This paper reports the effects of fiber breakage defects and waviness defects on the compressive fatigue behavior and the progressive damage evolution process of 3D Multiaxial Braided Composites (3DMBCs). Combined with finite element compression simulation and ultra-depth microscope, the internal defect content of composites with different braiding angles was determined. The results demonstrate that the weakening effect of waviness and fiber breakage defects is greater than the strengthening effect of the braiding angle. This causes the fatigue resistance of 3DMBCs with the 31° braiding angle being better in both directions of 0° and 90°. The increase of 4° waviness and 10% fiber breakage defect results in the average fatigue life of composites being shortened by 48% and the energy consumption rate increased by 10% at 85% stress level in 90° compression direction. The alteration in loading direction modifies the included angle corresponding to the stress component. The stress component parallel to the fiber direction under compressive fatigue load leads to interfacial debonding in the composites, whereas the stress component perpendicular to the fiber direction results in pronounced shear failure.

This paper reports a novel manufacturing process of preparing the Three-Dimensional Multiaxial Braided Composites (3DMBCs) and the effects of various defects generated in the manufacturing process on the compressive mechanical properties of 3DMBCs through the experimental and numerical methods. The five-step fabrication process of the 3D multiaxial braided preform was firstly introduced in detail. Then, the influences of various defects such as voids, waviness, and fiber breakage defects on the compressive properties of 3DMBCs were discussed. It is found that the fiber breakage defect and waviness defects were the two primary factors on the decrease of compressive properties of 3DMBCs. However, void defects in the resin and interface had little effect on the composites. When the fiber breakage defect content was 25% and the waviness was 7°, the composite compressive modulus decreased by 51%. The progressive damage process and failure mechanism of the composite under 90° compressive loading confirmed the validity of the numerical model by comparing with the experiments.

Conventional firefighting clothing and fire masks can protect firemen’s safety to a certain extent, whereas cannot perceive environmental hazards and monitor their physical status in real time. Herein, we fabricated two kinds of Janus graphene/poly(p-phenylene benzobisoxazole) (PBO) fabrics by laser direct writing approach and evaluated their performance as intelligent firefighting clothes and fire masks. The results showed that the Janus graphene/PBO fabrics were virtually non-combustible and achieved the highest thermal protection time of 18.91 s ever reported in flame, which is due to the intrinsic flame-retardant nature of PBO fibers. The graphene/PBO woven fabrics-based sensor showed good repeatability and stability in human motion monitoring and NO₂ gas detection. Furthermore, the piezoelectric fire mask was assembled with graphene/PBO nonwoven fabric as electrode layer and polyvinylidene fluoride (PVDF) electrostatic direct writing film as piezoelectric layer. The filtration efficiency of the fire mask reaches 95% for PM_2.5 and 100% for PM_3.0, indicating its effective filtration capability for smoke particles in fires. The respiratory resistance of the piezoelectric fire mask (46.8 Pa) was lower than that of commercial masks (49 Pa), showing that it has good wearing comfort. Besides, the piezoelectric fire mask can be sensitive to the speed and intensity of human breathing, which is essential for indirectly reflecting the health of the human body. Consequently, this work provides a facile approach to fabricate next-generation intrinsic flame-retardant smart textiles for smart firefighting.

Piezoelectric nanogenerators (PENGs) are promising for harvesting renewable and abundant mechanical energy with high efficiency. Up to now, published research studies have mainly focused on increasing the sensitivity and output of PENGs. The technical challenges in relation to practicability, comfort, and antibacterial performance, which are critically important for wearable applications, have not been well addressed. To overcome the limitations, we developed an all-nanofiber PENG (ANF-PENG) with a sandwich structure, in which the middle poly(vinylidene fluoride-co-hexafluoropropylene (P(VDF-HFP))/ZnO electrospun nanofibers serve as the piezoelectric layer, and the above and below electrostatic direct-writing P(VDF-HFP)/ZnO nanofiber membranes with a 110 nm Ag layer on one side that was plated by vacuum coating technique serve as the electrode layer. As the ANF-PENG only has 91 μm thick and does not need further encapsulating, it has a high air permeability of 24.97 mm/s. ZnO nanoparticles in ANF-PENG not only improve the piezoelectric output, but also have antibacterial function (over 98%). The multi-functional ANF-PENG demonstrates good sensitivity to human motion and can harvest mechanical energy, indicating great potential applications in flexible self-powered electronic wearables and body health monitoring.