Failure life estimation of sharp-notched circular tubes with different notch depths under cyclic bending

Kuo-Long Lee,Kao-Hua Chang,Wen-Fung Pan 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.60 No.3

In this paper, the response and failure of sharp-notched 6061-T6 aluminum alloy circular tubes with five different notch depths of 0.4, 0.8, 1.2, 1.6 and 2.0 mm subjected to cyclic bending were experimentally and theoretically investigated. The experimental moment-curvature relationship exhibits an almost steady loop from the beginning of the first cycle. And, the notch depth has almost no influence on its relationship. However, the ovalization-curvature relationship exhibits a symmetrical, increasing, and ratcheting behavior as the number of cycles increases. In addition, a higher notch depth of a tube leads to a more severe unsymmetrical trend of the ovalization-curvature relationship. Focusing on the aforementioned relationships, the finite element software ANSYS was used to continue the related theoretical simulation. Furthermore, the five groups of tubes tested have different notch depths, from which five unparallel straight lines can be observed from the relationship between the controlled curvature and the number of cycles required to produce failure in the log-log scale. Finally, a failure model was proposed to simulate the aforementioned relationship. Through comparison with the experimental data, the proposed model can properly simulate the experimental data.

Mechanical behavior and buckling failure of sharp-notched circular tubes under cyclic bending

Kuo-Long Lee 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.3

In this paper, an experimental investigation of the mechanical behavior and buckling failure of sharp-notched circular tubes subjected to cyclic bending is discussed. The unnotched and sharp-notched circular tubes of SUS 304 stainless steel were tested under symmetric curvature-controlled cyclic bending. It was found from moment-curvature curves that the loops show cyclic hardening and gradually steady after a few cycles for all tested tubes. The ovalization-curvature curves show an unsymmetric, ratcheting and increasing manner with the number of cycles. In addition, it was found that six almost parallel lines corresponding to unnotched and five different notch-depth (0.2, 0.4, 0.6, 0.8 and 1.0 mm) tubes were noted from the experimental relationship between the cyclic controlled curvature and the number of cycles necessary to produce buckling on a log-log scale. An empirical formulation was proposed so that it could be used for simulating the aforementioned relationship. By comparing with the experimental finding, the simulation was in good agreement with the experimental data.

Endochronic simulation for the response of 1020 carbon steel tubes under symmetric and unsymmetric cyclic bending with or without external pressure

Kuo-Long Lee,Chien-Min Hsu,Chao-Yu Hung 국제구조공학회 2008 Steel and Composite Structures, An International J Vol.8 No.2

This paper presents the theoretical simulation of the response of 1020 carbon steel tubes subjected to symmetric and unsymmetric cyclic bending with or without external pressure by using the endochronic theory. Experimental data of 1020 carbon steel tubes tested by Corona and Kyriakides (1991) were used for evaluating the theoretical simulation. Several cases were considered in this study, they were symmetric bending without external pressure, symmetric bending with external pressure, unsymmetric bending without external pressure, and unsymmetric bending with external pressure. The responses of the moment-curvature, ovalization-curvature and ovalization-number of cycles with or without external pressure were discussed. It has been shown that the theoretical simulations of the responses correlate well with the experimental data.

Pure bending creep of SUS 304 stainless steel tubes

Kuo-Long Lee,Wen-Fung Pan 국제구조공학회 2002 Steel and Composite Structures, An International J Vol.2 No.6

This paper presents the experimental and theoretical results of SUS 304 stainless tubes with different diameter-to-thickness ratio (D/t ratio) subjected to pure bending creep. Pure bending creep occurs when a circular tube is bent to a desired moment and held at that moment for a period of time. It was found that the magnitudes of the creep curvature and ovalization of tube cross-section increase faster with a higher hold moment than that with a lower one. Due to continuously increasing curvature, the circular tubes eventually buckle. Finally, a theoretical form was proposed in this study so that it can be used to describe the relationship between the creep curvature and time. Theoretical simulations are compared with the experimental test data, showing that good agreement between the experimental and theoretical results has been achieved.

Endochronic simulation for viscoplastic collapse of long, thick-walled tubes subjected to external pressure and axial tension

Kuo-Long Lee,Kao-Hua Chang 국제구조공학회 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.18 No.5

Viscoplastic collapse of titanium alloy tubes under cyclic bending

Lee, Kuo-Long,Pan, Wen-Fung Techno-Press 2001 Structural Engineering and Mechanics, An Int'l Jou Vol.11 No.3

This paper presents the experimetal result on the viscoplastic response and collapse of the titanium alloy tubes subjected to cyclic bending. Based on the capacity of the bending machine, three different curvature-rates were used to highlight the viscoplastic behavior of the titanium alloy tubes. The Curvature-controlled experiments were conducted by the curvature-ovalization measurement apparatus which was designed by Pan et al. (1998). It can be observed from experimental data that the higher the applied curvature-rate, the greater is the degree of hardening of titanium alloy tube. However, the higher the applied curvature-rate, the greater is the degree of ovalization of tube cross-section. Furthermore, due to the greater degree of the ovalization of tube cross-section for higher curvature-rates under cyclic bending, the number of cycles to produce buckling is correspondingly reduced. Finally, the theoretical formulation, proposed by Pan and Her (1998), was modified so that it can be used for simulating the relationship between the controlled curvature and the number of cycles to produce buckling for titanium alloy tubes under cyclic bending with different curvature-rates. The theoretical simulation was compared with the experimental test data. Good agreement between the experimental and theoretical results has been achieved.

Mechanical behavior and buckling failure of sharp-notched circular tubes under cyclic bending

Lee, Kuo-Long Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.3

In this paper, an experimental investigation of the mechanical behavior and buckling failure of sharp-notched circular tubes subjected to cyclic bending is discussed. The unnotched and sharp-notched circular tubes of SUS 304 stainless steel were tested under symmetric curvature-controlled cyclic bending. It was found from moment-curvature curves that the loops show cyclic hardening and gradually steady after a few cycles for all tested tubes. The ovalization-curvature curves show an unsymmetric, ratcheting and increasing manner with the number of cycles. In addition, it was found that six almost parallel lines corresponding to unnotched and five different notch-depth (0.2, 0.4, 0.6, 0.8 and 1.0 mm) tubes were noted from the experimental relationship between the cyclic controlled curvature and the number of cycles necessary to produce buckling on a log-log scale. An empirical formulation was proposed so that it could be used for simulating the aforementioned relationship. By comparing with the experimental finding, the simulation was in good agreement with the experimental data.

Endochronic simulation for viscoplastic collapse of long, thick-walled tubes subjected to external pressure and axial tension

Lee, Kuo-Long,Chang, Kao-Hua Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.18 No.5

In this study, the endochronic theory was used to investigate the collapse of thick-walled tubes subjected to external pressure and axial tension. The experimental and theoretical findings of Madhavan et al. (1993) for thick-walled tubes of 304 stainless steel subjected to external pressure and axial tension were compared with the endochronic simulation. Collapse envelopes for various diameter-to-thickness tubes under two different pressure-tension loadings were involved. It has been shown that the experimental results were aptly described by the endochronic approach demonstrated from comparison with the theoretical prediction employed by Madhavan et al. (1993). Furthermore, by using the rate-sensitivity function of the intrinsic time measure proposed by Pan and Chern (1997) in the endochronic theory, our theoretical analysis was extended to investigate the viscoplastic collapse of thick-walled tubes subjected to external pressure and axial tension. It was found that the pressure-tension collapse envelopes are strongly influenced by the strain-rate during axial tension. Due to the hardening of the metal tube of 304 stainless steel under a faster strain-rate during uniaxial tension, the size of the tension-collapse envelope increases.

Chemical Constituents from Lobelia chinensis and Their Anti-virus and Anti-inflammatory Bioactivities

Ping-Chung Kuo,Yann-Lii Leu,Tsong-Long Hwang,Ying-Ting Lin,Yuh-Chi Kuo 대한약학회 2011 Archives of Pharmacal Research Vol.34 No.5

In total, forty six compounds, including the novel compound lobechine (1), were characterized from the methanol extracts of Lobelia chinensis. The chemical structures of known metabolites were identified by comparing their spectroscopic and physical data with compounds reported in the literature. The structure of lobechine (1) was comprehensively established with the aid of 1D and 2D NMR spectroscopic analyses. In addition, selected isolates were screened for their inhibition of HSV-1 replication, superoxide anion generation, and elastase release. Among the tested compounds, scoparone (10) exhibited significant inhibition of superoxide anion generation with IC_50 of 6.14 ± 1.97 μM and lobechine (1) exhibited moderate inhibition of elastase release with IC_50 of 25.01 ± 6.95 μM, respectively.

Ginsenoside compound K reduces the progression of Huntington's disease via the inhibition of oxidative stress and overactivation of the ATM/AMPK pathway

Kuo-Feng Hua,A-Ching Chao,Ting-Yu Lin,Wan-Tze Chen,Yu-Chieh Lee,Wan-Han Hsu,Sheau-Long Lee,Hsin-Min Wang,Ding-I. Yang,Tz-Chuen Ju 고려인삼학회 2022 Journal of Ginseng Research Vol.46 No.4

Background: Huntington's disease (HD) is a neurodegenerative disorder caused by the expansion oftrinucleotide CAG repeat in the Huntingtin (Htt) gene. The major pathogenic pathways underlying HDinvolve the impairment of cellular energy homeostasis and DNA damage in the brain. The protein kinaseataxia-telangiectasia mutated (ATM) is an important regulator of the DNA damage response. ATM isinvolved in the phosphorylation of AMP-activated protein kinase (AMPK), suggesting that AMPK plays acritical role in response to DNA damage. Herein, we demonstrated that expression of polyQ-expandedmutant Htt (mHtt) enhanced the phosphorylation of ATM. Ginsenoside is the main and most effectivecomponent of Panax ginseng. However, the protective effect of a ginsenoside (compound K, CK) in HDremains unclear and warrants further investigation. Methods: This study used the R6/2 transgenic mouse model of HD and performed behavioral tests,survival rate, histological analyses, and immunoblot assays. Results: The systematic administration of CK into R6/2 mice suppressed the activation of ATM/AMPK andreduced neuronal toxicity and mHTT aggregation. Most importantly, CK increased neuronal density andlifespan and improved motor dysfunction in R6/2 mice. Conversely, CK enhanced the expression of Bcl2protected striatal cells from the toxicity induced by the overactivation of mHtt and AMPK. Conclusions: Thus, the oral administration of CK reduced the disease progression and markedlyenhanced lifespan in the transgenic mouse model (R6/2) of HD.