PSI - Issue 54

Claudia Barile et al. / Procedia Structural Integrity 54 (2024) 225–232 C. Barile et al. / Structural Integrity Procedia 00 (2023) 000–000

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It has been reported in the literature that the addition of cenospheres in thermoset polymer resins results in im proving their elastic modulus, while negatively influencing the tensile strength [Deepthi et al. (2010), Kulkarni and Mhanwar (2012)]. In the author’s previous work, the influence of the weight percentage of cenospheres in the improve ment of structural properties of the thermoset polymer systems is reported [Vimalathithan and Vijayakumar (2018)]. The average elastic modulus of the syntactic foams is 3.33 GPa. Specimens 1 and 2 show very similar stress-strain behaviour, while the strain deformation is comparatively high in Specimen 3. Since these specimens are prepared in a mould box, there is a possibility of agglomeration of cenosphere particles, which may have negatively influenced the tensile strengths of Specimens 1 and 2. SEM micrographs of the fracture surfaces are presented in Figure 5. Progressive fracture in the form of beach marks can be found in Figures 5a-5d, which confirms the brittle failure in the specimens. In most cases, the cracks initiate from the boundary edge of the test specimen and propagate through the surface (Figure 5(b)) and they culminate around the cenosphere particles, which resulted in their removal from the resin surface (Figure 5(c)). This mechanism possibly has improved the elastic modulus and fracture toughness of this composite system. Only in very few cases, the symmetrical cleaving of the cenosphere can be observed (Figure 5(d)).

4.2. Acoustic Emission Test Results

Fig. 6. ToA and Peak Frequency of the AE signals from a) Specimen 1, b) Specimen 2, and c) Specimen 3 classified using Density-based Unsuper vised Clustering

In thermoset polymer systems, the failure modes that generate AE signals are generally matrix cracking / friction or rubbing between the damaged portions of the matrix and the crack growth [Sause et al. (2012), Barile et al. (2020)]. However, in these syntactic foam test specimens, other failure modes apart from those above two can be observed, for instance, removal of cenospheres and fracture in cenosphere. These may also generate AE signals which vary in their