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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loading:

1) The save of full operability …0.2 2) The save of partial operability ….0.3 3) The full loss of operability … 0.5 Some patterns of crack location are observed: 1) Fatigue cracks occur mainly in the cross-sections of PET perpendicular to direction of tensile load. 2) The tend of more near crack location to middle cross section of PET is observed.

3) There is a relatively weak trend of predominant concentration of fatigue cracks in the extreme transducers of vertical groups (numbers 1 and 5): 21 cracks of their 36. 3. Numerical simulation: Investigation of stress state of PET embedded in the thin-walled structure. The measurement unit of ultrasound system of SHM contents two principal components: PET and its support which in this paper presents by the glue layer. The analysis of the stress state of measurement unit is needed for more detailed Figure 2. View of the PET number 5 before (left) and after (right) fatigue test and cracks evaluation by penetration method .

estimation of conditions of destruction at the operational load. Geometrical sizes of PET correspond to the PIC151 that is used in all tests of this paper, the thickness of the Hysol930.3NA glue layer obtained as a mean value of direct measurements and accepted to equal 0.2 mm. The Al2024-T3 sheet with sizes 1.015x80x240 mm presents the host structure for three collinear transducers with gap 1 mm between them (Fig.3). At the same Figure 3 two options of static loading by uniformly distributed stress of 150 MPa are showed. Mechanical properties of all materials of model are shown in Table 2. Table 2. Material elastic properties and tensile strength: Material E, MPa Poisson ratio Tensile strength, MPa Al2024-T3 71000 0.33 PIC 151 67000 0.34 ~45 Hysol930.3NA 2232 0.42 31 The mutual influence of the group arrangement of transducers on a thin-walled structure, like that described above in the experiment with the panel, was investigated. It has been established that this circumstance has a relatively weak effect on the local stress state of the transducers. Therefore, in the future, the main attention is focused on the study of the regularities of the influence of partial destruction of a separate transducer built into a thin-walled structure. In fig.2 the sample form used for FEA is presented: 1mm Al2024-T3 sheet equipped by PIC151 PET of 0.5x10x50 mm in the centre. The connection glue layer Hysol 9309 thickness nominally is equal to 0.2 mm. There is assumed that boundary conditions of this sample correspond to tension test in vertical direction (axis y). Double symmetry of the sample and its load allows restricting of finite element analysis (FEA) only by part of structure into first quadrant (indicated by rectangular frame).

Several stages of stress analysis were made. At each stage the deformed shape of the sample and its stress state were obtained. Principal difference between stages is degree of transducer damage. In the Figure 3 the consequence of transducer shapes is presented: a) Intact state in which the principal vector of direct stress in middle cross-section of transducer is shown by orange arrow. b) The full fracture of transducer in middle cross-section (orange arrow is removed). Figure 3. Sheet with glued transducer.