Strain sensors based on porous conductive polymers (CPCs) have garnered growing research interest for their potential applications in motion detection, healthcare, human–computer interaction, and artificial intelligence. However, the complexity of CPC processing makes it difficult to achieve the controlled design of microscopic porous structures, leading to simple and random porous structures, thus limiting their further use in the field of pressure sensing. This paper presents a strain sensor with a high-performance, wood-like structure composed of flexible conductive carbon black/plastic polyurethane foam (BWCT) using a bidirectional freeze casting process. The results show that, compared with conventional random freezing and unidirectional freezing, the bidirectional freeze casting process can effectively realize multiscale control of the composite structure, which results in a good laminar porous structure of the prepared BWCT. This parallel laminar structure not only contributes to the layered transfer of stresses but also avoids the local concentration of stresses. At the same time, it significantly increases the directional electrical conduction ability, which results in high sensing stability performance. In particular, the BWCT sensors had a wide detection range (80%), a lower limit of detection (0.2%), rapid response and relaxation times (200 ms), as well as exceptional durability (>2000 cycles). Furthermore, the BWCT was integrated into a wearable sensor to monitor various human motions, including arm bending, squatting, and walking, demonstrating reliable detection performance. Altogether, the BWCT sensors are promising in expanding the application but also offer guidance for designing high-performance wearable strain sensors.
Bidirectional freeze casting combined with pressure infiltration has demonstrated significant potential as an effective approach for fabricating bioinspired lamellar composites with excellent strength and toughness. However, their dynamic mechanical response remains underexplored. In this study, B 4 C/2024Al composites with long-range ordered nacre-like architectures were fabricated using bidirectional freeze casting followed by pressure infiltration. The mechanical properties and deformation behavior under both quasi-static and dynamic compression conditions were systematically investigated. The results reveal that dynamic compressive strength and strain were significantly higher than their quasi-static counterparts, largely attributed to strain rate hardening and localized matrix melting. Compared to unidirectionally structured composites, the bidirectionally structured ones exhibited superior mechanical performance, achieving a maximum compressive strength of 1088.6 MPa at a strain rate of 3000 s −1 (40 vol% B 4 C/2024Al composite). A clear dependence of flow stress and energy absorption capability on B 4 C volume fraction was observed. As B 4 C content increased, the compressive strength rose, but dynamic strain energy density showed a decreasing trend beyond 20 vol% due to reduced ductility. Specifically, the energy density peaked at 133.08 MJ/m 3 for the 20 vol% composite and declined with further ceramic addition, indicating a trade-off between strength and impact energy absorption. The enhanced toughness under dynamic loading is primarily attributed to adiabatic shear localization in the aluminum matrix, which facilitates localized softening and strain accommodation. Additional contributions include crack deflection and branching within the hard ceramic layers, as well as plastic deformation and thermal softening-induced toughening mechanisms in the metallic phase. These findings highlight the promise of nacre-inspired B 4 C/Al composites for advanced lightweight armor systems, offering an optimized balance between strength, toughness, and energy absorption under high-strain-rate loading.
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