Application of the Cyclic Strain Approach to the Fatigue Failure of Ship Structural Details

1987 ◽  
Vol 31 (03) ◽  
pp. 177-185
Author(s):  
Wolfgang Fricke ◽  
Hans Paetzold
Keyword(s):  
Fatigue Life ◽  
Plastic Region ◽  
Steel Structure ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Damage Parameter ◽  
Elastic Plastic ◽  
Strain Behavior ◽  
Structural Details ◽  
The Relationship

The cyclic strain approach is useful for determining the fatigue life of notches strained in the elastic-plastic region. Examples are the flame-cut edges of cutouts in the ship steel structure. After the description of the cyclic stress-strain behavior of the usual mild steel, the individual elements of the approach are described: the probability distribution of load amplitudes, the relationship between load and local elastic-plastic strain, the relationship between the damage parameter and fatigue life, and finally the damage accumulation law. The approach is illustrated by two examples of longitudinal/transverse web intersections. In the first, the predicted life is confirmed by experimental results. The second example shows the approach for complicated load combinations. It is hoped that this paper will contribute to sound and crack-free ship structural details, particularly if unusual loads are applied to well-tried details or if simplified designs are introduced.

Turbine Blade Life Prediction Using Fluid-Thermal-Structural Interaction Simulation

2016 ◽  
Author(s):  
I. A. Ubulom ◽  
A. Fien ◽  
A. J. Neely ◽  
K. Shankar
Keyword(s):  
Fatigue Life ◽  
Hysteresis Loop ◽  
Turbine Blade ◽  
Stable Condition ◽  
Cyclic Stress ◽  
Aerodynamic Load ◽  
Temperature Dependent ◽  
Strain Behavior ◽  
Softening Behavior ◽  
Interaction Simulation

In this study a fluid-thermal-structural simulation is performed to investigate cyclic stress-strain behavior and fatigue life of a gas turbine blade. The Hysteresis loop characteristic of the blade is presented under the coupled influence of various loading conditions, aerodynamic, thermal and static centrifugal loadings. Based on the predicted loading behavior, an energy-based method was used to analyze the fatigue and cumulative damage properties of the blade. The predicted hysteresis loop under aerodynamic load was purely of elastic nature and as such tends to assume a Masing behavior at the stable condition. The case for a combined thermal and aeromechanical loading showed a non-Masing behavior, but rather a temperature-dependent material softening behavior. The fatigue life was also estimated based on the energy density approach using the predicted thermal-structural predicted cyclic loops.

Damage Parameter Assessment for Energy Based Fatigue Life Prediction Methods

2012 ◽  
Author(s):  
Casey M. Holycross ◽  
John N. Wertz ◽  
Todd Letcher ◽  
M.-H. Herman Shen ◽  
Onome E. Scott-Emuakpor ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Energy Dissipation ◽  
Strain Energy ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Cyclic Strain ◽  
Damage Parameter ◽  
Fatigue Life Prediction ◽  
Cyclic Behavior ◽  
Fracture Processes

An energy-based method used to predict fatigue life and critical life of various materials has been previously developed, correlating strain energy dissipated during monotonic fracture to total cyclic strain energy dissipation in fatigue fracture. This method is based on the assumption that the monotonic strain energy and total hysteretic strain energy to fracture is equivalent. The fracture processes of monotonic and cyclic failure modes can be of stark contrast, with ductile and brittle fracture dominating each respectively. This study proposes that a more appropriate damage parameter for predicting fatigue life may be to use low cycle fatigue (LCF) strain energy rather than monotonic energy. Thus, the new damage parameter would capture similar fracture processes and cyclic behavior. Round tensile specimens machined from commercially supplied Al 6061-T6511 were tested to acquire LCF failure data in fully reversed loading at various alternating stresses. Results are compared to both monotonic and cyclic strain energy dissipation to determine if LCF strain energy dissipation is a more suitable damage parameter for fatigue life prediction.

Cyclic Plastic Deformation of a Circular Plate With Work Hardening

1984 ◽  
Vol 106 (4) ◽  
pp. 336-341
Author(s):  
R. Winter
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Nonlinear Behavior ◽  
Strain Curve ◽  
Strain Range ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Element Analysis

An experimental and theoretical study was performed of the nonlinear behavior of a simply supported flat circular aluminum plate under reversed cyclic central load. The application is for the analysis of cyclic stress and strain of structural components in the plastic range for predicting low-cycle fatigue life. The main purpose was to determine the relative accuracy of an elastic-plastic large deformation finite element analysis when the material properties input data are derived from monotonic (noncyclic) stress-strain curves versus that derived from cyclic stress-strain curves. The results showed that large errors could be induced in the theoretical prediction of cyclic strain range when using the monotonic stress-strain curve, which could lead to large errors in predicting low-cycle fatigue life. The use of cyclic stress-strain curves, according to the model developed by Morrow, et al., proved to be accurate and convenient.

Buckling Analysis of the Tube Compression-Bending Member in Elastic-Plastic State with ANSYS

2011 ◽  
Vol 327 ◽  
pp. 143-148
Author(s):  
Zhi Cai Jiang ◽  
Wei Lian Qu
Keyword(s):  
Axial Compression ◽  
Bending Moment ◽  
Steel Structure ◽  
Plastic Instability ◽  
Plastic State ◽  
Axial Pressure ◽  
Nonlinear Buckling ◽  
Elastic Plastic ◽  
Compression Stiffness ◽  
The Relationship

Stability is an important issue in steel structure design.When the steel member is subjected to elastic-plastic instability, the axial compression stiffness reduces with the increasing axial pressure and bending moment at end. Therefore, the authors analyze the process of steel member that is instable in elastic-plastic state in this paper by studying the degradation laws of axial compression stiffness. The eigenvalue buckling and nonlinear buckling analyses of axially compressed member and compression-bending member are carried out by using commercial package ANSYS in this study. The relationship curve between the axial force at end and the axial compression stiffness and the relationship surface among the axial pressure at end, bending moment at end and the axial compression stiffness are determined respectively. The made observations indicate that it is feasible to analyze the process of the steel member that is instable in elastic-plastic state by investigating the degradation properties of axial compression stiffness, which becomes lower with axial pressure at end and bending moment at end.

Low-Cycled Fatigue Life of S30408 Stainless Steel at Liquid-Nitrogen Temperature

2018 ◽  
Author(s):  
Yingzhe Wu ◽  
Huaijian Xu ◽  
Qunjie Lu ◽  
Jinyang Zheng ◽  
Ping Xu
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Liquid Nitrogen ◽  
Strain Amplitude ◽  
Hysteresis Loops ◽  
Cyclic Strain ◽  
Liquid Nitrogen Temperature ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Fatigue Tests

This paper is concerned with the low-cycled fatigue life of S30408 austenitic stainless steel at 77 K. Strain-controlled low-cycled fatigue tests were performed in a liquid-nitrogen bath covering a strain-amplitude range of 0.4%–1.0%. The role of the reduced temperature is examined during the low-cycled fatigue tests by comparing the fatigue performance to the one at ambient temperature that was obtained in our previous work. It is found that the cryogenic low-cycled fatigue life is significantly improved by a factor of 5–10 in the low strain-amplitude range of 0.4%–0.5%, resulting from the pronounced hardening effect due to the low temperature. However, the cryogenic improvement gradually reduces with the increasing strain-amplitude. At 77 K, the cyclic stress amplitude increases rapidly at the beginning of the fatigue test, and no cyclic softening is found due to the cryogenically constrained movement of the dislocations. The fatigue hysteresis loops and fatigue stress-strain curves shows that the cyclic plastic strain at cryogenic temperature accounts for a limited proportion in the total cyclic strain, and the damage may occurs explosively at the beginning of the cyclic load at 77 K.

Mean Strain Effect on the Cyclic Stress-Strain Behavior of Steel Structure Materials Q235

2012 ◽  
Vol 602-604 ◽  
pp. 430-434 ◽  
Author(s):  
Yi Guo ◽  
Yun Rong Luo ◽  
Qing Yuan Wang
Keyword(s):  
Low Cycle Fatigue ◽  
Steel Structure ◽  
Cyclic Hardening ◽  
Cyclic Stress ◽  
Strain Effect ◽  
Cycle Fatigue ◽  
Q235 Steel ◽  
Strain Behavior ◽  
Mean Stress Relaxation ◽  
Mean Strain

The low cycle fatigue (LCF) behavior of Q235 steel under mean strain control has been investigated. A serious of the strain controlled cyclic loading experiments with several combinations of strain amplitudes and mean strains have been performed. Significant cyclic hardening and mean stress relaxation were observed in all cases. Fractography by scanning electron microscopy (SEM) was used to determine the LCF failure mechanisms and fatigue crack propagation modes of the Q235 steel.

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