In Situ X-Ray Tomography of Sintered Metal Fiber Felts Exhibiting Auxetic Effect under Tension and Compression

Sintered metal fiber felts (SMFFs) are kinds of the strongest auxetic materials to date, but there are significant differences in the reported auxeticities, due to the lack of investigation on the fabrication process. This study is performed to analyze the influence of fabrication process and structural features on the auxetic effect exhibited by SMFFs. The sequence of compression and sintering processes determines the volume density of the interfiber-sintered joints and the resulting Poisson's ratio behavior under tension and compression. The SMFFs with a low volume density exhibit strong auxetic effect under tension and achiev a positive Poisson's ratio under compression because of the weak interfiber layer bonding. In contrast, the felts with a high density of interfiber joints reveal a relatively weak auxetic effect under both tension and compression. Moreover, an increase in the thickness and a decrease in the porosity reduce the auxetic effect. In addition, in situ X-Ray tomography of the tensile testing is performed to elucidate the mechanism of the auxetic effect. To explain the observed Poisson's ratio behavior under tension and compression, periodical finite-element modeling with real mesostructures is performed. Herein, a new insight into the relationship between the structure features and the Poisson's ratio behaviors is given.