• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.2
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• pp.594-599
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• 2011

In this paper, the effect of the boundary conditions on the reliability and the cumulative distribution characteristics of the fatigue failure life is analyzed in a magnesium alloy AZ31. The boundary conditions are specimen thickness, stress ratio, and maximum fatigue load. The statistical data of the fatigue failure life are obtained by fatigue crack propagation tests under the detail conditions for each boundary condition. The 3-parameter Weibull distribution is used to analyze a statistical characteristics of the fatigue failure life in magnesium alloy AZ31. It is found that the statistical fatigue failure life is long in the case of a thicker specimen, a larger stress ratio, and a smaller maximum fatigue load. Under the opposite cases, the reliability on the fatigue failure life is rapidly dropped.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.6
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• pp.804-811
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• 2010

The fatigue crack propagation is stochastic in nature, because the variables affecting the fatigue behavior are random and have uncertainty. Therefore, the fatigue life prediction is critical for the design and the maintenance of many structural components. In this study, fatigue experiments are conducted on the specimens of magnesium alloy AZ31 under various conditions such as thickness of specimen, the load ratio and the loading condition. The probability distribution fit to the fatigue failure life are investigated through a probability plot paper by these conditions. The probabilities of failure at various conditions are also estimated. The fatigue design life is predicted by using the Weibull distribution.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.38-51
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• 2000

The study on the mechanical behavior of a spot-welded specimen is largely divided into the quasi-static overload failure analysis and the fatigue failure prediction. The main issue in an overload analysis is to examine the critical loads, thereby providing a generalized overload failure criterion. As the welding spot forms a singular geometry of an external crack type, fatigue failure of spot-welded specimens can be evaluated by means of a fracture parameter. In this study, we first present the limit loads of 4 representative types of single spot-welded specimens in terms of the base metal yield strength and specimen geometries. Recasting the load vs. fatigue life relationships experimentally, obtained here, we then predict the fatigue life of spot-weld specimens with a single parameter denoted the equivalent stress intensity factor. This crack driving parameter is demonstrated to successfully describe the effects of specimen geometry and loading type in a comprehensive manner. The suggested fatigue life formula for a single spot weld can play a key, role in the design and assessment of spot-welded panel structures, in that the fatigue strength of multi-spots is eventually determined by the fatigue strength of each single spot.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.03a
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• pp.269-273
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• 1998

The failure of material structures or mechanical system is considered as a direct or indirect result of fatigue. In the design of mechanical structure for estimating of reliability, the prediction of failure life is the most important failure mode to be considered. However, because of a complicated behavior of fatigue in mechanical structure, the analysis of fatigue is in need of much researches on life prediction. This document presents a prediction of fatigue life of the SAPH45 steel, which is extensively for vehicle frame. The method using lethargy coefficient and stress distribution factor at pediction of fatigue life based on the consideration of the failure characteristics from the tensile test should be provided in this study.

• Journal of the Korean Institute of Gas
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• v.16 no.3
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• pp.29-34
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• 2012

Investigating safer ways to design and use to prevent a loss of life and property by failure of the structures are necessary and assessing total fatigue life with initiation and propagation of fatigue crack accurately through fatigue analysis is very important. The object of this study is to examine the initial life and propagation life when the fatigue crack is introduced from the root which is likely to appear in LOP(Lack of Penetration) cruciform fillet welded structure including bridges, ships and gas storage facilities which are impossible to be fully penetrated and to measure the rate of fatigue life until the final cleavage failure. As the result, each rate of fatigue life for fatigue failure is somewhat different in the range of 5% according to the thickness of material, however, the overall rate of initial life is in the range of 34~39% and propagation life showed the range of 61~66%.

• Steel and Composite Structures
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• v.51 no.1
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• pp.53-61
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• 2024

Aluminum foams sandwich panel (AFSP) has been used in engineering field, where cyclic loading is used in most of the applications. In this paper, the fatigue life of AFSP prepared by the bonding method was investigated through a three-point bending test. The mathematical statistics method was used to analyze the influence of different plate thicknesses and core densities on the bending fatigue life. The macroscopic fatigue failure modes and damage mechanisms were observed by scanning electron microscopy (SEM). The results indicate that panel thickness and core layer density have a significant influence on the bending fatigue life of AFSP and their dispersion. The damage mechanism of fatigue failure to cells in aluminum foam is that the initial fatigue crack begins the cell wall, the thinnest position of the cell wall or the intersection of the cell wall and the cell ridge, where stress concentrations are more likely to occur. The fatigue failure of aluminum foam core usually starts from the semi-closed unit of the lower layer, and the fatigue crack propagates layer by layer along the direction of the maximum shear stress. The results can provide a reference for the practical engineering design and application of AFSP.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.46-49
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• 2004

The spider of a drum washing machine receives the repeated fatigue loadings during laundering. Although the spider is designed statically safely, it often happens fatigue failure. Therefore it requires the safe design for fatigue and needs the prediction of quantitative fatigue life. The S-N diagram for a spider material is developed by fatigue test and statistical analysis. The stresses are measured directly from strain gages on the spider. To predict the fatigue life of spider, the rainflow counting method and Miner's rule are used. The data for fatigue life are analyzed statistically. From these data, reliability estimation for fatigue life can be done and also, equivalent fatigue life can be obtained. It will be applied to make and improve to a short period for design and prototype test.

• International journal of steel structures
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• v.18 no.4
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• pp.1384-1396
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• 2018

One of the failure modes observed in steel yield energy dissipating devices (SYEDs) excited by a strong earthquake would be the low-cycle fatigue failure. Fatigue cracks of a SYED are prone to initiate at the notch areas where stress concentration is usually occurred, which is demonstrated by the cyclic tests and analyses carried out for this study. Since the fatigue failure of SYEDs dramatically deteriorates their structural capacities, the thorough investigation on their fatigue life is usually required. To do this, sophisticated modeling with considering a time-consuming and complicate fracture mechanism is generally needed. This study makes an effort to investigate the low-cycle fatigue life of SYEDs predicted by a simplified method utilizing damage indices and fatigue prediction equations that are based on the plastic strain amplitudes obtained from typical finite element analyses. This study shows that the low-cycle fatigue failure of SYEDs predicted by the simplified method can be conservatively in good agreement with the test results of SYED specimens prepared for experimental validation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.671-678
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• 2019

In this paper, the low cycle fatigue failure and ratcheting behavior, as well as their interaction of AH32 steel were experimentally investigated under uniaxial cyclic loading. The effects of mean stress, stress amplitude and stress ratio on the low cycle fatigue life and ratcheting strain were discussed. It was found that the ratcheting strain increased while the fatigue life decreased with the increase of mean stress and stress amplitude, and the increasing stress ratio would result in smaller ratcheting and larger fatigue life. Two kinds of failure modes, i.e. low cycle fatigue failure due to crack propagates and ratcheting failure due to large plastic strain will take place respectively. Based on the experimental results, considered the effect of ratcheting on fatigue life, a model with the maximum stress and ratcheting strain rate was proposed. Comparison with the experimental result showed that the new model provided a good prediction for AH32 steel.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.24 no.68
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• pp.1-7
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• 2001

A probabilistic model for fatigue life of a structural component is derived when the component is in a variable-amplitude loading environment. The physical mechanism which governs fatigue failure is used to model the fatigue life. Especially, the judgement of rotational symmetry in the-stress-intensity-factors results in the probability distribution for fatigue life. The probability distribution is related to the familiar truncated Gaussian distribution, which has a single parameter with a direct physical meaning.