• International Journal of Precision Engineering and Manufacturing
• /
• v.9 no.4
• /
• pp.57-62
• /
• 2008

The aim of this investigation was to extract the fatigue properties at the designated fatigue life of copper foil and observe the mean stress and stress amplitude effects on both the fatigue life and the corresponding surface morphology. Tensile tests were performed to determine the baseline monotonic material properties of the proportional limit and ultimate tensile strength. Constant amplitude fatigue tests were carried out using a feedback-controlled fatigue testing machine. The mean stress and the stress amplitude were changed to obtain the complete nominal stress-life curves. An atomic force microscope was utilized to observe the relationship between the fatigue damage and the corresponding changes in surface morphology. A Basquin's exponent of-0.071 was obtained through the fatigue tests. An endurance limit of 122 MPa was inferred from a Haigh diagram. The specimen surface became rougher as the number of fatigue cycles increased, and there was a close relationship between the fatigue damage and the surface roughness evolution.

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.4
• /
• pp.44-50
• /
• 1998

The creep life fraction can be evaluated by the degree of grain deformation since the grain of Cr-Mo base metal deforms in the direction of stress. The grain deformation method using image processing technique is developed for life assessment of in-service high-temperature components. The new assessment model of grain deformation method is presented to apply to in-service components and is verified by interrupted creep test for ex-serviced material of 1Cr-0.5Mo steel. The proposed model, which is irrespective of stress direction, is to evaluate mean of the absolute deviation for the measured ratios which are diametrical maximum to minimum dimensions for grains.

• Journal of Aerospace System Engineering
• /
• v.3 no.2
• /
• pp.12-19
• /
• 2009

The research for the fatigue analysis is regarded greatly as important in aerospace field. Moreover, a study on the fatigue characteristic is very actively progressing. In this study, the fatigue life estimation was performed for Flaperon Joint which has FCL(fatigue critical location) of tilt-rotor UAV. The Flaperon Joint should be taken the various loads by several missions profiles of UAV. The fatigue load spectrum of Flaperon Joint is generated by the standard mission segment for the tilt-rotor UAV, and this spectrum is used for the fatigue test and analysis. The in-house fatigue analysis program is applied to calculate the fatigue life based on Stress-Life(S-N) method. The S-N curve is generated from the S-N data of Mil-Handbook by second order polynomial regression method. Moreover, the coefficient of determination is used to ensure how accuracy it has. In addition, the Goodman equation is used to consider the mean stress effect for evaluating more accurate fatigue life. Finally, the result of fatigue analysis is verified by comparing with the fatigue test result for the Flaperon Joint.

• Journal of Aerospace System Engineering
• /
• v.14 no.6
• /
• pp.58-67
• /
• 2020

In this study, finite element fatigue analysis combined with a fatigue correlation factor is proposed to predict the bending fatigue life of a gear in an electro-mechanical aircraft actuator. First, stress-life curves are obtained for the gear material via a round bar fatigue test. Subsequently, stochastic stress-life (P-S-N) curves are derived for 50% and 1% failure probabilities, separately. The curves are applied to the fatigue analysis model of a single gear tooth, and the effect of the fatigue correction factor is analyzed. The analytical P-S-N curves reflecting the fatigue correction factor matched the experimental data. This shows that the analytical fatigue life is reliable and that the analysis technique is effective.

• Steel and Composite Structures
• /
• v.33 no.6
• /
• pp.777-792
• /
• 2019

This paper presents a new efficient approach to estimate the S-N type fatigue life assessment curve for S550 high strength steels under low-cycle actions at -60℃. The proposed approach combines a single set of monotonic tension test and one set of fatigue tests to determine the key material damage parameters in the continuum damage mechanics framework. The experimental program in this study examines both the material response under low-cycle actions. The microstructural mechanisms revealed by the Scanning Electron Microscopy (SEM) at the low temperature, furthermore, characterizes the effect due to different strain ratios and low temperature on the low-cycle fatigue life of S550 steels. Anchored on the experimental results, this study validates the S-N curve determined from the proposed approach. The S-N type curve determined from one set of fatigue tests and one set of monotonic tension tests estimates the fatigue life of all specimens under different strain ratios satisfactorily.

• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.342-347
• /
• 2004

To evaluate the fatigue lives of welded joints taking into residual stress relaxation, two approaches are applied. One is based on the conventional local strain analyses. The other is based on a model developed by the authors. In the first approach, the Ramberg-Osgood relation, Lawrence model and S.W.T. parameter are used. In the second approach, The S-N curve for a welded joint is deduced from that of the parent material. Residual stress relaxation obtained by finite element analysis is considered. Finally, we evaluate the fatigue lives for four weld details using the two approaches.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.10 no.4
• /
• pp.38-43
• /
• 2011

Industrial reducer is in general use to Deck Crane. High-precision and high-efficient reducer is minimized the power-loss and energy-loss of a machine. So it contribute the price reduction and life extension. Reducer is usually using the Planetary gear reducer. Planetary gear reducer is composed the sun gear, planet gear, internal gear and casing. Industrial reducer's wear and breakage have a short-life. To solve this problem, it is using the profile-shifted-gear or tooth modification. This study was carried out the effect of addendum modification coefficient on tooth fillet bending strength to planetary reducer. Tooth fillet bending stress is calculate. And all parameter were expressed the function of addendum modification coefficient. And then stress concentration factor of tooth fillet curve was express the function of addendum modification coefficient using comparison between theory and finite element analysis.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.4
• /
• pp.437-442
• /
• 2014

The equipment or with a constant torque and a variable stress due to axial vibration such as the turbine-generator system in nuclear power plant show the fatigue fracture behavior. Thus this study whoul aim to measure the torsional stress and analyze the fatigue fracture behavior. To achieve this, we manufactured the equipment similar with turbine-generator system and applied various torsional vibration stress due to external load. In particular, the evaluation was conducted with the existing evaluation methods of the fatigue behavior of known stress-life, strain-life, crack growth assessment methods. With increasing the external load and independent methods tends to decrease the fatigue life was confirmed up to 10 times in 5 kV external load compared to without external load.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2002.10a
• /
• pp.75-78
• /
• 2002

A simplified methodology is presented to predict fatigue life and residual strength of composite structures. To avoid excessive amount of tests that are required for model characterization, strength degradation parameter is assumed as function of fatigue life. S-N curve is used to extract fatigue life that is required to characterize the stress levels comprising a randomly-ordered load spectrum. And different stress ratios are handled with Goodman correction approach(fatigue envelope). It is assumed that the residual strength is a function of the number of loading cycles and applied fatigue stress amplitude. And the residual strength distribution after an arbitrary load cycles is represented by two parameter Weibull functions.

• Anxiety and mood
• /
• v.15 no.1
• /
• pp.29-34
• /
• 2019

Objective : To determine predictors of posttraumatic stress disorder (PTSD) symptoms in burn injured patients and evaluate factors for identifying high risk group of PTSD. Methods : This study examined sixty one patients aged in the range of 19-65 years with burn injuries. All subjects completed self-assessment inventories about PTSD (The PTSD Check List for DSM-5. PCL-5), depression (Patient Health Questionnaire-9, PHQ-9), embitterment (Posttraumatic embitterment disorder self-rating scale, PTED scale) and meaning of life (Meaning in Life Questionnaire, MLQ). Stepwise multiple regression and ROC curve analysis were the tools used for analysis. Results : The results revealed higher depression, embitterment and lower presence of meaning in life predicted severe PTSD symptoms. ROC analysis indicated PTED scale and PHQ-9 were useful for discriminating high risk group of PTSD. Conclusion : The present study established that the need to consider embitterment, depression and meaning of life for alleviation and prevention of PTSD symptoms in burn patients.