With the increase of the operating pressure of gas compressors, the demand for a robust and reliable shaft end sealing solution, namely dry gas seal, has risen. The narrow sealing gap formed between the rotating and the stationary rings, about 2–5 micrometers wide, is subject to the hydrodynamic pressure on sealing surfaces and deflections on both rings due to mechanical forces and thermal loads. In order to estimate the seal performance in terms of film thicknesses, leakage flows and radial tapers, a numerical program which automatically couples the simulation of the pressure field in micro-scale based on the Reynolds equation for compressible fluids, the heat generation and transfer model between the fluid and solids as well as the structural and thermal distortion of both rings, has been developed by the authors to address the mechanical seal problem as a whole system. In this way, the interaction of all arising forces, mechanical deformations and thermal deviations is taken into account in the design process of the seals. The choked flow exit boundary is also taken into considerations for high pressure conditions. The method to solve this interactive problem as a whole is discussed. The paper presents the numerical analysis carried out with various groove parameters, seal geometries and operating conditions. Results are compared and show a good agreement with actual experimental data. Design parameters which have strong influences on the seal performance are as well discussed.

Oil-lubricated bearings are widely used in high speed rotating machines such as those found in the aerospace and automotive industries. However, environmental issues and risk-averse operations are resulting in the removal of oil and the replacement of all sealed oil bearings with reliable water-lubricated bearings. Due to the different fluid properties between oil and water, the low viscosity of water increases Reynolds numbers drastically and therefore makes water-lubricated bearings prone to turbulence effects. This requires finer meshes when compared to oil-lubricated bearings as the low-viscosity fluid produces a very thin lubricant film. Analyzing water-lubricated bearings can also produce convergence and accuracy issues in traditional oil-based analysis codes. Thermal deformation largely affects oil-lubricated bearings, while having limited effects on water lubrication; mechanical deformation largely affects water lubrication, while its effects are typically lower than thermal deformation with oil. One common turbulence model used in these analysis tools is the eddy-viscosity model. Eddy-viscosity depends on the wall shear stress, therefore effective wall shear stress modeling is necessary in determining an appropriate turbulence model. Improving the accuracy and efficiency of modeling approaches for eddy-viscosity in turbulence models is of great importance. Therefore, the purpose of this study is to perform mesh refinement for water-lubricated bearings based on methodologies of eddy-viscosity modeling to improve their accuracy. According to Szeri [1], ε m /v for the Boussinesq hypothesis is given by Reichardt’s formula. Fitting the velocity profile with experiments having a y + in the range of 0–1,000 results in Ng-optimized Reichardt’s constants k = 0.4 and δ + = 10.7. He clearly states that for y + > 1000 theoretical predictions and experiments have a greater variance. Armentrout and others [2] developed an equation for δ + as a function of the pivot Reynolds number, which they validated with CFD simulations. The definition of y + can be used to approximate the first layer thickness calculated for a uniform mesh. Together with Armentrout’s equation, the number of required elements across the film thickness can be obtained. For typical turbulence models, the y + must be within a certain range to be accurate. On the condition that the y + is fixed to that of a standard oil bearing for which an oil bearing code was validated, the number of elements across the film thickness and coefficients used in the eddy-viscosity equation can be adjusted to allow for convergence with other fluids other than that which the traditional oil bearing code was designed for. In this study, the number of required elements across the film for improved prediction quality was calculated based on the proposed eddy-viscosity model mesh correction from the known literature. A comparison between water lubrication using the parameter correction and oil lubrication was also made. The results of this study could aid in improving future designs and models of water-lubricated bearings.

Laser metal deposition (LMD) — also referred to as laser deposition welding — has been a well-established process for years. One example of its use is for tip repair for gas turbine blades from Siemens. The decision to also implement laser welding technology for the service of industrial steam turbines was based primarily on the fact that repairs — especially conventional welds and coatings including heat treatment and testing — are very time consuming and are very difficult to reconcile with the overhaul periods planned by customers. The robot supported automation of the LMD process and the fact of its lower heat input, reduced layer thicknesses and the resulting lowered deformation of the part due to reduced coating areas makes it possible to optimize lead times. The high level of process automation and reliability of a laser welding process represents another important benefit. Similarly, process parameters are constantly monitored and tracked, to ensure that the required quality standards are maintained and even increased. Furthermore, laser metal deposition completely replaced the conventional processes such as tungsten inert gas method (TIG), plasma transferred arc (PTA) and detonation spraying. In addition the technology unleashes now the possibility to repair and refurbish parts instead of new manufacturing, and therefore delivery times can be tremendously reduced. Based on the decision to six-axis robots it becomes possible enhancing the LMD process for complex 3D surfaces. After modeling a digital twin in Siemens NX CAM it is possible to generate, optimize and simulate the whole motion-sequences offline before starting the LMD process in the robot cell. So already designed parts in 3D-CAD can be used to develop the final robot program. In addition already existing technologies like 3D surface scanning will be implemented in the chain to support the LMD process. Digitalization turns from a buzzword to an established technology for industrial steam turbine manufacturing and repair.

The rubbing between static and moving parts of steam turbine is one of the frequent faults and difficult to diagnose accurately. In the high-speed rotation of steam turbine, if the clearance between the static and moving parts is too small, there is a possibility of rubbing accident, especially for the ends of LP steam turbine in a nuclear power plant, which will affect the safety operation of the steam turbine. In this paper, the gland seal housing deformation of LP casing in 1000MW nuclear steam turbine is calculated and analyzed. Based on ProE and ANSYS/Workbench software, the 3D geometry model and the finite element mathematical model of LP inner casing of nuclear steam turbine are established, and the boundary conditions are determined at first. Secondly, the deformation of the gland seal housing at the LP casing end is calculated and analyzed under different conditions. Thirdly, the influence of different components temperature rise on the deformation of gland seal housing is analyzed.

Over the service time, the rotating parts of turbine engine vary in their geometry. When aircraft take off or fly through a volcanic ash cloud, the particles are sucked into the engine, impinge the blade and gradually erode the surface. The impinging between particles and blades is responsible for the increase of the surface roughness. Also, during the long-time operation, the function of the blade’s stacking law combined with the centrifugal force could cause deviation of the stagger angle. Moreover, blade tip clearance could vary because of the casing deformation. All the deformation of geometry could severely reduce the engine performance and thus engine life. The work presented in this paper focused on the influence of geometry deformation in a real low-pressure compressor. The investigation is more difficult than most of the previously published researches with a total of five stages being considered. Due to the irregularities in geometry, it is difficult to numerically assess the performance of the compressor. The aim of this study is to give an analysis method that allows an efficient and accurate estimation of the performance for multistage compressor with geometry deformation. In the first step, the geometry models with different deviation in tip clearance, roughness and stagger angle were established respectively. A CFD study was then applied to the compressor with RANS method to calculate the flow field with different types of deformation. The variation of overall performance due to the deformation was finally analyzed to identify the dominant factor on influencing the performance of the compressor among different types of geometry deformation. A method based on polytropic efficiency analysis and flow field analysis was also established to specifically analyze which stage is most sensitive to the geometry deformation. The results show a significant influence of geometric deformation on the efficiency, total pressure rise and flow range of the multistage compressor. The conclusions of this study would provide an important guidance for engine overhaul in the factory.

In the conceptual and preliminary aircraft design phase the Free-Form Deformation (FFD) is one of various parametrization schemes to define the geometry of an engine’s nacelle. This paper presents a method that is able to create a C2 continuous periodic approximation of existing reference nacelles with the B-spline based FFD, which is a generalization of the classical FFD. The basic principle of this method is to start with a rotational symmetric B-spline approximation of the reference nacelle, which is subsequently deformed with a FFD grid that is placed around the initial geometry. A method is derived that computes the displacement of the FFD grid points, such that the deformed nacelle approximates the reference nacelle with minimal deviations. As this turns out to be a linear inverse problem, it can be solved with a linear least squares fit. To avoid overfitting effects — like degenerative FFD grids which imply excessive local deformations — the inverse problem is regularized with the Tikhonov approach. The NASA CRM model and the IAE V2500 engine have been selected as reference geometries. Both resemble nacelles that are typically found on common aircraft models and both deviate sufficiently from the rotational symmetry. It is demonstrated that the mean error of the approximation decreases with an increase of the number of FFD grid points and how the regularization affects these results. Finally, the B-spline based FFD with the classical Bernstein based FFD are compared for both models. The results conceptually prove the usability of the FFD approach for the construction of nacelle geometries in the preliminary aircraft design phase.

During rapid engine throttling operations, turbine airfoils can experience very rapid heating and cooling, particularly at take-off conditions. These rapid transient events lead to the generation of high thermal gradients and non-uniform stress distributions through the thermal barrier coating, environmental barrier/bond coating and substrate. This in turn can lead to coating delamination, overheat of the substrate materials, creep and thermo-mechanical fatigue of the part. We present the process and computer modeling methodology for a physics-based prediction of deformation, damage, crack propagation and local failure modes in coated turbine airfoils and other parts operating at hot section turbine environment conditions as a function of engine operational regimes, with a particular emphasis on rapid transient events. The overall goal is to predict the effects and severity of the cooling and heating thermal rates on transient thermal mechanical fatigue life of coated hot parts (turbine airfoils, blade outer air seals and combustor liners). The computational analysis incorporates time-accurate, coupled aerothermodynamics with non-linear deformation thermal-structural finite element modeling and fracture mechanics modeling for high rate thermal transient events. Thermal barrier coating thermal failure and spallation are introduced by the use of interface fracture toughness and interface property evolution as well as dissipated energy rate. The spallation model allows estimations of the part remaining life as a function of the heating/cooling rates. Applicability of the developed model is verified using experimental coupons and calibrated against burner rig test data for high flux thermal cycles. Our results show a decrease in TBC spall life due to high rate transient events.

One of the most urgent questions in aviation engine development is how to reduce the mass of composition details, while meeting the demands for strength and reliability. The production of complex, critical aircraft engine details is constrained by the limited capabilities of traditional fabrication methods. However, complex-shaped parts can now be created using emerging additive technologies that will avoid many of the traditional manufacturing methods’ limitations and reduce material and time costs. In addition, using additive technologies facilitates the manufacturing of details such as cellular and lattice structures, the production of which is impossible with traditional methods. The use of cellular structures is one way to reduce the weight of parts. Lattice structures are used to provide rigidity and strength in industries where parts are exposed to compression, bending and impact loads. The cell structures can withstand significant deformation without fracture and have a high resistance to fatigue. Since the weight of such structures is much less than the original prototypes, using them creates new opportunities for future aircraft applications. This article discusses the issue of creating lightweight structures for compressor components containing different cellular structures and their manufacturing using additive technology methods. We have examined several simple models of cellular structures and studied their geometrical, mass and stiffness characteristics. Analysis of the stress states of the cellular structures was conducted on the samples, with testing intended for three-point bending and cantilever beams. The influence of the geometrical parameters of the cells on the mass and strength characteristics of the structures was determined. The method for determining the density and elastic modulus of the equivalent homogenous material using these parameters in the calculations was complex. A few models containing the cellular region were proposed and the designs of several fan blades containing the cellular region were discussed. Samples to determine the strength of the developed structural elements were made from titanium alloy powder using Powder Bed Fusion (PBF). Continuous model samples and samples with different cellular structures were manufactured to test.

Aiming at the dynamic design of dual rotor of aero-engine, the dynamic model of dual rotor system was established. And then based on the simulation results of the dynamic model established above, the unbalance distribution of dual rotor and the strain energy distribution of the flexural deformation were analyzed. The results showed that the dynamic load on inter-shaft bearing is determined by the rotor vibration mode and the rotor vibration response at the position of bearing. The flexural deformation can also affect the dynamic load on inter-shaft bearing. Under the influence of elastic restoring force generated by the flexural deformation of rotors, the dynamic load on the inter-shaft bearing under flexural mode is higher than that under the rigid mode. It was found that large dynamic load may act on inter-shaft bearing even though the rotor is not operating in the resonance state. And due to the internal damping of the rotor, the large dynamic load on the inter-shaft bearing can be obviously reduced when the load transmit to other bearings via the rotor with flexural deformation.

One of the possible constraint configuration of an annular combustion chamber in a gas turbine is by means of radial pins. Radial pins usually connect the outer turbine casing to the combustor dome and fix combustor axial and circumferential displacements while allowing combustor free radial deformation, under thermal loads. In the typical mounting scheme, radial pins are screwed on the outer casing and then inserted into dedicated housing holes on the dome. Because of this arrangement the force (introduced by mechanical, thermal and dynamic loads) reacted by each pin is inherently not deterministic since it depends on the actual gap between the pin itself and the housing bush on the dome, which, in turn, is not explicitly known, being a function of the overall tolerance stack up. The scope of this study was to develop a method to design the radial pins of NovaLT™16 (*) combustion chamber, applicable since the conceptual phase, using a probabilistic approach [7]. Actual pin-bush gap distribution is calculated from stack up analysis and then used as input for a numerical simulation which computes the distribution of the reaction force on each pin, as a function of number of pins, stiffness of the pin, gap between pin and bush. Two different arrangements have been considered: the classic scheme and the floating pin configuration. The new probabilistic design approach allowed to have a robust understanding of the force distribution within the whole set of pins, to compute the optimal combination of pin number, pin stiffness, and gap and ultimately to select the floating pin configuration as the one to be implemented in NovaLT16 combustor. Test results revealed pin contact distribution was in line with predictions.

Large turbine bearings are usually equipped with hydrostatic jacking mechanisms to separate bearing and shaft during transient start-stop procedures. They are turned off once hydrodynamic operation is reached. In some cases, under severe operating conditions, the hydrostatic oil supply is kept running although the rotor already runs in full speed. The supplied amount of jacking oil is very small compared to the regular oil supply. However, experimental data of a large tilting-pad bearing shows that this hybrid operation has a considerable impact on the load carrying capacity in terms of lower pad temperature and larger film thickness. In this paper, a theoretical investigation to analyse the effect of increased load carrying capacity of a large tilting-pad journal bearing in hybrid operation is presented. The increase is driven by three different aspects: 1) hydrostatic pressure component, 2) increase in lubricant viscosity due to the injection of cold oil, 3) decrease of temperature gradients and thus thermal pad deformation. Subject of the approach is a ø500 mm five-pad, rocker-pivot tilting-pad journal bearing in flooded lubrication mode. The experiments are carried out on the Bochum test rig for large turbine bearings. The theoretical analyses are performed with a simulation code solving the Reynolds and energy equations for the oil film and calculating the thermomechanical pad deformations simultaneously. By considering each of the three above aspects separately and in combination, their share of load increase can be assessed individually. Contrary to expectations, the results indicate that the increase is not mostly based on the hydrostatic pressure component. Instead, the advantageously decreased pad deformations make the largest contribution to the increased load carrying capacity while the alteration in viscosity shows the least impact.

Tilting-pad journal bearings (TPJBs) ensure rotordynamic stability that could otherwise produce dangerously large amplitude rotor oil-whirl/whip motions in high speed rotating machinery. Currently, highly efficient turbo compressors demand an ever increasing rotor surface speed and specific load on its support bearings. The accurate prediction of bearing performance is vital to guarantee reliable products, specifically with regard to reducing maximum bearing pad temperature and drag power losses, and operating with the least flow rate while still maximizing load capacity. The hydrodynamic pressure and heat generation in an oil film acting on a bearing pad produce significant mechanical and thermal deformations that change the oil film geometry (clearance and preload) to largely affect the bearing performance, static and dynamic. In addition, a high surface speed bearing often operates in the turbulent flow regime that produces a notable increase in power loss and a drop in maximum pad temperature. This paper details a thermoelastohydrodynamic (TEHD) analysis model applied to TPJBs, presents predictions for their steady-load performance, and discusses comparisons with experimental results to validate the model. The test bearing has four pads with a load between pads configuration; its length L = 76.2 mm and shaft diameter D = 101.6 mm ( L / D = 0.75). The rotor top speed is 22.6 krpm, i.e. 120 m/s surface speed, and the maximum specific load is 2.94 MPa for an applied load of 23 kN. The test procedure records shaft speed and applied load, oil supply pressure/temperature and flow rate, and also measures the pads’ temperature and shaft temperature, as well as the discharge oil (sump) temperature. The TEHD model couples a generalized Reynolds equation for the hydrodynamic pressure generation with a three-dimensional energy transport equation for the film temperature. The pad mechanical deformation due to pressure utilizes the finite elemental method, whereas an analytical model estimates thermally induced pad crowning deformations. For operation beyond the laminar flow regime, the analysis incorporates the eddy viscosity concept for fully developed turbulent flow operation. Current predictions demonstrate the influence of pressure and temperature fields on the pads mechanical and thermally induced deformation fields, and also show static performance characteristics such as bearing power loss, flow rate, and pad temperatures. The comparisons of test results and analysis results reveal that turbulent flow effects significantly reduce the pads’ maximum temperature while increasing the bearing power loss. Turbulent flow mixing increases the diffusion of thermal energy and makes more uniform the temperature profile across the film.

A novel active bump type foil bearing (ABFB) is put forward aims at demonstrate the feasibility of applying active lubrication control of the aerodynamic gas bearing. The proposed active structure consists of (1) piezoelectric actuators (PZTs) amounted in the bearing housing to produce control forces, (2) flexure hinges machined in the bearing housing to produce pivot for the lever amplifier, (3) lever amplifier machined in the bearing housing to amplify the deformation of PZTs. The mechanical preloads of the ABFB can be actively adjusted by using lever amplifiers which is actuated and controlled by the controlling the driving voltage on PZTs to create variable multiple lobe clearance and realizing the real time shape changing of the lubricate gas film. The static load-deformation test of the ABFB is done to demonstrate that the preload of the bearing is significantly adjusted by changing the driving voltage on PZTs. The lift-off tests versus different driving voltages of the ABFB are done to illustrate that the change of the preloads can significantly affect the drag torque of the ABFB and illustrate the significance of the active control. Rotordynamic tests of the ABFB with different driving voltages have been conducted. Subsynchronous vibrations of the rotor have been suppressed significantly by increasing the driving voltage. The coast-down time increases with the increase of the driving voltage on PZTs. At the rotational speed of 33krpm, the amplitude of the whip motion can be suppressed timely and actively by controlling the driving voltage on PZTs.

Different forms of Reynolds equation are widely used to predict the performances of foil thrust bearings for air cycle machines. When analyzing bearings operating with highly dense CO 2 , computational fluid dynamics yields more accurate results, particularly at the high rotational speed. In addition, the structural deformation of the top and bump foils are also considered. For some applications, the high temperature increase caused by the viscous heating effect are also modelled in literature. The multi-physics effects within foil bearings, including the fluid flow, structural deformation and viscous heating create challenges and modelling complexity to accurately predict its performances. The aim of this paper is to review and compare different modelling approaches for foil thrust bearings with CO 2 at a range of operating conditions, including loads and rotational speed. For steady state performances, results from turbulent Reynolds equation and computational fluid dynamics are in close agreement for foil thrust bearings operating with low load (large rotor to top foil separations). However, considerable differences exist between turbulent Reynolds equation and computational fluid dynamics method at high loads (small rotor to top foil separation). Here the computational fluid dynamics method must be employed, as the centrifugal inertia effect becomes significant. The top foil deflection need to be considered as the corresponding deformation is significant compared to the initial separation between the rotor and the top foil. At the rotational speed larger than 30000 rpm, the results from the fully fluid-structure-thermal simulations differ from other modelling approaches. The additional deformation caused by temperature increase largely alters the separation between the rotor and top foil. For dynamic performance, the top foil deflection again must be considered as the equivalent stiffness and damping are influenced by bump foil structures. This work provides recommendations for the selection of the suitable modelling approaches for bump-type foil thrust bearings operating with supercritical CO 2 .

The optimization and evaluation of blading clearance is important for gas turbine efficiency and performance. The Ansaldo GT36 gas turbine offers high efficiency together with outstanding flexibility across a large load range. Active management of engine clearances during the complete development process followed by a thorough validation on the Ansaldo test plant facility in Birr, Switzerland enables the GT to attain ambitious clearance targets. The clearance at baseload must be minimized but is limited by the pinch point clearance during cold, warm and hot start-ups — including normal and fast ramp-up and/or shutdown. Therefore transient analysis is necessary for covering the different operating conditions. A well-established process of 2d finite element modelling of the whole engine model (WEM) comprised of axis-symmetric and plane stress elements was used during the design process from concept to detailed design to optimize the clearances. It delivers the transient stator and rotor deformation and together with the compressor and turbine airfoil deformation based on 3D models the basic clearance evaluation process is defined. The GT engine design was significantly influenced, starting with a simplified version of the WEM for identification of the most promising variants. Subsequently a detailed WEM was developed which is fully validated against measurements on the test engine. Different 3D effects are considered separately at identified critical transient conditions and overlaid on the 2d clearances which lead to the final optimized clearances. In addition to this, limitations from each step of the manufacturing process were identified and improved to reduce tolerances and uncertainties to their minimum. The results of the calculation and clearance prediction process are compared against clearance measurements during all kinds of GT operation and cooldown. Passive clearance indicators showing the remaining gap till rubbing would occur and rub marks, in areas that tolerate it, further validate the clearances and clearance prediction process.

In this paper, nonlinear instability of an elliptical jet is investigated by considering the impacts of orifice geometry variations using regular perturbation method. In the breakup mechanisms, created disturbances on the jet interfaces will grow owing to the nonlinear dynamics of fluid. In this study, a scrutiny of nonlinear cylindrical jet breakup is done initially. Next, Cosserat equations as a low order form of Navies-Stokes equations are solved on the nonlinear form to exert the impacts of orifice deformation on various aspect ratios. These nonlinear equations, Cosserat equations, are linearly solved in the past papers. As a result, the dispersion equation is derived to find the most unstable wavelength as well as the breakup length. Results reveal that the elliptical jet with low aspect ratio is more unstable rather than cylindrical jet with aspect ratio of one. Furthermore, the nonlinear equations can predict the break up length of elliptical jet more accurate than linear equations. The predicted results are shown to be in good agreement with the experimental results.

High-frequency (HF) thermoacoustic instabilities in stationary gas turbine combustors are receiving increased attention as they reduce the operational flexibility and increase the emissions of such machines. This paper deals with the numerical work regarding the acoustic and flow design needed to commission a reheat combustor test rig with the aim of revealing the physics behind high frequency flame-acoustics interactions. Methods and workflow that allow for the design of such a reheat test rig are presented. The ultimate objective of the testbed is to give insight into the response of non-compact flames to the first transverse (T1) resonant mode of the combustion chamber. Therefore, the acoustic design promotes a thermoacoustically unstable T1 mode. Furthermore, the combustor is of a flat quasi two-dimensional geometry, which allows to clearly distinguish between flame zones stabilized by auto-ignition and by aerodynamics, respectively. Details on the experimental setup and operation of the test rig are provided in a joint publication. In the paper at hand, first the acoustic design is presented. Second, the isothermal flow design to optimize the combustion regime is outlined. Third, the acoustic characterization of the test rig is performed. To do so, the Helmholtz equation for the whole test rig, including the first stage, is solved via FEM. The simulated T1 mode appears at about 1600 Hz, which matches the experimental observations. Finally, an a priori assessment of linear acoustic damping and driving for the T1 mode is carried out. For the damping part, the two main effects are taken into account: damping due to the acoustic boundary layer and damping due to mean flow-acoustic coupling i.e. acoustic energy dissipated in the shear layers. The linear acoustic driving is estimated by means of source terms of deformation and displacement. The required heat release fields are artificially created and later validated with experimental OH* chemiluminiscence images. Driving and damping together define the linear stability behavior of the test rig.

In this paper, the authors present a solid vane concept which uses 3D woven fabric based SiC/SiC CMC and the result of engine testing which was conducted to demonstrate this concept. The authors devised a design concept, in which a vane is made from a folded woven, for the uncooled turbine vanes of the aircraft engines. The advantage of this concept is that there is no structural weak point because a whole vane including outer / inner platform consists of one continuous woven. In order to demonstrate the applicability of this concept to the actual engine parts, CMC turbine vanes were tested with IHI-IM270 that is a small industrial gas turbine engine. After 862 hour testing, there was no defect such as cracks, wear, and deformation.

The complex structural architecture and inherent processing artefacts within ceramic matrix composites combine to induce inhomogeneous deformation and damage prior to ultimate failure. Sophisticated mechanical characterisation is vital in support of a fundamental understanding of deformation in ceramic matrix composites. On the component scale, “damage tolerant” design and lifing philosophies depend upon laboratory assessments of macro-scale specimens, incorporating typical fibre architectures and matrix under representative stress-strain states. Bulk measurements of strain via extensometry or even localised strain gauging will fail to characterise such inhomogeneity when performing conventional mechanical testing on laboratory scaled coupons. The current research project has, therefore, applied digital image correlation (DIC), electrical resistance monitoring and acoustic emission techniques to the room and high temperature assessment of a SiC f /SiC composite under axial fatigue loading. Data from these separate monitoring techniques plus ancillary use of X-Ray computed tomography and optical inspection were correlated to monitor the onset and progression of damage during cyclic loading.

Low alloy steels are often utilized in components experiencing decades of usage under aggressive operating conditions. Even though there has been remarkable advancement in the development of modern alloys, however, these materials continue to be applied in boilers, heat exchanger tubes, and throttle valve bodies in both turbomachinery and pressure-vessel/piping applications. These steels display excellent resistance to deformation and damage under creep and/or fatigue at moderate temperatures. For example, the material 2.25Cr-1Mo has exceptional balance of ductility, corrosion resistance, and creep strength under temperatures up to 650□C. Both creep and non-isothermal fatigue conditions have been the limiting factor for most 2.25Cr-1Mo components; therefore, a life prediction approach is constructed with the capability of approximating the number of cycles to failure for conditions where the material is experiencing creep and fatigue with thermal cycling. Parameters for the approach are built on regression fits in comparison with a comprehensive experimental database. This database includes low cycle fatigue (LCF), creep fatigue (CF), and thermomechanical fatigue (TMF) experiments. The cumulative damage approach was utilized for the life prediction model where dominant damage maps can be used to determine primary microstructural mechanism associated with failure. Life calculations are facilitated by the usage of a non-interacting creep-plasticity constitutive model capable of representing not only the temperature- and rate-dependence, but also the history-dependence of the material.