Strength, Fracture and Complexity - Volume 9, issue 1

Authors: Saxena, Ashok | Nikbin, Kamran | Yokobori Jr., A. Toshimitsu

Article Type: Editorial

DOI: 10.3233/SFC-150174

Citation: Strength, Fracture and Complexity, vol. 9, no. 1, pp. 1-1, 2015

Authors: Saxena, Ashok | Narasimhachary, Santosh B. | Kalyanasundaram, Valliappa

Article Type: Research Article

Abstract: Time-dependent fracture mechanics (TDFM) is used to predict the remaining life and safe inspection intervals as part of maintenance programs for components operating in harsh, high temperature environments. The influence of creep deformation and time-dependent damage accumulation presents very significant challenges in accurately predicting life of these components. A critical assessment of the current state-of-the-art of TDFM concepts, test techniques and analytical procedures is made to demonstrate the potential of this technology. In addition, future developments needed to enhance the application of this technology to interface with field data and online data from sensors to improve prognostics and assure reliable …performance are discussed in this paper. Show more

Keywords: Creep, fatigue, reliability, Ct parameter, neural-net

DOI: 10.3233/SFC-150175

Citation: Strength, Fracture and Complexity, vol. 9, no. 1, pp. 3-14, 2015

Authors: Nikbin, Kamran

Article Type: Research Article

Abstract: Crack growth and fracture predictions are used in high temperature equipment operating in the creep and creep/fatigue range by assessing crack initiation and growth from an existing defect. These procedures are relevant to fossil, nuclear power generation, chemical and aerospace industries. There are three key factors which determine a successful methodology for remaining life assessment of engineering components. The first is good testing techniques; the second is the development of appropriate and accurate correlating parameters to treat the results in a the unified and verifiable manner in order to produce ‘benchmark’ material crack growth properties and the third is an …accurate modelling procedure for life assessment methods. This presentation considers the first two aspects and identifies future trends and improvements in the developments of standardisations in creep and creep/fatigue crack growth testing. Under the auspices of the Versailles Agreement on Materials and Standards (VAMAS) committee a Code of Practice on creep crack growth of components has been developed. The procedure identifies methods of testing for non-standard, welded feature test components in VAMAS TWA31 Technical Working Area on Creep and Creep/Fatigue Crack Growth of weldments containing residual stress. The overview highlights the important points in these pre-standardisation collaborative efforts by presenting the methods of analyses and example of their application to feature type components. Show more

Keywords: Creep damage, damage mechanics, life assessment, crack growth, fatigue

DOI: 10.3233/SFC-150176

Citation: Strength, Fracture and Complexity, vol. 9, no. 1, pp. 15-29, 2015

Authors: Tabuchi, M. | Hongo, H. | Sugiura, R. | Yokobori Jr., A.T. | Yatomi, M. | Kobayashi, K.

Article Type: Research Article

Abstract: High Cr ferritic steels have been used in the 600°C class ultra-super critical (USC) thermal power plants. More than a decade has passed from the application of high Cr steels to USC power plants in Japan, and type-IV creep damages in the welded components become concerns. In the present paper, long-term creep tests for the welded joints of the high Cr steels (Gr.91 and Gr.122 steels) were conducted. Microstructures and creep damages in the heat affected zone (HAZ) were investigated using the thick plate specimens. Remaining life assessment methods of high Cr steel welds were discussed based on the experimental …results. Further, to assist the standardization of the testing method for creep crack growth in welded joints, we have conducted the round robin tests using the high Cr steels (Gr.91 and Gr.92 steels) and their welds as part of the VAMAS TWA31 collaboration. Show more

Keywords: High Cr ferritic steel, welded joint, creep, type-IV damage, creep crack growth

DOI: 10.3233/SFC-150177

Citation: Strength, Fracture and Complexity, vol. 9, no. 1, pp. 31-41, 2015

Authors: Ainsworth, R.A. | Booth, S.E.

Article Type: Research Article

Abstract: This paper proposes that the combined effects of ductile tearing and creep crack growth may be assessed by simple linear addition of the separately assessed crack growth components. Some limited comparisons with experimental data are made using results from compact tension tests on austenitic Type 316H stainless steel. It is demonstrated that experimental creep crack growth data can be misinterpreted if the data are not corrected for both ductile tearing and plastic displacement. However, these two effects tend to balance each other so that it is preferable to correct for neither rather than for only one factor. Alternatively, it is …shown that the time dependent failure assessment diagram approach for creep crack growth can automatically handle tearing-creep interactions by a suitable definition of toughness which does not separate tearing from creep crack growth or plastic displacement from creep displacement. Show more

Keywords: Ductile tearing, creep, crack growth

DOI: 10.3233/SFC-150178

Citation: Strength, Fracture and Complexity, vol. 9, no. 1, pp. 43-59, 2015

Authors: Holdsworth, S.R. | Hosseini, E.

Article Type: Research Article

Abstract: Since the LICON methodology was first developed in the late 1990s to predict the long term creep rupture behaviour of new generation martensitic 9% Cr steels from the results of relatively short duration multi-axial specimen tests, there have been a number of necessary refinements to this originally simple concept. These are reviewed.

Keywords: LICON, multi-axial creep damage enhancement

DOI: 10.3233/SFC-150179

Citation: Strength, Fracture and Complexity, vol. 9, no. 1, pp. 61-70, 2015

Authors: Parker, Jonathan

Article Type: Research Article

Abstract: EPRI has been providing technical support to key Global partners in the Electricity Supply Industry for over 40 years. In the Generation Sector, a key research imperative is knowledge creation and technology transfer linked to reliable, safe and economic flexible operation of power plants. The present paper outlines achievements related to assessment of transients in modern generating plant, highlights particular forms of damage and outlines considerations for additional research. In many cases, this future work will consider the behavior of creep strength enhanced steels. These steels, typically based on 9 to 12% Cr, offer significant benefits to the design and …fabrication of components in high efficiency fossil fuelled plants because, when properly processed, tempered martensitic steels offer an excellent combination of strength and toughness. EPRI collaboration has been focused on root cause assessment so that lessons learned can be used to establish best practice. EPRI facilitated activities have included annual creep–fatigue discussions, publication of summary documents and additional research. Excellence in science and engineering is necessary to underpin technology which will help to meet challenges associated with safe and reliable operation of plant. Show more

Keywords: Flexible operation, advanced steels, creep, fatigue

DOI: 10.3233/SFC-150180

Citation: Strength, Fracture and Complexity, vol. 9, no. 1, pp. 71-86, 2015

Authors: Yatomi, M. | Nikbin, K.M.

Article Type: Research Article

Abstract: This paper presents a numerical simulation technique which can be used to predict numerical creep crack growth (CCG) at elevated temperatures. The results of the numerical predictions are compared to experimental data taken from specimens with weld and parent properties. The experimental results consisted of uniaxial creep data and crack growth data taken from C–Mn steels and P22 welds tested at 360°C and 550°C, respectively. For C–Mn steels, compact tension (CT) specimen and internal pressurised shallow cracked pipe were tested for creep crack growth. Whilst, for P22 welded, HAZ CT specimens were used. The constitutive behaviour for these materials is …described by a power law creep model. A damage-based approach combined with a crack tip constraint model based on void growth is used to predict the crack propagation rates in the pipe component using a 2D finite elements (FE) mesh. Elastic–plastic–creep analyses are performed using a damage based node de-bonding criteria to simulate and predict crack extension under plane stress and plane strain conditions. It has been found that CCG the experimental data lies within the plane stress/strain range of 2D-FE model predictions irrespective of material and geometry. Show more

Keywords: Creep crack growth, finite element analysis, damage, C–Mn, P22

DOI: 10.3233/SFC-150181

Citation: Strength, Fracture and Complexity, vol. 9, no. 1, pp. 87-94, 2015

Authors: Kobayashi, Daisuke | Miyabe, Masamichi | Achiwa, Masahiro | Sugiura, Ruji

Article Type: Research Article

Abstract: To clarify the experimental background of characteristics of fracture life of the investment-cast polycrystalline Nickel-base superalloy IN738LC (typical gas turbine blade’s materials), in-situ observational tests under creep–fatigue conditions were carried out, and the effects of both the cycle- and the time-dependent mechanisms on the fracture life were investigated. Creep ductility, stress holding time and temperature were combined with the relationship between the inverse value of fracture life and applied load frequency as a promoting factor of the time-dependent mechanism. Then a three-dimensional curved surface representation of fracture life under arbitrary creep–fatigue conditions has been proposed theoretically according to the …non-equilibrium science. As the load frequency decreases or stress holding time and temperature increases, the time dependent mechanism begins to play a role in the manner of creep–fatigue interaction. In this region, the characteristics of the Relative Notch Opening Displacement (RNOD) and crack growth behavior change from a cycle-dependent mechanism caused by fatigue to a time-dependent mechanism caused by creep through an unstable equilibrium transition region. In this paper, comparison of the three-dimensional curved surface representation of fracture life which has unique characteristics and the actual damage behavior measured by the Electron Back Scattered Diffraction (EBSD) method was carried out. As a result, misorientation analysis based on the EBSD method has clarified that the unstable equilibrium transition region in the three-dimensional curved surface was the result of creep damage concentration in the vicinity of notches by a load frequency which has the effect of limiting the damage region. Show more

Keywords: Nickel-base superalloy, EBSD, misorientation, law of fracture life, creep–fatigue conditions

DOI: 10.3233/SFC-150182

Citation: Strength, Fracture and Complexity, vol. 9, no. 1, pp. 95-109, 2015

Authors: Ozeki, Go | Yokobori Jr., A. Toshimitsu | Sugiura, Ryuji | Ito, Michifumi

Article Type: Research Article

Abstract: Ni-base directionally solidified superalloy are used under complex conditions of high temperature creep and fatigue interaction. Under these conditions, the characteristics of load frequency for fracture life show a nonlinear behavior, and these characteristics show various features depending on material, temperature and stress holding time. In this study, crack growth tests were conducted under creep–fatigue interactive conditions with stress holding time, t H using the in-situ observational system for directionally solidified Ni-base superalloy CM247LC. To characterize the load frequency of fracture life for CM247LC, the separate estimation of cyclic dependent from time …dependent mechanisms was conducted. Additionally, a developed representation of the characteristic of fracture life under the conditions of creep fatigue interaction based on non-equilibrium science and chaos theory was proposed. Furthermore, verification of the established law of predicting the fracture life under creep–fatigue interactive conditions was conducted. Show more

Keywords: Ni-base directionally solidified superalloy, fracture life, non-equilibrium science, creep–fatigue interactive condition

DOI: 10.3233/SFC-150183

Citation: Strength, Fracture and Complexity, vol. 9, no. 1, pp. 111-123, 2015