Showing papers by "Rolls-Royce Holdings published in 2014"

Method of manufacturing a component

Abstract: An additive layer manufacture (ALM) machine generates a first electron beam for selectively melting a layer of metal powder, and a second electron beam for detecting defects in the selectively melted layer once it has solidified. The second electron beam has a lower power than the first electron beam so as to be used to identify any defects without performing further melting. If any defects are detected, they can be removed, for example by re-melting, before the next layer of powder is supplied. The process may be repeated to generate a finished component with good mechanical properties.

A comparative study on dwell fatigue of Ti-6Al-2Sn-4Zr-xMo (x= 2 to 6) alloys on a microstructure-normalized basis

Abstract: The dwell effects of Ti624x (x = 2 to 6) alloys, including dwell fatigue life debit, fracture mode and strain accumulation, were characterized and compared. With increasing Mo content, the dwell fatigue life debit decreases quickly, and dwell fatigue fracture exhibits a transition from subsurface to surface initiation. Accompanying these changes, the accumulated strain decreases, and the pattern of secondary cracks loses morphological features typical of dwell cracks. These variations in the fatigue behavior of Ti624x were attributed on the fundamental level to the dual effects of Mo: It decreases the β transus of titanium and, as a slow diffuser, reduces the rate of phase transformation from β to α. A higher Mo content encourages nucleation of multiple variants of α laths and promotes the transition from aligned colonies to basketweave microstructure during cooling after β forging. As a result both the grain size and microtexture intensity of α grains in the two-phase processed and heat treated microstructure are reduced. Smaller grain size of the alloys with higher Mo content produces smaller slip band spacing and reduces accumulated strain during dwell fatigue, thus reducing propensity for crack initiation. Microtexture was shown to be the direct cause of dwell sensitivity, and their relationship was described with the aid of a two-region redistribution model based on a previous two-element redistribution model proposed by Bache.

Physical, Mechanical, and Structural Properties of Highly Efficient Nanostructured n- and p-Silicides for Practical Thermoelectric Applications

Abstract: Cost-effective highly efficient nanostructured n-type Mg2Si1−xSnx and p-type higher manganese silicide (HMS) compositions were prepared for the development of practical waste heat generators for automotive and marine thermoelectric applications, in the frame of the European Commission (EC)-funded PowerDriver project. The physical, mechanical, and structural properties were fully characterized as part of a database-generation exercise required for the thermoelectric converter design. A combination of high maximal ZT values of ∼0.6 and ∼1.1 for the HMS and Mg2Si1−xSnx compositions, respectively, and adequate mechanical properties was obtained.

Shape memory alloy actuator design: CASMART collaborative best practices and case studies

Abstract: One goal of the Consortium for the Advancement of Shape Memory Alloy Research and Technology is to compile the collective design experiences of our member organizations into a single medium that researchers and engineers may use to make efficient and effective decisions when developing shape memory alloy (SMA) components and systems. Recent work toward this goal is presented through the framework of six fundamental design aspects we have identified, which include evaluation, alloy selection, processing and fabrication, testing and properties, modeling, and system integration considerations including control system design. Each aspect is documented in the light of enabling the design engineer to access the tools and information needed to successfully design and develop SMA systems. Application of these aspects is illustrated through case studies resulting from our own SMA designs. It is shown that there is not an obvious single, linear route a designer can adopt to navigate the path from concept to product. Each application brings unique challenges that demand a particular emphasis and priority for each engineering aspect involved in the development of a system actuated by SMAs.

A New Polycrystalline Co-Ni Superalloy

Abstract: In 2006, a new-ordered L12 phase, Co3(Al,W), was discovered that can form coherently in a face-centered cubic (fcc) A1 Co matrix. Since then, a community has developed that is attempting to take these alloys forward into practical applications in gas turbines. A new candidate polycrystalline Co-Ni γ/γ′ superalloy, V208C, is presented that has the nominal composition 36Co-35Ni-15Cr-10Al-3W-1Ta (at.%). The alloy was produced by conventional powder metallurgy superalloy methods. After forging, a γ′ fraction of ~56% and a secondary γ′ size of 88 nm were obtained, with a grain size of 2.5 μm. The solvus temperature was 1000°C. The density was found to be 8.52 g cm−3, which is similar to existing Ni alloys with this level of γ′. The alloy showed the flow stress anomaly and a yield strength of 920 MPa at room temperature and 820 MPa at 800°C, similar to that of Mar-M247. These values are significantly higher than those found for either conventional solution and carbide-strengthened Co alloys or the γ/γ′ Co superalloys presented in the literature thus far. The oxidation resistance, with a mass gain of 0.08 mg cm−2 in 100 h at 800°C, is also comparable with that of existing high-temperature Ni superalloys. These results suggest that Co-based and Co-Ni superalloys may hold some promise for the future in gas turbine applications.

Prioritisation of operations improvement projects in the European manufacturing industry

Abstract: To improve their competitive ability, organisations are turning towards implementing improvements into their operations and processes. Whilst operations improvement projects are often identified with relative ease, resource constraints limit the ability of organisations to conduct them simultaneously. This paper supports the limited empirical research on prioritisation of improvement initiatives by investigating how European manufacturing organisations conduct this activity. To do this, four hypotheses and two research questions were formulated and tested using a combination of descriptive statistics and two proportion T-tests, while data was collected through a survey questionnaire responded by 203 organisations. The results highlight the importance of objectively prioritising improvement projects and establish that the adoption of this method increases through the implementation of improvement methodologies, especially those that stipulate the use of objective methods towards project prioritisation. In ...

Influence of Surface Anomalies Following Hole Making Operations on the Fatigue Performance for a Nickel-Based Superalloy

Abstract: Aero-engine manufacturers are continuously striving to improve component performance and reliability while seeking to increase the efficiency of manufacturing to reduce costs. Efficiency gains by using higher rates of material removal, however, can be counterproductive if they give rise to surface anomalies that distort the material microstructure and reduce the resistance of the material to fatigue crack nucleation. This paper investigates the effect of hole making processes and parameters on surface integrity and the initiation of cracks from low-cycle fatigue (LCF). It reports the dependence of elevated temperature (600 degrees C) low-cycle fatigue performance of nickel alloy RR1000 from surfaces produced from hole making and subsequent surface conditioning. As-machined surfaces include a reference "damage-free" surface, and two distorted microstructures: (i) a white layer, produced to a depth of 5 and 10 mu m and (ii) a distorted gamma prime (gamma') structure, produced to a depth of 10 and 15 mu m. The effect of shot peening damage-free and 10 mu m deep white layer surfaces was also evaluated. It was found that the presence of white layer significantly reduced fatigue performance compared with that shown by the damage-free surface, regardless of whether the white layer was subsequently shot peened or not. In contrast, surfaces showing distorted gamma' structures produced much less debit in fatigue life and only from a depth of 15 mu m. These results have been rationalized from an examination of fracture surfaces and from measurement of residual stresses before and after fatigue testing. This research is of particular importance as it is among the few reports that quantify the effect of different levels of work piece surface integrity on the fatigue life of a nickel-based superalloy that has been developed for critical rotating components in aero-engine applications.

Bearing steel microstructures after aircraft gas turbine engine service

Abstract: The microstructure of aircraft gas turbine engine bearing steel has been characterised after service in Rolls-Royce Trent™ engines, with the focus on surface condition and the consequences of sliding contact. Carbide populations at the surfaces of rolling elements are found depleted by 30% after 30 000 h engine service. A single ball failure occurred after this period, leading to fatigue spalling that initiated below the contact surface. Comparisons between unused bearing raceways and those that have experienced service revealed that the microstructures resulting from secondary hardening remain remarkably stable. Plastic flow along the direction of rolling is confined to a shallow zone <2 μm beneath the contact surfaces. Transmission electron microscopy has revealed a new deformation mechanism in these bearing steels, in the form of mechanical twinning at interfaces and prior austenite grain boundaries. It is demonstrated that workhardening occurs to a depth of 1 mm in the raceway that has experie...

Influence of elevated Co and Ti levels on polycrystalline powder processed Ni-base superalloy

Abstract: The influences of elevated Co and Ti levels on the mechanical properties of the Ni-base superalloy RR1000 have been investigated. Following heat treatment, the modified alloys had the typical γ–γ′ microstructure, with γ′ precipitate sizes comparable to similarly heat treated RR1000, but with a slightly higher volume fraction. The modified alloys exhibited a higher proof stress than RR1000 across the entire 20 to 800°C temperature range investigated. Superior creep rupture lives, when compared to RR1000, were observed in the modified alloys at 700°C, but not at 750°C, where extensive precipitation of topologically close packed σ phase occurred on the grain surfaces. The formation of this deleterious phase was linked to Cr and Mo enrichment of the γ matrix, caused by the elevated Co and Ti additions.

In-service materials support for safety critical applications – A case study of a high strength Ti-alloy using advanced experimental and modelling techniques

Abstract: This paper introduces motivations and suitability for using advanced characterisation techniques to study industrially relevant materials, such as titanium alloys for the aerospace industry. These advanced research tools each provide unique information in fundamental research, and by designing appropriate datum studies and modelling support they can be combined with powerful effect to tackle ‘real world’ engineering issues. We demonstrate the use of orientation-corrected nanoindentation, micro-cantilever bend testing and 3D atom probe tomography to investigate a high strength, dual phase engineering alloy (Ti–6Al–4V) with a surface gradient of interstitials.

Characterization of Plastic Deformation Induced by Shot-Peening in a Ni-Base Superalloy

Abstract: The shot-peening process is currently employed in most industries to improve the longevity of components by inhibiting crack initiation as well as crack growth at the surface. The protective effect ...

Non-linear Ultrasonic NDE of Titanium Diffusion Bonds

Abstract: Diffusion bonding is an attractive solid-state welding technique that represents a valuable tool for reducing weight and improving performance in the aerospace industry. However, its full exploitation in titanium components is currently limited by a lack of robust NDE techniques capable of overcoming the crystallographic anisotropy of these important materials. Advanced ultrasonic techniques have been explored previously, but their sensitivity to imperfections is limited by the linear acoustic phenomena on which they depend. Non-linear ultrasonic methods have been shown to be significantly more sensitive than their linear counterparts to these types of imperfections, but suppressing extraneous contributions to the non-linear response of the interface is not trivial. An approach that succeeds in suppressing such contributions is presented here. The technique, which is based on the non-collinear mixing of ultrasonic waves to generate a spectrally, modally and spatially dissociable third wave, was used to reliably characterise a set of samples whose bond quality was indeterminable using conventional ultrasonic methods.

Additive layer manufacturing method

Abstract: An additive layer manufacturing method includes the steps of: a) laying down powder layer on powder bed, and b) focussing energy on an area of powder layer to fuse area of powder layer and thereby form a cross-section of the product; wherein steps a) and b) are repeated to form successive cross-sections of product, and wherein at least one of said steps b) involves focussing energy on an area of respective powder layer which is unsupported by a previously formed cross-section of product to thereby form a downwardly facing surface of product. Method is at least some of said successive steps b) involve focussing energy on a support area of respective powder layer, to fuse support area and thereby form successive cross-sections of a support pin within powder bed, support pin extending outwardly from downwardly facing surface of product when it is formed, so as to support downwardly facing surface.

The influence of Al:Nb ratio on the microstructure and mechanical response of quaternary Ni–Cr–Al–Nb alloys

Abstract: The influence of Al:Nb ratio on the microstructure and properties of Ni–Cr–Al–Nb alloys has been investigated following long-term exposure at elevated temperatures. The γ′ volume fraction, size and lattice misfit were seen to increase with a larger Al:Nb ratio, although these changes resulted in reduced hardness. The change in the critical resolved shear stress (CRSS) associated with strong dislocation coupling was determined to be the dominant strengthening mechanism and increased with decreasing Al:Nb ratio. A distribution of tertiary γ′ was observed to be necessary in maximising the mechanical properties of these alloys.

On the Optimization of a Geared Fan Intercooled Core Engine Design

Abstract: Reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, as well as the reduction of engine nacelle drag and weight. One alternative design approach t ...

Multifidelity Multidisciplinary Whole-Engine Thermomechanical Design Optimization

Abstract: Traditionally, the optimization of a turbomachinery engine casing for tip clearance has involved either two-dimensional transient thermomechanical simulations or three-dimensional mechanical simulations. This paper illustrates that three-dimensional transient whole-engine thermomechanical simulations can be used within tip clearance optimizations and that the efficiency of such optimizations can be improved when a multifidelity surrogate modeling approach is employed. These simulations are employed in conjunction with a rotor suboptimization using surrogate models of rotor-dynamics performance, stress, mass and transient displacements, and an engine parameterization.

Aircraft electrical system

Abstract: An aircraft electrical network including a first starter generator mechanically coupled to a first shaft of an aircraft main engine. The first starter generator is configured to turn the first shaft of the main engine in a starting mode, and to generate electricity from the first shaft of the gas turbine engine in a generating mode. The network further includes a DC electrical bus electrical coupled to one or more electrical loads and an AC electrical bus electrically coupled to the first starter generator. The DC electrical bus is electrically coupled to the AC electrical bus via a bi-directional AC/DC converter, which is configured to provide AC electrical power from the DC electrical bus to power the first starter generator when the first starter generator is in a starting mode, and DC electrical power to the DC electrical bus when the first starter generator is in a generating mode.

Pneumatic system for an aircraft

Abstract: A bleed air system for an aircraft has a gas turbine engine and operating method. The system includes an environmental control system (ECS) for providing cabin airflow to the aircraft, including operating modes such as first and second air cycle machine operating modes and heat exchanger operating modes. The ECS includes first, second and third bleed ports each configured to provide engine bleed air from gas turbine engine compressors to the ECS. The ECS includes a bleed air system sensor arrangement configured to sense one or more bleed air system conditions, an environmental control system controller that selects an environmental control system operating mode that provides required cabin air flow and temperature at an optimal specific fuel consumption of the gas turbine engine at the sensed system conditions, and a bleed port valve controller which determines an operating pressure required to operate the environmental control system in the selected mode.

Oxidation of a Commercial Nickel-Based Superalloy under Static Loading

Abstract: The current demands of the aviation industry for increased gas-turbine efficiency necessitate higher turbine entry temperatures, requiring that alloys exhibit superior oxidation resistance. The synergistic effects of oxidation and mechanical stresses pose a complex issue. The purpose of the current research was to examine the effects of stress on the oxidation and oxygen transport in a commercial nickel-based superalloy. Fine grain RR1000 in both polished and shot-peened conditions was studied for classic (zero load) and statically loaded conditions using integrated two-stage isotopic tracing combined with focused-ion-beam secondary ion mass spectrometry (FIB-SIMS). Cr2O3 external oxide formed with semicontinuous TiO2 above and below. Preferential grain boundary Al2O3 internal oxide formation, γ′-dissolution, and recrystallization occurred subsurface. Oxidation mechanisms were dominated by anionic/cationic growth in the external oxide with inward oxygen transport, initially through the partially unprotective external oxide, then along internal oxide/alloy interfaces. Loading did not influence the oxidation products formed but did bring about expedited oxidation kinetics and changes to the oxide morphology. The oxygen diffusivity D O (×10−13 cm2s−1) ranged from 0.39 for the polished alloy to 3.7 for the shot-peened condition under compressive stress. Arguably, the most significant effects took place in the subsurface regions. Increased oxidation kinetics were attributed to the development of fast cation diffusion paths as the alloy deformed by creep.

Influence of Intake on Fan Blade Flutter

Abstract: The main aim of this paper is to study the influence of upstream reflections on flutter of a fan blade. To achieve this goal, flutter analysis of a complete fan assembly with an intake duct and the downstream OGVs (whole LP domain) is undertaken using a validated CFD model. The computed results show good correlation with measured data. Due to space constraints, only upstream (intake) reflections are analyzed in this paper. It will be shown that the correct prediction of flutter boundary for a fan blade requires modeling of the intake and different intakes would produce different flutter boundaries for the same fan blade. However, the ‘blade only’ and intake damping are independent and the total damping can be obtained from the sum of the two contributions.In order to gain further insight into the physics of the problem, the pressure waves created by blade vibration are split into an upstream and a downstream traveling wave in the intake. The splitting of the pressure wave allows one to establish a relationship between the phase and amplitude of the reflected waves and flutter stability of the blade. By using this approach, a simple reflection model can be used to model the intake effects.Copyright © 2014 by Rolls-Royce plc