PSI - Issue 14

Sarthak S. Singh et al. / Procedia Structural Integrity 14 (2019) 915–921 Author name / Structural Integrity Procedia 00 (2018) 000–000

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materials’ response to compressive loading is rarely analyzed, even if the deformation and failure mechanisms under compression are significantly different when compared to the other loading cases. Some of the studies, reporting the effect of fillers on the mechanical characteristics of polymer composites, are reviewed here. Mallick and Broutman (1975) conducted several mechanical tests on 15 µm diameter glass bead epoxy composites with the filler volume fractions upto 40 %. It was observed that the compressive yield strength of the composites was enhanced with increase in the volume fraction but the composites’ ductility reduced when compared to the neat epoxy case. Kawaguchi and Pearson (2003) conducted quasi-static compression experiments on glass particle reinforced epoxy composites with mean filler diameter, 3.5 µm, 15.8 µm and 42 µm, and the volume fraction varying from 10 % to 30 %. It was observed that the yield strength increased with increasing filler volume fraction; however it decreased with the samples’ exposure to the moisture. Omar et al. (2013) studied the effect of particle size on the compression behaviour of poly-propylene/silica (PP/SiO 2 ) composites at several strain rates. The particles with average diameters, 3 µm, 1 µm, 20 nm and 11 nm, were chosen to conduct the study. The composites reinforced with smaller particle sizes (20 nm, 11nm) showed higher yield-strength, ultimate strength and stiffness when compared to the larger filler cases. It was also observed that the effect of strain rate on the mechanical behaviour of composites reduced with decrease in the filler size. Ma et al. (2015) studied both quasi-static and dynamic compression behaviour of silica nanoparticles (20-50 nm in diameter) filled epoxy composites prepared with up to 15% filler volume fraction. It was observed that the failure stress decreased beyond 10 % filler volume fraction however the increasing silica content increased the energy absorption capacity of composite with lesser craze formation under dynamic loading conditions. Among the metal particle filled polymer composites, Jordan et al. (2007) studied the compression behaviour of Al-epoxy composites at various strain rates by using the particles of 3.5 µm and 5.4 µm. They concluded that the smaller particle filled composites showed better mechanical characteristics when compared to the larger ones due to higher constrains to the flow of epoxy matrix. Herbold et al. (2008), while working with PTFE (Poly Tetra-flouro Ethylene) matrix filled with aluminum (2 µm) and tungsten (1 µm to 44 µm) fillers observed porous PTFE-Al-W composites with fine W particles exhibited maximum compression strength in case of both quasi-static and dynamic loading. They also demonstrated through numerical simulations that the mesoscale granular force chains between the fine metallic particles were improving the mechanical behavior of composites. While a few researchers have reported the compression behavior of filler composites, a systematic study of volume fraction effect along with a comparative computational analysis is largely unknown, especially in the post yield regime. In current investigation, quasi-static experiments are conducted to elucidate the effect of filler volume fraction on the compression behavior of glass filler reinforced epoxy composites. Computational analysis is carried out to understand the underlying deformation mechanisms in the post yield regime for a set of inclusions surrounded by the epoxy matrix. 2. Material Preparation The epoxy system is prepared by mixing Diglycidyl Ether of Bisphenol A (DGEBA) resin and Tri-ethyl tetra amine (TETA) hardener in a ratio of 10:1 by weight. The spherical glass particles with an average diameter of 34 µm are embedded into the epoxy matrix at volume fractions, ranging from 0 to 10% at a step of 2.5%. Homogenized dispersion of fillers into the matrix material is achieved by successive stirring, sonication and degassing. The details of processing steps and the uniformity of filler distribution are given by Yesgat and Kitey (2016). The prepared mixture is cured into a cylindrical mould of 8 mm diameter for 48 hours. This is followed by keeping the material at room temperature in humidity controlled environment for about 30 days to ensure complete curing. The test samples are prepared by machining the composites into 6 mm long cylinder maintaining the diameter as 8 mm. 3. Experimental details ASTM D695-10 is followed for conducting quasi-static compression experiments. The experiments are carried out by using universal testing machine at a cross head velocity of 1 mm/min. The maximum load cell capacity of the