• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1227-1234
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• 2012

In this study, fatigue tests were carried out using real-scale pipe bend specimens with wall-thinning defects under a cyclic bending load together with a constant internal pressure of 10 MPa. The wall-thinning defect was located at the extrados and the intrados of the pipe bend specimens. A fully reversed cyclic in-plane bending displacement was applied to the specimens. For the pipe bends with wall thinning at the extrados, an axial crack occurred at the crown of the pipe bend rather than at the extrados where the defect was located. In addition, the fatigue life was longer than that of a sound pipe bend predicted from the design fatigue curve in ASME Sec.III, and it was less dependent on the axial length of the wall-thinning defect. For the pipe bends with wall thinning at the intrados, a circumferential crack occurred at the intrados. In this case, the fatigue life was much shorter than that of a sound pipe bend predicted from the design fatigue curve, and it clearly decreased with decreasing axial length of the wall-thinning defect.

• Korean Journal of Agricultural Science
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• v.43 no.3
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• pp.441-449
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• 2016

Agricultural tractors are designed using the empirical method due to the difficulty of measuring precise load cycles under various working conditions and soil types. Especially, directly drives various tractor implements, the power take off (PTO) gear. Therefore, alternative design methods using gear design software are needed for the optimal design of tractors. The objective of this study is to simulate fatigue life of the PTO gear according to the operating point of the tractor engine. The PTO gear was made with SCr415 alloy steel with carburizing and quenching treatments. The fatigue life of the PTO gear was simulated by using bending and contact stress according to the torque of the load levels. The PTO gear simulation was conducted by the KISSsoft commercial software for gear analysis. Bending and contact stress were calculated by the ISO 6336:2006 Method A and B. The simulation of fatigue life was calculated by the Miner's cumulative damage law. The total fatigue life of tractors can be estimated to 3,420 hours; thus, 3,420 hours of fatigue life were used in the simulation of the PTO gear of tractors. The main simulation results showed that the maximum fatigue life of the PTO gear was infinite fatigue life at maximum engine power. Minimum fatigue life of the PTO gear was 19.61 hours at 70% of the maximum engine power. Fatigue life of the PTO gear changed according to load of tractor. Therefore, tractor work data is needed for optimal design of the PTO gear.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.1
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• pp.91-98
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• 2008

One of the two spindles in the X-lift fractured suddenly during normal operation. The fracture occurred at the notch where the bending moment might be the maximum. Macrofractographic features associated with rotating-bending fatigue are evident on the fracture surface. The 3-D finite element analysis of the X-lift reveals that the spindle rotated under bending. The measured surface strain of the spindle varies cyclically as the spindle rotates. It supports that the spindle rotated under bending. The X-lift is not perfectly symmetrical with respect to both the horizontal and the vertical plane. The slightly unsymmetrical deformation can cause the bending of the spindle.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1998.05a
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• pp.31-36
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• 1998

It is very important to have exact informations on the properties and characteristics of the sintered steel as a new material of machine elements. The bending fatigue tests are performed for sintered steel bend specimens and spur gears, which are notched by using a slicing blade. The fatigue test at a constant stress amplitude is performed by using an electrohydraulic servo-controlled pulsating tester Consequently, the S-N curves are obtained and the fatigue strength. is compared with flaw depth. Accordingly, this study presents the fatigue strength of sintered spur gears, the critical notch depth of sintered steel and the effects of flaw depth on the bending fatigue strength. The enhancement of fatigue strength due to carburized treatment is clarified.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.34-40
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• 1998

It is very important to have exact informations on the properties and characteristics of the sintered steel as a new material of machine elements. The bending fatigue tests are performed for sintered steel bend specimens and spur gears, which are notched by using a slicing blade. The fatigue test at a constant stress amplitude is performed by using an electrohydraulic servo-controlled pulsating tester. Consequently, the S-N curves are obtained and the fatigue strength is compared with flaw depth. Accordingly, this study presents the fatigue strength of sintered spur gears, the critical notch depth of sintered steel and the effects of flaw depth on the bending fatigue strength. The enhancement of fatigue strength due to carburized treatment is clarified.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.255-260
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• 2003

Most of the fatigue test were achieved in fully reversed condition that mean stress is zero. But, generally, mean stress can not be zero. This research was achieved the bending fatigue test that changes mean stress to spring steel and was studied relation with the mean stress and the fatigue life. The method to search effect about mean stress was extended S-N graph in two cases. One method was extended S-N graph using modified Miner's rule with considering damage. Another was extended using tendency of S-N graph. The exponential value(${\alpha}$) of mean stress-alternating stress equation is converged between the Goodman's and the Gerber's value even if fatigue life increases.

• Journal of Mechanical Science and Technology
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• v.17 no.2
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• pp.207-214
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• 2003

The fatigue behaviour of six different hollow section T-joints subjected to out-of-plane bending moment was investigated experimentally using scaled steel models. The joints had circular brace members and rectangular chord members. Hot spot stresses and the stress concentration factors. (SCFs) were determined experimentally. Fatigue testing was carried out under constant amplitude loading in air. The test results have been statistically evaluated, and show that the experimental SCF values for circular-to-rectangular (CHS-to-RHS) hollow section joints were found to be below those of circular-to-circular (CHS-to-CHS) hollow section joints. The fatigue strength, referred to experimental hot spot stress, was in reasonably good agreement with referred fatigue design codes for tubular joints.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.5
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• pp.120-126
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• 1998

Second step shot peening was applied on both smooth specimen and U-notch specimen in order to investigate the stress distribution and the improvement in fatigue strength. Various experiments and measurements such as rotary bending fatigue test and the measurement of compressive residual stress were performed. The results showed that the fatigue strength of second step shot peened specimens increased by 34 percent compared to that of unpeened ones. Compressive residual stress also considerably increased, which resulted in the increase of fatigue strength. finite element analysis showed that shot peening is effective in decreasing the bending stress by external force. The effectiveness of shot peening in reducing the compressive residual stress was anticipated by the superposition of the concentrated stress and the compressive residual stress.

• Journal of the Korean Ceramic Society
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• v.34 no.10
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• pp.1053-1059
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• 1997

The dynamic fatigue behavior of alumina ceramics was observed at room temperature using four point bending system. The dynamic fatigue fracture strength and the dynamic fatigue lifetime were observed as a function of crosshead speed and the notch length. The notched specimen showed the smaller deviation in dynamic fatigue fracture strength than the unnotched specimen. The crack growth exponent n and the material constant A of the notched specimen could be represented as functions of the notch length. Fracture strength of the specimen calculated from the notch length, when the notch length was regarded as the crack size, was in good agreement with the measured 4 point bending strength. Fracture surface of the specimen showed the different fracture modes according to the crosshead speed. The four point flexural strength, fracture toughness, Young's modulus and Weibull modulus of the alumina were measured as 360 MPa, 3.91 MPa.m1/2, 159GPa, 17.64, respectively.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.6
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• pp.12-19
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• 1994

This paper deals with the bending fatigue strength of SNC815 carburized spur gears. The test gears are heat-treated by two different treatments. One is the direct quenching after car-burization. The other is treated by reheating and quenching. The fatigue test at a constant stress amplitude is performed by using an electrohydraulic servo-controlled pulsating tester. The S-N curves are obtained and illustrated. The fatigue strength of direct quenched gears is higher than that of reheated quenched gears. The fatigue strength is estimated from the hardness and the residual stress by using the experimental formula proposed by Tobe and Inoue. The estimated strength is close to the test results, and the validty of the formular is confirmed.