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  • Hong, Liu  (3)
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  • 1
    Online-Ressource
    Online-Ressource
    Hindawi Limited ; 2021
    In:  Advances in Civil Engineering Vol. 2021 ( 2021-1-15), p. 1-16
    In: Advances in Civil Engineering, Hindawi Limited, Vol. 2021 ( 2021-1-15), p. 1-16
    Kurzfassung: To study the evolutionary characteristics of mesostructural damage to saturated limestone under different loading and unloading paths, three types of loading and unloading tests involving three different loading rates and initial peak stresses were performed. Nuclear magnetic resonance technology and scanning electron microscopy were used to investigate the evolutionary characteristics of pore water during the loading and unloading of the limestone. The results indicated that, with an increase in the initial peak stress, the rock viscoplasticity gradually decreased, and the variation of pore radius and the reduction of bound water decreased. With an increasing loading rate, the mesostructure evolution law under disturbance-increasing amplitude (DIA) cycling was opposite to those under increasing amplitude (IA) and repeated-increasing amplitude (RIA) cycling. With the increasing loading stress level, the porosity decreased and then increased. Under increasing amplitude cycling, a larger initial porosity resulted in higher pore compaction and expansion limits. Reducing the initial peak stress inhibited the pore expansion, whereas it had the opposite effect under RIA and DIA cycling. During loading and unloading, bound water exists in pores of organic matter and mesopores, and free water exists in macropores of intergranular and transgranular fractures. These changes indicate certain laws under different loading and unloading paths. The results of this study indicate that the mesostructure characteristics of rock depend on the loading and unloading paths.
    Materialart: Online-Ressource
    ISSN: 1687-8094 , 1687-8086
    Sprache: Englisch
    Verlag: Hindawi Limited
    Publikationsdatum: 2021
    ZDB Id: 2449760-5
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Online-Ressource
    Online-Ressource
    MDPI AG ; 2020
    In:  Energies Vol. 13, No. 15 ( 2020-08-03), p. 4003-
    In: Energies, MDPI AG, Vol. 13, No. 15 ( 2020-08-03), p. 4003-
    Kurzfassung: To analyse the effect of loading rate on the energy evolution of rocks under cyclic loading and unloading, tests on saturated limestone were conducted at loading rates of 0.15, 0.2, and 0.3 mm/min, and the evolution characteristics of plastic, elastic, dissipation, and input energies were examined under different loading rates. The results indicated that the plastic strain in the entire test was directly proportional to the loading rate. In addition, strength, residual stress, plastic energy, and dissipation energy under residual resistance were inversely proportional to the loading rate. The plastic strain exhibited a decreasing–stabilising–increasing trend, and the smaller loading rate delayed the “increasing” trend. The increasing extent of each energy exhibited the following trend: input 〉 elastic 〉 plastic 〉 dissipation energy. Furthermore, the first three types of energy exhibited a slow–fast–slow–fast increase trend. The dissipation energy exhibited a fast–steady–fast–slow–fast increase trend. Additionally, the elastic energy index exhibited a large increase–steady increase–decrease trend, which was proportional to the loading rate. The damping ratio exhibited a decrease–increase–decrease–increase–decrease trend which was proportional to the loading rate in the compaction stage and inversely proportional to the plastic stage.
    Materialart: Online-Ressource
    ISSN: 1996-1073
    Sprache: Englisch
    Verlag: MDPI AG
    Publikationsdatum: 2020
    ZDB Id: 2437446-5
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Online-Ressource
    Online-Ressource
    Frontiers Media SA ; 2020
    In:  Frontiers in Physics Vol. 8 ( 2020-12-4)
    In: Frontiers in Physics, Frontiers Media SA, Vol. 8 ( 2020-12-4)
    Kurzfassung: To study the acoustic emission evolution characteristics of saturated limestone under different loading and unloading paths, three cyclic loading and unloading tests were conducted with different loading rates and initial cyclic peak stresses, and acoustic emission monitoring was performed simultaneously. The results indicate that, during loading and unloading, the intermediate-frequency signals of saturated rock exhibit a variation trend of sparse–dense–sparse signals, whereas the low-frequency signals are continuously and massively produced. With the increase in the loading rate, the development trends of cumulative hits and energy become closer, and the development form of ringing count changes from N-type to U-type and then to N-type. The slight increase period and attenuation period are extended, whereas the intense growth period and postpeak calm period are shortened. With an increase in the initial cyclic peak stress, the change in cumulative energy is more obvious than that in cumulative hits near the rock failure. The development form of the ringing count changes from U-type to W-type and then to N-type, and each period is first shortened and then extended. With the increase in loading rate, the increase in the slow-change period tends to change from gradually increasing to increasing and then decreasing. By contrast, the increase in the step tends to change to a gradual increase. With the increase in the initial cyclic peak stress, the duration of and increase in the energy in the step and the slow-change period tend to decrease and then increase.
    Materialart: Online-Ressource
    ISSN: 2296-424X
    Sprache: Unbekannt
    Verlag: Frontiers Media SA
    Publikationsdatum: 2020
    ZDB Id: 2721033-9
    Standort Signatur Einschränkungen Verfügbarkeit
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