Parametric study to mitigate fretting fatigue in dovetail joint of aeroengine compressor

Fretting fatigue is most likely to occur in the dovetail joint of aero engine compressor resulting in small amplitude displacement of a few micrometers. This leads to degradation of the material in the form of fatigue strength and corrosion. This paper reports optimal conditions of blade geometrical parameters such as flank length, flank angle and coefficient of friction in order minimize the failure due to fretting fatigue. ANOVA indicated that Von-mises stresses, deformation, contact pressure and sliding distance were influenced by coefficient of friction and flank angle. While deformation, contact pressure and sliding distance decreased with increase in coefficient of friction and increased with increase in flank angle and flank length. Von-mises stress increased with increase in coefficient of friction. Response surface methodology results indicated that the optimum value of Von-mises stress (328.24 MPa), deformation (153.87 µm), contact pressure (275.48 MPa) and sliding distance (80.66 µm) were found at coefficient of friction 0.35, flank angle 65° and flank length of 12 mm which were in agreement with those of grey relational analysis results

Optimization of ventilated brake disc rotor geometry for enhanced structural characteristics

This paper focuses on analyzing the effect of geometrical parameters on structural performance of the ventilated brake disc. Multi-objective optimization through response surface methodology was deployed for improving the structural performance of ventilated brake discs. Simulation runs were designed based on central composite design technique. The second order regression models correlating the geometry parameters with maximum deformation and equivalent stress were developed. ANOVA was performed to test the significance of disc geometry parameters. The deformation and equivalent stress were influenced by flange outer peripheral radius. While the spigot radius had a significant effect on the deformation but not on equivalent stress. Also, the mounting surface radius influenced the equivalent stress developed on the ventilated brake disc rotor. The multi-objective optimization of geometrical characteristics for minimum deformation (4.2332 µm) and minimum equivalent stress (4.00989 MPa) yielded significant reduction in total deformation and equivalent stress i.e., 10.28 % and 9.12 % respectively at optimal levels of geometrical parameters

Assessment of thermal effects on the levitation speed of bump foil bearings made of low cost spring steel

The demand for higher speeds and torque capacity from micro turbines, heat pumps and turbochargers has necessitated the development of high temperature resistant foil bearings. This paper focuses on investigating the effects of successive thermal cycles on the levitation speed of bump foil bearings made up of low cost spring steel. Bump foil bearings were designed for high stiffness of 1.64 MN/m2. Rotor dynamic analysis indicated highest frequency of 4790.5 Hz corresponding to second flexure mode of rotor bearing system up to which it remained stable. The bump foil bearing fabrication procedure was established and rotor was tested under suitably designed bearing rig. The orbital analysis indicated that levitation speed decreased with increase in temperature. During second and third thermal cycle, at lower rotor speeds drastic variations in amplitude of vibrations and uneven waveforms were indicative of unbalance condition of rotor. With further increase in rotor speeds, the rotor - bump foil bearing system attained the balanced state indicative of safe design

Evaluation of nanosecond laser ablation and scratch resistance of tantalum carbide coated graphite substrates

The present work aimed at investigating the effect of nanosecond laser parameters on ablation characteristics such as ablation depth and surface roughness of plasma sprayed tantalum carbide coated graphite substrates. The micro scratch tests were performed on the laser ablated and as-sprayed coatings to evaluate the critical loads and coefficient of friction. The laser ablated surface with minimum ablation depth and surface roughness was found to exhibit 18% higher critical loads when compared to that of as-sprayed surface. However, laser ablated surfaces exhibited slightly higher friction coefficient than as-sprayed surfaces due to formation of metastable oxide layer (Ta6O) on the top surface of TaC coatings as indicated by XRD. The maximum ablation and scratch resistance could be found at maximum pulse energy of 250 μJ, maximum scanning speed of 1000 mm/s and moderate hatch spacing of 20 μm. While, the failure of as-sprayed TaC coatings was attributed to local collapsing of material due to degradation of mechanical properties such as elastic modulus, surface porosity and surface roughness, laser ablated surfaces exhibited wedge spallation at the end of scratch zone only

Optimization of laser texture geometry and resulting functionality of nickel aluminium bronze for landing gear applications

Nickel-aluminium bronze (NAB) is adopted in certain crucial applications such as nut threads of actuator screw assembly in nose landing gear, which forms the critical weakest link for landing gear operation. Surface engineering of such critical aircraft parts made of softer materials is required to improve their safety design life. This paper reports optimization of nanosecond laser parameters for enhancing the quality characteristics of surface textures formed on NAB. These characteristics include micro-texture depth, aspect ratio, average surface roughness, maximum height of the profile and kurtosis. Texture diameter and width was computed using an optical microscope. Dimples and grooves with minimum damage were obtained at higher laser power (18 W), moderate scanning speed (500 mm/s) and moderate frequency (50 kHz). The quality ellipse was obtained at moderate power of 14 W, higher scanning speed of 800 mm/s and moderate frequency of 50 kHz. However, the quality of textures deteriorated at moderate laser power (14 W), lowest scanning speed (100 mm/s) and moderate frequency (50 kHz)