Re: Litchenberg figures - do they weaken the acrylic?
Posted by Bert Hickman on 7/13/2010, 8:26 am, in reply to "Litchenberg figures - do they weaken the acrylic?"
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: Hello Bert, and everybody. I recently posted a message to the Musical
: Instrument Makers Forum (MIMF.COM) pertaining to acrylic zappery; as some
: makers of electric solid-body guitars have used thick acrylic bodies in
: the past.
: A reply to the forum indicated that a piece of acrylic containing the
: pattern of discharge will be quite weak, and will likely crack along one
: of the paths.
: Granted, many guitar players do not treat their gear like museum pieces.
: But I am curious - what has been the experience of many of you who have
: created Litchenberg figures? Has the material weakened to the point where
: actual discrete cracks have formed and is fragile? Thanks very much.
An interesting question! We have received several inquiries about the possibility of adding Lichtenberg Figures into acrylic guitar bodies, but have not actually done so (as yet).
We have not seen any evidence that the acrylic is substantially weakened, nor have we ever seen cracks further propagating from the discharge zone into previously unfractured material. During the actual creation process, the powerful internal electrical discharge is similar to an explosion, ans is accompanied by high pressure gaseous byproducts within the discharge channels. We were initially concerned that the electrostatic energy stored within larger pieces might be sufficient to cause the piece to explosively shatter when discharged. However, this has never happened, even for fully charged specimens that held over 5 kilojoules of energy. For process control purposes, we now use only cast acrylic. Extruded material may have hidden residual stresses that can initiate premature self-discharge while the specimens are being irradiated. We have also seen some small stress fractures in addition to the Lichtenberg Figures within experimental extruded cylinders, but never within (relatively stress-free) cast acrylic material.
It may be possible that a piece of acrylic with an embedded Lichtenberg Figure may fracture more easily than a virgin piece when subjected to very strong external mechanical stresses. However, we not taken any tensile or bending strength measurements on any specimens, and cannot quantify this. We do note that some specimens have been accidentally dropped onto concrete causing some to crack at the point of impact. We have not seen any tendency for these localized fractures to propagate into the Lichtenberg Figure regions or vice-versa.
If portions of an acrylic guitar body are under stress (from the tension of the strings), we would recommend that the Lichtenberg Figure layer be located nearer to the top surface (i.e., closer to the strings) so that the figure is under compressive/bending stress instead of tension. Normal bumping or handling should not be any problem.
We would be very interested in irradiating a customer-provided acrylic guitar body as an experiment during our next production run (4Q10). Please contact us if you might be interested (630-964-2600).