• Steel and Composite Structures
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• v.33 no.3
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• pp.433-444
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• 2019

Fatigue failure of a grid structure using bolt-sphere joints is liable to occur in a high-strength bolt due to the alternating and reciprocal actions of a suspension crane. In this study, variable amplitude fatigue tests were carried out on 20 40 Cr steel alloy M30 high-strength bolts using an MTS fatigue testing machine, and four cyclic stress amplitude loading patterns, Low-High, High-Low, Low-High-Low, and High-Low-High, were tested. The scanning electron microscope images of bolt fatigue failure due to variable amplitude stress were obtained, and the fractographic analysis of fatigue fractures was performed to investigate the fatigue failure mechanisms. Based on the available data from the constant amplitude fatigue tests, the variable amplitude fatigue life of an M30 high-strength bolt in a bolt-sphere joint was estimated using both Miner's rule and the Corten-Dolan model. Since both cumulative damage models gave similar predictions, Miner's rule is suggested for estimating the variable-amplitude fatigue life of M30 high-strength bolts in a grid structure with bolt-sphere joints; the S-N fatigue curve of the M30 high-strength bolts under variable amplitude loading was derived using equivalent stress amplitude as a design parameter.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.666-671
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• 1993

Fatigue life prediction under multi-axial variable load were performed for Aluminium 7075-T651 alloy using SAE Notched specimen & Torque tube shaft component specimen. When variable multiaxial load is applied to material, maximum damaged plane(critical plane) change. To clarify the situation, experiment is performed on two different changing load path. For multiaxial fatigue life prediction, miner rule is expanded to critical plane theory. Shear based parameter and Elliptical parameter give better correlation. This suggests that miner rule can be applicable on multi-axial variable load.

• Journal of the Korean Society for Railway
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• v.8 no.6 s.31
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• pp.525-532
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• 2005

Fatigue life of catenary wires in various environments is reduced when stress is concentrated on some points, which are often found in corroded areas by surrounding pollutants. Therefore, the fatigue test were performed in order to investigate the effect of the surface corrosion on the destructive behavior in service environment and accelerated corrosion environment as well as th examine the corrosive property and mechanism of the catenary wires. In the fatigue test of the messenger stranded wire, the corrosion degraded materials showed 35~50% of fatigue life at a same stress amplitude compared to original material. Because the catenary wires have variable load by the interaction of periodic contacts with pantographs the maximum stresses of trolley wire and messenger wire calculated by simulation at the messenger wire during operation was estimated thought the corrosion behavior interpretation of variable stress and fatigue test.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1350-1357
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• 1988

A computer software was developed for predictions of fatigue crack initiation life of notched members under variable loadings. The software was constructed based on a new fatigue life prediction method utilizing modified .epsilon.-N curves, which can account for the stress interaction effect. The effect of mean plastic strain on low-cycle fatigue life was also incorporated in the software. The software can be utilized for the first step approximation when fundamental data of material fatigue properties are not available.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.6
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• pp.753-759
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• 2010

The variable fatigue load is simulated in this study. The stability and the life of the material are analyzed theoretically by Ansys program. These results are successfully applied to the practical wheel to predict the prevention of fracture and the endurance. The life and the damage on the every part of the fatigue specimen can be predicted. As the available lives are compared for every loading variation, the rain flow and damage matrix results can be helpful in determining the effects of small stress cycles in any loading history. The rainbow and damage matrices illustrate the possible effects of infinite life. The safety and stability of wheel and the other practical structures according to the variable load can be estimated by using the results of this study.

• Journal of the Korean Society of Safety
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• v.6 no.4
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• pp.45-52
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• 1991

The purpose of a fatigue crack arrest desing is to prvent a fatigue fracture of machine and structure resulted from unstable crack growth. In all cases of load transfer to second elements such as stringers, doublers or flangers, crack arrest is possible; arrest occuring when the fatigue crack reaches the second element. In the present work, the possibility of crack arrest and the design criterion of fatigue crack arrest in the variable thickness plates are examined numericaiiy by using fatigue crack arrest thresthod $\Delta$K$_{th}$of SA-508 reactor vessel steel and stress intensity factor which was obtained in the previous work as a result of 3-dimensional finite element analysis for CT type variable thickness plates having discontinuous interface.e.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.4
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• pp.85-93
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• 2004

The variable fatigue load is simulated in this study, The stability and the life of the material are analyzed theoretically by the program of Ansys workbench. These results are successfully applied to the practical structures to predict the prevention of fracture and the endurance, The life and the damage on the every part of the fatigue specimen can be predicted. As the available lives are compared for every loading variation, the rainflow and damage matrix results can be helpful in determining the effects of small stress cycles in any loading history. The rainflow and damage matrices illustrate the possible effects of infinite life. The safety and stability of fatigue specimen according to the variable load can be estimated by using the results of this study.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.4
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• pp.654-661
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• 2001

In this study, fatigue growth behavior of the transverse crack, which was the most dangerous damage among the various types of rail defects, was investigated using the notched keyhole specimen under constant amplitude loadings. Fatigue limit of smooth specimen in rail steel at R=0 was 110MPa, and the fatigue crack initiation life in the region of the low stress amplitude (ie. long life) occupied the major portion of the total fatigue life. The fatigue strength under variable amplitude loading was converted to the equivalent fatigue strength based upon. Miners rule, which was estimated approximately 9% lower than that under constant amplitude loading. Also, in the low ΔK(sub)rms region ($\leq$21MPa√m), fatigue crack growth rate (da/dN) under constant amplitude loading was higher than that under variable amplitude loading, whereas the tendency was reversed in the high ΔK(sub)rms region. It is believed that this behavior is due to the transition of fracture appearance.

• Elastomers and Composites
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• v.42 no.4
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• pp.209-216
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• 2007

Fatigue life prediction methodology of the rubber component made of vulcanized natural rubber under variable amplitude loadings was studied. The displacement-controlled fatigue tests were conducted at different levels and the maximum Green-Lagrange strain was selected as damage parameters. A fatigue life curve of the rubber represented by the maximum Green-Lagrange strain was determined from the nonlinear finite element analysis. The transmission load history of SAE as variable amplitude loading was used to perform the fatigue life prediction. And then a signal processing of variable loading by racetrack and simplified rainflow cycle counting methods were performed. The modified miner's rule as cumulative damage summation was used. Finally, when the gate value is 30%, the predicted fatigue life of the rubber component agreed well with the experimental fatigue lives with a factor of two.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.2
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• pp.136-145
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• 2003

The integrity of stiffened panels with stringers in airplane structure is generally enhanced by investigating the fatigue crack propagation behavior in detail and providing the technical methodology to deal with the propagating crack. This paper attempts to clarify the effect of load-ratio on the fatigue crack propagation rate and the fatigue life for the thin aluminum 2024-T3. Both the variable and the constant fatigue loading conditions are considered for the fatigue crack propagation behavior in stiffened panels with stringers.