Location of Tensile Damage Source of Carbon Fiber Braided Composites Based on Two-Step Method.

Acoustic emission (AE) source localization is one of the important purposes of nondestructive testing. The localization accuracy reflects the degree of coincidence between the identified location and the actual damage location. However, the anisotropy of carbon fiber three-dimensional braided composites will have a great impact on the accuracy of AE source location. In order to solve this problem, the time-frequency domain characteristics of AE signals in a carbon fiber braided composite tensile test were analyzed by Hilbert-Huang transform (HHT), and the corresponding relationship between damage modes and AE signals was established. Then, according to the time-frequency characteristics of HHT of tensile acoustic emission signals, the two-step method was used to locate the damage source. In the first step, the sound velocity was compensated by combining the time-frequency analysis results with the anisotropy of the experimental specimens, and the four-point circular arc method was used to locate the initial position. In the second step, there is an improvement of the Drosophila optimization algorithm, using the ergodicity of the chaotic algorithm and congestion adjustment mechanism in the fish swarm algorithm. The smoothing parameters and function construction in the probabilistic neural network were optimized, the number of iterations was reduced, the location accuracy was improved, and the damage mode of composite materials was obtained. Then, the damage location was obtained to achieve the purpose of locating the damage source.

Biodegradable and flame-retardant cellulose-based wearable triboelectric nanogenerator for mechanical energy harvesting in firefighting clothing.

Integrating flexible triboelectric nanogenerators (TENGs) into firefighting clothing offers exciting opportunities for wearable portable electronics in personal protective technology. However, it is still a grand challenge to produce eco-friendly TENGs from biodegradable and low-cost natural polymers for mechanical-energy harvesting and self-powered sensing. Herein, conductive polypyrrole (PPy) and natural chitosan (CS)/phytic acid (PA) tribonegative materials were employed onto the Lycra fabric (LC) in turn to assemble the biodegradable and flame-retardant single-electrode mode LC/PPy/CS/PA TENG (abbreviated as LPCP-TENG). The resultant LPCP-TENG exhibits truly wearable breathability (1378.6 mm/s), elasticity (breaking elongation 291 %), and shape adaptivity performance that can produce an open circuit voltage of 0.3 V with 2 N contact pressure at a working frequency of 5 Hz with a limiting oxygen index of 35.2 %. Furthermore, facile monitoring for human motion of firefighters on fireground is verified by LPCP-TENG when used as self-powered flexible tactile sensor. In addition, degradation experiments have shown that waste LPCP-TENG can be fully degraded in soil within 120 days. This work broadens the applicational range of wearable TENG to reduce the environmental effects of abandoned TENG, exhibiting prosperous applications prospects in the field of wearable power source and self-powered motion detection sensor for personal protection application on fireground.