Multiscale Collaborative Optimization of Processing Parameters for Carbon Fiber/Epoxy Laminates Fabricated by High-Speed Automated Fiber Placement

Processing optimization is an important means to inhibit manufacturing defects efficiently. However, processing optimization used by experiments or macroscopic theories in high-speed automated fiber placement (AFP) suffers from some restrictions, because multiscale effect of laying tows and their manufacturing defects could not be considered. In this paper, processing parameters, including compaction force, laying speed, and preheating temperature, are optimized by multiscale collaborative optimization in AFP process. Firstly, rational model between cracks and strain energy is revealed in order that the formative possibility of cracks could be assessed by using strain energy or its density. Following that, an antisequential hierarchical multiscale collaborative optimization method is presented to resolve multiscale effect of structure and mechanical properties for laying tows or cracks in high-speed automated fiber placement process. According to the above method and taking carbon fiber/epoxy tow as an example, multiscale mechanical properties of laying tow under different processing parameters are investigated through simulation, which includes recoverable strain energy (ALLSE) of macroscale, strain energy density (SED) of mesoscale, and interface absorbability and matrix fluidity of microscale. Finally, response surface method (RSM) is used to optimize the processing parameters. Two groups of processing parameters, which have higher desirability, are obtained to achieve the purpose of multiscale collaborative optimization

Multi-Scale Low-Entropy Method for Optimizing the Processing Parameters during Automated Fiber Placement

Automated fiber placement (AFP) process includes a variety of energy forms and multi-scale effects. This contribution proposes a novel multi-scale low-entropy method aiming at optimizing processing parameters in an AFP process, where multi-scale effect, energy consumption, energy utilization efficiency and mechanical properties of micro-system could be taken into account synthetically. Taking a carbon fiber/epoxy prepreg as an example, mechanical properties of macro–meso–scale are obtained by Finite Element Method (FEM). A multi-scale energy transfer model is then established to input the macroscopic results into the microscopic system as its boundary condition, which can communicate with different scales. Furthermore, microscopic characteristics, mainly micro-scale adsorption energy, diffusion coefficient entropy–enthalpy values, are calculated under different processing parameters based on molecular dynamics method. Low-entropy region is then obtained in terms of the interrelation among entropy–enthalpy values, microscopic mechanical properties (interface adsorbability and matrix fluidity) and processing parameters to guarantee better fluidity, stronger adsorption, lower energy consumption and higher energy quality collaboratively. Finally, nine groups of experiments are carried out to verify the validity of the simulation results. The results show that the low-entropy optimization method can reduce void content effectively, and further improve the mechanical properties of laminates

Experimental Study of the Effect of Internal Defects on Stress Waves during Automated Fiber Placement

The detection technique of component defects is currently only realized to detect offline defects and online surface defects during automated fiber placement (AFP). The characteristics of stress waves can be effectively applied to identify and detect internal defects in material structure. However, the correlation mechanism between stress waves and internal defects remains unclear during the AFP process. This paper proposes a novel experimental method to test stress waves, where continuous loading induced by process itself is used as an excitation source without other external excitation. Twenty-seven groups of thermosetting prepreg laminates under different processing parameters are manufactured to obtain different void content. In order to quantitatively estimate the void content in the prepreg structure, the relation model between the void content and ultrasonic attenuation coefficient is revealed using an A-scan ultrasonic flaw detector and photographic methods by optical microscope. Furthermore, the high-frequency noises of stress waves are removed using Haar wavelet transform. The peaks, the Manhattan distance and mean stress during the laying process are analyzed and evaluated. Partial conclusions in this paper could provide theoretical support for online real-time detection of internal defects based on stress wave characteristics

Defect Characteristics and Online Detection Techniques During Manufacturing of FRPs Using Automated Fiber Placement: A Review

Automated fiber placement (AFP) is an advanced manufacturing method for composites, which is especially suitable for large-scale composite components. However, some manufacturing defects inevitably appear in the AFP process, which can affect the mechanical properties of composites. This work aims to investigate the recent works on manufacturing defects and their online detection techniques during the AFP process. The main content focuses on the position defect in conventional and variable stiffness laminates, the relationship between the defects and the mechanical properties, defect control methods, the modeling method for a void defect, and online detection techniques. Following that, the contributions and limitations of the current studies are discussed. Finally, the prospects of future research concerning theoretical and practical engineering applications are pointed out

A Non-Geodesic Trajectory Design Method and Its Post-Processing for Robotic Filament Winding of Composite Tee Pipes

With the advantages of high specific strength and well corrosion resistance, polymer-matrix composite tee pipes are widely used in aerospace and civilian fields. The robotic filament winding technology is suitable for forming complex shape parts. This paper aims to provide a novel non-geodesic trajectory design method to get a continuous trajectory for tee pipe winding. Furthermore, post-processing methods are proposed for realizing the full coverage of tee pipes by robotic filament winding. The CAD/CAM software is then designed to simulate the winding process and realize the cover of the whole tee pipe. Finally, experiments of winding a tee pipe with a desktop winding machine and a six-axis winding robot are carried out. The results show that the tee pipe is fully covered, verifying the accuracy of the design method and post-processing methods

Plant growth and diversity performance after restoration in Carex schmidtii tussock wetlands, Northeast China

Plant performance, which considers plant growth, community composition, and diversity, demonstrated the wetland plants’ restoration efficiency of wetland plants following restoration. Carex tussocks are widespread in temperate freshwater wetlands and streams, well as characterizing with rich biodiversity. However, tussock wetlands sharply shrank and plant performance has changed due to the interaction of long-term drought, and human disturbance (road construction, grazing and mowing). In recent decades, ecological restoration has been widely conducted in degraded tussock wetlands in semi-arid area. A field investigation was done in a restored tussock wetland (R) after restoration for 10 years in order to evaluate efficacy of tussock restoration. Tussock wetlands were chosen as reference wetlands, both natural (N) and degraded (D). In semi-arid zones, the results showed that wetlands were affected by drought and flooding. After 10 years, wetland restoration effectively restored the growth and yield of Carex schmidtii tussocks compared to D, but did not reach to the natural state. The importance value (IV) of C. schmidtii has sharply decreased in R. Xerophyte species (Artemisia integrifolia) have occupied dominant position growth. Furthermore, the IV of other wetland species has dropped through time, and some have even disappeared as a result of drought and flooding. R and N have much lower species richness and Shannon–Wiener index than D. Flooding in August, following a drought, boosted the Simpson index and Evenness index in R and N. Obvious differences in species composi- tion and community structure were found using principal component analysis among N, R, and D. Ecological restoration substantially alleviated wetland degradation in the semi-arid zone, but subsequent hydrological management is required to further promote plant growth and diversity performance

Preparation, characterization and foaming performance of thermally expandable microspheres

Thermal expansion microcapsules (TEMs) are widely used in various fields due to their unique structures. In recent years, TEMs have attracted much attention and have broad market application prospects. In this study, thermally expandable microcapsules with a core–shell structure were prepared by suspension polymerization using acrylonitrile (AN), methyl methacrylate (MMA), and methyl acrylate (MA) as monomers and low-boiling alkane as the core material. Through particle size analysis, morphology test, thermal analysis and other methods, the effects of core material types, single core material and mixed core material, dispersion system on the microcapsule structure, particle size distribution, and expansion properties were compared. Moreover, the core material with a content of 35% can make the expansion ratio of the microcapsules up to 4 times. The expansion performance of the microcapsules with a mixture of isopentane and isooctane (ratio 1:1) as the core material was increased by 27% compared with that of a single core material. In addition, comparing with colloidal SO _2 /PVP dispersant, the expansion ratio of the microcapsules with magnesium hydroxide as the dispersant was increased by 20%. Finally, the optimized method for preparing thermally expandable microcapsules was obtained

Development of Rapid Curing SiO2 Aerogel Composite-Based QuasiSolid-State Dye-Sensitized Solar Cells through Screen-Printing Technology

Gratzel's dye-sensitized solar cells (DSSCs) can readily convert sunlight into electricity, attracting considerable attention of global scientists. The fabrication efficiency of DSSCs was greatly limited by the slow fabrication (similar to 3.5-24 h) of quasi-solid (QS) electrolytes to date. In this study, novel composites of SiO2 aerogel with graphene (GR), multi-walled carbon nanotubes, or polyaniline were proposed in the fabrication of QS-state electrolytes. The morphology of these composites was characterized. The gels with SiO2 aerogels as QS electrolytes of DSSCs can be rapidly cured in similar to 3 s. Using the screen-printing technology, these QS electrolytes can be readily utilized to construct the QS-DSSC to provide high efficiency and great stability. The photovoltaic parameters and interfacial chargetransfer resistances of the QS-DSSC incorporated with our synthetic composites were investigated in detail. Specifically, the SiO2 aerogel composed of GR (SiO2@GR) as a gel can greatly improve the performance of QS-DSSCs up to 8.25%. It is likely that these SiO2 aerogel composite electrolytes could provide a rapid curing process in the preparation of QS-state DSSCs, which might be useful to promote the development of DSSCs for future industrialization