Inconel 718 (IN718) is a precipitation hardened nickel-base super-alloy exhibiting high strength and good corrosion resistance at elevated temperatures and on the downside; it is characterized by ...poor machinability. Abrasive water jet (AWJ) process offers a potential method to machining difficult-to-cut materials such as IN718. The present work investigates the influence of AWJ parameters on surface roughness, topography, depth of cut, and residual stress when milling IN718. Surface characterization was conducted through 3D optical microscopy and SEM techniques. Residual stresses were measured in longitudinal and transverse directions with respect to the machining path using X-ray diffraction (XRD) technique. The obtained results showed that milled surfaces have a homogeneous texture with embedded abrasive particles and high surface roughness. AWJ process introduced high compressive residual stresses with similar order of level in both directions (
X
and
Y
). In addition, it was observed that jet pressure is the most influencing parameter on roughness and depth of cut, whilst traverse speed and step-over distance had a significant effect on the residual stress. Based on the experimental analysis, an empirical model to predict the depth of cut was proposed. The validation of the proposed model has shown around 5% error in the predicted and actual pocket depth.
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Conventional milling during aircraft structural composite repair encourages defect generation and distortion, causing hindrance in milling depth control and thereby adversely affecting their ...mechanical behavior. Abrasive water jet (AWJ) milling can be an alternative to avoid these problems. In this study, carbon/epoxy laminates are milled using AWJ and machined surfaces are characterized at micro (surface texture) and macro (damage size) scales. Defects in the form of craters, ridges-valleys and broken fibers are identified and quantified. A new parameter “crater volume (Cv)” is proposed to quantify and qualify the machining quality in terms of induced damage. This introduces a novel approach to characterize the machined surface without ignoring the machining damage. Milled specimens with different damage levels are subjected to tensile and tension-tension fatigue tests instrumented with thermography and acoustic-emission transducers. Machined specimens with high Cv exhibited inferior fatigue behavior and X-ray tomography revealed that crack/fracture initiation occurred from the crater edges.
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Comparison of the performance of conventional drilling (CD) and fiber laser machining (FLM) of unidirectional (UD) and multidirectional (MD) glass (G) and carbon (C) fiber reinforced plastics (FRPs) ...has been presented with an emphasis on machining damage characterization. FLM induced damages are heat affected zone (HAZ), matrix recession, kerf width, and tapered cut whereas CD induced damage include fiber pull-outs, fuzzing, spalling, matrix cracking and delamination. Scanning Acoustic Microscopy (SAM) proved a useful technique to quantify machining damage by providing a ply-by-ply damage analysis. In addition, Scanning Electron Microscopy (SEM) provided detailed views of inherent damage mechanisms during FLM and CD. Machining damage investigation reveals a strong dependence on anisotropy of the composite laminate with greatest matrix recession occurring for UD-CFRP laminates. FLM was found to be efficient with decreased machining times and less set-up requirements. However, surface characteristics of CD specimens were found to be superior to FLM specimens.
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This work investigates the impact response, associated damage, the feasibility of repair and strength recovery of infusible thermoplastic based carbon fibre reinforced composites. Impact behaviour of ...the laminates is studied using drop tower impact tests at three energy levels i.e. 40 J, 30 J and 20 J resulting in delamination as the primary damage mode at lower energy levels with evidence of fibre breakage at 40 J. Repair is performed by thermally re-consolidating impact damaged specimens under vacuum at a temperature above the glass transition temperature of the matrix. X-ray micro computed tomography (CT) scans and ultrasonic C-Scans reveal significant post repair re-consolidation. Compression testing using compression after impact (CAI) fixture resulted in a retained strength of 78 %, 88 %, and 93 % for impacts at 40 J, 30 J, and 20 J respectively. Post-repair compression strength using CAI tests, recovered 85 % of the pristine strength for 40 J impacts and close to 100 % of pristine strength for both 30 J and 20 J impacts. Thermography during CAI testing revealed a difference in the location of damage initiation under compressive loading for impacted and repaired specimens. The overall results highlight the potential for effective on-site repair and strength recovery using a relatively simple thermal re-consolidation procedure.
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Controlled depth milling of composites structures by abrasive water jet (AWJ) is a new area of machining being explored and knowledge on this is bare minimum. Hence it is essential to investigate ...surface quality and damage induced to ascertain their mechanical reliability. Here, the mechanism of material removal is manifested by erosive wear. In this study, carbon fiber reinforced plastic (CFRP) laminates are milled using AWJ process and surfaces generated by varying process parameters are characterized using roughness systems, X-ray tomography and scanning electron microscopy (SEM). SEM images reveal presence of damages in form of craters, ridges, broken fibers and embedded abrasive particles. Crater formation due to erosion phenomenon is affected by jet pressure. It is seen that the crater volume increases by around 500% when pressure varies from 80MPa to 140MPa. In the literature reviewed correlation between roughness of the machined surface and the mechanical behavior is ambiguous and remains an open problem. Hence, novel attempt has been made to analyze the influence of damage (crater volume) on tensile strength. Mechanical tests on specimens with varying surface texture and crater sizes reveals that tensile strength of machined specimens is more influenced by crater volume rather than surface roughness.
•First work on influence of abrasive water jet CFRP milling on mechanical behavior.•High jet pressure milling increases broken fibers which increase surface roughness.•Craters, broken fibers, ridges, debonding and grit embedment are major damages.•Quantified damage a better indicator of mechanical behavior than surface roughness.•Crater is the most influential damage form which depreciates the tensile strength.
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Conventional machining of carbon fiber reinforced plastic composites (CFRPs) generates minute chips that get suspended in air causing a hazard compromising operator safety. This study investigates ...the influence of cutting parameters (feed speed, cutting speed, radial depth of cut, tool geometry and tool wear) during trimming of CFRP on the form and quantity of harmful particles dispersed. Also, performance of two classical PCD tool geometries (two straight flutes, two helix flutes) have been compared with newly designed (in collaboration with ASAHI Company) four serrated straight flutes for the purpose of dust emission reduction. The quantification of the number of harmful particles was estimated using laser spectroscopic dust monitor. The results reveal that, trimming with a combination of higher feed speed and lower cutting speed can reduce the dispersion of harmful particles. Further, the four serrated straight flutes recorded the least number of harmful particles compared to the conventional tools.
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Drilling Technology Davim, J. Paulo; Astakhov, Viktor P; Patel, Swapnil ...
2018, 2018-10-22, Volume:
3
eBook
This book aims to provide recent information on advances in drilling technology. The use of advanced machines, appropriate strategies and special drilling tools can signifi cantly reduce the ...machining time required for drilling operations, and consequently the production costs, and improve the quality of the holes produced. For these reasons an improvement of the drilling technology is very important for the modern manufacturing industries. This book can be used as a research book for fi nal undergraduate engineering course or at postgraduate level. It can also serve as a useful reference for academics, researchers, mechanical, industrial, production, manufacturing and materials engineers, professionals in drilling technology and related matters.
Abstract This study evaluates various quasi‐static mechanical properties of an in‐situ polymerizable thermoplastic and a bio‐based thermosetting composite comprising of non‐crimp fabric reinforcement ...for potential use in the next generation of Offshore Wind and Tidal Power platforms. Mechanical properties are characterized under tensile, flexural, in‐plane shear and interlaminar shear loading. Results reveal that the evaluated properties differ based upon matrix type. Fractographic evidence from scanning electron microscopy is used to explain the differences observed and was generally consistent in terms of revealing cohesive failure at the fiber‐matrix interface for the thermoplastic composite and contrasting adhesive failure for the thermosetting composite. For glass fiber reinforcement, the thermoplastic composite is superior in terms of flexural 90° properties (+20%) while the thermosetting composite performed better in flexure 0° in terms of both strength (+15%) and modulus (+25%). In terms of interlaminar shear, the thermosetting composite exhibited higher strength (+14%) while Tensile and in‐plane shear properties are similar for composites of both resin systems. Overall, neither composite is superior in terms of overall mechanical properties and both matrices show promise as a stepping stone towards the use of more sustainable constituents in offshore structures. Highlights Quasi‐static mechanical performance and failure analysis of relatively sustainable composites are presented. Failure analysis indicate cohesive failure of the thermoplastic based composite and interfacial failure of the thermosetting based composite. Proposed composites are benchmarked against the composites manufactured using conventional resins. Overall, both matrices show promise as a stepping stone towards more sustainable offshore structures.
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Abstract This experimental work involves characterization and fractography of a bio‐based epoxy and an in‐situ polymerisable thermoplastic polymer matrix based non‐crimp glass and carbon fiber ...composites under compressive loading. The laminates are characterized under compression loading using a combined loading compression (CLC) fixture. Laminates made using the thermoplastic matrix exhibit higher compressive strength (approx. 20% along fiber direction) compared to the bio‐epoxy based laminates. Further, both composites exhibit comparable compressive modulus characteristics. The tested composites are subjected to fractography analysis using Scanning Electron Microscopy (SEM) and Computed tomography (CT). SEM results indicate a difference in fiber‐matrix interface characteristics between the thermoplastic matrix and the bio‐epoxy matrix. Additionally, the CT scans reveal a difference in failure modes due to fiber orientations. A difference between failure mode of the exterior and interior plies of the specimens was also noticed. However, no specific influence of matrix type was observed on the overall macroscopic failure behavior. Highlights Bio‐epoxy and thermoplastic based laminates were characterized in compression. Post‐test fractography was performed using SEM and x‐ray CT scans. Use of thermoplastic matrix exhibits better fiber‐matrix adhesion compared to bio‐epoxy. Both laminates performed well in compression under laboratory test conditions.
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Abrasive water jet (AWJ) milling process, though being an effective alternative to conventional machining for difficult-to-machine materials, induces abrasive embedment which is an issue for repair ...application by structural bonding. In this context, the effectiveness of cleaning Ti6Al4V specimens by Plain Water Jet (PWJ) post AWJ milling is studied. For this, Ti6Al4V specimens are milled by AWJ process with varying parameters to create several levels of surface quality and contamination. Different characterization techniques have been used to perform a multi-scale analysis of the machined surfaces and surface quality has been quantified by an innovative criterion called “crater volume” (Cv). Then the specimens are subjected to PWJ cleaning operation (using a single set of parameters chosen after preliminary study). Finally, surface texture analysis and contamination quantification is performed and compared with the AWJ milled surfaces. The results revealed that PWJ cleaning reduced the surface contamination by 65% without any significant change in Cv, surface texture and topology. However, it was found that it was impossible to dislodge deeply embedded particles. The comparison of pre and post-cleaning contamination levels also revealed that PWJ cleaning process efficiency depends on the AWJ milling parameters (mainly pressure).
•Crater volume (Cv) well describes abrasive waterjet (AWJ) milling quality of TA6V.•Plain waterjet (PWJ) cleaning of Ti6Al4V reduces abrasive contamination by 65%.•The effectiveness of PWJ cleaning depends on the AWJ milling parameters.•PWJ cleaning does not lead to any significant change in Cv and topology.
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