Universal Slope Method Research Articles

Estimation of Low-Cycle Fatigue Life of Elbow Pipes Considering the Multi-Axial Stress Effect

The stress states of elbow pipes are complex and different from those of straight pipes. Manson's universal slope method cannot predict the low-cycle fatigue lives of elbow pipes under combined cyclic bending and internal pressure. In this work, fatigue tests and finite element analysis showed that the multi-axial stress factor (i.e., ratio of axial stress to hoop stress) is quite high at elbows. This paper proposes a revised Manson's universal slope method that considers the multi-axial stress factor to predict the low-cycle fatigue lives of elbows under combined cyclic bending and internal pressure with considerably high accuracy.

Life Estimation of a Steam Turbine Blade Using Low Cycle Fatigue Analysis

This work is primarily focused in utilising a technique to assess low cycle fatigue life of steam turbine blade. Two approaches are employed here, first is based on the linear elastic finite element analysis. Fictive elastic results are recalculated using Neuber's rule. Second approach is based on elastic-plastic Finite Element analysis (FEA). Strain amplitude approach is followed through Universal slope method and Coffin-Manson equation to determine the number of start-up and shut down cyclesProper blade design with conservative stress levels is important for reliability in rotor blade design. Finite Element Analysis based fatigue tools enable reliable fatigue life calculations to be done at the design stage of a development process and a proper design methodology is important to predict the catastrophic failure of turbine blade due to fatigue.

OS0822 修正共通勾配法によるエルボ配管の低サイクル寿命評価

OS0822 修正共通勾配法によるエルボ配管の低サイクル寿命評価

Characterization of high temperature long-term fatigue properties for advanced ferritic heat-resisting steels

Axial strain-controlled fatigue tests of a 9 mass% chromium (Cr)-2 mass% tungsten (W) and a 12Cr-2W ferritic heat-resisting steels were performed to obtain fatigue life curves (S-N curve) over a wide from 10 2 to 10 6 cycles at room tem- perature (RT), 400, 600, 650 and 700 ◦ C, respectively. As the results, Manson-Coffin relationships between plastic strain range and fatigue life for the both the steels appear linear at RT and 400 ◦ C, however the relationships have inflection around 10 4 cy- cles beyond 600 ◦ C. Moreover, it is cleared that subgrains became coarse uniformly in the low-cycle regions, while subgrains did coarse locally near grain boundaries in the high-cycle regions. Therefore it is suggested that differences in the mechanical factors and change in subgrain structure cause the inflection of Manson-Coffin relations at the elevated temperatures. Then, a modified universal slope method is proposed for S-N curves that considered to inflection in Manson-Coffin relations.

A Validity of Estimation Methods of Total Strain-Fatigue Life Curve about Copper and Copper Alloys

Before now, several estimation methods of total strain-fatigue life curve (Δεt-Nf curve) formulated by mechanical properties have been proposed. In these estimation methods, Universal slopes method, Modified universal slopes method and Medians method can be utilized effectively for preliminary fatigue design. However, it appears that the validity of three estimation methods about copper and copper alloys has been not investigated. Accordingly, in this report, actual fatigue life (Nf) of copper and copper alloys were compared to predicted fatigue life (Np) obtained by each three estimation methods in order to investigate their validity.The conclusions are obtained as follows :(1) Equation approximated on Medians method by strain controlled fatigue test results of copper and copper alloys was suggested as follows.Δεt=(2.70σB/E)Nf-0.0805+0.543Nf-0.529(2) Precision of Np obtained by Universal slopes method was the worst in three estimation methods. In addition, this Np was non-conservative prediction under 104cycles and conservative prediction over 105cycles. Consequently, It is decided that Universal slopes method was not practical for preliminary fatigue design.(3) Precision of Np obtained by Modified universal slopes method was better than one of Np obtained by Medians method. But, the advantages and disadvantages of two estimation methods could not be judged, because precisions of two may be change according to increase of experimental results. At the present time, It is thought that there is no difference of a practical use for preliminary fatigue design between Modified universal slopes method and Medians method.

Comparison of prediction methods for low-cycle fatigue life of HIP superalloys at elevated temperatures for turbopump reliability

Turbopumps which pressurize fuels and oxidizers are generally used to operate liquid rocket engine for space launch vehicles. It is considered very important to predict fatigue properties at elevated temperatures for the design and manufacturing of reliable turbopump systems. Hot isostatic pressing (HIP) is one of the most promising manufacturing methods for gas turbine rotors. In this research, five kinds of Ni-based superalloys (Inconel 718 HIP, Inconel 718 HIP and heat treated, MAR-M-247 HIP, MAR-M-247 HIP and heat treated and Rene 95 HIP) were investigated at elevated temperatures. Original universal slopes method, modified universal slopes method, Mitchell's method, Bäumel and Seeger's method, and Ong's method have been used for predicting the high temperature low-cycle fatigue performance. Among these methods, Mitchell's method showed the best adaptation results for the life prediction of Ni-based HIP superalloys. A novel equation was suggested by modification of Mitchell's method to predict Ni-based HIP superalloys at elevated temperature more accurately. The equation predicted well the low-cycle fatigue of HIP superalloys as well as of cast Rene 80 at elevated temperatures.

A Practical Use of Simplified Fatigue Life Prediction Method at Stress Concentration of Metals

Fatigue crack initiation life (FCI life) of stress concentration can be predicted according to compare between elastic-plastic strain at there and total strain-fatigue life curve (Δet-Nf curve) of smooth specimen. Elastic-plastic strain is estimated by use of Neuber's rule etc., and Δet-Nf curve is estimated by use of Manson's universal slope method (US method) etc. At this point, cyclic stress-strain curve (CSS curve) is needed in order to estimate the elastic-plastic strain using Neuber's rule etc. However, CSS curve formulated by Ramberg-Osgood relation can be transform from Δet-Nf curve formulated by Coffin-Manson & Basquin relation. Consequently, simplified fatigue life prediction methods can be constructed by only mechanical properties (tensile strength, true fracture ductility, Young modulus, etc.), according to combine these estimation methods (Neuber's rule, US method, etc.).In this report, we compared actual fatigue fracture life (FF life) of some stress concentration specimens with predicted FCI life of them obtained by use of simplified methods, and then evaluated about a practical use of simplified methods. The conclusions are obtained as follows :(1) About the precision of predicted fatigue life, modified universal slope method (MUS method) was better for steels, and Median method was better for aluminum alloys and titanium alloys.(2) For steels, the predicted fatigue life using ESED rule was more effective than using Neuber's rule.(3) In case of using elastic stress concentration factor Kt, the ratio of predicted FCI life Np and actual FF life Nf (Np/Nf) was conspicuously decreasing with increasing of Kt.(4) Taking account of decrease of Np/Nf, simplified method can be employed for preliminary fatigue design.

Low Cycle Fatigue Lives of Sn-37Pb and Sn-3.5Ag Solders at Low Temperatures

This paper describes low cycle fatigue lives of Sn-37Pb and Sn-3.5Ag solders at low temperatures. Push-pull low cycle fatigue tests were carried out at 253K and 273K to study the temperature effect on low cycle fatigue life. Plastic strain range was a suitable parameter for correlating the low cycle fatigue lives for the Sn-37Pb solder at the four temperatures but it was not for the Sn-3.5Ag solder. Strain energy parameter which is defined as the product of strain and stress ranges was a suitable parameter for the Sn-3.5Ag solder. Application of universal slope method was also discussed for predicting the low cycle fatigue lives of Sn-37Pb and Sn-3.5Ag solders.

A new energy-based fatigue damage parameter in life prediction of high-temperature structural materials

A new life prediction model has been developed with the energy-based fatigue damage parameter of a non-dimensional plastic strain energy density (PSED). Tensile tests and low cycle fatigue tests of 316L austenitic stainless steel and 429EM ferritic stainless steel have been performed at elevated temperature for the prediction. While the cyclic stress response of a material is not stabilized during fatigue deformation, it was found that PSED is stabilized at the early stage of fatigue life and nearly invariant through the whole cycles. Hence, PSED can be regarded as a suitable fatigue parameter for the materials. The Morrow model using PSED gave a good correlation on low-cycle fatigue under isothermal conditions for both stainless steels. A fatigue damage parameter, which is defined as the PSED non-dimensionalized by material toughness, was proposed to account for temperature effect on the fatigue life. The developed model, in which the fatigue exponent is obtained from the universal slope method and the true toughness measured from the tensile test is used as a temperature-compensating parameter, provided a good prediction on the fatigue behaviors of both stainless steels over the temperature range.

浸炭材の低サイクル衝撃疲労特性に及ぼす表層炭素濃度と硫黄含有量の影響

Effect of surface carbon and sulfur on the low cycle impact fatigue properties in carburized steels were studied by using gear impact testing machine and strain gauge. The results obtained are summarized as follows: The low cycle impact fatigue strength was especially improved by decreasing content of the surface carbon and content of sulfur. It was found that increasing the crack initiation life by decreasing content of the surface carbon, and the initial crack length shorten. Furthermore, It was explained that the crack propagation speed decreased with decreasing sulfide. The method for estimating the crack initiation life from tensile properties of carburized layer is proposed by modifying Manson's Universal Slope Method.

333 部分減肉を有するエルボ配管の繰返し荷重下における破損挙動評価(OS10-1 応力腐食割れ,減肉配管,OS10 エネルギー機器の経年変化に関する健全性評価手法の開発とその適用(1))

Cyclic bending tests were conducted using elbow pipe specimens with local wall thinning. Local wall thinning was machined on the inside of pipe in order to simulate erosion/corrosion metal loss. The effects of thinned locations on the failure behaviors of the pipes were investigated. As a result, when the wall thinning was located in intrados, fatigue life was the shortest. In addition, three-dimensional elasto-plastic analyses were also carried out using the finite element method. The analyses were carried out focusing on Mises' total strain range. As the results, the location of crack initiation and the crack growth direction were successfully predicted by the analyses. The fatigue life was predicted on the safe side by the Manson's universal slope method.

Fatigue Response and Life Prediction of Selected Reactor Materials

This paper analyzes experimental fatigue response for selected unirradiated and irradiated reactor materials: AISI 316 stainless steel, ferritic/martensitic MANET and HT9 steels. Available tensile test results on the same or similar materials are used to predict changes in fatigue response using the Universal Slopes method. The predictions are compared with the experimental data to assess the potential for using tensile data to predict reactor component fatigue response. It was found that the effect of irradiation on fatigue life was less severe than on tensile properties. However, tensile properties are useful for qualitative predictions of fatigue response.

Evaluation of Irradiation Effect on Fatigue Performance of Copper Alloys for High Heat Flux Applications

ABSTRACTThe influence of radiation damage on the fatigue performance of two selected copper alloys, a dispersion-strengthened CuAl-25 alloy and a precipitation-hardened CuCrZr alloy, was analyzed. The fatigue lives of the two alloys were predicted using their tensile properties before and after irradiation by the Universal Slopes method. The predicted lives are compared with experimental results, and the feasibility of using tensile properties to predict fatigue lives following irradiation is examined. The fatigue performance of these two copper alloys was degraded due to radiation exposure, but the radiation effect on the fatigue performance was not as severe as on the tensile properties. The life prediction agrees reasonably well with the measured fatigue response.

New Estimation Method of Fatigue Properties of Aluminum Alloys

A new method on estimating fatigue properties from simple tensile data was proposed for aluminum alloys. The method is based on experimental strain-life curves. An optimization technique was used to get the best fatigue properties. The four-point correlation method, the universal slopes method, Mitchell’s method, the modified universal slopes method, the uniform material law by Ba¨umel and Seeger, the modified four-point correlation method by Ong and a new method proposed in this work were evaluated in a quantitative manner. Mitchell’s method, the uniform materials law and the new method give good life predictions for aluminum alloys. In particular, the new method provided the best results.

Estimation methods for fatigue properties of steels under axial and torsional loading

Uniaxial and torsional fatigue tests have been conducted on eight steels. The cyclic equivalent stress and strain amplitudes can be fitted by the Ramberg-Osgood relationship. Fatigue lives are found correlated with the equivalent strain amplitude. Seven methods for estimating uniaxial fatigue properties from tensile properties or hardness have been evaluated. The modified universal slopes method by Muralidharan and Manson, the uniform material law by Bäumel and Seeger and the hardness method by Roessle and Fatemi predicted over 93% of test cases within the factor of 3 compared with observed lives. These methods are also found applicable to torsional fatigue with fatigue properties estimated from uniaxial fatigue properties based on the equivalent strain criterion.

Applicability of life prediction methods to the low cycle fatigue of braze clad AlMn1.0Mg0.5 alloys

The original and modified universal slope methods, the uniform material law, and the modified Diercks equation have been applied to the low cycle fatigue life prediction in the braze clad AlMn1.0Mg0.5 alloys. The experimental data from clad and non-clad, pre-strained and non-pre-strained AlMn1.0Mg0.5 alloys at room temperature and at 75 and 180°C have been used to evaluate the applicability of the life estimation methods. It is likely that there is no universal method to predict the low cycle fatigue lives of all kinds of aluminium alloys. However, the modified universal slope method and the modified Diercks equation provide reasonably good predictions in these braze clad aluminium alloys.

Effect of Temperature and Strain Rate on Mechanical Property of Sn-Pb Solders.

This paper describes the tensile property of six kinds of Sn-Pb solders. Static tension tests were carried out at strain rates ranging from 0.001%/sec to 2.0% / sec using 5Sn-95Pb, 10Sn-90Pb, 40Sn-60Pb, 60Sn-40Pb, 63Sn-37Pb, and 62Sn-36Pb-2Ag solders at 313-398 K. Strain rates faster than 2.0%/sec were required to obtain time-independent Young's modulus and yield stress of the solders. In tests at the strain rates slower than 2.0%/sec, creep deformation was included in the stress-strain relationship, and Young's modulus and yield stress which do not depend on time could not be obtained. A new equation which can predict tensile strength of Sn-Pb solders as functions of temperature, strain rate and chemical composition were proposed. New equations were also proposed for predicting Young's modulus and yield stress as functions of temperature and chemical composition. These equations predict Young's modules and yield stress within a factor of 1.25 and 1.15, respectively. Low cycle fatigue lives were discussed based on the universal slope method.

Low Cycle Fatigue Life Estimation of Pearlite Base Cast Irons.

In this study the auther carried out low cycle fatigue tests at room temperature in use of the flake graphite cast iron (FC-P) and the spheroidal graphite cast iron (FCD-P) of pearlite matrix structure, and then proceeded to estimate the fatigue life of the said two kinds of cast irons. Fatigue life prediction was made for each one of the testing materials in different graphite shapes by the Manson's universal slope method. As a result, the estimated life of FC-P was nearly as long as the life obtained from the experiment, but that of FCD-P was about 20% shorter than the one obtained from the experiment. Hence, the author introduced the modified universal slope method based on the plastic strain component under the Manson-Coffin rule obtained from the experiment, and applied it to the both testing materials. In this way, it became possible for the low cycle fatigue life of the two kinds of cast irons to be guided collectively by one formula.

Low-Cycle Fatigue Behavior of Spring Steels

Low-cycle fatigue tests were carried out on spring steels at room temperature under a triangular strain wave form to obtain basic information about low-cycle fatigue behavior of springs.The results obtained are summarized as follows:(1) Cyclic softening behavior was observed under cyclic straining with plastic strain component.(2) Fatigue life properties and cyclic deformation properties of spring steel are the same as those which obtained by extrapolating properties of tempered steels for machine structural use to higher level of hardness.(3) Estimation method of low-cycle fatigue lives from tensile properties is proposed by modifying Manson's Universal Slope Method.(4) Total damage under incremental step tests becomes 1 to 1.8 at failure. Miner's cumulative rule is applicable to fatigue life estimation under straining of randon amplitudes.(5) Total damage is very small compared with 1 at failure, when stress controlled fatigue tests are carried out after a part of strain controlled test with plastic strain component. Cyclic softening by strain cycling promotes fatigue damage due to stress cycling.

Detailed evaluation of methods for estimation of fatigue properties

Using extensive experimental strain-life curve data on 116 steels, 16 aluminium alloys and six titanium alloys, nearly all methods currently available for estimation of fatigue properties from simple tensile data are discussed in detail. The four-point correlation method, the universal slopes method, Mitchell's method, the modified universal slopes method, the uniform material law by Baumel and Seeger. and the modified four-point correlation method by Ong are evaluated in a quantitative manner by using new criteria proposed in this work, along with conventional error criterion. The modified universal slopes, Seeger's and Ong's methods give good life predictions. Among them, the modified universal slopes method provides best results.