Radkowski S., Szczurowski K., Galezia A.

The purpose of the study is an attempt at developing a non-invasive method of detecting changes of the distribution of stress in the cross-section of pre-stressed structures, with use of shock excitation, which leads to early stages of defect development, while relying on the information contained in a vibroacoustic signal generated during tests. Relying on the assumption that occurrence of damage in pre-stressed elements can result in change of stress distribution across the entire cross-section and appearance of tensile instead of compressive stresses, and the related emergence of a neutral axis, we proposed a method of evaluating early stages of defect formation that rely on the analysis of the process of vibroacoustic signal generation process. Assuming that changes of stress will lead to disturbance in the propagation of the stress wave across the pre-stressed structure that is incited by a pulse, the proposed diagnosis algorithm refers to the analysis of frequency structure, including the analysis of the envelope and frequency modulation in defined frequency bands that are characteristic for the examined object. Also modal analysis of pre-stressed structure was made to settle natural frequencies and there changes. Results of modal model were used for identification of numeric model parameters of pre-stressed structure. Model of propagation of the stress wave in pre-stressed structure was propose in paper. Changes of vibrations character after period of transition made after shock excitation with changes of load where remarked. In paper are presented results of experiments elaborate on real structures with simulated faults of different types. This experiments where made in frame of COST Action 534.