• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.488-493
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• 2011

Authors previously suggested the design sensitivity analysis based on transmissibility function and identified the sensitivity of measured point over the small modification of system dynamics. On the other hand, the acceleration data will not reveal the strain information at the same location and authors suggested energy isoclines that successfully predict the fatigue damage on the interesting location to overcome the drawback of acceleration over fatigue society. Both of methodologies, sensitivity analysis and fatigue damage prediction, commonly use the response acceleration response as main indicator. In this paper, authors investigate the advanced method of vibration fatigue prediction using design sensitivity analysis to enhance the accuracy of predicted accumulated fatigue. Uni-axial vibration testing is performed with finite element model of a simple notched specimen and the prediction of fatigue damage at notched location is conducted for accelerations at different measurement locations that show different sensitivity contribution, either.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.2
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• pp.123-129
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• 2012

It was previously suggested the design sensitivity analysis based on transmissibility function to identify the most sensitive response location over a small design modification. On the other hand, energy isoclines were used to predict the fatigue damage with acceleration response only. Both of previous studies commonly tackle the engineering problem using the acceleration response alone such that it may be possible to investigate the relationship between sensitivity analysis and accumulated fatigue damage. In this paper, it is suggested the novel method of vibration fatigue prediction using design sensitivity analysis to enhance the accuracy of predicted accumulated fatigue. Uni-axial vibration testing is performed with a simple notched specimen and the prediction of fatigue damage is conducted using accelerations measured at different locations. It can be concluded that the accuracy of predicted fatigue damage is proportional to the sensitivity index of the responsible location.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.73-82
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• 1998

This paper is especially concerned with the weldment between support beam and square bar that plays important roles in control box of Expansion Joint as a brdige structure. Fatigue strength ({TEX}$$\sigma$_{ult}${/TEX}) of the weldment is dependent on notch factor ({TEX}$K_{f}${/TEX}) become important factors to predict fatigue life. The fatigue notch sensitivity (η) for metals can be divided into two types ; high and low notch sensitivity. In this work, the Expansion Joint weldment was found to have low notch sensitivity. The maximum strain distribution during static loading is similar to the FEM analysis. Fatigue test of real structure was performed up to {TEX}$10^{6}${/TEX} cycles to be compared with predicted endurance limit.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.46-50
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• 1993

The sensitivity study to evaluate the effects of parameters on the fatigue crack propagation life under the constant loadings is executed in the previous study of the authors. It is shown that the effect of the crack opening ratio is large comparatively. The purpose of this paper is to evaluate the effects of parameters on the fatigue crack propagation life under the random loadings. A new method of evaluation of the effective stress under the random loadings is developed. The sensitivity study of parameters on the fatigue crack propagation life under the random loadings is executed by using it.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.491-496
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• 2010

The direct design modification of problematic component is disallowed in order to sacrifice other major factors such as a stability or a major performance. So, the best design policy is to risvise the immature structural medchanism under the minimal design change as soon as possible. For this paper presents a new design sensitivity analysis based on transmissibility rtio (TR) of response acceleration to find a proper candidate for the minimal design modification. The new sensitivity analysis is based on the fact that the sensitivity of TR over a small design change is inversly proportinal to the magnitude of TR. The theory of proposed design sensitivity analysis is simulated with the variance of TR over a dynamic change. Then, new methodology is appplied for a linear elastic specimen to detect the most sensitive node over a design change using measured accleration data during uni-axial vibration test, The physical verification of the sensitivity method is conducted on the CAE model of a linear elastic specimen by adding concentration mass and the vibration fatigue of the simple specimen is analyzed to estimate the relationship between fatigue behaviors and sensitivity consequences.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.3
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• pp.161-166
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• 2003

In order to improve the fatigue lift of a lower control arm in the vehicle suspension, a new shape optimization procedure is presented. In this approach, the shape control point concept is introduced to reduce the numbers of shape design variables. Also, the two-level orthogonal way is employed to evaluate the design sensitivity of fatigue life with respect to those shape design variables, because the analytical design sensitivity information is not directly supplied from the commercial CAE softwares. In this approach, only the six design variables are used to approximate the shape of lower control arm. Then, performed are only 10 fatigue life analyses including the baseline design, 8 DOE models and the final design. The final design, the best combination obtained from the sensitivity information, can maximize the fatigue lift nearly two times as that of the baseline design, while reducing the 12 percentage of weight than it.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.10a
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• pp.115-120
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• 1998

This paper is especially concerned with the weldment between support beam and square bar that plays important roles in control box of Expansion Joint as a bridge structure. Fatigue strength of the weldment is dependent on notch radius from welding defects and material properties. From which, tensile strength($\sigma$ult) and fatigue notch factor(Kf) become important factors to predict fatigue life. The fatigue notch sensitivity(η) for metals can be divided into two types : high and low notch sensitivity. In this work, the Expansion Joint weldment was found to have low notch sensitivity. Fatigue test of real structure was performed up to 106cycles to be compared with predicted endurance limit.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.3
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• pp.215-220
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• 1999

Rotary bending fatigue tests were carried out to investigate the artificial defect sensitivity of fatigue limit in annealed and austempered ductile irons. Artificial defect(hole, diameter${\leq}0.4mm$) machined on specimen surface did not bring about an obvious reduction of fatigue limit in austempered ductile iron as compared with annealed. As a result of investigation on $\sqrt{area}$ c which is the critical artificial defect size. $\sqrt{area}$ c of austempered ductile iron is larger than that of annealed. This means that the crack initiation at artificial defect in austempered ductile iron is more difficult in comparison with annealed. In case that the $\sqrt{area}$ c of artificial defect and graphite nodule are same, the rate of crack initiation for graphite nodule is higher than that of artificial defect.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.11 s.242
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• pp.1494-1502
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• 2005

Fatigue life and notch sensitivity of the ultrafine grained pure Ti produced by ECAP was investigated. The ECAPed sample with the true strain of 460$\%$ showed near equiaxed grains with an average size of about 0.3 $\mu$m. After ECAP, the ultimate tensile strength was increased by 60$\%$, while the tensile ductility was decreased by 31$\%$. The ECAPed ultrafine grained pure Ti samples showed high notch sensitivity and significant improvement of high cycle fatigue limit by a factor of 1.67. The ECAPed samples also show high notch sensitivity (K$_{f}$/K$_{t}$ = 0.96). It can be concluded that ECAP is the effective process for achieving high fatigue strength in Ti by increasing its tensile strength through grain refinement

• Journal of Aerospace System Engineering
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• v.15 no.2
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• pp.16-25
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• 2021

Reliability of fatigue strength on Aircraft Composites(GFRP) Structures was assessed in this paper. Fatigue strength of GFRP was used through the existing fatigue test data with Monte Carlo method. The S_a-N_f curve of composites fatigue strength was assumed as normal distribution and reliability was analyzed using SSIT model. Fatigue stress was designed IAW ASTM F3114-15 with special safety factor of S_sf=1.2~2.0. Reliability was calculated by analytic method and FORM. Sensitivity for the effect of mean and standard deviation of fatigue strength as well as fatigue stability was evaluated. This result can be usefully applied to reliability and fatigue design for composite structures of light weight aircraft.