טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGorelik Alexandra
SubjectDevelopment of Acoustic Method for Quality Control of
Laminated Elements in Construction
DepartmentDepartment of Quality Assurance and Reliability
Supervisor Professor Konstantin Kovler


Abstract

This research thesis is about the development of a cheap, objective and reliable NDT method for detection of delamination in building structures. It is based on the principle of acoustic impact (AI) and yields both qualitative and quantitative results, which indicate the actual condition of the building element. Delamination is detected by means of an acoustic hammer, and the information about its depth and extent is also provided. Defects can also be detected not only in the adhesive layer, but also inside the joined elements (honeycombs in concrete blocks).

The experimental part of the study involved several types of specimens, characterized by different delamination characteristics (size, depth, form, etc). All specimens were tested with two types of the hammer: calibrated and non-calibrated. The results were obtained in the form of the acoustic spectrum of the tested structure, recorded by a microphone. Full characterization of the delamination was obtained.

An algorithm was developed for performing transformation of the obtained result into a numerical value, called the “center of mass of the signal (by frequency)” (CM). In case where the CM does not yield an unambiguous indication, the cumulative energy curve can be used instead. If the curves of the tested and standard (non-delaminated) specimens diverge, delamination is indicated.  

Such kinds of testing might be performed in a short period of time, with minimal costs and with fair degree of accuracy.