Comparison of Evolution Fatigue With Simplified Elastic Plastic Analysis, Plastic Analysis and a Fracture Mechanics Approach

2020 ◽  
Author(s):  
Joakim Cedergren
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Strain Range ◽  
Axial Direction ◽  
Total Strain ◽  
Slow Heating ◽  
Total Strain Range ◽  
Elastic Plastic ◽  
Plastic Analysis ◽  
Pipe Geometry

Abstract Fatigue analyzes are performed to ensure that no damage leading to failure will occur in a component. In ASME III NB-3222.4(e), a method is provided for analyzing a component’s resistance against cyclic loads. In ASME NB-3228.5 or alternatively NB-3653.6 (c) a simplified elastic-plastic method is given to take plasticity into account. According to NB-3228.4 (c), fatigue evaluation is allowed with plastic analysis where the stress amplitude is determined from the numerically maximum principal total strain range. This report examines the fatigue life, using a continuum mechanics approach, of a pipe penetration that is subjected to a rapid cooling down followed by a slow heating up. Simplified elastic-plastic analysis and plastic analysis are performed. The analysis also takes into account the FEN-factor according to the method given NUREG/CR6909. The fatigue life is also determined by a fracture mechanics approach using a R6 based fracture assessment and crack growth analysis. The results show a large difference in fatigue life depending on the method used. For the plastic analyzes it is of great importance to the result in which direction the evaluation is made. For the present case the maximum principal total strain range is obtained in the radial direction. The stresses in this direction are small. A crack tangentially to this direction lacks physical significance to a pipe geometry and cannot lead to failure. In this case it is recommended that evaluation is made for the strain range in the axial direction for pipe geometries instead of the maximum principal total strain range.

Critical Review of Strain Measures for Characterisation of Fatigue Damage in ASME Section III Fatigue Assessments

2019 ◽  
Author(s):  
Daniel Leary ◽  
Chris Currie ◽  
Keith Wright
Keyword(s):  
Strain Range ◽  
Pressure Vessels ◽  
Total Strain ◽  
Multiaxial Loading ◽  
Critical Plane ◽  
Total Strain Range ◽  
Elastic Plastic ◽  
Fatigue Evaluation ◽  
Von Mises ◽  
Strain Measures

Abstract Rules for fatigue evaluation of nuclear pressure vessels and piping components are provided in Subsection NB of Section III of the ASME code. The code prescribed fatigue procedure requires the comparison of an alternating stress amplitude with fatigue allowables (design fatigue curves), usually derived through uniaxial specimen testing. For elastic assessments of multiaxial loading, typical from thermal shocks, a Tresca stress is used to characterise the stress field into a single effective stress measure for comparison with ASME fatigue allowables. For nonlinear elastic-plastic assessments, Appendix XIII-3440(b) of Section III specifies that “the numerically maximum principal total strain range” (interpreted as Maximum Total Principal (MTP) strain range) should be used for comparison with fatigue allowables. Two alternative methods for the characterisation of multiaxial strain fields are presented in the ASME code. Section VIII Division 2 provides alternative rules for the construction of pressure vessels, with Part 5 specifying the use of a Von Mises based Effective Strain Range (ESR) for elastic-plastic analysis. Section III Division 5 Subsection NBB provides rules for the assessment of components at elevated temperatures, also specifying the use of a Von Mises based Equivalent Total Strain Range (ETSR) measure. The two alternative strain measures are differentiated by their treatment of the elastic strain contribution. In the ESR method an equivalent elastic strain is calculated and summated with the plastic strain component. In the ETSR method the total strain (elastic plus plastic) is used thus evaluating the elastic and plastic contributions simultaneously. More complex critical plane approaches have also been proposed in recent years to better characterise multiaxial loading conditions. This paper presents a comparison of the various ASME specified strain measures and simplified critical plane approaches for fatigue evaluation of complex multiaxial loading. In support of this comparison, predictions of initiation lives to 0.254 mm defect in the stepped pipe specimen reported in PVP2004-2748 are provided to quantify the additional conservatism contained in elastic-plastic fatigue assessments of nuclear components. Predictions use the methodology presented in the companion paper PVP2019-93847 for the generation of short crack fatigue curves and the associated modification to environmental enhancement factors. It is concluded that use of the ASME specified strain measures, in conjunction with lower bound stress-strain data, conservatively underestimate the initiation life to a 0.254 mm defect by a factor of four for the example considered. However, use of more complex critical plane strain measures were observed to provide significant improvement in prediction accuracy of elastic-plastic fatigue evaluations.

Tensile and Fatigue Properties of Miniature Size Specimens of Sn-5Sb Lead-Free Solder

2016 ◽  
Vol 879 ◽  
pp. 2377-2382 ◽  
Author(s):  
Kyosuke Kobayashi ◽  
Ikuo Shohji ◽  
Hiroaki Hokazono
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Phase Boundary ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Total Strain ◽  
Effect Of Temperature ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Total Strain Range

Tensile and low cycle fatigue properties of Sn-5Sb (mass%) solder were investigated with miniature size tensile specimens. The effect of temperature and strain rate on tensile properties and the effect of temperature on low cycle fatigue properties were examined. Tensile strength increases with increasing strain rate regardless of temperature investigated. For elongation, the effect of temperature on it is negligible although it slightly increases with increasing strain rate. The low cycle fatigue life of Sn-5Sb obeys by the Manson-Coffin’s equation. The effect of temperature on the fatigue life is negligible in the temperature range from 25 oC to 150 oC. In the low cycle fatigue test with a high total strain range of 4%, cracking at phase boundary mainly occurs regardless of temperature investigated. In the case of a low total strain range of 0.4%, ductile fracture mainly occurs, and cracking at phase boundary with generation of grooves also occurs at high temperature.

Low cycle fatigue of steels under biaxial straining

1967 ◽  
Vol 2 (2) ◽  
pp. 117-126 ◽  
Author(s):  
K J Pascoe ◽  
J W R de Villiers
Keyword(s):  
Fatigue Life ◽  
Mild Steel ◽  
Test Specimen ◽  
Low Cycle Fatigue ◽  
Fracture Propagation ◽  
Strain Range ◽  
Shear Plane ◽  
Total Strain ◽  
Cycle Fatigue ◽  
Total Strain Range

A cruciform test specimen and a loading rig are described, by which any combination of biaxial strains can be applied to a specimen. With the pressurizing equipment so far available, three states of strains have been investigated for two steels. In the mild steel used, large inclusions oriented in the roll direction aided fracture propagation when a maximum shear plane coincided with the roll direction. When not influenced by inclusions, fatigue life is related to total strain range by Coffin's law         ∊ N a = C The values of α and C are different for different states of strains. Empirical formulae are given to predict results for other states of strains.

LOW CYCLE FATIGUE BEHAVIOR AND LIFE PREDICTION OF A CAST COBALT-BASED SUPERALLOY

2012 ◽  
Vol 06 ◽  
pp. 251-256
Author(s):  
HO-YOUNG YANG ◽  
JAE-HOON KIM ◽  
KEUN-BONG YOO
Keyword(s):  
Fatigue Life ◽  
Strain Energy ◽  
Life Prediction ◽  
Prediction Models ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Total Strain ◽  
Cycle Fatigue ◽  
Total Strain Range ◽  
Different Temperatures

Co -base superalloys have been applied in the stationary components of gas turbine owing to their excellent high temperature properties. Low cycle fatigue data on ECY-768 reported in a companion paper were used to evaluate fatigue life prediction models. In this study, low cycle fatigue tests are performed as the variables of total strain range and temperatures. The relations between plastic and total strain energy densities and number of cycles to failure are examined in order to predict the low cycle fatigue life of Cobalt-based super alloy at different temperatures. The fatigue lives is evaluated using predicted by Coffin-Manson method and strain energy methods is compared with the measured fatigue lives at different temperatures. The microstructure observing was performed for how affect able to low-cycle fatigue life by increasing the temperature.

Thermal Fatigue and Fracture Mechanics Analysis of Aluminium Alloy

2011 ◽  
Vol 201-203 ◽  
pp. 2476-2480
Author(s):  
Wen Xiao Zhang ◽  
Guo Dong Gao ◽  
Guang Yu Mu
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Fracture Mechanics ◽  
Thermal Fatigue ◽  
Low Carbon Steel ◽  
Strain Range ◽  
J Integral ◽  
Low Carbon ◽  
Thermal Fatigue Life ◽  
Energy Aspect

The in-phase and out-of-phase thermal fatigue of aluminum alloy were experimentally studied. The fatigue life was evaluated analytically by using the elastic-plastic fracture mechanics method (mainly J integral). The results of experiments and calculations showed that the life of out-of-phase fatigue was longer than that of in-phase fatigue within the same strain range. This is the same as the results of other materials such as medium and low carbon steel. On the other hand, the predicted life was consistent with experimental results. This suggests that J integral as a mechanics parameter for characterizing the thermal fatigue strength of aluminum alloy and the calculation method developed here is efficient. A parameter ΔW was proposed from energy aspect to characterize the capacity of crack propagation. The in-phase thermal fatigue life was the same as the out-of-phase thermal fatigue life for identical ΔW values.

Riveted single lap joints Part 2: Fatigue life prediction

1997 ◽  
Vol 211 (2) ◽  
pp. 123-128 ◽  
Author(s):  
C-P Fung ◽  
J Smart
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Effective Stress ◽  
Fatigue Testing ◽  
Strain Range ◽  
Lap Joints ◽  
Total Strain Range ◽  
Single Lap Joints ◽  
Data Points ◽  
Fretting Damage

Fatigue lives of snap and countersunk riveted single lap joints with either one-row or two- rows of rivets have been predicted with fatigue laws using either local total strain range or effective stress obtained from finite element analyses and data obtained from fatigue testing of plates with holes. The finite element models of the joints were subjected to an alternating cyclic load; plasticity and nonlinear geometry are considered. The failures have also been metallurgically examined and gave evidence of fretting damage. It was found that all the data points lie within a narrow band using the strain-life law although the band is wider when using the effective stress-life law, but it is impossible to predict the fatigue life from one kind of specimen to another using the conventional stress-life law.

Thermomechanical Fatigue Life Prediction of 63Sn/37Pb Solder

1992 ◽  
Vol 114 (2) ◽  
pp. 145-151 ◽  
Author(s):  
Q. Guo ◽  
E. C. Cutiongco ◽  
L. M. Keer ◽  
M. E. Fine
Keyword(s):  
Fatigue Life ◽  
Plastic Strain ◽  
Life Prediction ◽  
Strain Range ◽  
Thermomechanical Fatigue ◽  
Fatigue Tests ◽  
Experimental Results ◽  
Fatigue Life Prediction ◽  
Total Strain ◽  
Isothermal Fatigue

Isothermal and thermomechanical fatigue of 63Sn/37Pb solder is studied under total strain-controlled tests. A standard definition of failure is proposed to allow inter-laboratory comparison. Based on the suggested failure criterion, load drop per cycle, the Young’s modulus and the ratio of the maximum tensile to maximum compressive stresses remain constant, and the fatigue response of the solder is stable before failure, although cyclic softening was observed from the beginning. Experimental results of isothermal fatigue tests for a total strain range from 0.3 to 3 percent show that the log-log plot of the number of cycles to failure versus the plastic strain range has a kink at the point where the elastic strain is approximately equal to the plastic strain. In this paper, it is shown how the isothermal fatigue life of near-eutectic solder at lower strain ranges can be predicted by using the experimental data of fatigue tests at high strain ranges and early stage information of a fatigue test at the strain range in question. A thermomechanical fatigue life prediction is also given based on a dislocation pile-up model. Comparison with experimental results shows a good agreement.

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