PSI - Issue 14

Sameerkant Behera et al. / Procedia Structural Integrity 14 (2019) 112–118 Sameerkant Behera, S. K. Sahoo, Lokesh Srivastava, A. S. Srinivasa Gopal / Structural Procedia 00 (2018) 000 -000

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4

a

b

c

Healthy zone

Defective zone

Fig. 5. (a) Test set up; (b) reference thickness block; (c) reference block

3.3. Ultrasonic response in reference composite laminate  Ultrasonic response has been studied to know the ultrasonic attenuation with respect to varying thickness so as to select set dB on full scale component at different station. Figure 6 shows attenuation in dB with respect to thickness variation from 20mm to 100mm. It has been studied with and without pre-amplifier requirement. Also a best fit curve has been generated to estimate attenuation for a specific thickness.

0 10 20 30 40 50 60 70 80 90 0 20 40 60 80 100 120 140 Attenuation, dB Thickness in mm

y = 0.3114x + 40.867 R² = 0.9708

with pre amplifier

without pre amplifier

y = 0.3157x + 0.7333 R² = 0.9816

Fig. 6. Ultrasonic attenuation vs. thickness

 Ultrasonic response on reference block having healthy and delaminated zone has been studied. Figure 7(a) shows received ultrasonic signal through receiver from healthy zone which is more than 90% of the full scale height (FSH), however signal received from delaminated zone has been found to be less than 10% of the full scale height which is shown in figure 7(b). The significant attenuation of signal is attributed to the interfacial gap between layers.

b

a

Fig. 7. (a) Ultrasonic response (healthy zone); (b) ultrasonic response (delaminated zone)

4. Experiment on full scale composite pressure vessel A composite pressure vessel having diameter in order of 1000mm and length of 3000mm, made by wet filament winding technique having carbon –epoxy material system has been considered for study. Whole pressure vessel is mapped in to grid points both in axial as well as circumferential direction. In axial direction it is divided in to 24 zones and in circumferential direction divided in to 8 zones as shown in figure 8. Axial grid point is marked approximately 100mm distance apart. Testing has been carried out manually by point to point contact (A-scan). While testing it is highly essential to ensure probe to probe alignment so as to get exact signature.