Cr2O3 and TiO2 powders were deposited by atmospheric plasma spray (APS) on steel substrates. Microstructural analysis of the coatings showed typical lamellar structure with good coating quality. ...Fatigue strength was studied by using cyclic testing (measuring with an inhouse-built apparatus the strength of the coated systems under a wide range of impact cycles) and static loading tests (Vickers tests standards with 600N and 1500N) measuring the adhesion properties of the coatings. In low cycles (1x10
3
) Titania coatings exhibited better strength, while at intermediate (4.5x10
5
) and high (1x10
6
) number of impact cycles, both Chromia and Titania coatings exhibited quite similar strength characteristics. At low impact force the thickness of the coatings plays critical role with better performance obtained by Chromia coatings. During static loading both coatings exhibited similar characteristics at the crater diameter but with larger crater depth for Titania. Chromia coatings exhibited higher strength resistance than Titania coatings with better mechanical properties and coating structure.
Machinability of engineering materials is crucial for industrial manufacturing processes since it affects all the essential aspects involved, e.g. workload, resources, surface integrity and part ...quality. Two basic machinability parameters are the surface roughness, closely associated with the functional and tribological performance of components, and the cutting forces acting on the tool. Knowledge of the cutting forces is needed for estimation of power requirements and for the design of machine tool elements, tool-holders and fixtures, adequately rigid and free from vibration. This work investigates the influence of cutting conditions on machinability indicators such as the main cutting force Fc and surface roughness parameters Ra and Rt when longitudinally turning CuZn39Pb3 brass alloy. Full quadratic regression models were developed to correlate the machining conditions with the imparted machinability characteristics. Further on, an advanced artificial grey wolf optimization algorithm was implemented to optimize the aforementioned responses with great success in finding the final optimal values of the turning parameters.
Stellite 6 powder (CoCrSiW) was deposited using flame spray (FS) and high velocity oxygen fuel (HVOF) techniques on steel substrates. The microstructure of stellite coatings produced with these ...deposition techniques displayed a rather similar morphology consisting of cobalt-rich dendrites surrounded by hard (Cr
3
C
7
) carbide particles. The stellite (both FS and HVOF) coating was found to reduce the tensile strength of the steel. The failure of the coated steel specimens initiated by cracking on the coating surface, transverse propagation of the cracks towards the coating - substrate interface and diversion along the interface leading to local delamination and breakage. During the bend tests cracks developed along the coating and the main failure in the coating occurred due to the tensile-shear deformation, particularly in the coating-substrate material interface. The coating thickness does not appear to affect the bending strength. During bending the number of surface cracks per unit length decreased with increasing coating thickness. Stereoscopic analysis showed that the thicker the coating the deeper the surface cracks. When the critical stress for crack propagation reached defect sites at the substratecoating interface, the entire coating failed and peeled off from the substrate.
This paper analyses the causes of an incident in an aircraft propeller hub. The aluminum alloy propeller blade hub was detached from the plane bearing one of its two blades with the other one being ...jettisoned away. Stereoscopic examination of the fractured hub revealed that it was initially cracked by fatigue, with the crack initiating on the root of the third and fourth spirals and propagating form the inner to the outer. SEM analysis showed that the crack epicentres were created very close or/and on the spiral roots and were attributed to microcracks from corrosion pits and high stress concentration. Non Destructive Inspection was both used on the other side of the hub and the remaining three hubs of the plane and confirmed the presence of cracks similar to those which caused the fatigue failure of the fractured hub but at earliest stage of development.
Three Ti-6Al-4V bolts from mid-life jet aircraft failed during service operation. Each of the failed bolts were installed on a landing gear component. Metallurgical failure analysis indicated that ...the fracture mechanism is low temperature creep, possibly resulting from a sustained tension load over a long time. Visual inspection revealed ductile fracture morphology with no macroscopic deformation or corrosion. For all bolts fracture occurred close to the root at the first pitches of the thread. Scanning Electron Microscope (SEM) analysis revealed dimple morphologies with micro-void coalescence. Energy Dispersive X-Ray (EDX) analysis did not reveal any material deficiency that would have precipitated failure.
This investigation concerns the cutting force magnitude during turning of AISI D6 tool steel using both Taguchi Experimental Design (TED) and full factorial design (FFD). Three main cutting ...parameters namely spindle speed, feed rate and depth of cut were considered as the cutting parameters, each one having three levels, while the cutting force (Fc) was selected as the machinability process output. The full factorial design of the 27 (33) experiments was splitted in three sub-arrays, each one having 9 experiments. These three sub-arrays were orthogonal and were treated as Taguchi L9 orthogonal arrays. The performance of the FFD and each TED was analysed using stem-and-leaf plots, box plots, as well as analysis of means (ANOM) and analysis of variance (ANOVA). The results obtained indicate the suitability of all proposed experimental designs for machinability studies.
Machinability of engineering materials is crucial for industrial manufacturing processes since it affects all the essential aspects involved, e.g. workload, resources, surface integrity and part ...quality. Two basic machinability parameters are the surface roughness, closely associated with the functional and tribological performance of components, and the cutting forces acting on the tool. Knowledge of the cutting forces is needed for estimation of power requirements and for the design of machine tool elements, tool-holders and fixtures, adequately rigid and free from vibration. This work investigates the influence of cutting conditions on machinability indicators such as the main cutting force Fc and surface roughness parameters Ra and Rt when longitudinally turning CuZn39Pb3 brass alloy. Full quadratic regression models were developed to correlate the machining conditions with the imparted machinability characteristics. Further on, an advanced artificial grey wolf optimization algorithm was implemented to optimize the aforementioned responses with great success in finding the final optimal values of the turning parameters
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