We propose a numerical model based on static fatigue laws in order to model the time-dependent damage and deformation of rocks under creep. An empirical relation between time to failure and applied stress is used to simulate the behavior of each element of our finite element model. We review available data on creep experiments in order to study how the material properties and the loading conditions control the failure time. The main parameter that controls the failure time is the applied stress. Two commonly used models, an exponential tfexp (bs/s0) and a power law function tfsb0 fit the data as well. These time-to-failure laws are used at the scale of each element to simulate its damage as a function of its stress history. An element is damaged by decreasing its Young's modulus to simulate the effect of increasing crack density at smaller scales. Elastic interactions between elements and heterogeneity of the mechanical properties lead to the emergence of a complex macroscopic behavior, which is richer than the elementary one. In particular, we observe primary and tertiary creep regimes associated respectively with a power law decay and increase of the rate of strain, damage event and energy release. Our model produces a power law distribution of damage event sizes, with an average size that increases with time as a power law until macroscopic failure. Damage localization emerges at the transition between primary and tertiary creep, when damage rate starts accelerating. The final state of the simulation shows highly damaged bands, similar to shear bands observed in laboratory experiments. The thickness and the orientation of these bands depend on the applied stress. This model thus reproduces many properties of rock creep, which were previously not modeled simultaneously.

Brittle Creep, Damage and Time to Failure in Rocks

Thank you for downloading underwater electroacoustic transducers a handbook for users and designers. As you may know, people have search numerous times for their chosen books like this underwater electroacoustic transducers a handbook for users and designers, but end up in harmful downloads. Rather than enjoying a good book with a cup of coffee in the afternoon, instead they are facing with some malicious virus inside their desktop computer.

Underwater Electroacoustic Transducers A Handbook For Users And Designers

This paper theoretically and experimentally considers the pulsed mode of operation of the radiation-receiving system. The system contains two identical piezoceramic plates separated by a layer of immersion liquid (glycerin). The emitter was excited by the complex electrical signal of the special shape, which consisted of two half-cycles of the sine wave (exciting and compensating) on the natural frequency of the piezoplates. The forms of these signals were calculated by the authors and described in their previous papers using the d’Alembert method. The length of the electrical signal was estimated at the output of the piezoelectric receiver. The problem was solved theoretically using the finite element method. The acoustical system was simulated with the help of the COMSOL Multiphysics modeling environment. A comparative study of the theoretical and experimental results is carried out. The form of the signal at the output of the system was calculated by the d’Alembert method, and the simulated form by the finite element method was in good coincidence with the results of experimental and full-scale modeling. It is shown that the usage of complex waveforms allows achieving a significant pulse duration reduction of the electrical voltage at the output of the receiver.

/pdf/on-the-shaping-of-a-short-signal-at-the-output-of-the-1uhfa75cnf.pdf

On the Shaping of a Short Signal at the Output of the Receiving Piezoelectric Transducer in the Radiation-Reception System

Statistics and Experimental Design in Engineering and the Physical Sciences (Vols. I and II) (2nd ed.).

The working time of a single mine surveyor or the working time of a whole “Mine Surveying Ergatic System” (MSES) depends on various factors. These factors are: different qualities of a surveyor as a professional and a person, his emotion and attention, accuracy and comfort of mine surveying instruments, and the mine working environment. These factors make it possible to conclude the MSES working time to be a stochastic quality. In our research, a unimodal alpha-distribution was used. We have studied the working time of 1 type of MSES: “measurements of horizontal angle”. More than 80 mine surveyors and students have taken part in the experiments. The alpha-graphic line shows an accurate interpretation of different points, so it may be used in testing mine surveyors’ professional skills.

/pdf/theoretical-and-experimental-study-of-mine-surveyors-testing-2t1uda7byp.pdf

Theoretical and Experimental Study of Mine Surveyors Testing

The pulsed operation mode of an emission–reception system consisting of two immersion piezoelectric transducers separated by a liquid (glycerine) layer has been studied. Identical piezoceramic plates were used as active elements in the emitter and receiver. The rear sides of the plates were loaded on air. The emitting transducer was excited by composite-waveform electric signals consisting of two sine-wave half-periods with different amplitudes (with their sign taken into account). The length of each half-period corresponded to the half-period of emitting plate vibration at the antiresonance frequency. The first half-period was the exciting one, with the second, supplied at the appropriate moment, being the compensating one. The amplitudes of the compensating half-periods were precalculated based on a mathematical algorithm developed by the authors in their previous works. It has been shown that applying composite-waveform signals allows one to considerably reduce the duration of a signal at the receiver output as compared with the case where the emitter is excited by an electric pulse in the form of one half-period of vibration at the antiresonance frequency. Experimental data are in fair agreement with computation results.

Decreasing Pulse Duration at Receiver Output under Emitter Excitation with Complex Waveforms

The influence of noise on mine surveyors’ health was studied. The study was done by using the equivalent noise level. The harmful factors were measured in the mine of Vorkuta and in the metro tunnel. The noise was established to be the main harmful factor that influences mine surveyors’ health.

The Influence of the Noise on Mine Surveyer

Synthesis and correction of acoustic signals in radiation-reception systems. calculation and design algorithm

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