491 research outputs found
Design aspects of a CMC coating-like system for hot surfaces of aero engine components
No full textCeramic Matrix Composite (CMC) is an emerging material system that can be a game changer in the aerospace industry, both civil and military. CMCs components are, in fact, lighter and less prone to fatigue failure in a high temperature environment. However, at high temperatures, the diffusion of oxygen and water vapour inside the CMC can have detrimental effects. Therefore, the presence of protective coating is necessary to extend the life of CMC components. In the present work, a three-layers coating, consisting of a silicon bond (BND), adhesively bonded to the CMC, an Environment Barrier Coating (EBC) and a softer layer 3 (LAY3), is investigated for a CMC component. An aero-engine high pressure turbine seal segment was considered. Two design aspects are covered: (i) creep law is determined and calibrated in environment Abaqus from the experimental data of each coating layer available in the open literature, to provide a suitable instrument for the creep relaxation analyses of hot components; (ii) thickness sensitivity study of each layer of the coating is conducted to minimise the interface stresses of coating with substrate in order to mitigate cracking and removal/spalling phenomena when exposed to temperature gradients and to increase their service life. These two different aspects are combined together to predict the coating stress field as a function of service time
Thermo-Mechanical Finite Element Modeling of the Laser Treatment of Titanium Cold-Sprayed Coatings
No full textThis paper implements a thermo-mechanical model to simulate the laser treatment effects on a cold-sprayed titanium coating and aluminum substrate. The thermo-mechanical finite element model considers the transient temperature field due to the laser source and applied boundary conditions, using them as input loads for the subsequent stress-strain analysis. Numerical outcomes highlighted the relevance of thermal gradients and the presence of thermally-induced stress-strain fields responsible for promoting damage in the coating
Numerical and Experimental Analysis on selective Laser Post-Treatment of Cold Sprayed Titanium Coating
No full textCold gas dynamic spray is an innovative technology allowing the deposition of thin metallic layers on a bulk or sheet substrate. Titanium on aluminum deposition is very attractive to the aeronautic industry, due to the enhanced corrosion resistance and wear properties of titanium coating as well as its improved compatibility with CFRP, preserving the reduced cost of aluminum substrate. One main drawback, however, is related to the micro-porosity of the deposed layer, negatively affecting the corrosion barrier performance. In this paper, the effect of selective laser post-treatment on pure grade 2 titanium coatings on AA2020-T3 sheets was experimentally and numerically investigated. Morphological features, microstructure and chemical composition of the treated zone were assessed by means of optical microscopy, scanning electron microscopy and energy dispersive X-ray spectrometry. Microhardness measurements were also carried out to evaluate the mechanical properties of the treated coating. A numerical model of the laser treatment, based on a finite volume scheme, was implemented and solved to simulate the process and discuss the experimental outcomes. Obtained results highlighted the key role played by heat input and dimensional features on the effectiveness of the treatment
Peck drilling of CFRP/titanium stacks: effect of tool wear on hole dimensional and geometrical accuracy
No full textThe effect of tool wear on dimensional and geometrical accuracy of holes machined by peck drilling in carbon fibre reinforced plastic (CRFP) and titanium (Ti) stacks is studied. Coated and uncoated tungsten carbide drills of both fine and ultra-fine microstructures are employed to assess the importance of grain size and coating on hole accuracy. Hole profiles show two maxima: one at the hole entry and the other at the CFRP/Ti interface. Hole cylindricity as function of tool wear shows a minimum. It firstly decreases due to flank wear and subsequent reduction of the drill diameter. Then the rise of tool instability prevails with the result that an increase of the cylindricity with tool wear is brought about. Less wear-resistant drills attain this minimum in a shorter time of cutting
Artificial neural networks in advanced thermoset matrix composite manufacturing
No full textAutoclave curing is a common practice to manufacture high temperature thermoset matrix composites. The cycle design and optimization of the temperature-time curve is a key issue for a competitive production. In this paper artificial neural networks (ANN), as a technique of artificial intelligence, were used for prediction of the composite temperature profile during the autoclave curing process. Different neural network models have been investigated regarding their capabilities for prediction of the composite temperature profile. The new neural network model has been developed able to predict the composite temperature profile in the wide range of manufacturing conditions changing
Thermo-chemical, mechanical and resin flow integrated analysis in pultrusion
No full textThe present work discusses some numerical outcomes provided by an integrated analysis of impregnation, thermo-chemical and stress/strain aspects in a conventional pultrusion process. The impregnation models describes resin flow and pressure distribution in the initial portion of the die, solving a non-homogeneous non-isothermal/reactive multiphase problem, using a finite volume scheme. The thermochemical model describes the heat transfer and degree of cure evolution of the processing resin. Finally, the stress/strain model computes the part distortion and in process stresses due to thermal, chemical, mechanical strains. An applicative case study is presented, simulating the impregnation step of the pultrusion process of a fiberglass-epoxy resin composite rod
Thermoplastic Pultrusion Process of Polypropylene/Glass Tapes
No full text: The present work focuses on the pultrusion of pre-impregnated glass-reinforced polypropylene tapes. An appositely designed laboratory-scale pultrusion line, consisting of a heating/forming die and a cooling die, was used. The temperature of the advancing materials and the pulling force resistance were measured by using thermocouples embedded in the pre-preg tapes and a load cell. From the analysis of the experimental outcomes, we gained insight into the nature of the material-machinery interaction and the transitions of the polypropylene matrix. The cross-section of the pultruded part was analyzed by microscope observation to evaluate the distribution of the reinforcement inside the profile and the presence of internal defects. Three-point bending and tensile testing were conducted to assess the mechanical properties of the thermoplastic composite. The pultruded product showed good quality, with an average fiber volume fraction of 23% and a limited presence of internal defects. A non-homogenous distribution of fibers in the cross-section of the profile was observed, probably due to the low number of tapes used in the present experimentation and their limited compaction. A tensile modulus and a flexural modulus of 21.5 GPa and 15.0 GPa, respectively, were measured
Selective Laser Treatment on Cold-Sprayed Titanium Coatings: Numerical Modeling and Experimental Analysis
No full textTribological Characterization of SiC and B4C Manufactured by Plasma Pressure Compaction
No full textThe objective of the present study was to assess the tribological properties and the wear behavior of silicon carbide and boron carbide ceramics, produced by the plasma pressure compaction sintering process. Reciprocating sliding tests were executed to evaluate the tribological behavior of silicon carbide and boron carbide. Samples of each material with distinct values of surface roughness Ra were tested. Wear mass loss, coefficients of friction and wear mechanism of the boron carbide and silicon carbide were evaluated by means of microscopes and an energy-dispersive spectroscopy probe. The coefficient of friction of the evaluated boron carbide was found to be 0.8, and the surface roughness affects only the starting transient, while for silicon carbide the steady-state value ranges from 0.5 to 0.8 depending on the roughness value Ra
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