To fabricate large-scale or unusually shaped composite structures, pieces of fabric plies can be spliced to match size and shape requirements, forming ply splice structures. The junction of different plies can be considered as a defect in the resulting composite material, affecting the overall mechanical properties. In this paper, unidirectional carbon fiber-reinforced plastic (CFRP) with ply splices was used as a research object to study these potential material defects. The effects of ply splices at different positions on the tensile properties of CFRP and the coupling between position of ply splicing were analyzed. Simultaneously, a finite element model was established to analyze the damage evolution, in which a continuous damage model and a cohesive zone model were used to describe the damage of the composite and interface layers, respectively. The model results were in good agreement with observed experimental results. Our results showed that there were three main factors for this failure mechanism: boundary effects, whether the ply splices were independent, or whether they were close to each other. In short, when two ply splices were located at the edge or independent of each other, the failure mode was first delamination and then fiber fracture, and the tensile strength was high. However, when the two ply splices were close to the edge or close to each other, the failure mode was first local fiber fracture and then delamination damage, and the resulting tensile strength was low. Finally, different reinforcement methods to improve the tensile properties of composites were adopted for the splicing layers at different positions through the analysis via model simulation. The two-side patch repair method was used to reinforce the ply splices on or near the edge. Additionally, increasing the toughness of the adhesive layer was used to reinforce the ply splices that were inside the material. These results showed that the tensile strength was enhanced by these two methods of reinforcement, and the initial damage load was especially increased.
To fabricate large-scale or unusually shaped composite structures, pieces of reinforcement plies can be spliced to match specific size and shape requirements, forming ply splice structures. The junction of different plies can be considered a defect in the final material, affecting the mechanical properties. In this paper, ply splice carbon fiber reinforced plastics were studied to analyze the fracture mechanism caused by the ply splice, including the effects of the junction geometry and the ply angle. Tensile tests were performed, assisted with digital image correlation for strain distribution analysis and acoustic emission for break mode analysis. The finite element method was also performed using ABAQUS software to study the fracture mechanism. In order to analyze the interlaminar fracture, the interface was simulated with cohesive elements. The results showed that, for a unidirectional carbon fiber reinforced plastics with ply splice, fracturing occurred first at the junction location and then at the interfaces between the splicing layers and the continuous layers. The final strength was determined by the number of continuous layers. The ply-angle had evident effects on the properties of carbon fiber reinforced plastics with ply splices. For a stacking sequence of [± 30°]5S, the effects of the ply splice on the strength and the fracture mode were similar to the effect with unidirectional plates. For a stacking sequence of [± 45°]5S, the ply splice had no effect on the fracture mode, but it did decrease the strength slightly. For a stacking sequence of [± 60°]5S, almost no effect of the ply splice structure could be observed. PACS (optional, as per journal): 75.40.-s; 71.20.LP
The competition of comprehensive strength between nations is fundamentally the competition of talents. To make a nation powerful, the firth thing is to improve higher education because cultivation of talents must depend on education. Similarly, to make an army powerful, education also should be strong firstly. The important mission of training of senior scientific and technical and commanding talents for the building of national defense and armed forces is undertaken by National University of Defense Technology. On the basis of analyzing the reason and significance of the hierarchical culture, combining the analysis of the research of "Tsien Hsueshen Innovation Development Class " of the university, the conclusion can be reached that the "Tsien Hsueshen Innovation Development Class" is new hierarchical culture model conformed to the law of personnel training objective and actual demand. Corresponding suggestions are put forward about the hierarchical culture and the construction of "Tsien Hsueshen Innovation Development Class " based on the research results.
Punching shear failure of slab-column connections can cause the progressive collapse of a structure. In this study, a punching test database is first established. Then, based on the Levenberg–Marquardt (LM) algorithm and using the nonlinear function of the backpropagation neural network (BPNN), a prediction model of the punching capacity of slab-column connections without transverse reinforcement is established. Finally, the proposed model is compared with the formulas of the Chinese, American, and European standards using several methods. The statistical eigenvalue method shows that the BPNN model has the highest accuracy and the lowest dispersion. The defect point counting method shows that the BPNN model had the fewest total number of defects and was the safest and most economical. The influencing factor analysis suggests that factors in the BPNN model had the most reasonable influence on the punching bearing capacity of slab-column connections. Finally, the model is verified using a case study and the Matlab program. The results show that the average error of the formulas in the Chinese, American, and European standards are 21.08%, 30.21%, and 11.47%, respectively, higher than that of the BPNN model.
Abstract:The design and construction level of power grids are increasing rapidly with the development of China's power industry. The tower of Transmission line has become an important forced fulcrum. Safety and economy are basic requirements of conventional structural design. However, making the transmission lines and the environment in harmony and unity challenges structural designers. In this paper, a new-type transmission tower--bamboo transmission tower is designed and researched on the basis of a practical project. It can be found that the new-type of transmission tower makes the tower and the environment in harmony and unity when it meets the safety and economy requirements.
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