• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.23 no.7 s.166
• /
• pp.1120-1128
• /
• 1999

An elastic-viscoplastic finite element analysis is performed to investigate detailed growth behavior of creep cracks and the numerical results are compared with experimental results. In Cr-Mo steel stress fields obtained from the crack growth method by mesh translation were compared with both cases that the secondary creep rate is only used as creep material property and the primary creep rate is included. Analytical stress fields, Riedel-Rice(RR) field, Hart-Hui-Riedel(HR) field and Prime(named in here) field, and the results obtained by numerical method were evaluated in details. Time vs. stress at crack tip was showed and crack tip stress fields were plotted. These results were compared with analytical stress fields. There is no difference of stress distribution at remote region between the case of 1st creep rate+2nd creep rate and the case of 2nd creep rate only. In case of slow velocity of crack growth, the effect of 1st creep rate is larger than the one of fast crack growth rate. Stress fields at crack tip region we, in order, Prime field, HR field and RR field from crack tip.

• The Journal of Engineering Geology
• /
• v.13 no.2
• /
• pp.227-238
• /
• 2003

Understanding of a creep behavior in rocks under a constant load, due to visco-elastic properties of rock, is an essential element to predict a long term ground deformation. In order to clarify the creep characteristics of the mudstone in Duho formation at Pohang basin, deposited during Tertiary, a series of laboratory tests including physical properties, unconfined compressive strength and uniaxial creep tests, was performed. The mudstone showed a higher creep potential due to 26% of clay minerals such as illite and chlorite. The unconfined compressive strength of the rock was $462{\;}kg/\textrm{cm}^2$ in average, and four creep tests were performed under constant stress of 40 to 70 % of the strength. The creep constants in the empirical and theoretical equations were deduced from the time-strain curves obtained from the tests. Among the several equations, the empirical equation proposed by Griggs and theoretical equation of Burger’s model are appreciated as the best one to express the creep behavior of the mudstone. Instantaneous elastic strain was linearly increased with stress level but strain velocity during the first creep is decreased with a similar pattern by time lapse regardless the stress level.

• Proceedings of the KSME Conference
• /
• 2001.11a
• /
• pp.180-185
• /
• 2001

In the life assessment for plant structural component, the research on deterioration of toughness and material properties occurred in weldments has been considered as very important problems. In general, the microstructures composed in weldments are hugely classified with weld metal(W.M), fusion line(F.L), heat affected zone(HAZ), and base metal(B.M). It has been reported that the creep characteristics on weldments having variable microstructures could be unpredictably changed. Furthermore, it is also known that HAZ adjacent to F.L exhibits the decreased creep strength compared to those in base or weld metals, and promotes the occurrence of Type III and Type IV cracking due to the growth of grains and the coarsening carbides precipitated in ferritic matrix by welding and PWHT processes. However, the lots of works reported up to date on creep damage in power plant components have been mostly conducted on B.M and the creep properties on a localized microstructures in weldments have not as yet been throughly investigated. In this paper, for various microstructures such as coarse grain HAZ(CGHAZ), W.M and B.M in X20CrMoV121 steel weldment, the small punch-creep(SP-Creep) test using miniaturized specimen(t=0.5mm, 0.25mm) is performed to investigate a possibility for creep characteristics evaluation.

• Tunnel and Underground Space
• /
• v.19 no.6
• /
• pp.558-566
• /
• 2009

Time-dependent behavior is a basic mechanical property of rocks. Predicting the failure time of rock structures by analyzing the time-dependent characteristic is important and problematic. It is tried to predict the failure time of tunnel, slope & laboratory creep test specimen from measured displacement(or strain) and rate with relationship suggested by Voight($\ddot{\Omega}=A\dot{\Omega}^\alpha$, where $\Omega$ is a measurable quantity such as strain & displacement and A & $\alpha$ are constants). A & $\alpha$ are estimated through applying the nonlinear least square method to the single and double integrated Voight's equations and utilized to predict the failure time. Predicted failure time is in accordance with real one except minor error. Linear inverse rate method applied to creep strain and rate yields a poor linear correlation of data and precision of predicted failure time is not better than methods using strain and rate.