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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2. Materials, test coupons, equipments and protocols 2.1 Polymer laminate composites

Two flat rigid composite laminates of continuous carbon fiber (CF)-reinforced polymer matrix were evaluated in this study, respectively possessing thermosetting epoxy resin (EPX-CF) and thermoplastic polyphenylene sulphide polymer (PPS-CF) matrices. 2.2 Test coupons A total of four test specimens were evaluated, two of EPX-CF and two of PPS-CF composites, in the form of rectangular test coupons extracted from the original laminates by cutting with water cooled circular diamond saw. The specimens were subjected to intentional and controlled damage by applying three point flexural loading. Two fracture damage configurations were then created, namely, translaminar (Figures 1a and 1c, respectively for EPX CF and PPS-CF materials) and delamination (Figures 1b and 1d, respectively for EPX-CF and PPS-CF laminates).

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

(a)

(b)

(c) (d) Fig. 1. Specimens extracted from as-received CFRP laminates and subjected to intentional and controlled cracking process for subsequent immersion in SBF, followed by NMR imaging inspection: (a) EPX-CF with translaminar fracture; (b) EPX-CF with delamination damage; (c) PPS-CF translaminar; (d) PPS-CF delaminated. Regions of maximum damage are indicated by dashed white circles, while pre-notches in translaminar fractured specimens are indicated by white arrows. 2.3 Equipment and protocols The NMR device employed is based on a horizontal 2.0 Tesla superconducting magnet from Oxford Instruments™, model 85310HR, performing at 85 MHz with 310 mm internal diameter, equipped with a set of high-speed X, Y and Z gradient coils with 0.16 Gauss/(cm.Ampere) efficiency, which can produce magnetic field gradients of approximately 30 Gauss/cm in 160 microseconds. The system works with Bruker Biospin™ electronics and a Paravision™ V console, using the following image generator operating protocols: RARE-2D - Rapid Acquisition with Relaxation Enhancement, also known as turbo-spin-echo sequence, FLASH-2D and FLASH-3D. Parameters controlled by the operator included: field-of-view, slice thickness, interslice distance and matrix size, which define both the image acquisition time and the image resolution (0.1 mm/pixel in normal function mode, and up to 0.02 mm/pixel for higher resolutions). 3. Experiments All the specimens of composite laminates shown in Figure 1 (two of them are depicted in greater detail in Figures 2a,b) were completely immersed in simulated body fluid (SBF) for a period of 500 days at 25ºC. SBF was developed by Kokubo et al. (1990) based on human blood plasma. For the NMRI inspection, the four specimens were placed individually inside Falcon tubes containing SBF, which were positioned inside the superconducting