The Experts below are selected from a list of 168 Experts worldwide ranked by ideXlab platform

P A S Reed - One of the best experts on this subject based on the ideXlab platform.

  • a numerical study of the effects of shot peening on the short crack growth behaviour in notched geometries under bending fatigue tests
    International Journal of Fatigue, 2017
    Co-Authors: Mithila Achintha, Binyan He, P A S Reed
    Abstract:

    Abstract The current paper presents a numerical analysis of the effects of shot peening on short crack growth in a low pressure (LP) steam turbine material, FV448. The fatigue behaviour of this material has been experimentally evaluated using a U-notched specimen (representing the Fir Tree Root geometry of the turbine blade) under 3-point bend tests. Two different shot peening intensities were considered in this study: an industrially applied shot peening process and a less intense shot peening process. In the modelling work, a 2-D finite element (FE) model with static short cracks has been developed, incorporating both compressive residual stress and strain hardening distribution effects caused by shot peening. Both linear-elastic (LEFM) and elasto-plastic (EPFM) fracture mechanics were used to characterise the crack driving force in the un-peened and shot-peened conditions, taking into account the effects of stress redistribution caused by residual stress relaxation and crack opening. The stress intensity factor used in the LEFM approach was calculated using the weight function method, and the equivalent stress intensity factor used in the EPFM approach was calculated from the J-integral, which was evaluated using the cracked FE model. These results could explain the mechanism of (experimentally observed) retardation of crack growth through the shot-peening-affected layer and also quantified this influence on fatigue life. The relative contributions of compressive residual stresses and strain hardening were assessed by investigating them separately. The sub-surface compressive residual stress distribution produced by shot peening could effectively reduce crack propagation but the strain hardening distribution, in contrast, can accelerate it. However, strain hardening is expected to hinder the crack initiation process by restricting the plastic deformation during cyclic loading. Predictions of the fatigue life of the shot-peened notched specimens were made based on this numerical analysis. Acceptable results were obtained using both the LEFM and EPFM approaches and the difference between them is discussed.

Helmi Attia - One of the best experts on this subject based on the ideXlab platform.

  • An Experimental Study on Grinding Fir-Tree Root Forms Using Vitrified CBN Wheels
    Advanced Materials Research, 2014
    Co-Authors: Zhong De Shi, Amr Elfizy, Helmi Attia
    Abstract:

    An experimental study was undertaken to explore the conditions and performance on rough and finish grinding Fir-Tree Root forms of turbine blades made of a nickel-based alloy using vitrified CBN wheels and water-based grinding fluid. This work was motivated by switching the grinding of Fir-Tree Root forms from grinding with conventional abrasive wheels to vitrified CBN wheels for reducing overall production cost and enhancing productivity. Grinding experiments were conducted to measure grinding forces, power, surface roughness, and stress near the blade Roots under various dressing and grinding conditions. Wheel re-dressing life in terms of the total number of good parts ground between dressing was tested with the condition producing the maximum material removal rate while satisfying preset part quality and process requirements. It was found that the maximum material removal rate achievable in rough grinding was restricted by the stress limit and the wheel re-dressing life was dominated by the radial wheel wear limit. The targeting part quality and process requirements were achieved. It was proved that vitrified CBN grinding process is feasible and very promising to machine Fir-Tree Root forms.

  • Grinding characteristics of a nickel-based alloy using vitrified CBN wheels
    International Journal of Abrasive Technology, 2012
    Co-Authors: Zhongde Shi, Amr Elfizy, Benoit St-pierre, Helmi Attia
    Abstract:

    An experimental study is reported on the grinding of a nickel-based alloy using vitrified CBN wheels. This work was motivated by switching the grinding of Fir-Tree Root forms of jet engine blades from creep-feed grinding with conventional abrasive wheels to vitrified CBN wheels. The objective is to explore process limits and practical grinding parameters for judging the switch in terms of overall costs and productivity. Straight surface grinding experiments were conducted with water-based fluid on rectangular blocks at a fixed wheel speed vs = 45 m/s, various depths of cut a = 0.05–1.0 mm, and workspeeds vw = 2–40 mm/s. Grinding and dressing power, forces, surface roughness, and radial wheel wear were measured. Specific material removal rate of 8 mm3/(mm.s) was reached in rough grinding using a wheel dressed for achieving surface roughness Ra = 0.8 μm in finish grinding. It was found that shallow depths of cut combined with fast workspeeds, or less creep-feed modes, are more suitable for achieving high ma...

  • Experimental Study on Grinding of a Nickel-Based Alloy Using Vitrified CBN Wheels
    Advanced Materials Research, 2011
    Co-Authors: Zhong De Shi, Amr Elfizy, Benoit St-pierre, Helmi Attia
    Abstract:

    An experimental study is reported on the grinding of a nickel-based alloy using vitrified CBN wheels. This work was motivated by switching the grinding of Fir-Tree Root forms of jet engine blades from creep-feed grinding with conventional abrasive wheels to vitrified CBN wheels. The objective is to explore process limits and practical grinding parameters for judging the switch in terms of overall costs and productivity. Straight surface grinding experiments were conducted with water-based fluid on rectangular blocks at a fixed wheel speed vs = 45 m/s, various depths of cut a = 0.05 - 1.0 mm, and workspeeds vw = 2 - 40 mm/s. Grinding power, forces, surface roughness, and radial wheel wear were measured. Specific material removal rate of 8 mm3/(mm.s) was reached in rough grinding using a wheel dressed for achieving surface roughness Ra = 0.8 µm in finish grinding. It was found that shallow depths of cut combined with fast workspeeds, or less creep-feed modes, are more suitable for achieving high material removal rates with vitrified CBN grinding. Rough grinding is restricted by high grinding temperatures with newly dressed wheels and by chatters with worn wheels.

H. Van Swygenhoven - One of the best experts on this subject based on the ideXlab platform.

  • Origin of localized rafting in Ni-based single crystal turbine blades before service and its influence on the mechanical properties
    Acta Materialia, 2013
    Co-Authors: S. Pierret, T. Etter, A. Evans, H. Van Swygenhoven
    Abstract:

    Abstract The origin of localized rafting has been investigated in a single-crystal second-generation-superalloy Ni-based turbine blade. Localized rafting is observed at the center of the airfoil close to the platform. To explore the role of plastic deformation during the manufacturing process, the microstructure of a Fir-Tree-Root replica is also investigated. Chemical selective characterization methods and neutron diffraction measurements suggest that plastic strains are at the origin of the rafting and not chemical segregations, as is often reported. The formation of rafted microstructures leads to a reduction of ∼12% of the yield strength of the Ni-based superalloy measured at 20 °C.

Philippa Reed - One of the best experts on this subject based on the ideXlab platform.

  • Experimental and numerical investigation of the effects of shot peening on low-cycle fatigue behaviour of notched geometries
    2015
    Co-Authors: Chao You, Mithila Achintha, K.a. Soady, Philippa Reed
    Abstract:

    In service, turbine components are subjected to low-cycle fatigue (LCF) during start-up and shut-down operations, especially at the Fir Tree Root blade-disc connection which has a complex geometry and corresponding high stress concentration. Shot peening generates compressive residual stress (CRS) and strain hardening which can improve fatigue life. However, prediction of the fatigue life of shot-peened components under LCF is challenging due to the complex interaction between the shot peening induced effects and service conditions, especially in regions of high stress concentration. The current study aims to develop a validated 3-D eigenstrain-based modelling tool, which is capable of simulating the stress/strain evolution under LCF in shot-peened notched samples representative of the real turbine blade Fir Tree geometry. The residual stress and strain hardening profiles caused by shot peening were First evaluated by experiments and then incorporated into the finite element (FE) model separately. In addition, the Smith – Watson – Topper (SWT) method was used to predict the fatigue life of shot peened samples, based on the stress/strain data generated using the developed FE model.

  • Fracture Mechanics Analysis of a Single Crystal Turbine Blade
    Volume 6: Structures and Dynamics Parts A and B, 2010
    Co-Authors: W. Beres, Z. Zhang, Philippa Reed
    Abstract:

    Single crystal superalloy turbine blades exhibit anisotropic behaviors, and the stress at the Fir-Tree Root often reaches the yield stress of the material when the turbine operates at the peak rotational speed and at the maximum temperature. The nonlinear behavior of the material character at these operating conditions poses a significant challenge to prediction of the blade behavior using the conventional linear elastic fracture mechanics approach. In this paper a fracture mechanics analysis was performed for a single crystal turbine blade using the J-integral concept. First of all, the elastic-perfectly plastic J-integral and CTOD was used to correlate with the fatigue crack growth rates obtained in a single crystal blade in [100] and [110] directions, with the [001] direction as the loading direction under typical service conditions. The weight function method was used to evaluate the stress intensity factor for a crack growing along the serration bottom of the blade Fir-Tree Root under small-scale yielding conditions and the crack growth analysis was performed using the correlated fatigue crack growth data. In addition, crack growth simulations were also performed using the Zencrack software. The simulated crack growth profile was compared with the actual crack profile on the component.Copyright © 2010 by ASME and National Research Council of Canada

  • Effect of temperature and secondary orientation on notch fatigue resistance of CMSX4
    2005
    Co-Authors: M. D. Miller, Philippa Reed, M.r. Joyce
    Abstract:

    A turbine blade Root contains notches that locate into a “Fir-Tree” Root fixing in the turbine disc. Fatigue initiation in these stress concentrating features is of some concern. When a turbine blade is cast, the primary orientation along the blade is controlled (usually in the direction) to within certain limits, however the secondary orientation (i.e. the orientation of any notches) is not generally controlled. The notch fatigue crack initiation and growth behaviour of CMSX-4 under low cycle fatigue conditions has been investigated at 650°C and 725°C. Two secondary orientations have been investigated and a separate oxidation study has been conducted. Heavy oxidation is observed in the notch Root after a short amount of time at 650°C. At high temperatures, crack initiation occurs at subsurface pores.

Mithila Achintha - One of the best experts on this subject based on the ideXlab platform.

  • a numerical study of the effects of shot peening on the short crack growth behaviour in notched geometries under bending fatigue tests
    International Journal of Fatigue, 2017
    Co-Authors: Mithila Achintha, Binyan He, P A S Reed
    Abstract:

    Abstract The current paper presents a numerical analysis of the effects of shot peening on short crack growth in a low pressure (LP) steam turbine material, FV448. The fatigue behaviour of this material has been experimentally evaluated using a U-notched specimen (representing the Fir Tree Root geometry of the turbine blade) under 3-point bend tests. Two different shot peening intensities were considered in this study: an industrially applied shot peening process and a less intense shot peening process. In the modelling work, a 2-D finite element (FE) model with static short cracks has been developed, incorporating both compressive residual stress and strain hardening distribution effects caused by shot peening. Both linear-elastic (LEFM) and elasto-plastic (EPFM) fracture mechanics were used to characterise the crack driving force in the un-peened and shot-peened conditions, taking into account the effects of stress redistribution caused by residual stress relaxation and crack opening. The stress intensity factor used in the LEFM approach was calculated using the weight function method, and the equivalent stress intensity factor used in the EPFM approach was calculated from the J-integral, which was evaluated using the cracked FE model. These results could explain the mechanism of (experimentally observed) retardation of crack growth through the shot-peening-affected layer and also quantified this influence on fatigue life. The relative contributions of compressive residual stresses and strain hardening were assessed by investigating them separately. The sub-surface compressive residual stress distribution produced by shot peening could effectively reduce crack propagation but the strain hardening distribution, in contrast, can accelerate it. However, strain hardening is expected to hinder the crack initiation process by restricting the plastic deformation during cyclic loading. Predictions of the fatigue life of the shot-peened notched specimens were made based on this numerical analysis. Acceptable results were obtained using both the LEFM and EPFM approaches and the difference between them is discussed.

  • Experimental and numerical investigation of the effects of shot peening on low-cycle fatigue behaviour of notched geometries
    2015
    Co-Authors: Chao You, Mithila Achintha, K.a. Soady, Philippa Reed
    Abstract:

    In service, turbine components are subjected to low-cycle fatigue (LCF) during start-up and shut-down operations, especially at the Fir Tree Root blade-disc connection which has a complex geometry and corresponding high stress concentration. Shot peening generates compressive residual stress (CRS) and strain hardening which can improve fatigue life. However, prediction of the fatigue life of shot-peened components under LCF is challenging due to the complex interaction between the shot peening induced effects and service conditions, especially in regions of high stress concentration. The current study aims to develop a validated 3-D eigenstrain-based modelling tool, which is capable of simulating the stress/strain evolution under LCF in shot-peened notched samples representative of the real turbine blade Fir Tree geometry. The residual stress and strain hardening profiles caused by shot peening were First evaluated by experiments and then incorporated into the finite element (FE) model separately. In addition, the Smith – Watson – Topper (SWT) method was used to predict the fatigue life of shot peened samples, based on the stress/strain data generated using the developed FE model.