Monitoring of Acoustic Emission During the Disintegration of Rock

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Procedia Engineering 149 ( 2016 ) 481 – 488

Peer-review under responsibility of the organizing committee of ICMEM 2016 doi: 10.1016/j.proeng.2016.06.695

ScienceDirect

* Corresponding author. Tel.:+917631053241; fax: +0-000-000-0000. E-mail address: rupam.tripathi10@gmail.com

International Conference on Manufacturing Engineering and Materials, ICMEM 2016,

6-10 June 2016, Nový Smokovec, Slovakia

Monitoring of acoustic emission during the disintegration of rock

Rupam

Tripathi*

a

,Madhulika Srivastava

a

, Sergej Hloch

b

, Pavel Adamčík

c

,

Somnath Chattopadhyaya

a

, Alok Kumar Das

a

Department of Mechanical Engineering,Indian school of Mines Dhanbad,Jharkhand, India(826004) b

Institute of Geonics of the CAS, v.v.i, Ostrava-Poruba, Czech Republic

Abstract

Many factors and complexities are involved in breaking rock with conventional methods. Water jet technique is an effective solution to the problems faced in the conventional method. Rock deterioration is the most important step in the mining, civil, mineral engineering, the technology of water jet cutting and disintegration of various material attained continuous growth during the last decades. Water jet is widely used in industrial application such as disintegration of materials and rock, cleaning and removal of surface layers.The literature is reviewed the particular attention to the detection, recording and monitoring of fracture evolution, monitoring of collision healing and creep in rock and other material using acoustic emission. Acoustic emission has been widely used in industries and other various field such as steam pipes and pressure vessels, composites materials, monitor the welding and corrosion progress ,metals and also applied numerous structural components. It is a technique to direct monitor defects formation and failure in structural materials. However, it can also provide information on the stress field, fatigue and the fracture pattern behaviour.

Peer-review under responsibility of the organizing committee of ICMEM 2016

Keywords: Acoustic emission,Rock Disintegration,Waterjet

1. Introduction

In the past two decades, the use of natural stone has been made more significant. The growing commercial market and competition for natural stone have resulted in increased demand for innovative manufacturing process. Due to the composition of natural stone (granite, shale, concrete) especially granite machining and processing with traditional system have some difficulties. Therefore new technology comes in the picture that is abrasive water jet machining. Due to this increase machining efficiency by minimizing production time and cost required. Among the innovative manufacturing process water jet have developed broad application[1],[2]. This technology (WJ) is a new innovative tool for cutting rocks and rocklike materials. It can be used for cutting, pre-weakening and drilling of rocks .The technology is a promising tool not only for manufacturing industries but also for the other industries including civil and mining engineering fields due to its distinctive features of precise shape cutting, a good surface finish, smaller kerf widths, extended tool life, complex free-form cutting, process automation, no dust, better working conditions, and environment [4],[3],[5],[10],[11].

Nomenclature

WJ Water Jet AWJ Abrasive Water Jet AE Acoustic Emission FFT Fast Fourier Transform

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AERMS Acoustic Emission Root Mean Square

These features make the technology an environmentally friendly technique over other traditional cutting processes such as circular sawing in natural stone machining and processing applications. The effective parameters on the rock cutting or erosion performance is important due to its unique characteristics and attractive properties such as, high durability and resistance to scratches,cracks, stains, spills, heat, cold, and moisture, granite has been widely used as dimensional stone in public and commercial applications in today’s life.[4]

The cutting device working with high pressure jet, called water cutter or water jet is currently being used for cutting of various types of hard material. New technology is continually being developed and limitations are being challenged as a matter of routine.A continuous water jet can be modified to Abrasive or Pulsating water jets[2] .This is also happening in the field of high-pulsating water jets. In the recent years, there are so many applications where it is more useful and economical than standard (conventional) machining processes. This technology is excellent for the cutting of complex shapes, and in fragile materials such as ferrous and nonferrous material, concrete, and rock [5],[6 ], as well as with the addition of abrasive agents to the water jet. Whatever industrial need, Water jet is an accurate, flexible, and efficient cutting system.

A continuous water jet is the basic type, in which modified form is abrasive and pulsating water jet. Both technologies are widely used in cutting of natural stone in with different areas. Presently water jet is usually adopted water cutter. Further research has also been conducted worldwide using pulsed water jets to investigate the effect of operational parameters such as: nozzle diameter, standoff distance, pulse frequency and jet pressure on rock breakability When the working pressure is above 200 Mpa that is the problem is nozzle wear. Due to which the device has the limitation of poor interaction and is hard to process the graphics. Therefore it is difficult to users to operate. So that, the application of water jet is limited [3]. The method and inspection of surface quality by continuous control(online) still remain the issue[6],[22],[23],[24],[25],[26],[27],[28],[29].In accordance with the performed measurements we are searching for the dependence between acoustic emission and its factors of the WJ factor. Acoustic emission has been widely used in industries and other various field such as steam pipes and pressure vessels, composites materials, monitor the welding and corrosion progress ,metals and also applied numerous structural components. It is a technique to direct monitor defects formation and failure in structural materials. However it can be provide information on the stress field, fatigue and the fracture pattern behavior. AE can be divided into two main groups first is traditional acoustic emission and second is source wave form analysis. Preliminary research demonstrate that the problem of acoustic emission is noise reduction, reliability, and difficulty in solving the inverse problem of the wave propagation in source function and wave form analysis. AE detects the activities inside the material that only needs one or more small sensors on the surface of the structure, in contrast to this non-destructive evaluation (NDE) examine the internal structure of the whole material.

2. Mechanism for disintegrating the rock

The basic phenomena that occurs during the breakage of the rock is that when the water jet strikes the surface it starts penetrating into the pores between the grains. As the jet traverse over the surface the penetration stops at that point when the jet has left the point has left the striking point. This penetration takes place during the time of exposure T=d/v, where d and v are the diameter and transverse velocity at the jet respectively. This concept leads to two approaches: (a) when the stagnation pressure of the jet p0 is less than the threshold pressure of the rock pththe jet does not cause any damage to the rock (b) when the stagnation

pressure of the jet is greater than the threshold pressure of the rock the grains are spelled at a rate equal to the mean rate of the water that passes through the grain. [10],[11]. To estimate the velocity at the water primates the pour with the help of Darcy’s law through porous media. dynamic viscosity of the water and pressure of the water pores, modified permeability of different rocks also plays vital role during disintegration of rocks.

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Fig.1.(a)A water jet having pressure less than threshold pressure of the rock ,traversed over the rock face (b) A water jet having pressure greater than threshold pressure of the rock ,traversed over the rock face[10]

3. The nature of acoustic emission

An acoustic emission plays a significant role in rock disintegration. It is consist of different type of wave which is associated with velocity since these wave front will increase the distance. During the disintegration components arise at interface due to reflection and refraction of the materials. Further high frequency material may be travel to the different velocity so that the result comes out lower frequency. Therefore a single impulse can give the elastic waves energy and frequency spectra although further modification occurs during travel through the material. In the laboratory has shown to be largely determined by the material of the geometry mechanical characteristics and by the loading condition. Therefore it is the most useful tool for the mechanical behavior of the materials. In addition The pattern of the acoustic emission as a function of time will be determined by the time distribution of impulsive deformation which occurs within the material. It depends on the type of material and the way which is loaded [7],[17]. Acoustic emission techniques play a vital role in monitoring of rock under bending and shear loading. A.C. Mpalaskas et.al [17] while investigating the bending and shear fracture experiments on granite samples (healthy and repair) with concurrent acoustic emission, it was observed the stress field and the fracture pattern which cannot be provided by other non invasive technique. The characterization of the difference between the fracture mode by using simple feature analysis i.e. based on the activity of loading. It is the first attempt in case of granite that such a direct correspondence between the stress fiend and result of using monitoring technique.

Fig:2 (a)Three point bending and (b) shear test of granite with concurrent AE monitoring by two sensors.

Fig.3. Acoustic emission wave form

Jerome Fortin et .al [16] investigated the three modes of the deformation during the compaction of the porous rock, large mechanical decrease of porosity is observed at a critical pressure, where pore collapse and grain crushing occur. Under axis-symmetric compression, the mechanical response of the sample deformed at 10 MPa to 70 MPa .However it can be observed that the confining pressure is characterized by brittle faulting [16][17]. Acoustic emission records depicted :i) the mean distance between two acoustic emission locations is associated with the total damage volume during the formation of compaction bands than during shear localization.

ii) these locations allowed to characterize the spatial evolution of the damage in rock during the three modes of deformation i.e. strongly affected by the material heterogeneity and indicate the stages of the deformation during the formation of compaction band and cataclastic compaction are similar

ii) The results revealed that the micro mechanism taking place during the formation of compaction bands and cataclastic compaction are characterized by similar acoustic emission signature in comparison to the shear localization which are characterized by different acoustic emission signature.

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(a)

(b)

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Fig:4 SEM micrographs (backscattered of the formed bleurswiller sandstone loaded (a) under hydrostatic pressure (cataclastic compaction) (b) in triaxial compression at an effective confining pressure of 10MPa(shear localization) (c) in triaxial compression at an effective press ure of 70 MPa (compaction band) of

acoustic emission monitoring during compaction of sandstone

Hloch et.al [2][6] during the analysis of acoustic emission hydro abrasive cutting for indirect control i.e. observed that the behaviour with the exactly scheduled change of the cutting condition and cutting head transverse. Analysis and comparison of the examined section of the experimentation through FFT spectral analysis. they performed the experimental procedure on the single variable factor of the AWJ, to be analysed the C sample monitored as solely i.e. the represent part of the large experiment. Application of the remaining sample A, B, D shows dependency on the variable factor changing speed, abrasive mass flow rate ma and focusing tube diameter df.these dependency or regulation equation are monitored through the online control process.

Fig:5 Dependence of AERMS (t) values on the cutting head traverse speed v with p=350 MPa, ma=400 gmin−1,df=1.4 mm

Wahyu Caesarendra et.al [9] focused a review of the application of the acoustic emission based condition monitoring parameter on occurring slew bearing defects. Researcher has been worked on the application of AE for very low-speed bearing with natural damage. they investigated the three primary conclusion:

i)The AE result shows that the counts, energy, duration, amplitude, ASL and RMS effectively. These changes, however, are too sudden and this means that they cannot provide adequate information for the maintenance engineer in practice.

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ii)Due to the limitation of the parameters in certain analysis of rolling element bearing AE signals revealed that the LLE feature can be considered as an alternative feature extraction method, therefore undesirable side effect occurs. It requires the more computation time for the more accurate result.

Fig:6 Naturally occurring roller damage photographs and SEM images: (a) a photo of roller number 40, (b) a SEM of roller number 40, (c) a photo of roller number 81 and (d) a SEM of roller number 81. Note that the total number of roller is 82. The roller was marked in clockwise direction.

4. Experiments and results

In order to study the disintegration processes of marble and granite by pulsating water jet via accoustic emission and vibration we used Software National Instruments (NI), LabView 2012 SP1 f5 ver. 12.0.1, Sound and Vibration Measurement Suite 12.0.0, Spectral Measurements Toolkit 2.6.3, Advanced Signal Procesing Toolkit 12.0.0 and hardware (NI) accelerometer WR712F-M4 up to 65 kHz. The tests were performed at the Institute of Geonics of the CAS in Ostrava. The technological set up consisted : plunger pump Hammelmann HDP 253, and robot ABB IRB 6640-180 for handling the pulsating water head (Figs. 2 and 3). The technological conditions of the tests are summarized in Tab.1 As a source of acoustic waves for the generation of pulsating water jet, an Ecoson WJ-UG_630- 40 generator specially designed for pulsating water jetting tools was used. Experiments were performed with pulsating water jet and the modulation frequency of 20.2 kHz. The MVT circular nozzle with an orifice diameter of 0.9 mm, standoff distance from the target material was 6 mm and traverse speed varied from 2 - 16 mm/s,pump pressure 60 MPa was used for water jetting .

Table1 Process paramater of different type of rock

Frequency Pressure Nozzle Stand off Traverse speed Material Amplitude Power Liquid

kHz P [MPa] d [mm] z [mm] v [mm/s] A [mm] P [W]

20.2 60 0.9 30 2,4,6,8,10,12,14,16 marble 6 380 H2O

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Fig 7 Experimental setup

Fig.8 The time course of disintegration of marble by puslating water jet by vibration.

The measured sample was cut through the entire thickness. Separate samples often -leafed marble - began at the end of the cut vigorously vibrate - vibrate. This led to affecting the measurement signal (amplitude spikes on the last 20% of the time record).

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Fig.10 The time course of disintegration of granite by water jet by vibration.

Fig.11 Traces on granite created by pulsating water jet (upper trace) and plane water jet (lower trace)

In above shows the frequency pulse with respect to time with pulsating or without pulsating. From the preliminary experimental data the differnce during the time course of disintegration of granite by water jet and pulsating water jet by vibration can be seen in fig.9,10.During the disintegration of rock by pulsating water jet the link between the material being cut and the optimum frequency of the pulse for different materials can show the change in the response to the pulse frequency.

5. Conclusion

AE will provide more significant role such as unique insight in damage process, In distegration of the rock, the main limitations of the process is including noice redution, and difficulty in solving the waveform analysis.There is also need to devlope the theory and application[16].It can be concluded that the reaseachers contribution in their own field the influencial effect on material in WJ & AWJ however they will be enable to create of highly effective WJ with required properties. Quality of rock breakage in WJ & AWJ during monitoring of acoustic emission depending on so many procees parameter which has more effect on the cutting of various material such as SS,rock and composite material.types of abrasive size, flowrate,transverse speed, surface roughness, fracture and fatique from the litrature review compare to above all mentioned parameter.Different approaches to effective cutting and motoring of rock can now be identified both of which can be applied to hard rock. During the past few years several advancement in equipment an incresed understanding of jet behaviour in accordance with the monitoring of acoustic emission will allow waterjet to effective and economically assist mechanical excavtion technique.

From the previous studies it can be concluded that :

x AE pressure shows the relationship between surface rougness and cut depth, which are functionally linked to the transverse speed of Vp of cutting head.[20 ]

x passive monitoring by AE can give information about the stress field and fracture pattern which is not possible by other techniques.[17]

x The AE waveform characteristic is dependent on the loading pattern. [18 ]

x AE has the capability to monitoring parameters for naturally occuring slew bearing defects.[9]

x From the preliminary experimental data the differnce during the time course of disintegration of granite by water jet and pulsating water jet by vibration can be seen in fig.9,10

6. Future

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The process waves can be determined by different possible technique.and control by the suitable devices.It can be obtained by controlling of the no. of impact that are responsible for the failure and creating zone.The previous research paper have proved that the acoustic emission is an emerging technique to monitor and control, and fracure fatigue analysis to the different type of rocks and materials. For future developments of source function and waveform analyses, analytical formulations and closed form solutions are not possible for complex AE sources and boundary conditions. Numerical techniques, such as finite element and finite difference methods, and largescale computational facilities will be very helpful for forward analyses when the sources of AEs are known by observations and proper assumptions. However this technique is still need moremodification.[14][15][16][30]. During the disintegration of rock by pulsating water jet the link between the material being cut and the optimum frequency of the pulse for different materials can show the change in the response to the pulse frequency.

Acknowledgement

This work was supported by the Slovak Research and Development Agency under contract no. APVV-207-12. Experiments were conducted with the support of the project of the Institute of Clean Technologies for Mining and Utilization of Raw Materials for Energy Use—Sustainability Program, reg. no. LO1406 financed by the Ministry of Education, Youth and Sports of the Czech Republic, and with support for the long-term conceptual development of the research institution RVO: 68145535.

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