• 한국압력기기공학회 논문집
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• 제13권1호
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• pp.75-83
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• 2017

This study investigated deformation behavior of major nuclear structural materials under cyclic loading conditions via cyclic stress-strain test. The cyclic stress-strain tests were conducted on SA312 TP316 stainless steel and SA508 Gr.3 Cl.1 low-alloy steel, which are used as materials for primary piping and reactor pressure vessel nozzle respectively, under cyclic load with constant strain amplitude and constant load amplitude at room temperature (RT) and $316^{\circ}C$. From the results of tests, the cyclic hardening and softening behavior, stabilized cyclic stress-strain behavior, and ratcheting behavior of both materials were investigated at both RT and $316^{\circ}C$. In addition, appropriate considerations for cyclic deformation behavior in the structural integrity evaluation of major nuclear components under excessive seismic condition were discussed.

• International Journal of Railway
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• 제5권2호
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• pp.71-76
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• 2012

Recently, axle load, operating speed and traffic density on railroads have had a tendency to increase and thereby cause additional pressure applied on used track. These operating conditions frequently result in service failure due to wear caused by wheel-rail contact and fatigue damage under cyclic loading. Among rail defects, the transverse crack, which has been the most dangerous type of fatigue damages, is developed from the subsurface crack near the rail running face and grows perpendicular to the rail surface. Therefore, it is necessary to investigate systematically the growth behavior of transverse crack for rail steel under mixed mode. In this study, the fatigue crack growth behavior of the transverse crack in rail steel was experimentally investigated under mixed-mode variable amplitude loadings.

• 대한기계학회논문집
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• 제13권4호
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• pp.670-679
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• 1989

본 연구에서는 항공기 구조용 재료로서 널리 사용되는 국산 고장력 7075-T73 알류미늄 합금을 준비하고 일정진폭하중 및 단일과대하중에 의한 피로균열 진전거동에 미치는 두께의 영향과 이의 기구를 검토하였다.

• 대한기계학회논문집A
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• 제26권3호
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• pp.415-427
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• 2002

A clip-on type displacement gage was designed and manufactured to use for fatigue crack growth tests of M(T)(Middle-Tension) specimens. The displacement gage has good response for the deformation of the specimen and has been successfully used not only for constant amplitude loading tests but also far variable amplitude loading tests like as single peak overloading and random loading tests. All the materials for the gage can be obtained easily in domestic market, and the manufacturing cost is very low. It is expected that the designing procedure presented in this study can be applied usefully for designing other displacement gages.

• 대한토목학회논문집
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• 제8권2호
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• pp.167-175
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• 1988

본 연구의 목적은 변동하중을 받는 구조부재의 피로거동을 해석하는 것이다. 이 연구의 해석과정은 다음과 같다. (1) 도로교의 실동응력파측정 및 통계적해석 (2) 등가의 일정진폭하중과, 통계적해석에 의해 모형화된 변동하중하(下)의 피로시험 (3) 등가응력개념의 RMC 모델에 의한 변동하중하(下)의 피로해석 등가응력개념에 의한 변동하중하(下)의 피로해석은 대부분의 구조용강재의 균열성장속도회귀지수가 $m{\fallingdotseq}3$이므로 이론적으로 RMC 모델이 합당하다. 변동하중하(下)의 피로시험해석결과 RMC 모델이 기존의 RMC 모델보다 변동하중에 의한 피로거동치(da/dN-${\Delta}K$, $N_f$)에 더 가까웠다. 또 변동하중하(下)에서 응력범위의 변화로 인한 interaction효과나 응력범위적용순서(sequence)효과 등은 피로수명에 거의 영향을 미치지 않으며, 응력범위변화속도가 클수록 피로균열성장속도가 빨라짐을 알 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.213-219
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• 2003

Acoustic emission behavior during fatigue crack growth test was investigated under various loading condition. To describe the acoustic emission activity, counts rate (d/dn) was related with SIFR (stress intensity factor range, K). Results indicated that SIFR could be divided into two parts according to its relationship with counts rate. For $K<25_{MPa\sqrt{m}}$, counts rate was increased as the SIFR increased. However, for values greater than $25_{MPa\sqrt{m}}$ , decreasing behavior was shown. This behavior of counts rate corresponding SIFR was keeping the same trend regardless of load range or crack length. Acoustic emission response to the single overload was sudden drop and slow recovery in counts rate like crack growth retardation. Under variable loading condition, counts rate of each loading block was same as that of constant amplitude loading. Overall experimental data was somewhat scattered since sensitive characteristics of acoustic emission method. However, these empirical relations indicated that counts rate was uniquely correlate with single parameter, SIFR.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.73-78
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• 2002

Ships and ocean structures are generally under random loading. Various type of variable-amplitude loading affects fatigue crack growth and fatigue life. However interaction effects due to irregularity of loading including random loading have not explained exactly and it is difficult to examined fatigue crack growth behaviour and fatigue life for this reason. Therefore in this paper crack growth tests with constant-amplitude loading including a single overload were conducted to measure plastic zone size near crack tip of DENT specimen. And the observed plastic zone sized were discussed in terms of crack growth rate. As a result of this the effect the plastic rue size due to the overload is examined on the effect on crack growth rate and, consequently, fatigue life.

• Steel and Composite Structures
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• 제25권5호
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• pp.571-579
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• 2017

The grid structure with bolt-sphere joints is widely adopted by industrial plants with suspending crane. The alternating reciprocating action of the suspending crane will cause fatigue problems of the grid structure with bolt-sphere joints with respect to the rod, the cone, the sealing plate, the bolt ball and the high strength bolt; while the fatigue of the high strength bolt is the key issue of fatigue failure. Based on efficient and smooth loading equipment with the AMSLER fatigue testing machine, this paper conducted a constant amplitude fatigue test on 18 M20 and 14 M30 high strength bolts with 40Cr material, and obtained 19 valid failure points, 9 unspoiled points with more than 2 million cycles, and 4 abnormal failure points. In addition, it established the constant amplitude fatigue design method, ${[{\Delta}{\sigma}]_{{2{\times}10}}{^6=58.91MPa}$, and analyzed the stress concentration and the fatigue fracture of high strength bolts. It can be explained that the geometrical stress concentration of high-strength bolt caused by spiral burr is severe.

• 한국해양공학회지
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• 제6권1호
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• pp.96-104
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• 1992

Aircraft structures and engineering structures are always subject to variable amplitude loads. Variable amplitude loads include some kind of loading history; for example, constant amplitude load, single peak overload and block overload etc. Crack growth under variable amplitude loading exhibits retardation effect. In this study, the 4 point bending fatigue test was performed by hydrolic servo fatigue testing machine on 7075-T6 Al-alloy. The retardation effect of overload ratio and numbers of overload cycle was quantitatively studied. 1) Change of retardation effect against increment of overload ratio is more evident when the multiple overload is applied than single overload is done. 2) The number of overload cycle is very important factor about the crack growth retardation effect when the overload ratio is more than 1.75; that is not when the overload ratio is less than 1.75. 3) Overload affected zone size increased gradually by increment of crack growth retardation effect. 4) Crack driving force is more greatly reduced when the crack tip branched off two direction than it sloped to one direction.

• Steel and Composite Structures
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• 제39권3호
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• pp.229-241
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• 2021

This work focused on aluminum foam sandwich (AFS) with different foam core densities and different face-sheet thicknesses subjected to constant amplitude three-point bending cyclic loading to study its fatigue performance. The experiments were conducted out by a high frequency fatigue test machine named GPS-100. The experimental results showed that the fatigue life of AFS decreased with the increasing loading level and the structure was sensitive to cyclic loading, especially when the loading level was under 20%. S-N curves of nine groups of AFS specimens were obtained and the fatigue life of AFS followed three-parameter lognormal distribution well. AFS under low cyclic loading showed pronounced cyclic hardening and the static strength after fatigue test increased. For the same loading level, effects of foam core density and face-sheet thickness on the fatigue life of AFS structure were trade-off and for the same loading value, the fatigue life of AFS increased with aluminum foam core density or face-sheet thickness monotonously. Core shear was the main failure mode in the present study.