Relation of impact strength to the microstructure of functionally graded porous structures of acrylonitrile butadiene styrene (ABS) foamed by thermally activated microspheres

- This work provides new processing guidelines to fabricate FG porous structures of ABS.
- Processing-microstructure relations were established to provide a route for fabricating microstructures with desired features.
- The relationship between different microstructure measures and impact energy was investigated.
- Impact energy was found to correlate more to the pores' diameter gradient than to porosity.
- FG porous structures provide higher impact strength compared to the solid precursor and uniform foam.

Functionally graded (FG) materials owe their advantage over conventional composites to the continuous microstructure that eliminates many problems like delamination and stress jumps. Functionally graded porous structures have the added advantage of significant weight reduction while maintaining comparable strength to the solid precursor. One of the attractive applications of FG porous polymers is impact energy absorption. This is due to their viscoelastic nature that helps in energy dissipation, in addition to their light weight compared to metals and ceramics. In this work, FG porous structures of Acrylonitrile Butadiene Styrene (ABS) were fabricated with thermally activated microspheres. One-dimensional heat flow was introduced across the thickness with different terminal temperatures to induce a thermal gradient. Different compositions and processing conditions were carried out to investigate the relationship between impact energy and microstructure. Impact energy showed stronger correlation to pores' diameter gradient than to porosity. The fairly strong correlation between diameter gradient, permitted expansion ratio, and porosity indicates the potential to control the microstructure and hence impact energy absorption. Functionally graded porous structures of ABS demonstrated their superiority for impact absorption with strength-to-weight ratio of 46.02 J cm3/g compared to 25.71 J cm3/g for solid ABS. This work provides processing guidelines to fabricate FG porous structures of ABS in relation to impact energy.

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