•The tar yield decreased with increasing temperature and excess air ratio.•Gasification tar derived from lignin was more stable and harmful.•PAHs were primary component of gasification tar at ...relatively higher temperature.•Gasification tar of biomass components had different composition.•Tar formation mechanisms for biomass components were different.
This study compares the major biomass components (i.e., cellulose, hemicellulose and lignin) with respect to their differing tar formation characteristics during the gasification process. To better understand the tar formation mechanism, the tar content and composition were analysed via gas chromatography coupled with mass spectrometry (GC–MS). The tar yields of the three components all decreased with increasing temperature or excess air ratio (ER). However, lignin has a higher tar yield and produces more stable components in tar due to its molecular structure. At higher temperatures, the tar composition shifts toward higher-molecular-weight substances, such as polycyclic aromatic hydrocarbons (PAHs). For lignin, PAHs are derived primarily from phenols and its derivatives. For cellulose and hemicellulose, PAHs are derived primarily from benzene, toluene, ethylbenzene and xylene isomers (BTEX) and miscellaneous hydrocarbons. During the gasification process of real biomass materials, it is crucial to remove the tar compounds derived from lignin for tar control.
Seismic actions inevitably cause cyclic plastic deformations in steel frame connections, which is a common cause of failure in steel structures. Nonlinear finite element (FE) static analysis has been ...employed in the study of the cyclic plastic behavior of a T-stub connection based on the reported cyclic test on the corresponding extensively tested T-stub connection made of Q235 steel. In particular, the isotropic-hardening and Chaboche constitutive models were employed to predict both the stress distribution and plastic development on the T-stub and the hysteretic curves of the entire T-stub connection. The two constitutive models were calibrated by four material tests to describe the yield and hardening behaviors of the Q235 steel used to make this T-stub connection. The two sets of simulation results obtained from the simulations of the two FE models employed by the two different constitutive models were compared with each other and with the experimental results. The comparisons reveal that the simulation results are similar and in good agreement with the experimental results when the cumulative plastic deformation in the T-stub is small. However, the results of the FE analysis using the Chaboche model are in better agreement with the experimental results when the cumulative deformation in the T-sub is large. This study can provide a reference for FE simulation of the cyclic plastic behavior of steel connections, including the T-stub connection.
Highlights
A solvent-free thermoplastic forming processing of graphene materials is invented by polymer intercalation from graphene oxide precursor.
The correlation between interlayer spacing and ...thermoplastic forming capability of polymer-intercalated graphene oxide solid is uncovered.
The multi-scale forming of graphene materials from Gaussian curved shapes to surface relief patterns with size precision down to 360 nm is realized.
The processing capability is vital for the wide applications of materials to forge structures as-demand. Graphene-based macroscopic materials have shown excellent mechanical and functional properties. However, different from usual polymers and metals, graphene solids exhibit limited deformability and processibility for precise forming. Here, we present a precise thermoplastic forming of graphene materials by polymer intercalation from graphene oxide (GO) precursor. The intercalated polymer enables the thermoplasticity of GO solids by thermally activated motion of polymer chains. We detect a critical minimum containing of intercalated polymer that can expand the interlayer spacing exceeding 1.4 nm to activate thermoplasticity, which becomes the criteria for thermal plastic forming of GO solids. By thermoplastic forming, the flat GO-composite films are forged to Gaussian curved shapes and imprinted to have surface relief patterns with size precision down to 360 nm. The plastic-formed structures maintain the structural integration with outstanding electrical (3.07 × 10
5
S m
−1
) and thermal conductivity (745.65 W m
−1
K
−1
) after removal of polymers. The thermoplastic strategy greatly extends the forming capability of GO materials and other layered materials and promises versatile structural designs for more broad applications.
Graphical abstract
Highlights
Monodomain liquid crystals of graphene oxide over 30 cm is realized by boundary-free sheargraphy.
The achieved monodomain liquid crystals have bidirectional sheet ordering, exhibiting ...unique optical, rheological, and conductive properties.
Boundary-free sheargraphy extends to freely design delicate topology of two-dimensional colloids, including topological structures with defect strength from − 2 to + 2 and complex polydomain.
Eliminating topological defects to achieve monodomain liquid crystals is highly significant for the fundamental studies of soft matter and building long-range ordered materials. However, liquid crystals are metastable and sensitive to external stimuli, such as flow, confinement, and electromagnetic fields, which cause their intrinsic polycrystallinity and topological defects. Here, we achieve the monodomain liquid crystals of graphene oxide over 30 cm through boundary-free sheargraphy. The obtained monodomain liquid crystals exhibit large-area uniform alignment of sheets, which has the same optical polarized angle and intensity. The monodomain liquid crystals provide bidirectionally ordered skeletons, which can be applied as lightweight thermal management materials with bidirectionally high thermal and electrical conductivity. Furthermore, we extend the controllable topology of two-dimensional colloids by introducing singularities and disclinations in monodomain liquid crystals. Topological structures with defect strength from − 2 to + 2 were realized. This work provides a facile methodology to study the structural order of soft matter at a macroscopic level, facilitating the fabrication of metamaterials with tunable and highly anisotropic architectures.
Summary
The feature layers of different layers in the single shot multibox detector (SSD) are independently used as the input of the classification network, so it is easy to detect the same object. ...This article proposes an improved SSD model based on deep feature fusion. In the SSD algorithm, the deep feature fusion between the target detection layer and its adjacent feature layer is used, including convolution kernels and pooling kernels of different sizes, down‐sampling of low‐level features and up‐sampling of deconvolution of high‐level features. The network is improved by combining the target frame recommendation strategy in the SSD algorithm and the frame regression algorithm. The experimental results show that the improved SSD algorithm improves the detection accuracy and detection rate of the target, and the effect is more obvious for the relatively small‐scale target.
Excellent through‐plane thermally conductive composites are highly demanded for efficient heat dissipation. Giant sheets have large crystalline domain and significantly reduce interface phonon ...scattering, making them promising to build highly thermally conductive composites. However, realizing vertical orientation of giant sheets remains challenging due to their enormous mass and huge hydrodynamic drag force. Here, we achieve highly vertically ordered liquid crystals of giant graphite oxide (more than 100 µm in lateral dimension) by microwire shearing, which endows the composite with a recorded through‐plane thermal conductivity of 94 W m−1 K−1. Microscale shearing fields induced by vertical motion of microwires conquer huge hydrodynamic energy barrier and vertically reorient giant sheets. The resulting liquid crystals exhibit extremely retarded relaxation and impart large‐scale vertical array with bidirectional ordering degree as high as 0.82. The graphite array‐based composites demonstrate an ultrahigh thermal enhancement efficiency of over 35 times per unit volume. Furthermore, the composites improve cooling efficiency by 93% for thermal management tests compared to commercial thermal interface materials. This work offers a novel methodology to precisely manipulate the orientation of giant particles and promote large‐scale fabrication of vertical array with advanced functionalities.
Highly vertically ordered liquid crystals of giant graphite oxide (more than 100 µm in lateral dimension) is realized by microwire shearing, which endows the composite with a record high through‐plane thermal conductivity of 94 W m−1 K−1, 15% higher than that of pure Indium foil (81.8 W m−1 K−1).
This study presents an experimental and numerical investigation on the Extremely-Low Cycle Fatigue (ELCF) behavior of Q235 structural steel under different stress states and large strain amplitudes. ...A set of Q235 structural steel cylindrical specimens of different radii of curvature were selected to examine the effect of the triaxial state of stress on the fracture behavior. Cyclic axial tension-compression loading tests characterized by large strain amplitudes were conducted to obtain the hysteresis loops and the failure process by measuring both macroscopic and microscopic fracture morphologies. The results shows that, the failure behavior of Q235 steel in ELCF loading is a mixture of fatigue fracture and ductile fracture. Specimens with different stress triaxialities are characterized by different failure modes. A fracture criterion, namely the Combinatory Work Density Model (CWDM), was calibrated based on the test results. Furthermore, a cyclic plasticity constitutive model, i.e., the Chaboche model, was calibrated to describe the yield and cyclic hardening behaviors of the Q235 structural steel. Finite element (FE) simulations in the commercial software ABAQUS accounting the calibrated CWDM and Chaboche model were carried out to evaluate the fracture characteristics with different stress triaxialities and their stress-strain hysteretic curves under ELCF loading. The simulation results demonstrate that the developed FE model can reproduce the hysteretic characteristics and capture the failure process of Q235 structural steel. The proposed practical numerical tool can be used for the ELCF failure prediction in steel structures under complex stress state.
•Extremely- low cycle fatigue (ELCF) loading tests were conducted on Q235 steel.•Effects of different stress states and large strain amplitudes were investigated.•Microscopic and macroscopic morphological were examined.•ABAQUS subroutine VUMT was developed accounting the calibrated models.
Processing 2D sheets into desired structures with high precision is of great importance for fabrication and application of their assemblies. Solution processing of 2D sheets from dilute dispersions ...is a commonly used method but offers limited control over feature size precision owing to the extreme volume shrinkage. Plastic processing from the solid state is therefore a preferable approach to achieve high precision. However, plastic processing is intrinsically hampered by strong interlayer interactions of the 2D sheet solids. Here, a hydroplastic molding method to shape layered solids of 2D sheets with micrometer‐scale precision under ambient conditions is reported. The dried 2D layered solids are plasticized by intercalated solvents, affording plastic near‐solid compounds that enable local plastic deformation. Such an intercalated solvent‐induced hydroplasticity is found in a broad family of 2D materials, for example graphene, MoS2, and MXene. The hydroplastic molding enables fabrication of complex spatial structures (knurling, origami) and microimprinted tubular structures down to diameters of 390 nm with good fidelity. The method enhances the structural accuracy and enriches the structural diversity of 2D macroassemblies, thus providing a feasible strategy to tune their electrical, optical, and other functional properties.
A general approach to mold 2D sheet microstructured materials based on hydroplasticity is described. An innovative interlayer‐spacing‐induced brittle–plastic transition in 2D materials is revealed. The approach enables direct forming with high design freedom and accuracy from 2D layered solids. The molded assemblies possess tunable electrical, optical, and other functional properties.
Summary
Target localization in unknown environment is one of the development directions of mobile robots. Simultaneous localization and mapping (SLAM) can be used to build maps in unknown ...environments, but it has the problem of poor readability and interactivity. In this article, target detection and SLAM are combined to search and locate the target by using rich RGBD images information. The determined position in the global map is conducive to the follow‐up operation of the target by mobile robots. By establishing a local dense point cloud map of the target object, the current state of the target object is directly displayed, the readability of the map is improved, and the disadvantages of difficult understanding of the global sparse map and slow construction of the global dense map are avoided. A target localization algorithm under the framework of yolov4 is designed to apply in the process of SLAM global mapping. Our works are helpful for obtaining positions of objects in three‐dimensional space. The experimental results show that the time‐consuming of this method in dense mapping is reduced by 50%–70%, and the number of point clouds is also reduced by 60%–70%.
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