Toshihide Igari

Ratchetting characteristics of 316FR steel at high temperature, part I: Strain-controlled ratchetting experiments and simulations

The paper is concerned with characteristics in ratchetting of 316FR steel at high temperature. In Part I, first, by discussing isothermal and nonisothermal “strain-controlled” ratchetting experiments, it is shown that 316FR steel exhibits the almost perfect closure of stress and strain hysteresis loops as well as the isotropic hardening depending on maximum plastic strain rather than accumulated plastic strain. Second, it is demonstrated that the experiments are simulated well using the nonlinear kinematic hardening model proposed in 1993 by Ohno and Wang (Int. J. Plasticity 9, 375–403) if the model is extended by taking account of the isotropic hardening depending on maximum plastic strain. On the basis of these findings, thermal ratchetting of 316FR steel cylinders subjected to the axial variation of temperature is analyzed in Part II.

Evaluation of inelastic constitutive models under plasticity-creep interaction for 214Cr—1Mo steel at 600°C

Abstract Uniaxial tests to identify plasticity-creep interaction in 2 1 4 Cr —1 Mo steel at 600°C were carried out as the Benchmark Project by the Subcommittee on Inelastic Analysis and Life Prediction, JSMS. The purpose of this paper is to present recent experimental data and predictions of constitutive models obtained in the project. Ten types of constitutive models were utilized to compare analytical predictions to sixteen benchmark experiments which are grouped into four categories: (I) tensile and creep tests under monotonic loading, (II) mixed mode tests under plastic and creep loading, (III) ratcheting deformation tests under program loads, and (IV) cyclic deformation tests under the combination of different strain rates. The benchmark tests in Group IV are used to estimate the creep-fatigue life of 2 1 4 Cr —1 Mo steel; the results will be published in a separate paper.

Ratchetting characteristics of 316FR steel at high temperature, part II: Analysis of thermal ratchetting induced by spatial variation of temperature

Abstract On the basis of the material characteristics discussed in Part I, thermal ratchetting of 316FR steel cylinders subjected to the axial variation of temperature is analyzed by implementing in a finite element method three kinds of models, i.e. the elastic-perfectly plastic model, the Armstrong-Frederick model, and the first version of the Ohno-Wang model. The latter two models are specified in two forms, i.e. the combined hardening form verified in Part I and the kinematic hardening form with isotropic hardening neglected. It is shown that the analysis depends greatly on the models examined while it is influenced relatively little by the neglect of isotropic hardening, and that the Ohno-Wang model, which can express the closure of stress and strain hysteresis loops, gives good simulations to experiments in the two cases of long and short travel distances of temperature distributions.

Fatigue-creep life prediction of 214Cr—1Mo steel by inelastic analysis

Abstract This paper covers the second part of the Benchmark Project by the Subcommittee on the Inelastic Analysis and Life Prediction of High Temperature Materials, JSMS, concerning the life prediction methods under fatigue—creep interaction by taking into account the plasticity—creep interaction described by the constitutive models treated in the first part. By specifying a normalized and tempered 2 1 4 Cr —1 Mo steel at 600°C, uniaxial fatigue—creep tests under six patterns of strain waves are performed. Adopting eight types of life estimation methods, two kinds of life prediction procedures are examined: one is a normal way based on an experimentally obtained stress—strain hysteresis loop; and the other is a way of employing the calculated stress—strain hysteresis loop by use of ten types of constitutive models. Predicted lives of the material are compared with observed failure lives, and discussions on the evaluation of the methods are included.

Inelastic behaviour of 214Cr-1Mo steel under plasticity-creep interaction condition: An interim report of the Bench Mark project by the subcommittee on inelastic analysis and life prediction of high temperature materials, JSMS

Some of the interim results of the Bench Mark Project by the Subcommittee on the Inelastic Analysis and Life Prediction of High Temperature Materials, JSMS, is presented. The purpose of the present bench mark study is to review and evaluate the inelastic constitutive models relevant to material response under the plasticity-creep interaction. n nBy specifying normalized and tempered 214Cr-1Mo steel at 600°C, sixteen bench mark problems of four categories are first established: (I) tensile stress-strain relations and creep curves, (II) material response under mixed modes of plastic and creep loading, (III) ratcheting and deformation under program loads, and (IV) cyclic deformation behaviour under the combination of different strain rates. Then, the outline of seventeen inelastic constitutive models of nine types discussed in this project is presented. Finally, the interim results of these bench mark tests are compared with the corresponding predictions of the constitutive models to evaluate their accuracy in simulating the actual behaviour of the material.

Mechanism-Based Evaluation of Thermal Ratcheting due to Traveling Temperature Distribution

Recently, a structural design against a new type of thermal ratchetting under null-primary-stress condition has been required. The representative case is the thermal ratchetting caused by the movement of hot sodium level during, operation in the reactor vessel of FBR. In this paper, the mechanism of this ratchetting is proposed, and the evaluation method of ratchetting strain is proposed based on this mechanism. The proposed evaluation method is basically based on the hoop-membrane stress due to the axial temperature distribution, and considers the influence of axial bending stress and moving distance of temperature distribution. Predicted results by this equation correspond to analytical results by FEM and can conservatively estimate the experimental results with several kinds of moving distance, stress level and two types of temperature hold for Type 316 and 316FR stainless steels.

Evaluation of fatigue-creep life prediction methods in multiaxial stress state

Abstract The present report covers the results of the benchmark project (B) by the Subcommittee on Inelastic Analysis and Life Prediction of High Temperature Materials, the Society of Materials Science, Japan, concerning the fatigue-creep life prediction under multiaxial stress condition of combined tension-compression and cyclic torsion. Multiaxial fatigue-creep tests for 2 1 4 Cr −1 Mo steel at 600°C were performed under both in-phase and out-of-phase strain-controlled wave patterns. Seven types of life prediction methods were employed; they are linear damage rule, strain range partitioning method, and methods by Majumdar, Ostergren, Krempl, Lemaitre-Plumtree-Chaboche and Bui-Quoc. In applying these methods two sets of life prediction schemes are adopted. One is the normal way that the fatigue-creep lives are predicted by the experimentally obtained stress-strain response. Life prediction in the other way is made by employing the calculated stress-strain relation by means of ten kinds of constitutive models described in the report of benchmark project (A). The predicted lives thus obtained were compared with the experimental data, and the accuracy of the life prediction methods was extensively discussed.

Crack propagation life prediction of a perforated plate under thermal fatigue

Abstract Superheater outlet headers of boilers are well known to be subjected to the cycling of high pressure and high thermal stress during plant operations. Thermal stresses during cyclic operation are generally severest on the inside surface of the ligaments between the stub-tube holes, where many examples of ligament cracking due to thermal fatigue have been found recently. A method to predict the crack propagation life of the ligaments of boiler headers under thermal fatigue has been required. Firstly in this paper, to model the crack propagation behavior of the ligament regions of boiler headers, a perforated plate of normalized and tempered 2xa01/4Cr–1Mo steel was examined under out-of-phase thermal fatigue at a maximum temperature of 600°C in the air. Inelastic analysis of the perforated plate under thermal fatigue was carried out, and the nonlinear fracture mechanics parameters such as the J and C∗ integral were obtained by the line integral for observed cracks. A simplified method was proposed for predicting these parameters under displacement-controlled conditions such as thermal fatigue. In this method, the change of the macroscopic stress–strain relation of the perforated plate with propagating cracks was combined with the reference stress concept under displacement-controlled conditions. The predicted fracture mechanics parameters from this method coincided well with those from the inelastic analysis. The prediction of the crack propagation life on the basis of the proposed method provided a good correspondence with the test results of the perforated plate under thermal fatigue.

Advanced evaluation of thermal ratchetting of FBR components

Abstract A new prediction method for the thermal ratchetting of a cylinder subjected to an axially moving temperature distribution is proposed in this paper. This ratchetting is quite different from the conventional Bree-type ratchetting, and an advanced evaluation method has been required in the structural design of FBR components. The proposed method considers the work hardening of actual materials for FBR components. Firstly the basic scheme of the prediction method is shown, and secondly the application procedure to the actual design is shown. Predicted results by using this method coincide well with experimental results, when compared with the case by using the previous method.

Fatigue-creep life prediction for a notched specimen of 214Cr1Mo steel at 600°C

Abstract This paper presents the life prediction of 2 1 4 Cr ue5f81 Mo notched specimens subjected to fast-fast, slow-slow and hold-time loadingsat 600°C. The crack initiation lives of notched specimens were estimated based on the local stress-strain calculated by inelastic finite element analyses. For the life prediction, combinations of seven different constitutive models and five fatigue-creep damage laws were used. The applicability of the constitutive model and damage law is discussed. The constitutive models predict similar stress-strain relations at the notch root, leading to similar predicted lives. The damage model, however, has a much larger influence on the life prediction.