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RISS 인기검색어
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- 저자 : Xiaozhao Li (검색결과 3 건)
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A Study on the Creeping Failure related to Crack Inclination of Brittle Rocks
Xiaozhao Li,Chengzhi Qi,Zhushan Shao 대한토목학회 2019 KSCE Journal of Civil Engineering Vol.23 No.1
A new micro-macro modelling approach is presented for predicting the creeping failure behaviors in brittle rocks. Effect of crack inclination angle is especially considered in this approach. This method is formulated by the combination of an improved stress intensity factor, a time- dependent cracking law, and a correlation of crack extension and axial strain. This improved stress intensity factor is derived by drawing crack inclination effect into Ashby and Sammis’ wing crack model. This correlation of crack extension and axial strain is established by coupling the expressions of micro-damage with macro-damage. The analytical stress- strain relation and creep equation considering crack inclination effect are derived. Furthermore, crack inclination φ, crack size a, crack friction coefficient μ, and parameter β are predicted by using the experimental data of crack initiation stress related to confining pressure, which provides a novel method in applying the proposed micro-macro model to natural rock. Influences of confining pressure on creep behaviors subjected to step axial loading and quasi-static behaviors are analyzed. The creep and quasi-static failure properties related to crack inclination are also discussed. Rationality of this proposed micro-macro approach is validated by comparing with experimental results.
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A Meso-Macro Method of Evaluating Water Content Effect on Direct Tensile Fracture in Brittle Rocks
Xiaozhao Li,Xing Che,Haifeng Li,Chengzhi Qi 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.4
Tensile stress is one of the primary forms of loading triggering the fracture in brittle rocks. Water content strongly affects the fracture process induced by meso-crack extension under the direct tensile loading of brittle rocks. Due to limitation of current equipments, the experiment of direct tensile fracture considering water content effect of brittle rocks is hardly implemented. Furthermore, the meso-macro model simultaneously considering the influence of water content and tensile loading on fracture behaviours of brittle rocks is also rarely studied. This paper proposes a meso-macro mechanical model to evaluate the water content effect on the fracture process under direct tensile loading of brittle rocks. This model is developed by combining the suggested model of meso-crack extension under direct tensile loading, the correlation of macroscopic strain and meso-crack extension, and considering the effect of water content on fracture toughness KIC and initial damage D0. This meso-macro model is linking the development process of meso-crack initiation, extension and coalescence to macroscopic fracture. The axial stress-strain curves during progressive tensile fracture under different water contents were studied, and the rationality of the suggested theoretical model was validated by the test results. The influences of water content on the relation between wing crack length and axial stress, the relation between wing crack length and stress intensity factor KI, crack initiation stress, peak stress, and elastic modulus were analyzed. The influences of the model parameter and the initial crack angle on the peak stress and crack initiation stress under the different water contents are also discussed.
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( Xiao Zhao ),( Ya-juan Cui ),( Sha-sha Bai ),( Zhi-jie Yang ),( Miao-cai ),( Sarah Megrous ),( Tariq Aziz ),( Abid Sarwar ),( Dong Li ),( Zhen-nai Yang ) 한국미생물 · 생명공학회 2021 Journal of microbiology and biotechnology Vol.31 No.8
Casein-derived antioxidant peptides by using microbial proteases have gained increasing attention. Combination of two microbial proteases, Protin SD-NY10 and Protease A “Amano” 2SD, was employed to hydrolyze casein to obtain potential antioxidant peptides that were identified by LC-MS/MS, chemically synthesized and characterized in a oxidatively damaged HepG2 cell model. Four peptides, YQLD, FSDIPNPIGSEN, FSDIPNPIGSE, YFYP were found to possess high 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging ability. Evaluation with HepG2 cells showed that the 4 peptides at low concentrations (< 1.0 mg/ml) protected the cells against oxidative damage. The 4 peptides exhibited different levels of antioxidant activity by stimulating mRNA and protein expression of the antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px), as well as nuclear factor erythroid-2-related factor 2 (Nrf2), but decreasing the mRNA expression of Kelch-like ECH-associated protein 1 (Keap1). Furthermore, these peptides decreased production of reactive oxygen species (ROS) and malondialdehyde (MDA), but increased glutathione (GSH) production in HepG2 cells. Therefore, the 4 casein-derived peptides obtained by using microbial proteases exhibited different antioxidant activity by activating the Keap1-Nrf2 signaling pathway, and they could serve as potential antioxidant agents in functional foods or pharmaceutic preparation.
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