Improvement of reverse-engineered turbine blades using construction geometry

The paper reports the latest outcomes of using design-based reverse engineering on turbine blades. For a long time, the focus of the reverse engineering methods has been the trend toward higher accuracies and faster measurements. Authors introduce a different viewpoint which focuses on design intent of a part. How to reverse engineer a complex shape like a turbine blade is the subject of current research. The attempt toward taking advantage of the construction geometry behind a sample heavy duty turbine blade is thoroughly discussed in three phases. First phase consists of 2D analysis of the reference sections. Then, the stacking axis is introduced as an important non-tangible feature which has the main role to connect the sections in 3D in lean and tilt directions. The third phase uses the concept of blade twist to provide a constraint to define rotational position of the sections with respect to neighbor sections. All the three phases have been applied to different types of original and non-original products which are available in the gas turbine market. The presented comparisons show clearly that the new method of reverse engineering incorporating construction geometry and design intent of the part is quite useful and recognizes many features behind the external geometry which is impossible to follow by the previous conventional methods. The turbine blade 3D model resulted from this new method will have a smooth arc-based surface, straight stacking line passing through turbine axis with maximum section tilt of 0.2 mm and maximum section lean of 0.3 mm to original equipment manufacturer parts and linearly increasing stagger angle from hub to tip which are some of considerable improvements compared to conventional method.     

Offshore wind turbine blades measurement using Coherent Laser Radar

To maximize aerodynamic efficiency, large-scale offshore wind turbine blades require inspection during the production stage to ensure strict tolerance requirements are met. During production, the blade is fixed at the root, restricting movement in the Z direction. X, Y, Rx, Ry and Rz remain unconstrained causing blade flex due to gravity. This deforms the blade away from the theoretical CAD blade location, causing measurement results that do not accurately represent the blade profile. Measurement error can be minimized using rigorous B-spline data alignment. Such alignment compensates for blade flex by varying the constrained Degrees of Freedom (DoF), and provides manufacturers with confidence in the design process. This paper used Coherent Laser Radar and Spatial Analyzer to establish the optimal constrained DoF variation, giving the most accurate data alignment solution. Of the constraints investigated, the optimal data transformation solution was found with a double B-spline alignment method, whilst constraining movement in Y, Z and Ry.     

Effects of adding aluminum oxide or zirconium oxide fibers on ceramic molds for casting hollow turbine blades

To satisfy the requirements of mechanical performances of integral Al₂O₃-matrix ceramic mould for fabricating hollow turbine blades, Al₂O₃ or ZrO₂ fibres were added to the slurry in gelcasting. The microstructures of Al₂O₃-matrix ceramic mould were tested by scanning electron microscope and micron X-ray imaging system besides their bending strengths at different temperatures. The result showed that when Al₂O₃ fibre or ZrO₂ fibre were added, the room-temperature bending strength of the ceramic mould was remarkably improved after pre-sintering at 1,250 °C. The medium-temperature bending strength was about between 0.5 and 2 MPa from 400 to 600 °C and reached the minimum at 500 °C. At 1,300 °C, the high-temperature bending strengths decreased gradually with an increase of Al₂O₃ fibre content and increased with an increase of ZrO₂ fibre content. The specimens expanded first in pre-sintering and then shrunk in final sintering, respectively. According to the test results, we used ZrO₂ as the additive with 10 wt% content, and the overall performances of Al₂O₃-matrix ceramic mould were the best. Finally, hollow turbine blades were successfully fabricated.     

Value range optimization of ply parameter for composite wind turbine blades based on sensitivity analysis

Journal of Mechanical Science and Technology - Blade ply parameters are important design factors that influence the performances of wind turbine blades. This paper proposes a sensitivity analysis...     

Long-term durability of offshore wind turbine composite blades based on nonlinear load behavior due to pitch movement

This study proposes a fatigue life prediction method for offshore wind turbines consisting of a fatigue load calculation method that accounts for external     

Enhancement of combined cycle performance using transpiration cooling of gas turbine blades with steam

Gas/steam combined cycle is synergetic combination of Brayton cycle based topping cycle and Rankine cycle based bottoming cycle, which have capability of operating independently too. Combined cycle performance depends on the constituent cycles and it can be reasonably improved by enhancing gas cycle performance using gas turbine blade cooling. Amongst different cooling techniques the transpiration cooling offers effective utilization of coolant as compared to film cooling because of better shrouding of blade surface as the coolant is discharged from entire blade surface. The present work deals with evaluation of performance enhancement of combined cycle by using steam transpiration cooling of gas turbine blades. The combined cycle performance parameters e.g. overall efficiency and specific power output etc. have been compared for air transpiration cooling and steam transpiration cooling. The results revealed that for the specified conditions the steam is superior coolant in comparison to air and the combined cycle performance can be enhanced by applying transpiration cooling in gas turbine blades with steam as coolant. With a turbine inlet temperature of 1800 K and compressor pressure ratio of 23, the combined cycle efficiency with steam transpiration cooling of gas turbine blades is higher by 1.94 percent approximately as compared to the efficiency of combined cycle with air transpiration cooling of gas turbine blades.     

Rapid casting of turbine blades with abnormal film cooling holes using integral ceramic casting molds

Film cooling is an important cooling method to decrease the turbine blade surface temperature, and its average cooling efficiency is mainly dependent on the cooling structures of internal passageways and the shapes of film cooling holes. Compared with standard cylindrical film cooling holes, abnormal film cooling holes have higher average cooling efficiency. But it is difficult to manufacture these holes using traditional machining methods. In this paper, a novel process was developed to fabricate turbine blades with abnormal film cooling holes by combining stereolithography (SL) technology with gelcasting technology. To decrease the drying shrinkage, the freeze-drying technique was applied to treat the wet ceramic casting mold green body surrounded by the SL mold, and the proper sintering process parameters were determined for lowering the sintered shrinkage. Finally, the integral ceramic casting mold was obtained, and a turbine blade with converging–diverging film cooling holes was rapidly cast to verify the feasibility of the proposed process.     

Automatic inspection of turbine blades using a 3-axis CMM together with a 2-axis dividing head

Turbine blades are widely used in turbo-engines and generators. The complex geometry of turbine blades and the limited space between two adjacent blades cause difficulties in both machining and inspection. This paper is focused on the use of a 3-axis coordinate measurement machine (CMM), together with a dividing head with two rotational axes, to undertake the task of precision inspection of turbine blades that surround the periphery of an axial wheel. Based on the geometrical relationship between the probe stylus and the turbine blades, a methodology is proposed to find the angle of rotation of the axial wheel when a collision is likely to occur between them. Other issues related to system implementation are also discussed in this paper, including: (1) Data transformation from the turbine blade’s geometric model to the CMM control codes, (2) Planning of the traveling paths of the stylus, and (3) Analysis of the measured data.     

On studies of tensile properties in injection molded short carbon fiber reinforced PEEK composite

Both elastic modulus and strength of injection molded carbon fiber filled poly-ether-ether-ketone (PEEK) composite are studied under tension. The measured moduli and ultimate strengths of injection molded carbon fiber reinforced PEEK have been compared with the model predicted values. For injection molded PEEK composite, the experimentally obtained values of tensile modulus show a fair agreement but those of the tensile strength show a poor agreement with the theoretically predicted values. Many processing factors seem to be more critical issue for the strength than the stiffness of short-fiber reinforced composites. Considering the service performance of composites depends on three interactions — material, design and processing, monitoring the processing can be critical to have a best performance of composite. Processing factors have been discussed in cases of short carbon fiber reinforced PEEK composite based on the comparision between experimental and theoretically predicted data to obtain the best composite material.     

Delamination analysis of the helical milling of carbon fiber-reinforced plastics by using the artificial neural network model

As carbon fiber-reinforced plastics are widely used in aeronautical and aerospace industries, the improvement of their processing quality is a crucial task. In recent years, helical milling, a brand new machining process that results in better hole quality with one-time machining, has been attracting increasing attention. Based on full factor experimental design, helical milling experiments were performed by using a special cutter. Using the data obtained from the experiments, the correlation between the delamination and the process parameters was established by developing an artificial neural network (ANN) model. MATLAB ANN Toolbox was used for modeling. The effects of the process parameters on delamination at the exit of the machined holes were analyzed by using this model and the predicted results. The significance of the process parameters in the improvement of the hole quality in helical milling was also assessed.     

Buckling analysis of circular and annular composite plates reinforced with carbon nanotubes using FEM

The critical compressive load in the buckling of circular and annular composite plates reinforced with carbon nanotubes (CNTs) is calculated using finite element method. The developed model is based on the third-order shear deformation theory for moderately thick laminated plates. Effects of CNTs orientation angles and thickness-to-inner radius ratio on the buckling of composite plates are discussed. The results are compared with those obtained by analytical method based on classical plate theory. The finite element method shows lower values for critical buckling load because of the elimination of shear strain in the classical plate theory.     

Measuring the thicknesses of the walls of carbon composite materials using the eddy-current phase method

The principles of designing transducers for measuring the thicknesses of walls of products from carbon composite materials, the issues of calculation and optimization of their characteristics and suppression of interfering parameters are considered. The design and main metrological characteristics of the developed transducers are presented.     

Characterization of the fibre–matrix interfacial structure in carbon fibre-reinforced polycarbosilane-derived SiC matrix composites using STEM/EELS

This paper presents a characterization study of the microstructural evolution of various carbon fibre-reinforced polycarbosilane (PCS)-derived SiC matrix composites during high temperature heat treatment. Both surface-treated and untreated carbon fibre reinforcements were investigated. The STEM/EELS technique was found to be a particularly useful characterization tool. The results of quantitative EELS linescans have been interpreted in terms of the migration of gaseous SiO and CO, produced by the reaction between the small amount of SiO₂ and excess carbon within the PCS-derived SiC matrix, from the central matrix region towards the fibre–matrix interfaces. Generally, the migration of gaseous SiO and CO results in an enrichment of SiO₂ at the region adjacent to the fibre–matrix interface. However, differing final composite microstructures are formed depending on the strength of the fibre–matrix bonding. In the case of strong fibre-matrix interfacial bonding where few escape channels are present, a distinct Si–C–O layer was identified within the matrix adjacent to the fibre–matrix interface; both crystalline β-SiC and the segregated Si–O–C phase coexist in this microstructure up to at least 1450 °C. In the case of weak fibre–matrix bonding this oxygen segregated interfacial layer is eventually removed at high enough temperatures. The final interfacial microstructure has important consequences for the mechanical properties of the composite material.     

Multi response optimization of machining parameters of drilling Al/SiC metal matrix composite using grey relational analysis in the Taguchi method

This paper presents a new approach for the optimization of drilling parameters on drilling Al/SiC metal matrix composite with multiple responses based on orthogonal array with grey relational analysis. Experiments are conducted on LM25-based aluminium alloy reinforced with green bonded silicon carbide of size 25 μm (10% volume fraction). Drilling tests are carried out using TiN coated HSS twist drills of 10 mm diameter under dry condition. In this study, drilling parameters namely cutting speed, feed and point angle are optimized with the considerations of multi responses such as surface roughness, cutting force and torque. A grey relational grade is obtained from the grey analysis. Based on the grey relational grade, optimum levels of parameters have been identified and significant contribution of parameters is determined by ANOVA. Confirmation test is conducted to validate the test result. Experimental results have shown that the responses in drilling process can be improved effectively through the new approach.     

Prediction of cutting force, tool wear and surface roughness of Al6061/SiC composite for end milling operations using RSM

The results of mathematical modeling and the experimental investigation on the machinability of aluminium (Al6061) silicon carbide particulate (SiCp) metal matrix composite (MMC) during end milling process is analyzed. The machining was difficult to cut the material because of its hardness and wear resistance due to its abrasive nature of reinforcement element. The influence of machining parameters such as spindle speed, feed rate, depth of cut and nose radius on the cutting force has been investigated. The influence of the length of machining on the tool wear and the machining parameters on the surface finish criteria have been determined through the response surface methodology (RSM) prediction model. The prediction model is also used to determine the combined effect of machining parameters on the cutting force, tool wear and surface roughness. The results of the model were compared with the experimental results and found to be good agreement with them. The results of prediction model help in the selection of process parameters to reduce the cutting force, tool wear and surface roughness, which ensures quality of milling processes.     

Prototypes using metal, carbon fiber and composite field emission sources modulated by a laser beam.

Field emission of electrons from a variety of metallic, carbon fiber and composite metal-insulator micropoint cathodes was employed in this study. Tungsten, carbon fiber and ZrC tips, were studied using a field emission microscope. These cathodes were characterized and the current-voltage (I-V) characteristics were determined. A variety of surface treatment procedures were carried out to increase the stability of emission. These electron sources were mounted in sealed prototype field emission tubes, while others were tested under medium, high and UHV conditions. The emission current switch-on phenomenon was found with all non-metallic cathodes. The emitters were then subjected to a square wave-modulated, maximally focused laser diode beam (lambda = 658 nm, 30mW). The beam impedance (approximately 1 Gohms) and the anode capacitance (approximately 10 pF) act as a low-pass filter.     

Multiple-response optimization of turning machining by the taguchi method and the utility concept using uni-directional glass fiber-reinforced plastic composite and carbide (k10) cutting tool

This paper presents a utility concept for multi-response optimization in turning uni-directional glass fiber-reinforced plastics composite using Carbide (K10) cutting tool. The single response optimization resulted in the non-optimization of other responses. The Taguchi method (Orthogonal L₁₈ array) was employed in the experimental work. The process parameters selected for this study were tool nose radius, tool rake angle, feed rate, cutting speed, depth of cut, and cutting environment. Statistically significant parameters were found to simultaneously minimize surface roughness and maximize the material removal rate by ANOVA. The results were further verified by confirmation experiments.     

Reduced stress shielding with limited micromotions using a carbon fibre composite biomimetic hip stem: a finite element model

Total hip arthroplasty (THA) enjoys excellent rates of success in older patients, but younger patients are still at risk of aseptic loosening and bone resorption from stress shielding. One solution to the stress shielding problem is to use a hip stem with mechanical properties matching those of cortical bone. The objective of the present study was to investigate numerically the biomechanical performance of such a biomimetic hip stem based on a hydroxyapatite (HA)-coated carbon fibre composite. A finite element model (FEM) of the biomimetic stem was constructed. Contact elements were studied to model the bone-implant interface in a non-osseointegrated and osseointegrated state in the best way. Three static load cases representing slow walking, stair climbing, and gait in a healthy individual were considered. Stress shielding and bone-implant interface micromotions were evaluated and compared with the results of a similar FEM based on titanium alloy (Ti-6Al-4V). The composite stems allowed for reduced stress shielding when compared with a traditional Ti-6Al-4V stem. Micromotions were slightly higher with the composite stem, but remained below 40 microm on most of the HA-coated surface. It is concluded that a biomimetic composite stem might offer a better compromise between stress shielding and micromotions than the Ti-6Al-4V stem with the same external geometry.     

Parameter design for cut surface characteristics in abrasive waterjet cutting of Al/SiC/Al2O3 composite using grey theory based RSM

The abrasive mixed waterjet was successfully employed to cut many materials including austenitic steel, inconel and glass for a variety of industrial applications. The present work focusses on studying the surface roughness, striation zone and striation angle in Abrasive waterjet cutting (AWJC) of Al/SiC/Al₂O₃ composite. The water pressure, traverse speed, abrasive flow rate and stand-off distance were included as the dominant parameters in the study. The features of striation zone (length and angle) and surface roughness were observed as the responses for each of the cutting trials planned as per Taguchi’s L₁₈ orthogonal array. Parameter design was performed using the grey theory based response surface methodology (g-RSM) by following the method of simultaneous optimization to forecast the optimal cutting condition. All the studied parameters and their interactions were found to have a substantial effect on the observed responses. Significant improvements were observed in the responses obtained with the optimal parameter setting predicted by the g-RSM approach. The Atomic force microscopy (AFM) images and P-profile plots were also studied to observe the texture of the cut surface.