As one of third-generation high strength steels, medium-Mn high strength steels provide excellent mechanical properties, but their weldability is very poor, which hinders their applications. In this paper, 1.6 mm cold-rolled medium-Mn steel was laser welded in a butt joint configuration. The fracture failure mechanism of laser welded joints was studied, and the mechanical properties of the joints were greatly improved by designated intercritical annealing (IA) process. Experimental results showed that the elongation of the as-welded joint of medium-Mn steel was very low, and many dissociation surfaces appeared on the fracture surface, which showed typical brittle fracture characteristics. Energy dispersive spectroscopy (EDS) test showed that there were a large number of Mn segregation bands in the joint, and electron backscatter diffraction (EBSD) surface scanning test further demonstrated that a large number of Mn23C6 carbides were produced at the martensite grain boundary (GB) of the fusion zone (FZ), which was the main reason for the occurrence of brittle fracture in the weld. Furthermore, The existence of Mn23C6 carbide was verified by thermodynamic calculation. By partitioning the C and Mn elements at grain boundary with the designated IA process, the Mn segregation was improved, the existence of Mn23C6 carbide and the intergranular brittleness were reduced. Meanwhile, more reverted austenite was formed in the FZ after IA, which was mainly attributed to increased amounts of Fe3C in the early stage of the IA process, providing a nucleation center for the formation of reverted austenite. Compared to as-welded joint, the product of strength and elongation (PSE) of the IA treated joint was dramatically increased by 2693.65%. Digital image correlation method revealed that the Lüders band passed through the FZ during the tensile process of the IA-treated weld, resulting in a secondary yield in the stress-strain curve. At the same time, serrated oscillation was observed in the stress-strain curve in a form of Portevin-Le Chatelier (PLC) band.
Abstract Today, there is a rising demand and ongoing search for novel plant‐derived phytochemicals in the cosmetic market owing to the growing consumer expectations worldwide for green and natural health products. Various plant ingredients, including polyphenols, oils, volatile oils, vitamins and other herbal extracts, have been extensively used in herbal cosmetics. Recent advances in encapsulation technologies have greatly improved their chemical stability, biocompatibility, skin permeability and dermocosmetic efficiency when applied topically. This comprehensive review summarizes the up‐to‐date information on encapsulated plant ingredients tailored for dermocosmetic application with a focus on the development of novel delivery systems. An overview of the commonly used techniques for carrier characterization, performance‐related properties and toxicological evaluation is also included, which might provide guidance for researchers to select or develop appropriate assay systems.
We present the flexible delivery of picosecond laser pulses with up to 20 W average power over a 3-m-long sample of anti-resonant hollow-core fiber (AR-HCF) for laser micromachining applications. Our experiments highlight the importance of optical mode purity of the AR-HCF for the manufacturing precision. We demonstrate that compared with an AR-HCF sample with a capillary to core (d/D) ratio of ~0.5, the AR-HCF with a d/D ratio of ~0.68 exhibits better capability of high-order-mode suppression, giving rise to improved micromachining quality. Moreover, the AR-HCF delivery system exhibits better pointing stability and set-up flexibility than the free-space beam delivery system. These results pave the way to practical applications of AR-HCF in developing advanced equipment for ultrafast laser micromachining.
Thick plates with different gauges have increased their use in various industries such as the shipyard and offshore industries. The arc welding techniques are the common ways to join the thick plates, which usually requires multi-pass and interlayer control. In addition, high heat input during arc welding also leads to the large distortion in the weld. Industries have shown increasing interest in using the hybrid laser-GMAW welding techniques to join different types of thick plates due to their high productivity, low distortion and excellent synergy of laser welding advantages and arc welding advantages. In this study, a 4 kW fiber laser is combined with gas metal arc welding (GMAW) to hybrid welding of half-inch mild steels. A 4 kW fiber laser, which leads a GMAW, is used to join the root of weld groove. Then, the following GMAW fills the groove. By using this welding procedure, the weld with full-penetration is achieved by one pass. In addition, a high-speed CCD camera is used to real-time monitor the welding process. Influences of different welding parameters such as the distance between laser power and GMAW torch and the gap on the weld quality are investigated.
Resistance spot welding (RSW) is a widely used technique in the automotive industry. The weld size is the critical parameters for evaluating the quality of RSW. In this study, an innovative non-destructive inspection method based on fiber-optic sensing was proposed. The relationship between the change of the fiber optic sensor signals during the welding process and the weld size is established. The results show that there is a strong correlation between the maximum wavelength change of the fiber optic sensing signal during the welding process and the weld size. The method shows good generalizability to different welding parameters and materials. In addition, the signal vibration difference can accurately predict the occurrence of expulsion.
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