Precursor-derived ceramic SiOC (PDC-SiOC) microlattices exhibit excellent oxidation resistance, high-temperature stability, and superior mechanical properties. However, the printing accuracy of the PDC-SiOC microlattices by 3D printing is still limited, and mechanical properties of the PDC-SiOC microlattices have not been studied systematically. Here, PDC-SiOC octet microlattices were fabricated by projection micro stereolithography (PμSL) 3D printing, and photoabsorber (Sudan III)’s effect on the accuracy was systematically analyzed. The results showed that the addition of Sudan III improved the printing accuracy significantly. Then, the ceramization process of the green body was analyzed in detail. The order of the green body decreased, and most of their chemical bonds were broken during pyrolysis. After that, the PDC-SiOC microlattices with different truss diameters in the range of 52–220 μm were fabricated, and their mechanical properties were investigated. The PDC-SiOC microlattices with a truss diameter of 52 μm exhibited higher compression strength (31 MPa) than those with bigger truss diameters. The size effect among the PDC-SiOC microlattices was analyzed. Our work provides a deeper insight into the manufacturing of PDC-SiOC micro-scaled architectures by 3D printing and paves a path to the research of the size effect in ceramic structures.
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In order to improve the explosion and impact resistance of the protective structures of unmanned underwater vehicles (UUVs), autonomous underwater vehicles (AUVs), air bottles, etc., the structural response and failure modes of carbon fiber reinforced plastic (CFRP) cylindrical shells under underwater explosion and high hydrostatic pressure are investigated.
A computational model of CFRP cylindrical shell implosion under the combined action of hydrostatic pressure and impact load is established using ABAQUS software and the coupled Euler-Lagrange (CEL) method. The effectiveness of the numerical simulation method is then verified by comparison with the experimental results. On this basis, the failure modes and parametric effects of CFRP cylindrical shell implosion are obtained.
The underwater implosion of composite cylindrical shells can be divided into three stages: buckling, wall contact and failure propagation. Reducing the length-to-diameter ratio of the CFRP cylindrical shell can improve the impact resistance ability and affect the failure mode of the structure. With the increase in the number of fiber layers, the static water bearing capacity and impact resistance ability of the shell structure increase. With the increase in the impact block velocity, the wall boundary contact and failure propagation of the cylindrical shell become more obvious, matrix fractures occur more frequently and the cracks show an obviously increasing trend in the lengthwise direction of the cylindrical shell.
The results of this study can provide data guidance for the structural design of underwater vehicles and promote the application of composite materials in the field.
The addition of thermoplastic phase materials between the layers of traditional marine composite laminates can effectively improve the impact resistance properties of marine composites. This study carries out experiments to explore the impact damage characteristics of such materials.
The thermoplastic/thermoset interface of laminates is observed with an optical microscope, and the bonding mode of the two-phase materials is analyzed. Composite laminates with different structures are impacted at low velocity with three different energies. The damage morphology of each specimen is observed via ultrasonic C-scan and electron microscopy to obtain the impact response and damage mechanism of each specimen.
The results show that marine composite laminates embedded with PEI film have better damage resistance than carbon fiber laminates. Under 8 J and 12 J of impact energy , the delamination damage is reduced by 19% and 39% respectively, and they showed better integrity after 12 J impact.
Embedding PEI thermoplastic film inside laminates can improve their toughness and significantly reduce internal delamination damage. Compared with carbon fiber laminates and double-sided coated laminates, PEI thermoplastic film can significantly improve the impact resistance of internal film embedded laminates.
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Cellular ceramic structures (CCSs) are promising candidates for structural components in aerospace and modern industry because of their extraordinary physical and chemical properties. Herein, the CCSs with different structural parameters, i.e., relative density, layer, size of unit cells, and structural configuration, were designed and prepared by digital light processing (DLP)-based additive manufacturing (AM) technology to investigate their responses under compressive loading systematically. It was demonstrated that as the relative density increased and the size of the unit cells decreased, the mechanical properties of one-layer CCSs increased. The mechanical properties of three-layer CCSs were more outstanding than those of the CCSs with one and two layers. In addition, structural configurations also played a vital role in the mechanical properties of the CCSs. Overall, the mechanical properties of the CCSs from superior to inferior were that with the structural configurations of modified body-centered cubic (MBCC), Octet, SchwarzP, IWP, and body-centered cubic (BCC). Furthermore, structural parameters also had significant impacts on the failure mode of the CCSs under compressive loading. As the relative density increased, the failure mode of the one-layer CCSs changed from parallel–vertical–inclined mode to parallel–vertical mode. It was worth noting that the size of the unit cells did not alter the failure mode. Inclined fracture took a greater proportion in the failure mode of the multi-layer CCSs. But it could be suppressed by the increased relative density. Similarly, the proportions of the parallel–vertical mode and the fracture along a specific plane always changed with the variation of the structural configurations. This study will serve as the base for investigating the mechanical properties of the CCSs.
In order to improve the anti-shock perfomance of ships subjected to underwater explosion, this paper studies the energy absorption and impact resistance of the new protective structure consisted of carbon fiber reinforced plastic (CFRP)-lattice aluminum sandwich plates.
First, finite element software ABAQUS is used to establish the numerical simulation model of CFRP-lattice aluminum sandwich plates under non-explosive and non-contact underwater explosion load, and its reliability is verified. Single variables are then controlled to analyze the influence of the fiber layer thickness of the upper and lower panels and the rod diameter of the sandwich lattice structure on the energy absorption characteristics and structural deflection of the CFRP-lattice aluminum sandwich plates. Finally, based on the above three design parameters, a surrogate optimization model is established using the experimental design method and numerical simulation methodology to optimize the energy absorption of the CFRP-lattice aluminum sandwich plate structure.
The results show that when the mass of the CFRP-lattice aluminum sandwich plates is constant, the specific absorption of the optimized results can be increased by 284%. In full consideration of the deformation of the lower plates, the specific energy absorption of the optimized results can be increased by 59%.
This study shows that the proposed optimized structure of CFRP-lattice aluminum sandwich plates can effectively improve their energy absorption capacity, and the response surface method is an optimization method that can effectively improve the energy absorption characteristics of the structure.
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