PSI - Issue 54

Norman Osa-uwagboe et al. / Procedia Structural Integrity 54 (2024) 44–51 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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3

LVDT

Indenter

Sample

QSI jig

Fig. 1. QSI experimental setup. The force-displacement graph was analyzed after with the total energy and specific energy absorption (SEA) calculated according to the following equations: = ∫ ( ) 0 (2) = (3) where is the total energy absorbed, obtained by integration of the area under the force-displacement curve and is the area density. Post-impact samples were scanned using a high-resolution X- ray μ -CT system NIKON XTH X Tex 160Xi (NIKON Metrology Europe, Leuven, Belgium) with an effective pixel size of 27.79 μm. The beam energy, beam current, and power settings were 65 kV, 65 μ A, and 4.2 W, respectively, with an exposure time of 500 ms. A total of 3,016 tiff images were created per sample scan, with the region of interest limited to the areas surrounding the damaged portion of the samples, The acquired microscopy data were first processed in VG Studio Max 3.1 software (Volume Graphics, Charlotte, NC, USA) and then further post-processed with commercial software (Dragonfly ORS, Australia). Thereafter a SEM analysis was carried out at an acceleration voltage of 10 kV and a probe current of 200 pA. Image post-processing was performed with Aztec software (Oxford Instruments, Oxford, UK), and the damage

mechanism was identified. 3. Results and Discussion 3.1. Moisture Uptake

The moisture uptake for GS and CS over the degradation period of 16 weeks is shown in Fig. 2. Generally, moisture absorption increases with time in line with the Fickian law with a maximum moisture content of 5 % and 5.8 % for GS and CS, respectively until saturation [4]. The absorption curve can be divided into 3 phases by two distinct times (t 1 and t 2 ). In stage I (0 ≤ t ≤ t 1 ), the moisture absorption increased almost linearly with the square root of exposure time. This is primarily driven by the concentration gradient between the environment and the internal parts of the studied composites. In stage II (t 1 ≤ t ≤ t 2 ), the concentration gradient gradually reduced to 0 as the phenomenon approaches equilibrium or moisture saturation, while complete saturation was achieved at stage III (t 1 ≥ t 2 ). It is worth noting that this phenomenon up to saturation was as a result of the creation of cracks and voids in the epoxy polymer resulting in its plasticization and hydrolysis which increased with exposure time.