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Shear failure and mechanical behaviors of granite with discontinuous joints under dynamic disturbance: laboratory tests and numerical simulation

Gong Hangli, Wang Gang, Luo Yi, Liu Tingting, Li Xinping, Liu Xiqi

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e171, 2023

EN

To investigate the fracture mechanical behavior and failure mechanism of jointed rock mass under compression and shear load. Conventional shear tests and shear tests under normal disturbances were conducted using an electro-hydraulic servo-motor loading system. Meanwhile, the discrete-element program particle flow code was adopted to establish a numerical shear model, and to discuss the microscopic deterioration characteristics and energy dissipation mechanism during shear fracture of rocks with discontinuous joints under joint action of normal static loads and dynamic disturbance. Compared with the conventional shear tests, shear test results under normal disturbances show the following specificities in terms of their macroscopic and microscopic mechanical properties as well as energy evolution: (1) frequent dynamic disturbances accelerate the non-steady fracture process of jointed rock samples and promote occurrence of the weakening effect of shear fracture. (2) The step-like abrupt increase in micro-cracks becomes more obvious before reaching the peak shear stress. (3) The energy-storage capacity and failure resistance of the rocks are weakened. The research results are of great significance for further understanding the dynamic catastrophe effect of deep rock mass.

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Research on parameters of MMC fracture criterion for advanced high strength dual-phase steel sheets

Fu Qiutao, Li Di, Song Hui, Liu Xingfeng, Lu Zipeng, Cui Hongjian

Journal of Theoretical and Applied Mechanics

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2022

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Vol. 60 nr 2

253--265

EN

To predict the shear fracture, tests of advanced high-strength DP steels have been carried out, and fracture models of DP steels have been established using the MMC fracture model. The MMC fracture parameters were obtained through multiple sets of experiments and stress triaxiality solved by simulation. The result was verified by stretch-bending, Nakazima tests and simulations. It shows that the MMC criterion is suitable for predicting ductile fracture of DP980, 1180. The correlation between the parameters of the MMC criterion and DP steel material properties can reduce the amount of tests data required.

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Relationships between microstructural features and mesoscopic fracture density in a Pleistocene till (Konin area, central Poland)

Włodarski Wojciech

Geologos

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2010

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Vol. 16, No. 1

3--26

EN

The qualitative and quantitative characteristics of microstructures in a till were analysed with SEM; it was also investigated whether the results depend on the till’s mesostructural characteristics. The till, exposed in a few open-cast browncoal mines near Konin in central Poland, is cut by numerous fractures which correspond to Riedel shear patterns, P-type structures and C-S type foliations. The fractures developed as a result of simple shearing induced by movement of the base of the Odranian ice sheet. On the basis of fracture density, two till types are distinguished: coarsely-brecciated till (wide spacing of fractures) and finely-brecciated till (closely spaced fractures). It is found that the fracture density is reflected in the microstructure of the till. The finely-brecciated till is characterised by a high porosity and has predominantly anisometric and fissure-like pores that also show a more clearly preferred orientation than the pores in the coarsely-brecciated till. In contrast, the coarsely-brecciated till has anisometric pores that show a less preferential orientation. The porosity of the coarsely-brecciated till is lower than in the finely-brecciated till. The finely-brecciated till probably represents a strongly deformed deposit, related in some cases to zones developed along thrusts that cut the till. Positive correlation between the porosity, the spatial arrangement of pores, and the density of fractures suggests a synsedimentary origin of the shear strain. This strain was accommodated by a particulate flow developed within both wide, pervasive zones and narrow, localised zones. The hydraulic conditions within the subglacial shear zone controlled rheological differences within the till during deformation and thus influenced the degree of the microstructure alteration.

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Jak projektować, wytwarzać i eksploatować rury do bezpiecznej pracy pod ciśnieniem

Dzidowski E. S.

Rudy i Metale Nieżelazne

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2008

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R. 53, nr 11

714-721

PL

Tradycyjne projektowanie, wytwarzanie i eksploatacja rur pracujących pod ciśnieniem bazuje na klasycznej wytrzymałości materiałów. Oznacza to brak możliwości przewidywania czasu do uszkodzenia rurociągu wskutek podkrytycznego rozwoju pęknięć. W ślad za tym niemożliwe staje się skuteczne monitorowanie rozwoju pęknięć i zapobieganie katastroficznemu pękaniu rurociągów. Problem ten potęguje zarówno coraz częstsze stosowanie wysoko wytrzymałych stopów metali (w tym nieżelaznych), jak i niedostateczny stan wiedzy inżynierskiej na temat mechaniki i mezomechaniki pękania materiałów. Bez znajomości mezomechaniki pękania trudno bowiem unikać pęknięć podczas eksploatacji rurociągów. Dlatego też, zasadniczym celem niniejszego opracowania jest omówienie mało znanych zasad stosowania tych teorii przy projektowaniu procesów wytwarzania rur oraz przy projektowaniu i bezpiecznej eksploatacji rurociągów.

EN

Traditional design, manufacture and exploitation of the pipes operating under pressure is based on the classical strength of materials. This means that the time required to damage the pipeline due to the sub-critical fracture development cannot be predicted. Consequently, efficient monitoring of fracture development, as well as the prevention of catastrophic pipeline fracture become impossible. The above problem is intensified not only by the increasing application of high-strength metal alloys (including non-ferrous metals) but also by insufficient level of engineering knowledge on the mechanics and mesomechanics of material fracture. Without the knowledge of fracture mesomechanics, it is difficult to avoid the fractures appearing during pipe manufacturing process, while the lack of knowledge of fracture mechanics makes it impossible to prevent catastrophic crack development during pipeline operation. Therefore, the key objective of this paper is to present the little known principles of applying the aforementioned theories to the design and manufacture of pipes resistant to catastrophic fractures. Further to the above, the considerable limitations of the classical strength of materials have been indicated. As a result, the need for applying fracture mesomechanics to the design of pipe manufacture process has been demonstrated. This need results from the necessity to prevent pipe fracture not only during the manufacture process, but also during their exploitation. The presence of post-manufacture mesoscopic fractures accelerates the sub-critical development of such fractures during pipeline operation. Resultantly, the general principles of applying fracture mechanics to monitor sub-critical fracture development have been discussed. What is crucial, it has been proved that the same principles may be applied to designing and selecting of pipes resistant to catastrophic damage. However, conscious prevention of such destruction requires further research to enable the development and application of the so-called processing maps, as well as the research on determining material resistance to catastrophic fracture development. Such research is indispensable to optimize the manufacture process and to associate the pipe geometry closed with their resistance to catastrophic damage. Only then it will be possible to avoid the catastrophes of construction operating under pressure. What is more, human and material losses which accompany the catastrophic fracture development in pipelines will be prevented.