Synthesis and Compressive Response of Microcellular Foams Fabricated from Thermally Expandable Microspheres
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Cellular foams are widely applied as protective and energy absorption materials in both civil and military fields. A facile and simple one-step heating method to fabricate polymeric foams is measured by adopting thermally expandable microspheres (TEMs). The ideal foaming parameters for various density foams were determined. Moreover, a mechanical testing machine and split Hopkinson bar (SHPB) were utilized to explore the quasi-static and dynamic compressive properties. Results showed that the cell sizes of the as-prepared TEMs foams were in the micrometer range of 11 μm to 20 μm with a uniform cell size distribution. All the foams exhibited good compressive behavior under both quasi-static and high strain rate conditions, and were related to both foam densities and strain rates. The compressive strength of the TEMs foams at 8400 s−1 was up to 4 times higher than that at 10−4 s−1. The effects exerted by the strain rate and sample density were evaluated by a power law equation. With increasing density, the strain rate effect was more prominent. At quasistatic strain rates below 3000 s−1 regime, initial cell wall buckling and subsequent cellular structure flattening were the main failure mechanisms. However, in the high strain rate (HSR) regime (above 5000 s−1), the foams were split into pieces by the following transverse inertia force.
KeywordsThermally expandable microspheres Compressive response Split Hopkinson bar (SHPB) Microcellular Failure mechanism
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This work was financially supported by the National Natural Science Foundation of China (Nos. 51572208 and 51521001), the National Key R&D Program of China (No. 2018YFB0905600), the 111 Project (No. B13035), the China Postdoctoral Science Foundation (No. 2018M632935), and the Nature Science Foundation of Hubei Province (No. 2016CFA006).
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