• Journal of Welding and Joining
• /
• v.16 no.2
• /
• pp.111-121
• /
• 1998

It is well recognized that a excessive temperature gradient from the junction of head to skirt in axial direction in a hot pressure vessel can cause unpredicted high thermal stress at the junction and/or in axial direction of a skirt. this thermal stress resulting from axial thermal gradient may be a major cause of unsoundness of structural integrity. In case of cyclic operation of hot pressure vessels, the thermal stress becomes one of the primary design consideration because of the possibility of fracture as a result of cyclic thermal fatigue and progressively incremental plastic deformation. To perform thermal stress analysis of the junction and cylindrical skirt of a vessel, or, at least, to inspect quantitatively the magnitude and effect of thermal stress, the temperature profile of the vessel and skirt must be known. This paper demonstrated the temperature distribution and thermal stress analysis for the junction of skirt to head using F.E. analysis. Effect of air pocket in crotch space was quantitatively investigated to minimize the temperature gradient causing the thermal stress in axial direction. Effect of the skirt height on thermal stresses was also studied. Analysis results were compared with theoretical formulas to verify th applicability to the strength calculation in design field.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.05a
• /
• pp.794-799
• /
• 2005

The failure of blades frequently happened in the 300MW LP turbine until now and they are maintaining the blades periodically during outage. So the blade-disk system is analysed by FEM in order to identify the main cause of failure of blade row. It is found that the stress of root's hole is highest in comparison with other parts from the result of the steady stress analysis. Also, the two dangerous frequencies which is related to the resonance condition are found in the interference diagram. one is 1,516 Hz which is related to the operating speed. The other is 2,981 Hz which is related to the 1 nozzle passing frequency. The dynamic stress analysis is per-formed to identify more accurate root cause for failure of blade row. It is confirmed that the dynamic stress of the latter is higher than one of the former. From these results, it is concluded that the former has deeply something to do with the failure of blades more than the latter. Based on versatile investigation and deliberation, the change of blade's grouping is determined to avoid the resonance condition with the operating speed. After the blade grouping is changed, the former frequency vanish completely but the latter is still in existence in the interference diagram. Fortunately, It is confirmed that the dynamic stress of the new blade grouping is lower than one of the old blade grouping. 2 years has passed since modification and the LP turbine is operated well without failure so far.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.9 s.102
• /
• pp.1100-1107
• /
• 2005

The failure of blades frequently happened in the 300 MW LP(low pressure) turbine until now and they are maintaining the blades periodically during outage. So the blade-disk system is analysed by FEM in order to identify the main cause of failure of blade row. It is found that the stress of root's hole is highest in comparison with other parts from the result of the steady stress analysis. Also, the two dangerous frequencies which is related to the resonance condition are found in the interference diagram. One is 1,316 Hz. The other is 2,981 Hz which is related to the 1 nozzle passing frequency. The dynamic stress analysis is performed to identify more accurate root cause for failure of blade row It is confirmed that the dynamic stress of the former is higher than one of the latter From these results, it is concluded that the former has deeply something to do with the failure of blades more than the tatter. Based on versatile investigation and deliberation, the change of blade's grouping is determined to avoid the resonance condition with the operating speed. After the blade grouping is changed, the former frequency vanish completely but the latter is still in existence in the interference diagram. Fortunately, It is confirmed that the dynamic stress of the new blade grouping is lower than one of the old blade grouping. 2 years has passed since modification and the LP turbine is operated well without failure so far.

• 한국방재학회:학술대회논문집
• /
• 2007.02a
• /
• pp.289-292
• /
• 2007

Stress concentration have a effect on commission of structures and sometimes it cause the fracture of structures. Stress concentration is appeared where have a sudden section change like pipe connections. So stress concentration is a potent influence at pipe connentions. This paper make a study of pipe connections to alleviate stress concentration, and propose the stress concentration alleviation method that will make better efficient pipe system and will have a good effect on economic, social aspect.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.1
• /
• pp.8-13
• /
• 2020

Stress is the main cause of warpage failure of very thin substrates with thickness of several hundred ㎛, such as IC packages. Stress usually results from differences in crystal structures and corresponding thermal expansion coefficients when depositing different substances on a substrate. In this study, the behaviors of stress occurring in substrates were numerically analyzed by the thin-film pattern of the rectangles stacked on the substrates. First, the substrate displacement was obtained and the substrate strain and stress were obtained using it. When the tensile force is concentrated at the edge of the thin film pattern, normal and shear stresses are generated around the edge of the thin film pattern. Normal stress occurs near the edges of the thin film pattern and the vertexes. Shear stress also occurs around the edge of the thin film pattern, but unlike normal stress, it does not appear near the vertexes. It was also confirmed that the magnitude and direction of shear stress are changed around the edge. When edge forces of thin-film pattern are equal, the normal stress was about 10 times larger than the shear stress. This indicates that normal stress is the biggest cause of warpage failure.

• International Journal of Safety
• /
• v.10 no.1
• /
• pp.16-21
• /
• 2011

In this thesis, appearance inspection, compressive strength of concrete test, arrangement of bar inspection, survey, and bearing stress analysis were performed on a damaged coping of reinforced concrete pier to investigate the damage cause. According to the performed a series of inspections, it was found that the coping of pier was damaged during PSC (Pre-stressed Concrete) beam construction. In this thesis, the repair method for damaged pier was studied. The repair procedure used in this thesis was follows : chipping for damaged part, clean by high-pressure, installation of wire mesh, coating of surface hardening, construction of section restoration material, copula grinding, and prevent coating for far-infrared radiation.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.19 no.4
• /
• pp.1-8
• /
• 2020

Mechanical components that support structures in aerospace and power generation industries require high-strength materials. Particularly, in the aerospace industry, aluminum alloys, titanium alloys, and composite materials are increasingly used due to their high maneuverability and durability to withstand low temperature extreme environments; however, ultra-high-strength steel is still used in key components under heavy loads such as landing gears. In this paper, the fault cause analysis and troubleshooting of aircraft parts made of ultra-high-strength steel (300M) broken during normal operation are described. To identify the cause of the defect, a temporary inspection of the same aircraft was performed, and material testing, non-destructive inspection, microstructure examination, and fracture area inspection of the damaged parts were performed. Fracture analysis results showed that a crack in the shape of a branch developed from the tool mark in the direction of the intergranular strain. Based on the results, the cause of fracture was confirmed to be stress corrosion.

• Proceedings of the KSR Conference
• /
• 2004.10a
• /
• pp.674-679
• /
• 2004

In this study, we investigated the cause analysis on fracture of diesel locomotive engine liner, which was trouble assuming the inflow of cooling water. In order to reveal the cause of fracture, we studied the use history of engine, the drawing of production appearance and the stress distribution of engine in use. Also, we conducted experiments such as tension strength test, bending test and hardness test. Next, we observed fractured sections by SEM for the purposed of explaining the fracture mechanism of engine liner. Test results showed that fracture mechanism was brittle fracture due to coarse casting structure and stress concentration caused by manufacturing badness.

• Journal of Biomedical Engineering Research
• /
• v.15 no.2
• /
• pp.183-188
• /
• 1994

In clinical orthopaedics, bone resoption in the cortex is often seen post operatively on X-rays or bone densitometry after total hip replacement (THR) in the form of cortical osteoporosis or atropy. Stress shielding of bone occurs, when a load, normally carried by the bone alone, is shared with an implant as a result, the bone stresses are abnormal and with remodelling analysis this may cause extensive proximal bone resoption, possibly weakening the bone bed to the point of failure. The author made finite element models of the cemented and non-cemented type implanted femoral stem with bone resorption of the proximal medial femur and studied the feed back effect of the various degree of bone resoption to THR system by parametric analysis on the stress of the femoral stem and interface. The results of the present finite element analysis implied that the extent of proximal bone resorption has the effect of more increasing stress on the distal stem tip, cement mantle and interface in both type of femoral stem and this high distal stress possibly can cause the mechanical failure of loosening or failure after THR.

• Journal of the Korean earth science society
• /
• v.39 no.4
• /
• pp.349-360
• /
• 2018

This study analyzed variations of learning stress by comparing the salivary cortisol levels of students who participated in Earth Science inquiry activities. The cortisol concentrations between the pre- and post-inquiries of the sample of 34 university students, who had taken the course of 'Basic Earth Science and Experiments', were analyzed. The Earth Science inquiries consisted of geology and astronomy activities. The observational geology activities consisted of a session of 'structure contours and map patterns' and the cognitive astronomy activities consisted of a session of 'representations of horizontal and equatorial coordinates'. These Earth Science inquiry activities were found to cause students to have anxiety, and the thought processes that these activities involved were found to cause learning stress. The variations in cortisol concentrations of students increased by $1.6{\pm}5.9ng\;mL^{-1}$ after conducting observational activities in geology compared with $2.1{\pm}6.2ng\;mL^{-1}$ after doing cognitive activities in astronomy. The analysis of the observational activities in the geology inquiry activities indicated that they were consistent with low levels of learning stress. Conversely, the analysis of the cognitive activities in the astronomy inquiry activities showed significant individual variations in cortisol concentrations. Furthermore, individual differences in cognitive ability were reflected in the astronomy inquiry activities. While students, who received high scores, exhibited low levels of stress in the geology inquiry activities, they showed high levels of stress in the astronomy inquiry activities. It was concluded that, in the case of students with high scores in the study, the level of learning stress increased due to the raised anxiety in cognitive inquiry activities. In contrast, students, who received low scores in the study, exhibited high levels of stress in the geology inquiry activities, and low levels of stress in the astronomy inquiry activities.