PSI - Issue 2_A

Tarpani J.R. et al. / Procedia Structural Integrity 2 (2016) 136–143 Tarpani et al. / Structural Integrity Procedia 00 (2016) 000–000

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magnet as illustrated in Figure 2c, which shows the three main imaging planes, orthogonal to each other, evaluated in this study: A (Axial), S (Sagittal) and C (Coronal).

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Face exposed to tensile stress during previous 3-point-bend loading

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(c) Fig. 2. EPX-CF test coupons damaged in translaminar (a) and delamination (b) modes, where specimens dimensions (length, width and thickness) are indicated by arrows; (c) Schematic of the positioning of a tablet-like testpiece inside the NMR supermagnet, where the main tomographic planes evaluated in this work are indicated as follows: A (Axial), S (Sagittal) and C (Coronal). 4. Results and Discussion 4.1 Technical protocols used for NMR imaging Figure 3 shows A section views of the delaminated PPS-CF specimen (similar to Fig. 2b), which were obtained from the very same maximum damaged position in the test coupon (at its half-length) using different technical protocols of the NMRI system. RARE-2D, FLASH-2D and FLASH-3D operational protocols were used, the latter one with two distinct image resolutions, i.e., the highest and the lowest ones, respectively. Based on Figure 3b, it can be concluded that the RARE-2D protocol affords a good view of both the delamination fracture in the PPS-CF laminate and the SBF concentrated in this region of maximum damage. However, a significantly higher spatial image resolution is provided by the FLASH-2D protocol (Figure 3c), though it required a significantly longer image capture time than RARE-2D. With regards to the FLASH-3D protocol, despite the obvious difference between the achieved results via the highest and the lowest resolution modes (respectively Figures 3a and 3d), its performance fell far short of the other two imaging protocols. 4.2 Type of fracture / damage The NMR image in Figure 4a shows EXP-CF specimen (according to C section view) immersed in SBF and containing a translaminar fracture highlighted in a dashed gray square, while the image in Figure 4b shows another EPX-CF test coupon (S section view) also immersed in SBF but instead exhibiting delamination damage, which is as well spotted by a dashed gray square. The images of both damage types, translaminar and delamination, respectively, leave no doubt about the high potential for non-destructive inspection enabled by the NMR technique for CFRP laminates immersed in SBF.