The goal of this study is to investigate the influence of Abrasive Water Jet (AWJ) parameters (standoff distance, water pressure and abrasive flow rate) on the machining quality (diameter, circularity, abrasive contamination, surface roughness and types of damage) during drilling of thick hybrid material viz. GLARE (Glass Laminate Aluminium Reinforced Epoxy) Fibre Metal Laminates (FML). The novelty of this work is the use of X-ray tomography and image post-processing for the quantification of abrasive contamination in function of the machining parameters. Moreover, the indicator called 'power of erosion' (E), depending on the AWJ drilling parameters chosen, has permitted to estimate a threshold below which no delamination is found. The results have shown that oversized holes (up to 6.2 mm in diameter) were produced under all cutting parameters regardless of their level. Increasing the standoff distance increased the hole size and cylindricity. The main types of damage consecutive AWJ drilling are in form of barrelling at plies level and delamination with embedded particles. For 'power of erosion' (E) values below 0.17, no delamination is found. As increasing this indicator further, delamination occurs in-between plies closer to the jet entry and more contamination is observed (up to 4 % of the total scanned surface). The surface roughness was found to be in a similar range to that reported in conventional drilling studies of GLARE (<6 μm), which suggests that AWJC could provide a similar machining performance suitable for aerospace applications.
In this paper, high speed trimming of a multidirectional CFRP using unused and used burr tools is considered in order to investigate the influence of the machining parameters (e.g., feed speed, cutting speed and cutting distance) on the cutting forces, machining temperature, and the machined surface quality. To estimate the effect of the tools' wear and cutting parameters on the cutting forces and surface roughness, a statistical method (ANOVA) has been used. When considering an unused tool, the recorded temperatures were below the glass transition temperature of the composite material (Tg). In the case of used tools, these temperatures were mostly higher than the Tg. Furthermore, SEM observations of the machined surface showed damaged areas. These areas were wider when the cutting distance increased. Statistical analyses have shown that the machining parameters have a significant influence on the variation of the machined surface quality and the cutting forces.
In recent days, automobile and construction industries are focus on the light weight, environmental friendly materials with good mechanical properties. Glass fiber reinforced composites have excellent specific properties and are widely used because of reduced mass. However the manufacturing of glass fibers and end of life disposal are the major problem to the environment. To overcome these problems, natural fibers are used to manufacture composites. Flax is the one of the naturally available fiber having good mechanical properties than other natural fibers. It needs to be pointed out that most of research effort about the flax fiber reinforced composites focuses on the manufacturing techniques and primary mechanical properties and not on the secondary properties like sound absorption and vibration damping. In this paper, sound absorption and vibration damping properties of flax fiber reinforced composites were characterized and compared with the glass fiber reinforced composites. It was experimentally observed that the sound absorption coefficient of flax fiber reinforced composites has 21.42% & 25% higher than that of glass fiber reinforced composites at higher frequency level (2000 Hz) and lower frequency level (100 Hz). From the vibration study it was observed that the flax fiber reinforced composites have 51.03% higher vibration damping than the glass fiber reinforced composites. The specific flexural strength and specific flexural modulus for flax fiber reinforced composites also good. These results suggest that the flax fiber reinforced composites could be a viable candidate for applications which need good sound and vibration properties.
Inconel 718 (IN718) is a precipitation hardened nickel-base super-alloy exhibiting poor machinability and used in the hot section of aircraft engines. These components are subjected to severe thermo-mechanical loads in a highly corrosive environment, limiting their service life due to cracks and wear. Due to their high added-value, repair of damaged IN718 components is an interesting alternative instead their replacement. Repair process involves material removal of the damaged zone and subsequent cavity refill. Nevertheless, material removal of IN718 by conventional methods is a challenging task. Abrasive Water Jet (AWJ), a non-conventional machining process, offers a potential alternative to mitigate IN718 machining problems. However, research on the impact of AWJ process parameters during IN718 milling on the surface and material integrity is limited in the literature. Furthermore, in repair context, no study proposes AWJ machining as material removal process. The present work focuses on a multi-scale characterization of the influence of AWJ process parameters (pressure, traverse speed, step-over distance and abrasive size) on surface roughness, depth of cut, abrasive embedment and residual stress, during milling of untreated IN718. Surface integrity characterization on the milled surfaces was conducted through 3D optical microscopy, profilometry and SEM techniques. Residual stress measurements were performed in longitudinal and transverse directions with respect to the machining path using XRD technique. The results showed that all milled surfaces presented abrasive embedment and a compressive residual stress state with similar values in both directions. Up to 15% of the area of a milled surface consisted of abrasive embedment. The tool path has not influenced the residual stresses. Furthermore, surface roughness is dependent on pressure and traverse speed; depth of cut is influenced by pressure, traverse speed and grit size; abrasive embedment depends on pressure, step-over distance and grit size; whilst, residual stresses are influenced by traverse speed and grit size.
Une eprouvette technologique en materiau composite dotee d'une instrumentation a coeur par fibre optique a reseaux de Bragg (RB) est soumise a des essais de flexion 3 et 4 point afin d'analyser le materiau au sein de la structure. L'eprouvette de type poutre presente une zone centrale renforcee. Les RB sont integres et repartis dans l'epaisseur de cette zone pour estimer la distribution des deformations lors des sollicitations. Des champs de deformation obtenus par correlation d'images numeriques delivrent des informations en surface. Les deux techniques de mesure montrent que la distribution est globalement lineaire. Un dialogue essai-calcul est etabli dans le cadre de l'essai de flexion 4 points. Les modules de traction et de compression sont ajustes. Le modele et les parametres adjoints sont exploites pour la sollicitation en flexion 3 points. Une bonne correlation avec les valeurs experimentales est observee a l'echelle des efforts.
This work is part of an ongoing research on the development of a bio-based material for use as an orthopedic long bone fracture plate. Specifically, the overall research effort aims at examining flax/epoxy composites as a potential material for fractured femur bone implants. The mechanical properties of unidirectional flax fiber reinforced epoxy composites manufactured under different processing conditions are investigated. Two different processes namely, Compression molding and Autoclave, were used to manufacture composites under different pressure and cure cycle temperatures and the mechanical properties obtained by both processes were compared. The longitudinal elastic modulus of the composite specimens did not change with the manufacturing condition and the value of elastic modulus was 25 GPa. However, composites cured at 110 degrees C showed a lower ultimate tensile strength of 275 MPa and their stress/strain plots exhibited a nonlinear behavior compared to composites cured at 150 degrees C which exhibited linear behavior and higher ultimate tensile strength (307 MPa). The difference is due to the presence of defects (porosities) in the composites cured at 110 degrees C and to the lower crosslink density of the epoxy resin. A similar behavior was observed for the bending properties. Furthermore, we investigated the influence of water absorption on the mechanical behavior of these composites. For all composite plates, the water uptake affected severely the composite's stiffness and reduced it from 25 GPa to 11 GPa, however the strength remained unchanged for all composites. The shear property of the composites was the most affected by the processing conditions since it is a matrix and interface dominant property. The autoclave process produced composites with the highest shear modulus (2 GPa). This shear modulus was decreased by 60% due to the water uptake.
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