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1

Experimental and numerical investigations on dynamic tensile behavior of a ZrB2-SiC ceramic

He R., Cao J., Yang K., Wang L., Kong D.

Archives of Mechanics

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2023

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Vol. 75, nr 1-2

53--73

EN

The dynamic tensile behavior of a ZrB2-SiC ceramic was investigated via split Hopkinson pressure bar tests and a bond-based peridynamic model. The experimental results showed that the peak dynamic splitting tensile stress increased linearly with the strain rate. The dynamic tensile stress history and fracture pattern exhibited a significant strain-rate dependence. In simulation, the strain-rate dependent on the critical energy release rate was introduced to predict the dynamic tensile behavior of the ZrB2-SiC ceramic. The numerical results were in good agreement with the experimental results, verifying the applicability of the peridynamic model. The maximum error of the peak dynamic splitting tensile stress between the experimental and numerical results was no greater than 6%. Moreover, the effect of the strain rate on the fracture patterns of the ZrB2-SiC ceramic composite can be well predicted by the peridynamics method. The ZrB2-SiC composite specimen split into two large fragments with additional small fragments under dynamic splitting tension. With the increase of strain rate, the main crack propagation and branching led to a larger fracture region in the middle of the specimen.

2

Effect of an eccentric decoupled charge on rock mass blasting

Kim Jung-Gyu, Ali Mahrous A.M., Kim Jong-Gwan

Journal of Sustainable Mining

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2020

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Vol. 19, iss. 1

1--10

EN

Experimental and numerical analyses were conducted to investigate the effect of an eccentric loaded contour hole on a rock mass. In the concrete blocks used for the analyses, detonating cords were placed at the centre of the blast hole and eccentrically against the wall of the blast hole. PFC2D and AUTODYN were used for the numerical analyses, and the results of these software showed that an eccentric decoupled charge can result in the directional development of fractures, thereby enabling the control of cracks in the opposite direction. Even though both types of blasting have identical decoupling indexes, the crack and fracture patterns were affected by the location of the explosive, tamping, and other conditions. The results showed that an eccentric charge holder can be applicable to control the fracture direction and the damaged zone. For an eccentric charge, the initial crack was generated at 0.01 ms and expanded in the intended direction. For the eccentric charge, the maximum pressure at the area in contact with the blast hole wall exceeded that for the central decoupled charge by a factor of 5.5. Furthermore, the pressure in the intended direction was twice of that in the opposite direction.

3

Thermal shock effects on the mechanical behavior of granite exposed to dynamic loading

Li Xiang, Li Baijin, Li Xibing, Yin Tubing, Wang Yan, Dang Wengang

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

30--40

EN

Under certain extreme conditions in rock engineering works, fast change in temperature in the load-bearing rocks can happen. Known as thermal shock (TS), such process involves rapid temperature rise or drop, which causes fracturing in the rock material and thus can pose as a threat to the stability of the rock structures. To investigate the influence of thermal shock caused by fast cooling on the mechanical property of rock, laboratory tests are performed on heated granite which are cooled with different methods, with the highest cooling rate reaching 167.4 °C/min. The dynamic loading tests are performed on the heated granite specimens utilizing the split Hopkinson pressure bar (SHPB) system. The test results show that the dynamic compressive strength drops with the increase in heating level or cooling rate. This pattern is explained by the nuclear magnetic resonance (NMR) test data that the pores inside the heated granite increase both in size and quantity as heating level or cooling rate rises. Damage patterns of the tested granite specimen fragments are analyzed based on the observation with scanning electron microscope (SEM), and the mechanisms of thermal shock in granite are also discussed.

4

Experimental investigation of the strength and failure behavior of layered sandstone under uniaxial compression and Brazilian testing

Yin P.-F., Yang S.-Q.

Acta Geophysica

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2018

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Vol. 66, no. 4

585--605

EN

As a typical inherently anisotropic rock, layered sandstones can differ from each other in several aspects, including grain size, type of material, type of cementation, and degree of compaction. An experimental study is essential to obtain and convictive evidence to characterize the mechanical behavior of such rock. In this paper, the mechanical behavior of a layered sandstone from Xuzhou, China, is investigated under uniaxial compression and Brazilian test conditions. The loading tests are conducted on 7 sets of bedding inclinations, which are defined as the angle between the bedding plane and horizontal direction. The uniaxial compression strength (UCS) and elastic modulus values show an undulatory variation when the bedding inclination increases. The overall trend of the UCS and elastic modulus values with bedding inclination is decreasing. The BTS value decreases with respect to the bedding inclination and the overall trend of it is approximating a linear variation. The 3D digital high-speed camera images reveal that the failure and fracture of a specimen are related to the surface deformation. Layered sandstone tested under uniaxial compression does not show a typical failure mode, although shear slip along the bedding plane occurs at high bedding inclinations. Strain gauge readings during the Brazilian tests indicate that the normal stress on the bedding plane transforms from compression to tension as the bedding inclination increases. The stress parallel to the bedding plane in a rock material transforms from tension to compression and agrees well with the fracture patterns; ‘‘central fractures’’ occur at bedding inclinations of 0–75, ‘‘layer activation’’ occurs at high bedding inclinations of 75–90, and a combination of the two occurs at 75.

5

Fatigue fracture of nitrided and carbonitrided layers

Nakonieczny A.

Journal of Theoretical and Applied Mechanics

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2006

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Vol. 44 nr 3

713-730

EN

The phenomenon of fatigue fracture of nitrided and carbonitrided layers is described in the paper. Fatigue bechaviour is described by analysing properties of the substrate and surface layer. The effect of microhardness of the substrate on fatigue properties of nitrided layers is obtained. Smith's diagrams for carbonitrided layers are presented. A graphical pattern for prediction of the place of failure initiation is suggested. Future directions of the examination with tribology and corrosion effects taken into account are marked in the paper.

PL

W artykule opisano zjawisko pękania zmęczeniowego warstw azotowanych i węgloazotowanych. Właściwości zmęczeniowe opisano przez analizę właściwości podłoża i warstwy wierzchniej. Określono wpływ mikrotwardości podłoża na właściwości zmęczeniowe warstwy azotowanej. Prezentowane są wykresy Smith'a dla warstwy węgloazotowanej. Przedstawiono graficzną metodę dla przewidywania miejsca inicjacji pękania zmęczeniowego. Przedstawiono kierunki badań właściwości tribologicznych i korozyjnych.

6

Spin and twist motions in a homogeneous elastic continuum and cross-band geometry of fracturing

Teisseyre R.

Acta Geophysica Polonica

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2004

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Vol. 52, nr 2

173-183

EN

A uniform continuum with rotation motions of spin and twist type is presented; in this approach we supplement the ideal elasticity constitutive law, the strain-stress relation, by the rotation-asymmetric stress relation. In such a way, we can evade an influence of the Hook law, which, when used as the unique law in the ideal elasticity, rules out an existence of rotation waves. Thus, in the ideal elastic continuum the rotation vibrations can propagate and are not attenuated. The asymmetric elastic rotation fields and their relation to asymmetric elastic stresses are proposed and discussed, under the condition that the total fields with the elastic and self parts remain symmetric or antisymmetric as required by the compatibility conditions. The tensor of incompatibility splits into the symmetric or antisymmetric parts. The conservation and balance laws for spin and twist fields and the stress -related equations of motion for symmetric and antisymmetric parts of stresses are given. The relations obtained for elastic fields, expressed by difference of the total and self-fields, can be split into the self-parts prevailing on the fracture plane and the total parts describing seismic radiation field in a surrounding space. The role of rotation processes in premonitory and rebound time domains is considered in estimating the most effective fracture patterns.