• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.6
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• pp.609-617
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• 2011

There is a trend towards the progressive use of higher operating temperatures and stresses to achieve improved efficiencies in power-generation equipment. It is important to perform the crack assessment under hightemperature and high-pressure conditions. The C(t)-integral is a key parameter in crack assessment for transient creep states. The estimation of the C(t)-integral is complex when considering the mechanical and thermal loads simultaneously. In this paper, we study estimation of C(t)-integral under combined mechanical and thermal load depending on loading conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.9
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• pp.851-857
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• 2015

In this paper, we estimate the time-dependent C(t) integrals under elastic-plastic-creep conditions. Finite-element (FE) transient creep analyses have been performed for single-edge-notched-bend (SEB) specimens. We investigate the effect of the initial plasticity on the transient creep by systematically varying the magnitude of the initial step load. We consider both the same stress exponent and different stress exponents in the power-law creep and plasticity to elastic-plastic-creep behavior. To estimate the C(t) integrals, we compare the FE analysis results with those obtained using formulas. In this paper, we propose a modified equation to predict the C(t) integrals for the case of creep exponents that are different from the plastic exponent.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1065-1073
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• 2009

In this paper, the estimation method of C(t)-integral for combined mechanical and thermal loads is proposed for elastic-plastic-creep material via 3-dimensional FE analyses. Plasticity induced by initial loading makes relaxation rate different from those produced elastically. Moreover, the interactions between mechanical and thermal loads make the relaxation rate different from those produced under mechanical load alone. To quantify C(t)-integral for combined mechanical and thermal loads, the simplified formula are developed by modifying redistribution time in existing work done by Ainsworth et al..

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.9
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• pp.949-956
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• 2009

The C(t)-integral describes amplitude of stress and strain rate field near a tip of stationary crack under transient creep condition. Thus the C(t)-integral is a key parameter for the high-temperature crack assessment. Estimation formulae for C(t)-integral of the cracked component operating under mechanical load alone have been provided for decades. However, high temperature structures usually work under combined mechanical and thermal load. And no investigation has provided quantitative estimates for the C(t)-integral under combined mechanical and thermal load. In this study, 3-dimensional finite element analyses were conducted to calculate the C(t)-integral of elastic-creep material under combined mechanical and thermal load. As a result, redistribution time for the crack under combined mechanical and thermal load is re-defined through FE analyses to quantify the C(t)-integral. Estimates of C(t)-integral using this proposed redistribution time agree well with FE analyses results.

• Journal of the KSME
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• v.27 no.2
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• pp.132-136
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• 1987

최근 저자는 혼합모우드에 대한 Budiansky와 Rice의 $J_k$ 적분에 모순이 있음을 지적한 바 있다. 그러나, Kishimoto등은 파괴진행영역을 고려한 경로 독립적분J/^/을 제시하여 주목을 끌고 있다. Landes등은 Rice의 J적분을 정상상태 크리이프에까지 연장 적용하기 위한 $C^*$적분을 소개하였다. 그후 크리이프파괴에 대한 매개변수로서 Liu등에 의한 $C_{gk}{\;}^*$, Brust등에 의한 $T_k{\}^*$등이 소개되어 계속 연구중이다. 여기에서는 이러한 매개변수들에 대해 개괄적으로 서술하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.7
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• pp.759-768
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• 2012

This paper proposes a method to determine the elastic follow-up factors for the $C(t)$-integral under secondary stress. The rate of creep crack growth for transient creep is correlated with the $C(t)$-integral. Elastic follow-up behavior, which occurs in structures under secondary loading, prevents a relaxation of stress during transient creep. Thus, both the values of $C(t)$ and creep crack growth increase as increasing elastic follow-up. An estimation solution for $C(t)$ was proposed by Ainsworth and Dean based on the reference stress method. To predict the value of $C(t)$ using this solution, an independent method to determine the elastic follow-up factors for cracked bodies is needed. This paper proposed that the elastic follow-up factors for $C(t)$ can be determined by elastic-plastic analyses using the plastic-creep analogy. Finite element analyses were performed to verify this method.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.1
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• pp.51-59
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• 1998

The purposes of the paper are to consider the failure phenomenon based on delamination and crack when the encapsulant of plastic IC package under hygrothermal loading in the IR soldering process is on elastic and viscoelastic behavior due to the temperature and to show the optimum design using fracture mechanics. The model for analysis is the plastic SOJ package with a dimpled diepad. The package model with the perfect delamination between chip and diepad is chosen to estimate the resistance to fracture by calculating J-integrals in low temperature and C(t)-integrals in high temperature with the change of the design under hygrothermal loading. The optimum design to depress the delamination and crack in the plastic IC package is presented.

• Applied Biological Chemistry
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• v.48 no.3
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• pp.267-272
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• 2005

trans-Cinnamaldehyde, a major component of Cinnamomum cassia, was quantitatively analyzed using the $^1H-NMR$ spectrometry. Applicability of this method was confirmed through observing the variation of chemical shift in the $^1H-NMR$ spectrum of t-cinnamaldehyde and the integration value according to various sample concentrations or running temperatures. When the $^1H-NMR$ spectrometry was run for t-cinnamaldehyde (7.1429 mg/ml) at 19, 25, 30, 40 and $50^{\circ}C$, the chemical shifts of the doublet methine signal due to an aldehyde group were observed at 9.7202, 9.7184, 9.7169, 9.7142 and 9.7124 ppm, respectively, to imply that the running temperature had no significant variation in the chemical shift of the signal. The integration values of the signal were $1.37\;(19^{\circ}C),\;1.37\;(25^{\circ}C),\;1.37\;(30^{\circ}C),\;1.37(40^{\circ}C)$ and $1.37(50^{\circ}C)$, respectively, to also indicate running temperature gave no effect on the integration value. When the sample solutions with various concentrations such as 0.4464, 0.8929, 1.7857, 3.5714, 7.1429 and 14.286 mg/ml were respectively measured for the $^1H-NMR$ at $25^{\circ}C$, the chemical shifts of the aldehyde group were observed at 9.7206, 9.7201, 9.7196, 9.7192, 9.7185 and 9.7174 ppm. Even though the signal was slightly shifted to the high field in proportion to the increase of sample concentration, the alteration was not significant enough to applicate this method. The calibration curve for integration values of the doublet methine signal due to the aldehyde group vs the sample concentration was linear and showed very high regression rate ($r^2=1.0000$). Meantime, the $^1H-NMR$ spectra (7.1429 mg/ml $CDCl_3,\;25^{\circ}C$) of t-cinnamaldehyde and t-2-methoxycinnamaldehyde, another constituent of Cinnamomum cassia, showed the chemical shifts of the aldehyde group as ${\delta}_H$ 9.7174 (9.7078, 9.7270) for the former compound and ${\delta}_H$ 9.6936 (9.6839, 9.7032) for the latter one. The difference of the chemical shift between two compounds was big enough to be distinguished using the NMR spectrometer with 0.45 Hz of resolution. The contents of cinnamaldehyde in Cinnamomum cassia, which were respectively extracted with n-hexane, $CHCl_3$, and EtOAc, were determiend as 94.2 \;mg/g (0.94%), 137.6 mg/g (1.38%) and 140.1 mg/g(1.40%) t-cinnamaldehyde in each extract, respectively, by using the above method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.676-684
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• 2000

In this study, behavior of $C_t$ which is a well-known fracture parameter characterizing creep crack growth rate, is investigated for weld interface cracks. Finite element analyses were per formed for a C(T) specimen under constant loading condition for elastic-plastic-creeping materials. In modeling C(T) geometry, an interface was employed along the crack plane which simulated the interface between weld and base metals. The $C_t$ versus time relations were obtained under various creep constant combinations and plastic constant combinations for weld and base metals, respectively. A unified $C_t$ versus time curve is obtained by normalizing $C_t$ with $C^*$ and t with $t_T$ for all the cases of material constant variations.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.83-91
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• 1998

Cracking problems which high temperature plant components suffer during long-term service, occur very often at welded locations. The crack occurs due to accumulated creep damage near fusion line or at heat affected zone (HAZ). However, most of the studies on creep crack growth behavior have been performed with matrix metal not wit welded metal due to the difficulty of interpreting the test results. In this study, creep crack growth rates were measured with C(T) specimens whose cracks were formed along the fusion line or HAZ. The measured crack growth rates were characterized by {TEX}$C_{t}${/TEX}-parameter derived for elastic-primary-secondary creeping material. Since contribution of primary creep was significant for the tested 1Cr-0.5Mo steel, its effect was carefully studied. Effects of crack tip plasticity and material aging were also discussed.