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1

The role of water content in rate dependence of tensile strength of a fine-grained sandstone

Cai Xin, Cheng Chuanqing, Zhao Yuan, Zhou Zilong, Wang Shaofeng

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e58, 2022

EN

Rocks in nature are commonly in partially saturated conditions and exposed to dynamic loads. In this study, to explore the coupled effects of water content and loading rate, dynamic Brazilian disc experiments were conducted on Yunnan sandstone samples with four levels of water content (from air-dried to water-saturated) under various loading rates (from 100 to 600 GPa/s) using a split Hopkinson pressure bar. The test results show that for each water content, the dynamic tensile strength of sandstone is positively sensitive to loading rate. The rate dependence of tensile strength increases as the rise of water content. The change trends of tensile strength against water content depend on loading rate: as water content rises, the tensile strength displays the manner of “no change followed by fast drop” at loading rates of 10–4 and 100 GPa/s. However, when the loading rate is above 200 GPa/s, the tensile strength increases first and then declines. The turning point occurs at water content between 1.0 and 2.0%. These observations can be interpreted with the competition between water weakening and enhancing effects under different loading conditions.

2

A multi-layered ring under parabolic pressure

Markides Ch. F., Pasiou E. D., Kourkoulis S. K.

Engineering Transactions

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2016

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Vol. 64, iss. 4

433--440

EN

The stress- and displacement-fields developed in a circular ring consisting of a finite number of linearly elastic homogeneous and isotropic concentric layers are determined. The composite ring is subjected to a distribution of radial stresses (acting along two finite arcs of its periphery) varying according to a parabolic law. The problem is solved analytically adopting Savin’s approach for an infinite plate with a hole strengthened by rings. Taking advantage of the analytic solution, a numerical model is properly calibrated and validated by considering the case of a three-layered ring. It is concluded that the constructed model simulates reality in an excellent manner and therefore it can be safely used for a thorough parametric analysis of the numerous factors influencing the stress- and displacement-fields.

3

Smooth elastic contact of cylinders by caustics: the contact length in the Brazilian disc test

Kourkoulis S. K., Markides Ch. F., Bakalis G.

Archives of Mechanics

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2013

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Vol. 65, nr 4

313--338

EN

The smooth contact of two elastic cylinders compressed against each other along a common generatrix is studied analytically and experimentally. The main objective is the quantification of the length of the contact arc. For the analytic study, the complex potentials method is employed while experimentally the contact arc’s length is determined by extending the reflected caustics technique. A series of experiments are then carried out using the device suggested by the International Society for Rock Mechanics for the standardized implementation of the Brazilian test and the typical set-up of the reflected caustics method. The experimental results are compared to the analytically determined ones. The agreement is satisfactory especially for low load levels, ensuring validity of the linear elasticity assumption.