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Laser transmission welding (LTW) plays an important role in plastic connection for fabricating large and complex products. The laser profile as a key parameter determines the spatial energy distribution, affecting the temperature gradient of the welding path and the quality of the weld seam. In this study, the effect of two laser profiles, the Gaussian and Flat-top beams on the temperature field and weld quality was studied through experiments and simulation. First, the transmission behavior of the laser beams is studied through the spectrometer and photosensitive paper, revealing the laser spot energy distribution and spatial changes after passing through the laser-transparent layer. Furthermore, the tensile force test demonstrated that the weld seam prepared by the Gaussian beam present higher tensile force, with a tensile force of 634.18 N at the line density of 11.2 J/mm, 24.23 % higher than that of the Flat-top beam. Moreover, the simulation result from the finite element model found that the maximum welding temperature of the Flat-top beam is 39.42 % higher than that of the Gaussian beam, consistent with the results of morphological and mechanical results. This study might present a potential way for selecting the laser profile in LTW, further improving weld quality through optimizing process windows. [ABSTRACT FROM AUTHOR]

Cellulose as the most abundant biopolymers on Earth, presents appealing performance in mechanical properties, thermal management, and versatile functionalization. Developing fabrication methods to design functional materials and open new application areas. However, cellulose is hard to be dissolved or melt due to its recalcitrant property. Herein, the recent progress of fabricating cellulose is summarized. First, the unique hierarchical structure of cellulose is fully investigated and the resulted processability is analysed in directions of down to nanocellulose, dissolution, and thermoplastic processing. Then, the reported fabrication methods are summarized in three aspects: (1) self‐assembly from nano/micro cellulose suspensions, especially the formation of cellulose nanocrystals; (2) dissolution–regeneration–drying, covering spinning and solvent infusion processing; and (3) thermoplastic processing, focusing on the setup and the morphology changes of the prepared products. In each aspect, the flowchart of the fabrication method, the mechanism, fabricated products, and effects of processing parameters are explored. Finally, this review provides a perspective on the further direction of fabricating cellulose, especially the challenges toward mass production. [ABSTRACT FROM AUTHOR]

The electromagnetic field and the droplet profile in electroslag remelting (ESR) process play a pivotal role in the quality of final steel products. Numerical simulation remains a central challenge to investigate ESR process with a high‐efficiency and high‐accuracy method. Herein, a strategy embedding an adaptive mesh refinement (AMR) method in 3D‐coupled model is proposed to speed up the simulation of ESR process. The coupling phenomena of the electromagnetic field and the droplet profile are successfully predicted using this method. Compared with the results of uniform mesh, the deviation of AMR results is less than 2.2%, whereas the computational speed of the AMR method is 10 times faster. Moreover, the effects of two key parameters in AMR method, maximum refinement level and refinement interval, on computational accuracy and speed are studied. With the increasing maximum refinement level, the computational accuracy is improved obviously first and then slightly, but the computation time increases exponentially. The increasing refinement interval has little effect on the computational accuracy but can greatly save the time of mesh operation. The proposed strategy can promote the application of numerical simulation in industrial ESR process. [ABSTRACT FROM AUTHOR]

• Analyzed the enhancement mechanism of MZAP on the fracture process. • Demonstrated positive effect of MZAP on mechanical riveting structure. • Effects of MZAP feature on the joint is investigated firstly. Effectively joining dissimilar transparent thermoplastics plays an important role in lightweight design in vehicles and automotive industry. However, their different physical–chemical properties hamper the welding of thermoplastics directly with diode laser. In this study, magnesium zinc alloy particles (MZAP) are chosen as laser-absorbent to join polycarbonate (PC) and polyarylsulfone (PASF) specimens. First, the comparison of PC/PASF weldments with different laser-absorbents was performed, including adding carbon black (CB) as laser-absorbents. The morphology and mechani-cal properties show the weldments prepared with MZAP have advantages of cleaner appearance and stronger shear strength. Furthermore, the fracture surface and joint microstructure reveal that the mechanical riveting structure, composed of defused MZAP and filled thermoplastics in the gaps between adjacent MZAP, forms when the MZAP was used as laser-absorbent. Comparing with CB aggregates, the fused MZAP has a stronger ability to resist external force and leads to a higher shear strength. Finally, the analysis of factors of MZAP feature reveals that the mechanical riveting structure contributes to improving the shear strength, the defects, such as creaks, holes and bubbles should be eliminated in the welding. The results of analysis of variance illustrated the particle size and the standoff distance are statistically significant for the shear strength. This study provides a potential avenue to effective weld dissimilar thermoplastics. [ABSTRACT FROM AUTHOR]

• The effect of process parameters on the thermal degradation behavior is investigated. • The thermal history model during LTW is simulated by FEM. • The thermal degradation kinetics model is solved from TGA with multi-heating rates. • The prediction model is proposed and matched well with LTW results. Reducing thermal degradation of plastics during laser transmission welding (LTW) process is the key to obtain high-quality weld seam. In this study, a thermal degradation prediction model is proposed. First, using polymethyl methacrylate (PMMA) as an exemplary material, the weld seams are prepared at different process parameters, including the laser power, welding velocity and carbon black (CB) content. Full characterization of the prepared weld seams was performed through shear tests, scanning electronic images, and ultra-depth-of-field microscope. The results reveal that thermal degradation occurs with bubbles at the interface and decreases the shear strength of the weld seam. Second, the thermal history model during LTW is simulated through a 3-D transient heat transfer finite element method (FEM), where the highest temperature is extracted to aid in comprehension of thermal degradation mechanism. Third, a thermal degradation prediction model is proposed based on the thermal history model and thermal degradation kinetic model which is solved by the thermogravimetric analysis (TGA). The results from the proposed prediction model is consistent with the occurrence of the initial thermal degradation and the trend of shear strength of the weld seam. Therefore, this study might present a potential way to optimize the processing window by effectively suppressing the appearance of thermal degradation. [ABSTRACT FROM AUTHOR]

The metal powder absorbents have the advantage of fabricating clean and high-strength joints in the process of laser transmission welding dissimilar transparent thermoplastics. However, the joining behavior between metal powders and thermoplastics is vague. Herein, polyarylsulfone (PASF) and polycarbonate (PC) are selected as model materials to investigate the joining behavior using magnesium zinc alloy (MZA) powders at different laser line energies. The shear force test was performed to reveal the effect of laser line energy on the welding. The µ-CT images reveal the evaluation of welding strength is attributed to the specific joint morphology. The multi-scale morphology characterization shows that the fractured surface height increases with increasing the laser line energy. The voids between MZA powders and resins increase the risks of interface failure, and the bubbles in the resins increase the risks of cohesion failure. The effects of laser line energy on the joint characteristics are elaborated based on the thermo-physical property test and transient temperature field analysis. The above results indicate the optimized welding temperature locates the melting temperature of PASF, because of the good fusion of PASF and less decomposition of PC. The study can provide a guideline for choosing proper process parameters when choosing metal powders as laser absorbents in welding dissimilar transparent thermoplastics. [ABSTRACT FROM AUTHOR]

Fig. 1 (a) the figure of the cellulose film, (b) SEM of the cellulose film, inset is the SEM of the raw cellulose powders. (c) a comparison with other cellulose films prepared by the complete or surface selective dissolution method. Data sources: A (Yang, Qin and Zhang,2011); B (Yang, Lue and Zhang,2010); C (Li, Zhang and Xu,2012); D (Gindl and Keckes,2005); E (Duchemin, Newman and Staiger,2009); F (Zhao, He, Wanget al,2014); G (De Silva and Byrne,2017); H (Pang, Liu, Zhanget al,2013); I, J, K, O (Pang, Liu, Wuet al,2014); L (Ma, Zhou, Liet al,2011); M (Sirviö, Visanko and Hildebrandt,2017); N (Liu, Pang, Zhanget al,2013); ★ This paper. (d) TGA curves of MCC, the cellulose film and regenerated cellulose (Richard P. Swatloski, 2002). • A process combing shear force and surface selective dissolution was proposed. • The tensile strength reached 94 MPa. • Thermal decomposition temperature improved by 64 °C compared with that of regenerated cellulose. • A surface dissolution and reconnection mechanism was proposed. Cellulose is a promising and advantageous material because it is low-cost, abundant and biodegradable. Nonetheless, dealing with this material is extremely challenging because cellulose cannot dissolve in most solvents or melt at any temperature or pressure in the air owing to strong hydrogen-bonding networks. In this work, a surface selective dissolution with shear force process was proposed to prepare cellulose films with high strength from microcrystalline cellulose powders. The tensile strength reached 94 MPa and the thermal decomposition temperature improved by 64 °C compared with that of regenerated cellulose. A mechanism of surface dissolution and reconnection was proposed to explain the process. The outstanding mechanical property attributes to tight reconnection of the undissolved cores via dissolved surfaces in cellulose powders, and the improved thermal decomposition temperature is due to preserved cellulose Ⅰ crystalline structure of microcrystalline cellulose. We believe that this cost-effective and facile method holds promise for industrial-scaleproduction of cellulose materials. [ABSTRACT FROM AUTHOR]

Measuring orientation dynamics of carbon fibers is important for manufacturing high-performance composite materials, however, conventional methods fail to timely and non-destructively measure due to destructive sample preparation or complicated data processing from numerous fibers. Herein, we report a timely and non-destructive method that uses two pairs of interdigital electrodes to record dielectric anisotropy induced by carbon fibers orientation. As a proof-of-concept, orientation dynamics of carbon fibers is successfully characterized, the accuracy of which in measuring the final degree of orientation and dynamic orientation process is evidenced by theoretical calculations and optical observations. Experimental results reveal that increasing the fiber aspect ratios, viscosities of solvents and shear rates, could shorten orientation time or increase the final degree of orientation. Meanwhile, a modified model is proposed to explain orientation dynamics with a maximum error of 4.7%. This method has the potential for measuring the orientation dynamics of carbon fibers in the complex structure during processing. [Display omitted] • A timely and non-destructive method is reported to measure carbon fiber orientation. • The theory is introduced and the accuracy is validated by firm evidence. • Effects of fiber aspect ratios, viscosities of solvents and shear rates, are studied. • A modified model is proposed to explain the orientation dynamics precisely. [ABSTRACT FROM AUTHOR]

High‐temperature heating is ubiquitously utilized in material synthesis and manufacturing, which often features a rapid production rate due to the significantly improved kinetics. However, current technologies generally provide overall and steady‐state heating, thereby limiting their applications in micro/nano‐manufacturing that require selective patterning and swift heating. Herein, significantly improved control over small‐scale heating is reported by utilizing 3D printed reduced‐graphene‐oxide (RGO) probe triggered by electrical Joule heating, which enables precise heating with high spatial (sub‐millimeter scale) and temporal (milliseconds) resolutions. The block copolymer‐modified aqueous‐based RGO ink enabled 3D printing of high‐precision structures, and a bio‐inspired cellular microstructure is constructed to achieve control of the electrical conductivity and maximize structure robustness (benefit for efficient heating and operability). In particular, a thermal probe featuring a microscale tip with excellent heating capabilities (up to ≈3000 K, ultra‐fast ramping rate of ≈105 K s−1, and durations in milliseconds) is fabricated. This thermal probe is ideal for surface patterning, as it is demonstrated for the selective synthesis of patterned metal (i.e., platinum and silver) nanoparticles on nano‐carbon substrates, which is not possible by traditional steady‐state heating. The material construction and heating strategy can be readily extended to a range of applications requiring precise control on high‐temperature heating. [ABSTRACT FROM AUTHOR]

Efficient electrocatalysts are critical in various clean energy conversion and storage systems. Polyelemental nanomaterials are attractive as multifunctional catalysts due to their wide compositions and synergistic properties. However, controlled synthesis of polyelemental nanomaterials is difficult due to their complex composition. Herein, a one‐step synthetic strategy is presented to fabricate a hierarchical polyelemental nanomaterial, which contains ultrasmall precious metal nanoparticles (IrPt, ≈5 nm) anchored on spinel‐structure transition metal oxide nanoparticles. The polyelemental nanoparticles serve as excellent bifunctional catalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The mass catalytic activity of the polyelemental nanoparticles is 7‐times higher than that of Pt in ORR and 28‐times that of Ir in OER at the same overpotentials, demonstrating the high activity of the bifunctional electrocatalyst. This outstanding performance is attributed to the controlled multiple elemental composition, mixed chemical states, and large electroactive surface area. The hierarchical nanostructure and polyelemental design of these nanoparticles offer a general and powerful alternative material for catalysis, solar cells, and more. [ABSTRACT FROM AUTHOR]

Because of the insoluble and infusible properties of cellulose, it is difficult to directly apply cellulose in the manufacture of pure cellulose films (PCFs). Although progress has been achieved in developing eco-friendly fabrication methods including chemical modifications, wet process or thermoplastic process in recent decades, their extreme dependence on a large amount of solvents makes it impossible to attain green manufacturing due to the production of waste liquids and by-products. Herein, by recycling green ionic liquids (ILs) as cellulose plasticizers, a green manufacturing strategy was investigated, in which PCFs, which can be used as flexible cellulose electronic substrates, were successfully manufactured. The results indicated that the properties and structures of PCFs and ILs were essentially unchanged after four cycles; meanwhile, ILs were almost completely recycled and maintained high quality. Compared with the tensile strength of 84.3 MPa and the maximum transmittance of 64.8% of the original PCFs, the mechanical and optical performances of PCFs remained at 83.0 MPa and 64.4% after four cycles, respectively. Moreover, the recovery rates of ILs were higher than 95.0 wt%. Therefore, this study opens a green manufacturing window, which promotes the industrialization of cellulose processing using ILs and the cellulose electronic substrates to substitute the existing artificial polymer electronic substrates. [ABSTRACT FROM AUTHOR]

Aerosol spray coupled with high-temperature pyrolysis is an emerging technique for continuous manufacturing of nanomaterials at large scale that demonstrates extremely high production efficiency. Current aerosol spray techniques using a tube furnace can only attain a low temperature range (generally <1500 K), rendering limited products as well as inhomogeneous heating within the comparatively bulky furnace chamber (typical dimensions of ≥2 cm in diameter and ≥40 cm in length), which leads to difficulties in product quality control. Here we report a "droplet-to-particle" aerosol technique coupled with a high-temperature (∼2000 K) micro-channel reactor, which provides ∼100-times smaller dimensions compared to conventional tube furnaces, enabling homogeneous and high-temperature nanomaterial manufacturing. To demonstrate the unique capability of this carbonized wood micro-channel reactor, we successfully synthesized multielement high entropy alloy/oxide nanoparticles (which typically require a high temperature (2000 K) to achieve uniform elemental mixing) in a continuous and support-free manner. Droplets atomized from the multielement precursors fly through the micro-channels heated to 2000 K by Joule heating with a residence time of only tens of milliseconds with a high energy conversion efficiency (>95%), during which salt decomposition and particle nucleation/growth occur. The high temperature critically enables homogeneous mixing of elements in the resultant nanoparticles and the short residence time is key to suppress particle growth and agglomeration. Compared with the traditional aerosol spray pyrolysis, the carbonized wood reactor can achieve a record high temperature (≥2000 K), a much shorter residence time (∼tens of milliseconds), highly efficient, uniform heating, and provide a platform for continuous nanomaterial manufacturing for a broad range of applications. [ABSTRACT FROM AUTHOR]

Chatter is one of the most unexpected and uncontrollable phenomenon during the milling operation. It is very important to develop an effective monitoring method to identify the chatter as soon as possible, while existing methods still cannot detect it before the workpiece has been damaged. This paper proposes an energy aggregation characteristic-based Hilbert–Huang transform method for online chatter detection. The measured vibration signal is firstly decomposed into a series of intrinsic mode functions (IMFs) using ensemble empirical mode decomposition. Feature IMFs are then selected according to the majority energy rule. Subsequently Hilbert spectral analysis is applied on these feature IMFs to calculate the Hilbert time/frequency spectrum. Two indicators are proposed to quantify the spectrum and thresholds are automatically calculated using Gaussian mixed model. Milling experiments prove the proposed method to be effective in protecting the workpiece from severe chatter damage within acceptable time complexity. [ABSTRACT FROM AUTHOR]

The purpose of this work is to characterize the mechanical behavior of blends of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) during monotonic and cyclic loading. Compression experiments were performed using a SHIMADZU universal testing machine (10 −4 to 10 −2 s −1 ) and a split Hopkinson pressure bar (1600–5000 s −1 ), with, the test temperatures ranging from 293 to 353 K. The influence of the rate and temperature on the deformation of PC/ABS is discussed in detail. Based on the investigation of numerous constitutive models, a phenomenological model called DSGZ was chosen to describe the compression behavior of PC/ABS. This model could not accurately reproduce the deformation of polymers at high strain rates when utilizing the same material coefficients for the low and high strain–rate deformations. In addition, this model was unable to capture the deformation features during unloading and subsequent reloading when adopting the original stress–strain updating algorithm. Hence, some improvements to the model have been implemented to better predict the deformation. Finally, the model predictions are shown to be consistent with the experimental results. [ABSTRACT FROM AUTHOR]