Доклад: Acoustic Emission
Moscow State Technical University named after Bauman
The appearance of new technologies as well as the perfection of
traditional ones is mostly based on the results of research in the fields of
solid physics, quantum mechanics, physical chemistry and other fundamental
disciplines. That is why perspective methods
of technological diagnostic must have an advanced trend of development
comparing to the development of new structure and shape forming methods.
Intensification of science research in the fields of emission methods
analysis reflects the above-mentioned matters. Emission diagnostics methods are
based on the effect of radiation of elastic deformation waves, electrons and
electromagnetic waves by studied object. Object condition is identified
registration and analysis of radiation parameters based on the condition change
can be made. The above methods represent so called inner energy methods and
have a number of advantages allied with anomalies of material structure.
Amongst diagnostic methods the most widely spread in field of machinery
construction is an acoustic emission method based on generation of elastic
deformation waves in solid body caused by defect development, phase
transformation and other elapsing processes. Analysis of all parameters allows
to make judgement, regarding damage dynamics of material. It is used
effectively for undamaging control while testing and using articles.
It is necessary to mention that an acoustic emission method is one of
the newest and most prospective diagnostic methods. It is physical nature
causes expanding fields of application for the method in technology.
First works by acoustic emission method appeared in 70s. This works
fulfilled in the late 70s and early 80s are characterized by fairly narrow
range of technological tasks, connected mostly with tool wear control.
Sources of an acoustic emission are divided into internal and external.
First ones are sources located on object’s surface. For example, acoustic
emission caused by friction, blow, turbulent fluid and gas streams. Processes
of local dynamic redistribution of tension fields in material apply to internal
sources of acoustic emission. For example, acts of plastic deformation, micro-
and macro destruction and phase transformation. Analyzing the cut zone from
these positions can make a conclusion about existence in this zone whole number
of acoustic emission sources of different power and spectral density. Acoustic
emission parameters depend on a way plastic deformation, destruction and
friction processes go. It is possible to carry out acoustic emission diagnostic.
Beside, frequency range of registration of acoustic emission parameters usually
estimates in tens, hundreds and thousands kilohertz and is well protected from
noises, which accompany work of technological equipment units.
In many aspects the acoustic emission method reminds those of
low-frequency acoustic spectrometry, although in other aspects it is completely
different. Acoustic emission methods are a clear shown wave process accompanied
by variable space-time localization of elastic energy.
The increase of mechanical processing efficiency is tied with search and
realization of new speeding-up methods of technological preparation for shape
forming processes. Methods of rational carving conditions determination are
being developed as one of the most important tendencies in practical use of
emissive technological diagnostic means.
An important direction in the practical use of progressive technology
diagnostic methods for carving process is the quality analysis of surface
detail layer during the processing. The quality of a surface processed is
formed as a result of friction, plastic deformation and the destruction of
ingot material in carving zone. This is the reason why emissive process
parameters must contain information regarding surface’s condition. It is
possible to use acoustic emission method to identify the moment of contact
between a tool and an ingot.
Thus, as shown by preliminary analysis, the acoustic emission method has
great technological potential, which needs to be yet studied. The lack of
knowledge regarding method’s opportunities constrains its effective use in
theory and practice of mechanical carving of materials.