IETeasy: an open source and low-cost instrument for impulse excitation technique, applied to materials classification by acoustical and mechanical properties assessment

In the past twenty years, impulse excitation technique (IET) has become a widelydiffused non-destructive technique in metal industry field. This success resides in its capability todetermine with high precision and accuracy some elastic properties of materials, such as Young’smodulus, shear modulus and Poisson’s ratio. The technique, which is very fast andnon-destructive, consists in exciting a sample by a mechanical input and registering the acousticoutput that, once analyzed by Fast Fourier-Transformation (FFT), provides the resonantfrequencies of the sample, with a fast data analysis procedure. The approach is thus very easy tobe applied to most materials and cost and time effective. Despite these many advantages, IET isstill an under exploited technique in academic research centres, that mainly rely on traditionaldestructive methods for the evaluation of such properties, for instance by the measurement ofstrain-stress curves. Commercial IET instruments, similarly to traditional ones, have costsspanning from many hundreds to thousands of dollars, limiting their diffusion in academic worldbut also in small companies with limited R&D or quality control expenses. Non-professionalinstruments can also give very precise results and can be successfully used in basic research and inquality control even if not certified as commercial ones. Moreover they can be easily customizedaccording to specific user needs and sample features. Since no examples of low cost IET designscan still be found in the scientific literature, we fill the gap in this paper, giving instructions for aself-assembled instrument for IET analysis, with a cost in the range of 70-85 USD. Moreover, thecollected calibration data are analyzed to prove that the instrument can be used for otherpurposes than the common elastic properties determination, but also for a fast and cheapmaterial characterization exploiting a multivariate analysis approach. Calibration results showthat IETeasy can be used in both academic and industrial field for quality control purposes as alow-cost, fast and efficient alternative to tensometers. Principal component analysis, applied inthis paper for the first time to IET data analysis, was able to distinguish and classify steel fromAl or Cu alloys from polymers, but also different steel grades, demonstrating its potential inmassive and eventually automatic IET data analysis. Calculated mechanical properties fittedwith good approximation the ranges expected for each sample.