Issue 66

B. Chahira et al, Frattura ed Integrità Strutturale, 66 (2023) 207-219; DOI: 10.3221/IGF-ESIS.66.13

Uncracked plate frequencies (Hz)

Cracked plate frequencies (Hz)

Modes

Differences (%)

1 2 3 4 5 6 7 8 9

60.39 85.62

55.93 79.50

-7.39 -7.15

110.25 140.75 170.87 182.63 200.37 250.59 274.62 282.94

115.12 133.12 165.00 176.25 198.75 244.87 265.12 273.00

4.42

-5.42 -3.44 -3.49 -0.81 -2.28 -3.46

10 -3.51 Table 3: Experimental natural frequencies of a clamped cracked and crack-free plate.

Experimental frequencies (Hz)

Numerical frequencies (Hz)

Modes

Differences (%)

1 2 3 4 5 6 7 8 9

55.93 79.50

53.20 79.43

-4.88 -0.09 1.40 3.25 0.76 -0.69

115.12 133.12 165.00 176.25 198.75 244.87 265.12 273.00

116.73 137.44 166.26 175.04 201.44 244.73 264.24 275.13

1.35

-0.06 -0.33

10 0.78 Table 4: Numerical and experimental natural frequencies of a cracked plate having a crack length of 120mm inclined by 35°. First, an estimate of the natural frequencies of the cracked and the crack-free plate is obtained by means of a hammer test. The plate is impacted by the hammer, and an estimate of the natural frequencies is obtained from the peaks on the frequency spectrum (Tab. 3). An average of several readings is taken for each natural frequency. Tab. 4 relates the numerical values of the natural frequencies of the cracked plate, given by a finite element analysis with Abaqus software, and the experimental frequencies.

E STIMATION AND RESULTS

Numerical case n order to assess the accuracy of the identification algorithm, we took a plane steel sheet containing a linear inclined crack. After computing the ten first natural frequencies with a direct modal simulation by FEM we used the inverse identification by SHADE algorithm to evaluate the identity parameters of the crack given by Tab. 5. The approach was initiated by taking several random initial identities of the crack. I

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