Strain Range Partitioning Method Research Articles

Grain boundary sliding model for assessing creep-fatigue life of Sn37Pb eutectic solder

This study discusses the creep-fatigue life prediction of eutectic Sn37Pb solder. Creep-fatigue lives were experimentally obtained at 313 K using fast-fast, slow-slow, slow-fast, fast-slow, and strain-hold waveforms. Conventional four creep-fatigue life prediction rules, time fraction rule, strain range partitioning method, frequency modified fatigue life, and ductility exhaustion model was used to predict the creep-fatigue lives. However, not all the rules were able to properly estimate them. Since the grain boundary sliding rates were closely related to creep-fatigue lives, a new life prediction method based on grain boundary sliding rates was proposed.

Thermo-Mechanical Fatigue Life Evaluation for Ni-23Cr-7W Alloy by Strain Range Partitioning Method

Thermo-Mechanical Fatigue Life Evaluation for Ni-23Cr-7W Alloy by Strain Range Partitioning Method

Creep-Fatigue Behaviors and Life Assessments in Two Nickel-Based Superalloys

The aim of this paper is to investigate different factors, including dwell time, strain range, and strain ratio on creep-fatigue endurances in nickel-based Inconel 718 and GH4169 superalloys. We also summarize classic approaches for life assessments based on the generalizations of Coffin–Manson equation, linear damage summation (LDS), and strain-range partitioning (SRP) method. Each approach does have some degree of success in dealing with a specific set of creep–fatigue data. In order to evaluate the prediction capabilities of the validated approaches, a Bayesian information criterion (BIC) allowing for maximum likelihood and principle of parsimony is used to select the best performing model.

Thermo-mechanical fatigue behavior of nickel-based 23Cr-45Ni-7W alloy for boiler pipes and tubes

This study focuses on thermo-mechanical fatigue (TMF) behaviors of nickel-based 23Cr-45Ni-7W alloy for pipes and tubes in high-efficiency power boilers. TMF tests (maximum temperature = 700 °C; minimum temperature = 100 °C) were conducted under in-phase (IP) and out-of-phase (OP) conditions. The lives under the IP condition is 0.30–0.44 times of that under the OP condition when same total strain range, Δεt, is applied. The TMF properties obtained via the tests are compared with the results of isothermal fatigue (ITF) tests conducted at 700 °C and bithermal fatigue (BTF) tests with maximum and minimum temperatures of 700 °C and 100 °C, respectively. The fracture morphology for each type of TMF, ITF, and BTF is similar under the test conditions of this study. Intergranular cracking is predominant under application of cyclic tensile creep strain during the fatigue tests, and transgranular cracking is predominant under application of cyclic compressive creep strain during the fatigue tests. The inelastic strain range–fatigue life (Δεin–Nf) relation in the TMF test and the inelastic strain range components–life (Δεij–Nij) relation determined using the strain range partitioning method show a good agreement within a factor of 1.5 scatter band. These results indicate the possibility of predicting the TMF life of the 23Cr-45Ni-7W alloy using the results of the ITF test by considering the amount and direction (tension or compression) of creep strain applied to the alloy.

Creep–fatigue endurance of 304 stainless steels

In this paper, the effects of different factors on the combined creep–fatigue endurance of 304 stainless steel as well as the strength and limitation of the different approaches for creep–fatigue life prediction are reviewed. The factors, which influence on the creep–fatigue endurance, include hold time, strain range, temperature, and stress relaxation behavior. Some relationships between time or number of cycles to failure and the individual factors are summarized from the available data. A phenomenological approach is proposed to describe the synergistic effects of different factors. The approaches used for creep–fatigue life prediction range from purely empirical to mechanistic models based on microstructural observations. Each approach does have some degree of success in dealing with a specific set of creep–fatigue data. The comparison of the prediction capacities of linear damage summation method, strain-range partitioning method, and damage rate approach is made for the same set of creep–fatigue data through Bayesian information criterion analysis. The damage rate model exhibits higher accuracy than other two models.

Creep-fatigue life assessment for three kinds of solders

This paper presents a creep-fatigue life evaluation for three kinds of solders of Sn–37Pb, Sn– 3.5Ag and Sn – 3.0Ag – 0.5Cu. Strain controlled push – pull creep-fatigue tests were performed for solid bar specimens under fast–fast, fast–slow, slow–fast and strain–hold strain waveforms and the effect of strain waveforms on creep-fatigue lives is discussed. Sn– 3.5Ag and Sn– 3.0Ag – 0.5Cu solders showed stronger creep-fatigue resistance compared to Sn –37Pb solder. The applicability of the linear damage rule, the strain range partitioning method and the grain boundary sliding model is discussed for predicting creep-fatigue lives of the three solders. The strain range partitioning method and the grain boundary sliding model satisfactorily predicted creep-fatigue lives within a small scatter.

Prediction of fatigue life of high-heat-load components made of oxygen-free copper by comparing with Glidcop

Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep-fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep-fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment.

Creep-fatigue life assessment for three kinds of solders

This paper presents a creep-fatigue life evaluation for three kinds of solders of Sn–37Pb, Sn– 3.5Ag and Sn – 3.0Ag – 0.5Cu. Strain controlled push – pull creep-fatigue tests were performed for solid bar specimens under fast–fast, fast–slow, slow–fast and strain–hold strain waveforms and the effect of strain waveforms on creep-fatigue lives is discussed. Sn– 3.5Ag and Sn– 3.0Ag – 0.5Cu solders showed stronger creep-fatigue resistance compared to Sn –37Pb solder. The applicability of the linear damage rule, the strain range partitioning method and the grain boundary sliding model is discussed for predicting creep-fatigue lives of the three solders. The strain range partitioning method and the grain boundary sliding model satisfactorily predicted creep-fatigue lives within a small scatter.

Isothermal, Thermo-Mechanical and Bithermal Fatigue Life of Ni Base Alloy HR6W for Piping in 700 °C USC Power Plants

Three types of high temperature fatigue tests are carried out for HR6W, which is one of the candidate materials for piping in an advanced ultra super critical (A-USC) power boiler operating over 700°C steam condition. The first test is the isothermal fatigue test at 700°C, the second one is the thermo-mechanical fatigue (TMF) test between 100°Cand 700°C under in-phase and out-of-phase conditions, the final one is the bithermal fatigue (BTF) test at 100°C and 700°C. The relations between the partitioned inelastic strain range determined by the strain range partitioning method and the life in those tests show good agreement, while the relations between the total strain range and the life show some differences.

Creep-Fatigue Life Evaluation of Sn-3.5Ag-0.5Cu-Ni-Ge Solder at Low Temperatures

This paper describes creep-fatigue lives of Sn-3.5Ag-0.5Cu-Ni-Ge solder at low temperatures. Push-pull creep-fatigue tests under four types of strain wave form were carried out at 253K and 273K to study an application of creep-fatigue life evaluation method for Sn-3.5Ag-0.5Cu-Ni-Ge. There were effects of temperatures on stress amplitude, and tension stress amplitude at 253K was larger than that at 273K in fast-fast wave form test. The higher stress amplitude reduced the creep-fatigue lives. The creep-fatigue lives with slow strain rate were shorter than the creep-fatigue lives with fast strain rate. A linear damage rule and a strain range partitioning method estimated the creep-fatigue lives in a large scatter. A grain boundary sliding model was a suitable parameter for creep-fatigue life estimation for Sn-3.5Ag-0.5Cu-Ni-Ge.

Investigation and modeling of low cycle fatigue behaviors of two Ni-based superalloys under dwell conditions

The ability to predict fatigue behaviors of turbine-disk-materials under operating conditions is an important aspect of designing a safe turbine engine. Studies of two Ni-based superalloys, powder metallurgy (PM) FGH95 and Cast GH4169, have been undertaken to investigate their low cycle fatigue (LCF) behaviors with different dwell conditions reflecting the fatigue–creep interaction at high temperature of 650 °C. Based on the deformation behaviors obtained by the tests, the effects of dwell on mean stress and shape of hysteretic loop at half life have been analyzed and considered to be introduced in developing a new fatigue model. For the purpose, two groups of parameters are defined in order to introduce the effects of mean stress and shape of hysteretic loop, especially due to their changes caused by dwell. Finally, an energy-based fatigue model is given with modifying of the original energy-type damage parameter. As a comparison, four typical models of LCF are used to model the experimental results, which are the Strain Range Partitioning method (SRP), the Frequency Separation method (FS), the Damage Rate method (DR) and the Ostergren method. The experimental data of LCF of cast and wrought (CW) Rene95, and PM Rene95 from open resources are also used to verify abilities of the newly-developed model. The results show that the model can describe fatigue behaviors well, and the scatter bands are within ±2, even considering the dwell effects. The accuracy and adaptability of predicting LCF life of the model are better than those of the four existing models.

Creep-Fatigue Life Assessment for Sn-3.0Ag-0.5Cu Solder

This paper describes the creep-fatigue life assessment of Sn-3.0Ag-0.5Cu solder under pull-push loading using fast-fast, fast-slow, slow-fast and strain-hold strain waveforms. Strain controlled creep-fatigue tests were carried out using solid bar specimen, and the effect of strain waveform on the creep-fatigue life was discussed. Creep-fatigue damage was evaluated by the linear damage rule, the frequency modified fatigue life, the ductility exhaustion model, the strain range partitioning method and the grain boundary sliding model. The strain range partitioning method and the grain boundary sliding model only predicted the creep-fatigue lives within a small scatter.

Life Estimation of SUS304 Steel Subjected to Nonproportionally Combined Push-Pull and Cyclic Torsion at 973K

The present paper summarizes the fully reversed strain-controlled creep-fatigue tests conducted on thin-walled tubular specimens of SUS304 austenitic stainless steel at 973K in air under push-pull, cyclic torsion, in-phase straining and 90deg out-of-phase straining of push-pull and cyclic torsion. It is shown that, as the results of analysis of the experimental data by the strain-range partitioning methodand the critical plane model parameter, a new inelastic-strain based parameter was proposed for life estimation of SUS304 subject to nonproportionally combined push-pull and cyclic torsion by the strain-range partitioning method.

Effect of Multiaxial Stress State on High-Temperature Low-Cycle Fatigue Properties of SUS304 Steel

Fully reversed strain-controlled low-cycle fatigue tests, so called PP tests, were conducted on thin-walled tubular specimens of SUS304 austenitic stainless steel at 973K in air under proportional and nonproportinal loading conditions. Push-pull straining, cyclic torsion straining and in-phase straining of push-pull and cyclic torsion were selected as proportional loading, and 90deg out-of-phase straining of push-pull and cyclic torsion as nonproportional loading. Experimental data were analyzed by using both the Manson-Coffin equation and the critical plane model proposed by Brown and Miller, and the effects of the multiaxial stress state on the strain range versus life relationship were discussed. As the results, a new parameter was proposed that has a hopeful potential to estimate the effect of nonproportional loading on creep-fatigue life quantitatively based on the strain range partitioning method.

Power-exponent function model for low-cycle fatigue life prediction and its applications – Part II: Life prediction of turbine blades under creep–fatigue interaction

This paper is concerned with the applications of the proposed models, namely the modified linear damage summation (MLDS) method and the modified strain range partitioning (MSRP) method described in Part I of the series papers, to life prediction of turbine blades under creep–fatigue interaction. To begin with, a detailed FEM analysis is conducted considering peak loading of thermal load, centrifugal force and airflow force to determine life assessment positions. Secondly, according to the blades rig testing load, a stress–strain response analysis is performed for pure low-cycle fatigue (LCF) and creep–fatigue interaction, in which steady-state temperature field, plastic kinematic hardening and contact between the blade body and hoop segment are taken into consideration to achieve accordance with practical conditions. Finally, based on FEM simulation results, the life of turbine blades is predicted using the five different models for creep–fatigue loading. A minimum safe and conservative life of 1293 h is given by the MLDS method based on power-exponent function model. The predicted lives by the MLDS and MSRP methods show reasonable agreement with the rig testing life, which further illustrates the validity of power-exponent function model and its applications.

Power-exponent function model for low-cycle fatigue life prediction and its applications – Part I: Models and validations

Based on power transformation method, this paper advances a power-exponent function model for low-cycle fatigue (LCF) life prediction and then introduces it to creep–fatigue life prediction methods – the strain range partitioning (SRP) method and the linear damage summation (LDS) method for comprehensive assessment of power-exponent function model. Power transformation exponents ( p) are given for some typical materials. Through LCF and creep–fatigue life predictions for these materials, we illustrate the validity of power-exponent function model and its applications. The comparisons between different models show that the power-exponent function model has better performances for LCF life prediction. In nature, Manson–Coffin law is the first order Taylor expansion approximation of power-exponent function model in log–log scale coordinates, corresponding to p = 1. The enhancement of nonlinearity makes the power-exponent function model and its applications to creep–fatigue life prediction methods more precise than the corresponding unmodified methods, whereas these models still use linear parameter regression method and remain simple for engineering applications. An example of these models’ applications to life prediction of turbine blades under creep–fatigue interaction is given in the accompanying paper.

3556 Sn-3.5Agはんだの低温度におけるクリープ疲労寿命評価(S23-1 疲労特性,S23 電子実装用はんだの強度特性評価)

This paper describes the creep-fatigue lives of Sn-3.5Ag solder at low temperatures. Push-pull creep-fatigue tests were carried out at 273K to examine the effect of temperature and strain rate on fatigue life. Slow tension-going straining was more detrimental to lifetimes than slow compression-going straining. Strain range partitioning (SRP) method was a suitable parameter for the correlation of creep-fatigue lives. The SRP method using 313K data predicted almost all of the experimental lifetimes within a factor of 2 scatter band. Many small cracks with roughened surface were observed in the specimen after tests.

Creep-Fatigue Life Evaluation for Sn-3.5Ag Solder

This paper studies the creep-fatigue life evaluation of Sn-3.5Ag solder under push-pull loading using fast-fast, fast-slow, slow-fast, slow-slow, and strain-hold strain waves. Extensive creep-fatigue data were generated using these strain waves and the applicability of four conventional creep-fatigue damage rules, the linear damage rule, the frequency modified fatigue life, the ductility exhaustion model, and the strain range partitioning method, was examined. No conventional damage rules evaluated creep-fatigue lives accurately. Only the grain boundary sliding model, developed recently for solders, predicted creep-fatigue lives with a small scatter.

A Strain Rate Ratio Approach for Assessing Creep-Fatigue Life of 63Sn-37Pb Solder Under Shear Loading

This paper studies creep-fatigue life prediction under shear loading by making extensive torsion creep-fatigue experiments using four kinds of strain waves. The linear damage rule, strain range partitioning method, frequency modified fatigue life, and ductility exhaustion model were applied to the experimental data, but no methods accurately predicted the creep-fatigue life. A new method based on the strain rate ratio, which predicted the creep-fatigue life within a factor of 4 scatter band, was developed.

永久磁石式渦電流リターダのクリープ疲労寿命予測

The strain range partitioning method was applied to a creep-fatigue life prediction of the rotor of the permanent magnet type eddy current retarder, which is a braking system equipped in heavy trucks. Transient heat transfer analysis and elastic-plastic-creep thermal stress analysis were conducted with a three-dimensional finite element model in order to evaluate the inelastic strain caused by repetition of braking. On the basis of analytical results and creep-fatigue properties of rotor steels, creep-fatigue life of the rotor was predicted by the strain range partitioning method and creep-fatigue damage rule based on the strain range partitioning concept. The predicted lives were well corresponded with those in thermal cycle tests with the actual retarder. Furthermore, in order to increase the braking torque and extend the life of the rotor, the new rotor steel was developed. The developed steel has lower electrical resistivity and higher strength at high temperature than the conventional rotor steel. It was found that the developed steel rotor has higher braking torque and longer creep-fatigue life than those of the conventional steel rotor.