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Deterioration law of intermittent jointed sandstone mechanical properties under water-rock interaction

Chen Guangbo, Li Yuan, Li Tan, Zhang Guohua

Acta Geophysica

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2022

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Vol. 70, no 4

1923--1935

EN

In water-rich mines, water conservancy, and hydropower projects, the rock mass is immersed in water for a long time, which leads to changes in its mechanical properties and affects the safety and stability of the engineering rock mass. Based on the long-term immersion of rock mass with intermittent joints by water, uniaxial compression tests were carried out on prefabricated intermittent jointed sandstone with five inclinations (0°, 30°, 45°, 60°, 90°) and three connectivity ratios (0.25, 0.50, 0.75) under different immersion times to study sandstone with intermittent joints’ mechanical response and deterioration mechanism. The research shows that: (1) With the increase of the joint inclination, the compressive strength and elastic modulus of the sandstone with intermittent joints first decreased and then increased, showing a U-shaped distribution. The compressive strength and elasticity of the sample with an inclination of 60° reach the minimum value; at the initial stage of immersion, the deterioration effect of the sample is more significant, and the deterioration effect decreases gradually with the increase in immersion time; in the initial stage of water immersion, the deterioration effect of the sample is more significant, and with the increase of the immersion time, the deterioration effect gradually weakens. (2) Immersion time and joint inclination have a great influence on the included angle, number, and mode of failure cracks. With the increase in immersion time, the plastic characteristics of the sample increase obviously, showing the characteristics of loose and weak; with the increase in joint inclination, the failure mode of the sample gradually changes from tension failure to tension shear failure, and tension failure. The influence degree of joints on failure is weak-induction-control-induction. (3) Under the water–rock action, the cement between mineral particles of the sample is gradually dissolved, the cementation of mineral particles is weakened, and the mineral particles develop into layered and fake structure, which gradually evolves from dense structure to porous loose structure. (4) The deterioration mechanism of the mechanical properties of the sandstone with intermittent joints under the water–rock action was analyzed from the perspectives of physics, chemistry, and mechanics. The deterioration of the mechanical properties of the sample is a process of gradual accumulation of damage.

2

Comparing of High-Cycle Fatigue Lifetimes in Un-corroded and Corroded Piston Aluminum Alloys in Diesel Engine Applications

Azadi M., Aroo H., Azadi M., Parast M. S. A.

Archives of Foundry Engineering

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2021

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Vol. 21, iss. 1

89--94

EN

Diesel engine components in the combustion chamber have been exposed to cyclic loadings under environmental effects, including high temperatures and corrosive fluids. Therefore, knowing the corrosion-fatigue behavior of materials is essential for designer engineers. In this article, pure fatigue and corrosion-fatigue behaviors of the piston aluminum alloy have been experimentally investigated. For such an objective, as-cast and pre-corrosive standard samples were tested by the rotary bending fatigue machine, under 4 stress levels. Some specimens were exposed to the corrosive fluid with 0.00235 % of the sulfuric acid for 100 and 200 hours. The results showed higher weight losses for 200 hours immersion times. As another result, it could be concluded that the lifetime decreased in pre-corrosive samples for both 100 and 200 hours of the immersion time, compared to that of as-cast specimens. However, such a lifetime reduction was more significant for 200 hours of the immersion time, especially within the high-cycle fatigue regime (or lower stress levels). Under high stress levels, both pre-corrosive sample types had almost similar behaviors. The field-emission scanning electron microscopy images of specimen fracture surfaces indicated that the brittle region of the fractured surface was larger for specimens after the 200 hours of corrosion-fatigue testing than the other specimen.

3

Experimental study on electrokinetic of kaolinite particles in aqueous suspensions

Min F., Zhao Q., Liu L.

Physicochemical Problems of Mineral Processing

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2013

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Vol. 49, iss. 2

659--672

EN

Influence of aqueous phase properties and process parameters on kaolinite particle zeta potential was quantified by electrophoresis experiments. The results indicated that pH strongly altered the zeta potential of kaolinite and it decreases at the beginning and then increases in the range of pH = 2–13. The activity of different cations changes the zeta potential and has the following tendency of Al3+ > Ca2+ > Mg2+ > Na+ and the zeta potential increases due to heterocoagulation of different mineral particles in suspension. It was found that the zeta potential of kaolinite particles increases after the suspension was stirred and decreases at the beginning, and then increases with soaking time. The FTIR results showed that the zeta potential takes into account ion adsorption and the change of Si–O, Al–O and Al–OH groups on the surface of the kaolinite particles.

4

Time scale of the three-phase contact formation by the bubble colliding with hydrophobic surface in n-pentanol and n-octanol solutions

Krasowska M., Małysa K.

Physicochemical Problems of Mineral Processing

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2005

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Vol. 39

21-32

EN

Phenomena occurring during collisions of the bubble rising in distilled water, n-pentanol and n-octanol solutions with hydrophobic Teflon plates of different roughness were studied using highspeed Camera (1182 Hz). It was found that even in the case of such hydrophobic solid surface as Teflon the bubble attachment didn't need to occur at first collision. In distilled water the bubble could bounce a few times without attachment. Presence of surface active substance facilitated the attachment as well as lowered the bubble local velocity. Time-scale was shortened in the case "medium rough" Teflon from ca. 40 ms (in distilled water) to 16 ms (in the case of 0.00003 M n-octanol solution), while at the "rough" surface the attachment occurred in 4 ms in both systems. It was observed that surface roughness and presence of gas bubbles at Teflon surface were crucial for the time-scale of the bubble attachment. With increasing surface roughness and immersion time into solution of the Teflon plate the probability that the bubble be attached at once was increased.

PL

Przy użyciu szybkiej kamery (1182 klatki na sekundę) badano procesy zachodzace podczas kolizji bańki z hydrofobowymi płytkami teflonowymi o różnym stopniu szorstkości. Pomiary wykonano w wodzie destylowanej oraz w roztworach n-pentanolu i n-oktanolu. Zaobserwowano, że nawet przy tak hydrofobowej powierzchni, jaką jest Teflon, przyczepienie bańki nie musi nastąpić podczas pierwsz kolizji. W wodzie destylowanej bańka może odbić się kilkakrotnie zanim utworzy się kontakt trójfazow Obecność substancji powierzchniowo aktywnej przyspiesza przyczepienie bańki, jak również zmniejs? jej prędkość. Ze wzrostem szorstkości badanych powierzchni ulegał skróceniu czasu potrzebny d utworzenia kontaktu trójfazowego i przyczepienia bańki do powierzchni teflonu. W przypadku teflonu "i średnim stopniu" szorstkości powierzchni czas ten został skrócony z 40 ms (dla wody destylowanej) d( 16 ms (dla 0.00003 M roztworu n-oktanolu). W przypadku teflonu "szorstkiego" zarówno dla wód) destylowanej, jaki i 0.00003 M roztworu n-oktanolu czas potrzebny do utworzenia kontaktu trójfazowego wynosił 4ms. Szorstkość powierzchni i obecność mikro-pęcherzyków na badanych powierzchniach teflonu wydają się być kluczowymi czynnikami decydującymi o czasie tworzenia kontaktu trójfazowego. Wraz ze wzrostem szorstkości powierzchni oraz wydłużaniem czasu immersji płytki w roztworze ulega) skróceniu czas potrzebny do przyczepienia bańki.