reliable surface roughness and damage characterisation measurements. The performance and tool wear rate of three different state of the art CVD and PCD cutting tools manufactured for carbon fibre machining were compared in wet and dry conditions. Machined surfaces were characterised by areal surface roughness parameters using a novel focus variation optical system. The tool wear and cutting forces were recorded up to 50 linear meters of machining or until tool failure. Results showed that wet machining conditions reduced tool failure; and that the CVD tool in wet conditions machined the greatest distance of 26m before reaching an average roughness limit of 3μm. The tool type was found to be the most significant parameter on the surface quality. The optical system was found to be a useful tool for measuring roughness of individual plies and characterising machining induced surface damage

The evolution of cutting forces during slot milling of unidirectional carbon fiber reinforced polymer (UD-CFRP) composites

Cutting forces generated during traditional machining of fiber reinforced polymer composites play an important role in determining machined surface quality. The cutting force signals also provide a live indicator of the dynamic behavior of the chip formation process. Cutting forces in machining FRPs are dependent primarily on the instantaneous fiber cutting angle, chip thickness, cutting edge geometry and the current state of cutting edge wear. In this study, effects of the cutting edge rake angle and tool wear on cutting force evolution during slot milling of unidirectional carbon fiber reinforced polymer (UD-CFRP) composite was investigated. The cutting forces were measured in the feed and normal directions and then transformed to the tangential and radial directions of the tool path. A simplified cutting force model consisting of a shearing region and a pressing was used to determine the shearing and friction force components. This allowed determination of the friction coefficient on the clearance face of the tool. It was found that the friction coefficient varied significantly with rake angle and fiber cutting angle. The effect of rake angle on cutting forces is more discernable in the shearing region with positive rake angle tool providing the most efficient cutting. Furthermore, correlations were found between machining damage and the magnitude and orientation of the resultant shearing force

Abrasive water jet machining of multidirectional CFRP laminates

Abrasive water jet machining (AWJM) is widely used in aerospace, marine and automotive industries for trimming composites. However, AWJM demonstrates some challenges when cutting carbon fibre reinforced plastic (CFRP) composites materials such as cut accuracy and quality. More experimental work is needed to provide sufficient machinability databases for manufacturing engineers. This paper presents an experimental study and statistical analysis for cutting 2 lay-up configurations of multidirectional CFRP laminates. Different AWJM conditions including jet pressure, feed rate, and standoff distance are experimented using full factorial design of experiments. Machining process responses such as top and bottom kerf width, kerf taper, machinability and surface characteristics have been evaluated using analysis of variance (ANOVA) technique. A process cost model for the AWJM is presented

Characterization of Enterococci- and ESBL-Producing Escherichia coli Isolated from Milk of Bovides with Mastitis in Egypt

This study aimed to investigate the prevalence and antimicrobial resistance of enterococci- and ESBL-producing E. coli isolated from milk of bovine mastitis cases in Egypt. Fifty milk samples of dairy animals were collected from localities in the Nile Delta region of Egypt. Isolates were identified using MALDI-TOF MS, and antibiotic susceptibility testing was performed by the broth microdilution method. PCR amplifications were carried out, targeting resistance-associated genes. Seventeen Enterococcus isolates and eight coliform isolates could be cultivated. Vancomycin resistance rate was high in Ent. faecalis. The VITEK 2 system confirmed all E. coli isolates as ESBL-producing. All Ent. faecalis isolates harbored erm(B), tetL and aac-aphD genes. The vanA gene was detected in Ent. faecalis isolate, vanB was found in other Enterococcus, while one isolate of E. casseliflavus exhibited the vanA gene. E. coli isolates exhibited high prevalence of erm(B) and tetL. E. coli isolates were analyzed by DNA microarray analysis. Four isolates were determined by O-serotyping as O8 (n = 1), O86 (n = 2) and O157 (n = 1). H-serotyping resulted in H11, H12, H21 (two isolates each) and one was of H16 type. Different virulence-associated genes were detected in E. coli isolates including lpfA, astA, celB, cmahemL, intI1 and intI2, and the iroN gene was identified by DNA microarray analysis

LISTERIA MONOCYTOGENESIN RAW MILK AND DAIRY PRODUCTS;OCCURRENCE AND TRIALS FOR THEREDUCTION OF THEIR RESISTANCE TO ANTIBIOTICS.

Listeria monocytogenes is a facultative intracellular pathogen responsible for severe infection in animals and humans. This study aimed to determine the occurrence of Listeriamonocytogenes in 200 samples of raw milk and dairy products marketed in Egypt, with detection the antimicrobial resistance profiles of the isolates for different antimicrobial agents. The synergistic effects of three plant extracts in combination with the used antimicrobials to control resistant L. monocytogenes isolates were assessed, with evaluation of relationship between the antibacterial activity and composition of plant extracts. A total of 5 (2.5%) L. monocytogenes isolates were identified (3 isolates from raw milk and two isolates from kariesh cheese and ice cream, one each). The isolates were sensitive to ciprofloxacin and sulphadimidine, while for amoxicillin and oxytetracycline, were resistant. The higher antimicrobial effects of basil and cinnamon extracts were detected, in addition, low concentrations of them were enough to show synergistic effect with the amoxicillin and oxytetracycline to control resistant isolates, these might be attributable to their chemical compositions. In conclusion, there is need for effectively pasteurized raw milk consumption or usage in the production of dairy products. In addition, the chemical composition of these plant extracts might help in its use to control resistant isolates with appropriate antibiotics without the need for increasing the used dosage doses

Characterization of Staphylococci and Streptococci Isolated from Milk of Bovides with Mastitis in Egypt

The aim of this study was to characterize staphylococci and streptococci in milk from Egyptian bovides. In total, 50 milk samples were collected from localities in the Nile Delta region of Egypt. Isolates were cultivated, identified using matrix-assisted laser desorption/ionization time-offlight mass spectrometry (MALDI-TOF MS), and antibiotic susceptibility testing was performed by the broth microdilution method. PCR amplifications were carried out, targeting resistanceassociated genes. Thirty-eight Staphylococcus isolates and six Streptococcus isolates could be cultivated. Staphylococcus aureus isolates revealed a high resistance rate to penicillin, ampicillin, clindamycin, and erythromycin. The mecA gene defining methicillin-resistant Staphylococcus aureus, erm(C) and aac-aphD genes was found in 87.5% of each. Coagulase-negative staphylococci showed a high prevalence of mecA, blaZ and tetK genes. Other resistance-associated genes were found. All Streptococcus dysgalactiae isolates carried blaZ, erm(A), erm(B), erm(C) and lnuA genes, while Streptococcus suis harbored erm(C), aphA-3, tetL and tetM genes, additionally. In Streptococcus gallolyticus, most of these genes were found. The Streptococcus agalactiae isolate harbored blaZ, erm(B), erm(C), lnuA, tetK, tetL and tetM genes. Streptococcus agalactiae isolate was analyzed by DNA microarray analysis. It was determined as sequence type 14, belonging to clonal complex 19 and represented capsule type VI. Pilus and cell wall protein genes, pavA, cadD and emrB/qacA genes were identified by microarray analysis. © 2020 by the authors

Current limiting and negative differential resistance in indium oxide based ceramics

Indium oxide based ceramics with bismuth oxide addition were sintered in air in the temperature range 800-1300 ºC. Current-voltage characteristics of In2O3-Bi2O3 ceramics sintered at different temperatures are weakly nonlinear. After an additional heat treatment in air at about 200 ºC samples sintered at a temperature within the narrow range of about 1050-1100 ºC exhibit a current-limiting effect accompanied by low-frequency current oscillations. It is shown that the observed electrical properties are controlled by the grain-boundary barriers and the heat treatment in air at 200 ºC leads to the decrease in the barrier height. Electrical measurements, scanning electron microscopy and X-ray photoelectron spectroscopy results suggest that the current-limiting effect observed in In2O3-Bi2O3 may be explained in terms of a modified barrier model; the observed current-limiting effect is the result of an increase of barrier height with increasing electric field, due to additional oxygen absorption. It is found that In2O3-Bi2O3-Co3O4-Cr2O3 ceramic exhibits current-voltage characteristics with negative differential resistance due to Joule micro heating.This study was performed in part in the frames of the project SEP-2003-C02-42821, CONACYT, México. Funding from the Royal Society, United Kingdom (2007R1/R26999) is gratefully acknowledged

Investigations of geometrical structure and morphology of samples made of hard machinable materials after wire electrical discharge machining and vibro‐abrasive finishing

In this article the results concerned influence of processing conditions of the wire electrical discharge machining and vibro‐abrasive machining on the surface layer and morphology of samples made of hard machinable materials used in aircraft industry like: Titanium 5553 β, Inconel 617, Hastelloy X and Magnesium AZ31 have been presented. For this purpose the cubic and cylindrical samples made of hard machinable alloys have been prepared using optimal electric parameters of wire‐cut electrical discharge machining and finally they have been polished using circular vibratory finishing technology and different ceramic shaped stones.ENSAM (professeur invité