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1

The influence of loading rate on the mechanical behavior and energy evolution characteristics of hard and soft rock under triaxial compression

Deng Jihui, Chen Chao, Wu Xiaoning

Journal of Theoretical and Applied Mechanics

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2022

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Vol. 60 nr 3

495--508

EN

To investigate the influence of loading rate and confining pressure on the mechanical behavior and energy evolution characteristics of hard and soft rock, high strength sandstone and low strength granite were subjected to triaxial compression tests with different loading rates. The results show that significant differences exist in the stress-strain curves for sandstone and granite. The confining pressure has a significant effect on the stress-strain curve, while the loading rate has a smaller effect on the stress-strain curve. As the confining pressure increases, the peak axial strain, peak axial stress, total energy, elastic energy and dissipated energy of sandstone and granite increase, the proportion of dissipated energy to total energy of sandstone and the proportion of elastic energy to total energy of granite are reduced. As the loading rate goes up, the peak axial stress, total energy and elastic energy increase in both sandstone and granite. The ultimate failure pattern of sandstone is a typical single inclined plane shear failure, while the ultimate failure pattern of granite consists of a single inclined plane shear failure and a vertical split failure. The loading rate has no significant effect on the macroscopic failure pattern, the elastic and dissipated energies are proportional to the total energy of sandstone and granite.

2

Influences of the diameter and position of the inner hole on the strength and failure of disc specimens of sandstone determined using the Brazilian split test

Zhu Tantan, Huang Da

Journal of Theoretical and Applied Mechanics

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2019

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Vol. 57 nr 1

127--140

EN

The Brazilian split test on a centrally holed disc (referred to as a ring-disc specimen) is an important indirect method for determining the tensile strength of rock. This paper studies the effect of the diameter d of the center hole and its position, defined by the eccentricity b and the inclination angle of the eccentric hole, on the peak load, failure pattern and horizontal stress of the disc specimen via laboratory experiments and numerical modeling using the finite element method (FEM). Static Brazilian split tests are conducted on an intact disc and three types of holed discs: C-specimens containing a central hole with different diameters, EH-specimens with a horizontally eccentric hole and ER-specimens with a rotationally eccentric hole.

3

Strength — stress model of the wear-out process, part two

Drapella A.

Zeszyty Naukowe Akademii Marynarki Wojennej

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2015

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R. 56 nr 3 (202)

15--22

EN

In the previous part (i.e. part one) of this paper a differential equation intended to model a wide class of physical failure processes that may take place in technical devices was put forward. What relates model’s applicability — among the multitude of users of technical devices there surely will be ones that find the model to be relevant to real processes that cause their devices to fail. A set of relevant devices comprises these ones that are exploited (in an exact meaning of this word). Let us remember a term strength that is crucial to the model. The failure results from loss of strength that, in turn, is impacted by external stress. In part one we ‘injected’ randomness into physics expressed by means of the differential equation. Parameters that govern failure process in question were treated as random variables. Each failure process ends in failure, so time to failure is the random variable. In part two of this paper we will, with the Monte Carlo method, investigate how variability of process parameters shapes the hazard rate function.

PL

W drugiej części artykułu przedstawiono schemat eksperymentu numerycznego przeprowadzonego metodą Monte Carlo. Eksperyment polegał na generowaniu czasów pracy do uszkodzenia obiektów, w których zachodzi proces zużycia typu wytrzymałość — obciążenie, opisany w części pierwszej. Zrealizowano eksperyment trzykrotnie, oznaczając realizacje jako No. 1, No. 2 i No. 3. W każdej realizacji inny z parametrów mających wpływ na przebieg procesu uszkodzeniowego czyniono zmienną losową. Realizacje eksperymentu przyniosły bogaty materiał statystyczny, bowiem w każdej z nich przebieg procesu powtarzano tysiąc razy. Wyznaczono doświadczalnie uśrednione funkcje ryzyka uszkodzenia. Porównano je z tak zwanym wzorcem uszkodzeniowym, czyli funkcją ryzyka o przebiegu wannowym, która jest powszechnie tłumaczona w literaturze niezawodnościowej różnorodnością procesów uszkodzeniowych zachodzących w obiektach technicznych tworzących tę samą populację generalną. W artykule poddano w wątpliwość to tłumaczenie, pokazując, że wannowa funkcja ryzyka może być obserwowana w populacjach obiektów technicznych, w których zachodzi tylko jeden proces prowadzący do uszkodzenia. Pokazano płynne przejście od funkcji ryzyka monotonicznie rosnącej do wannowej powodowane jedynie zwiększeniem wariancji losowego parametru wpływającego na przebieg procesu uszkodzeniowego.

4

Antirandom Test Vectors for BIST in Hardware/Software Systems

Mrozek I., Yarmolik V.

Fundamenta Informaticae

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2012

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Vol. 119, nr 2

163-185

EN

Antirandom testing has proved useful in a series of empricial evaluations. It improves the fault-detection capability of random testing by employing the location information of previously executed test cases. In antirandom testing we select test pattern (test vector) such that it is as different as possible from all the previous executed test cases. Unfortunately, this method essentially requires enumeration of the input space and computation of each input vector when used on an arbitrary set of existing test data. This avoids scale-up to large test sets and (or) long input vectors. In this paper, we propose a new algorithm for antirandom test generation that is computationally feasible for BIST (Built In Self Test) tests. As the fitness function we use Maximal Minimal Hamming Distance (MMHD) rather than standard Hamming distance as is used in the classical approach. This allows to generate the most efficient test vectors in term of weighted number of generated k-bits tuples. Experimental results are given to evaluate the performance of the new approach.