Acoustic emission (Акустическая эмиссия)

            Moscow State Technical University named after Bauman



                                    Essay


                              Acoustic Emission



                      Post-graduate                     Golenkov N.S.
                      English Teacher                   Kislova V.M.



                                   Moscow
                                    2001
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.