PSI - Issue 52

Vitalijs Pavelko et al. / Procedia Structural Integrity 52 (2024) 382–390 Vitalijs Pavelko/ Structural Integrity Procedia 00 (2019) 000 – 000

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c) Progress of transducer fracture by occurring of the full crack in middle cross-section of half-transducer. d) and e) Further с rushing of the transducer.

a) e) Figure 4. Five stages of transducer state: intact state (a) and four states of damages development b) c) d)

The load on the PET embedded in the structure is transmitted through the adhesive layer and with the considered loading option, the greatest tensile directions in the transducer arise at the points of the boundary with the adhesive layer. At the points of the free outer surface of the transducer, lower tensile stresses occur. Therefore, the analysis

presented here focuses on the stresses at the points of the lower boundary and in the cross-sections of the PET. In Fig. 4 the results of finite element analysis, which are most important for the purposes of this study, are presented. These stresses are generated by the external tension 100 MPa stress of the host panel. Here the stress component in the transducer’s low surface (boundary plane with the glue layer) is presented for intact state and four stage of damage development. These stresses correspond to points of longitudinal axis of symmetry of boundary surface and are almost evenly distributed across the width of the transducer.

Figure 5. Comparison of tension stress in low surface of transducer at intact state and at different degree of damages.

The appearance of each new crack causes decreasing stress in adjusting parts of transducer. In Figure 5 the normalized mean stress ̅ = / of each separate fragment of a transducer in its middle cross-section is presented (here is the tension stress of a host sheet of structural panel). It is seen that for fragments of the same length those stresses are approximately equal to one other. Similar is effect of cracking to electrical potential of PET (Fig.6).

Figure 7. Influence of cracks on the electrical potential of transducer (electrodes non-damaged)

Figure 6. Influence of cracks on the mean stress at different sections of transducer