Robustness of Empirical Vibration Correlation Techniques for Predicting the Instability of Unstiffened Cylindrical Composite Shells in Axial Compression

Abstract

Thin-walled carbon fiber reinforced plastic (CFRP) shells are increasingly used in aerospace industry. Such shells are prone to the loss of stability under compressive loads. Furthermore, the instability onset of monocoque shells exhibits a pronounced imperfection sensitivity. The vibration correlation technique (VCT) is being developed as a nondestructive test method for evaluation of the buckling load of the shells. In this study, accuracy and robustness of an existing and a modified VCT method are evaluated. With this aim, more than 20 thin-walled unstiffened CFRP shells have been produced and tested. The results obtained suggest that the vibration response under loads exceeding 0.25 of the linear buckling load needs to be characterized for a successful application of the VCT. Then the largest unconservative discrepancy of prediction by the modified VCT method amounted to ca. 22% of the critical load. Applying loads exceeding 0.9 of the buckling load reduced the average relative discrepancy to 6.4%.

Sensitivity analysis for buckling characterisation using the vibration correlation technique

“…showing analytically that indeed there is a second order relation between (1 − 𝑝) 2 and 1 − 𝑓 2 𝑘 , as proposed by Arbelo in [19]. This approach was also experimentally validated in multiple campaigns [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. A thorough review on the VCT methods for different types of structures was also provided by Abramovich in [14].…”

“…Furthermore, the maximum load ratio needed to reduce the clusters amplitude within ±0.1 also increased with increasing the magnitude of the introduced frequency deviation. On GFRP 300 160 1.5 32 1.9 Labans classic tow [28] CFRP 790 600 1.45 207 1.3 Labans variable tow [28] CFRP 835 600 1.45 207 1.4 R07 [24] CFRP 500 500 0.63 399 1.0 R08 [24] CFRP 500 500 0.63 399 1.0 R09 [24] CFRP 500 500 0.63 399 1.0 R15 [26] CFRP 500 500 0.52 478 1.0 D100H200L1-HS (1, 2) [31,32] CFRP 200 100 0.29 170 2.0 D100H200L1-PP (3-9) [31,32] CFRP 200 100 0.29 170 2.0 D100H200L2 (1-3, 3a, 5) [32] CFRP 200 100 0.27 183 2.0 D100H400L1-HS (1-3) [31,32] CFRP 400 100 0.3 168 4.0 D100H400L1N-PP (4-6) [31,32] CFRP 400 100 0.3 168 4.0 D100H400L2 (2) [32] CFRP 400 100 0.36 141 4.0 D300H150L1 (1, 3) [32] CFRP 150 300 0.36 418 0.5 D300H150L1-HS (2) [31,32] CFRP 150 300 0.36 418 0.5 D300H150L2 (1) [32] CFRP 150 300 0.36 418 0.5 D300H150L2N (3) [32] CFRP 150 300 0.36 418 0.5 D300H150L1N-PP (5) [31,32] CFRP 150 300 0.36 418 0.5 D300H300L1-PP (3) [31,32] CFRP 300 300 0.34 446 1.0 D300H300L1N-PP (4, 5) [31,32] CFRP 300 300 0.34 446 1.0 SST1 [26] Al 500 500 0.5 500 1.0 SST2 [26] Al 800 800 0.5 800 1.0 Z37 [26] CFRP 800 500 0.79 318 1.6 Z38*, ** [23] Al 1000 801 2.18 183 1.2 ZD27 [27] CFRP 560 502 0.58 432 1.1 ZD28 [27] CFRP 560 502 0.48 523 1.1 ZD29 [27] CFRP 560 502 0.52 482 1.1 the other hand, the influence of the number of load steps used on the VCT predictions was relatively weak, with increasing the number of load steps mainly reducing the magnitude of the errors given by the introduced frequency deviations.…”

Vibration Correlation Technique for Cylindrical Structural Safety Assessment

“…In 2020, Skukis et al (Skukis, 2020) modified the work done by Arbelo et al (Arbelo, 2014) proposing a novel VCT based on the characteristic chart between the parametric forms (1 -p) 2 and 1 -f. The authors empirically verified a second-order relationship as illustrated in Fig. 2.17, which reproduces the results from (Skukis, 2020) for a schematic view.…”