(43)
i.e. the relation of the crack speed allocation in the solid body to the sound speed in the same environment
is directly proportional to the difference of observed dimesions and emitted crack waves to the emitted wave length.
Let’s investigate the received appropriateness (43), when
is assuming the extremes meanings.
At Z=0 we have:
, i.e. U
cr = 0
At the same time
, where from λH
= λ
emiss .
n is coming from the experimental graphics, described below. In this case Vcr/Vsound
= n = min and, hence, the crack’s developing has been continued with the minimal velocity of Ucr, which is proceeding
to the crack velocity sudden leap into the solid Vcr=max.
At Vcr=max. = N we have:
,
where from
(44)
Hence, at its start point of crack’s developing Ucr has the tendency to increasing up to maximum and then decreases
up to its minimal significance. After the definite period of time t increases by the sudden leap up to its maximum significance. Observed
wave has the value of (1+N) time exceed the value of wave emitted by the crack.
So, the sharp increasing of observed wave’s length that is corresponds to the sudden leap of Z=Vcr/Vsound shows
the destroying time coming.
Horizontal area on the plots (Fig.28) which proceeds the Z sharp increasing corresponds to the period of time before the destroying start point.
In is known that the most of materials subjected to mechanical influence possess by the acoustic emission (AE), i.e. where the destroying and
deformation of the materials’ molecular structures are taking place.
Short-time mechanical waves impulse, generating into the area of material’s structural integrity destroying, are spreeded into the
construction of the object, which is subjected to the mechanical forces and could be detected on its surface by the help of the appropriate
apparatus.
By the determination of Z according to formula (42) and (43) it would be possible to predict the materials (construction) and rocks ultimate
strength condition.
Hence, received appropriateness consisting in that: "THE RELATION OF THE CRACK SPEED ALLOCATION IN THE SOLID BODY TO THE SOUND SPEED
IN THE SAME ENVIRONMENT IS DIRECTLY PROPORTIONAL TO THE DIFFERENCE OF OBSERVED DIMENTIONS AND EMMITTED CRACK WAVES TO THE EMMITTED
WAVE LENGTH" allows us to predict the start point of ultimate strength condition of the materials (constructions) being under the dynamic
(seismic) loads influence, in particular, it is possible to predict the TIME of EARTHQUAKE coming.
For the confirmation of the received appropriateness correction experimental investigations had been carried out directed to the samples
of different nature and artificial materials loading by the gradually changed loads beginning from the loading start-point up to the sample’s
complete destroying.
At the some types of rocks destroying process laboratory investigations and at the nature investigations provided into the tunnel workings,
the device for the acoustic emission signals as the cracking indicator had been used. The resonance and bandwidth piezoelectric transducers
had registered signals.
At the laboratory experiments testing of such rocks as garnet, obsidian, black shale, basalt as well as cement and concrete cement samples
of different marks had been carried out.
EXAMPLE.
By the help of AF-5 device joint to the IN-10 acoustic impulses parameters measuring and treating blocks the concrete cement sample
loading up to it complete destroying had been tested. Loading mode and some of the destroying parameters behavior in the time domain had been
fixed on the magnetic disk. As the loading the acoustic emission signals filtration had been carried out as well as their amplification
and storage on the magnetic disk with the formation of files of equal prescribed duration. Each file corresponds to definite time period
in the real time scale. Simultaneously with the changing of interval duration the acoustic emission spectral density and signals power at
the linear law of load increasing to the sample from the micro cracks complete meas
Fig. 12
Acoustic emission signals frecuency changing at the
rockcracks origin and developing
On the starting stage of tool’s loading the frequency range, correspond to coherent function’s maximum was equal
to 361-362 kHz. At the further insignificant increasing of external influence the acoustic energy’s shock had been taking place. Along with
this the displacement of coherent function’s maximum frequency into the area of from 106 to 56 kHz up to the last avalanche destroying
stage had been registered.
So, the fixed leaps in the acoustic energy changing and displacement of the coherent function’s maximum frequency ranges from the
ultrasonic area to the sound one allowed to determine the duration of each destroying stage, beginning from the defects origin, their junction,
macro and micro cracks developing, cracks derivation with the formation of arterial ones.
Fig. 12 illustrates the sample of acoustic emission spectral density maximum changing during the increasing of the destroying degree. The
frequency, corresponding to the spectral density maximum is plotted on the ordinate; the strength loss is plotted on the abscissa.
The dependence shows that as the destroying degree increasing the spasmodic changing in frequency is taking place – from high, ultrasonic
frequencies to sound ones correspond to the avalanche stage of destroying.
Based on the analyzed sample’s result let’s consider the phenomenon of the oscillations drooping at the load increasing according
to linear law from the start point of micro cracks origin to the complete destroying (see the afore-sited formula),
Fig. 13
Changing of "seismic effect’s" magneting during
The increase of loading beginning from the microcracks
origin till estroyi estroying
Fig. 13 shows the Z changing as the load increasing (Z=0.0042) to the complete destroying (Z=0.67). The appropriateness of Z
changing had been received accordin to the before mentioned formula (10). Table 1 represents the Z numerical values which is corresponding
to the given oscillation frequency f.
| Z numerical values |
Table 10 |
f kHz |
252 |
182 |
106.4 |
56 |
9 |
6 |
3 |
Z |
0.0042 |
0.276 |
0.416 |
0.474 |
0.839 |
0.391 |
0.67 |
As obvious from the Table 1 and Fig.3 the appropriate increasing of load up to the arterial micro crack formation is observed. Then
the sharp decreasing of Z from 0.839 to 0.391 occurs after which – pause and rising up to 0.67 where the destroying is taking place.
This phenomenon had been repeated in the all-numerous experiments with the rocks. The precise appropriateness of Z decreasing with
maximum is observed, and then its growth which lead to the blocks’ failure, i.e. to the earthquake and to the receiving of appropriateness
between the values of different type of waves.
On this appropriateness of Z is possible to judge about the time of material structure’s changing and about the time of limited strength
condition.
As it is known, the earthquake centers possess the possibility to inform about their preparation to the earthquake by the help of sound
information. The only problem is to trap these sounds, reject interference and reinforce.
By registering the time sequence of waves coming from the developed earthquake center λ1, λ2 … according
to formula (47), it would be possible to predict the earthquake’s start point moment. Sum of maximal horizontal and subsequent minimal
horizontal areas in time (Fig.13) represents the period of time before the earthquake beginning, which always corresponds
to the "calm" before the earthquake.
As it is known this period of time is in the range of 8 to 30 hours before the earthquake starting depending on the given region grounds.
What we claim is:
It was established previously unknown appropriateness of the connection between the lengths of observed and emitted plane
(seismic) waves into the solid, destroyed under the mechanical force (static, dynamic, temperature) influence consists in that
the ratio between the lengths of observed and emitted waves to the emitted wave at the crack developing into the destroying center
increased up to maximum, distinguished by that after maximum the ratio sharp dropping is taking place and after some period of time
before the destroying start point the sharp increasing is observed characterizing the starting of strength loss, i.e. destroying
(earthquake beginning).
is the emitting wave period.
That’s why the wave must be pass long way and device in the point A will fix a large interval of time between the two waves crest coming
one after another,
