•Dynamic cold expansion (DCE) based on electromagnetic load was proposed.•DCE showed lower resistance than static cold expansion (SCE).•DCE samples show evener hole diameter than SCE samples along ...axial direction.•DCE specimens exhibited more fatigue life improvement than SCE specimens.•DCE specimens show different crack propagation compared to SCE specimens.
In this study, a novel dynamic cold expansion (DCE) method based on electromagnetic load was developed to enhance the fatigue life of open hole structures. The experiments were conducted to investigate the enhance properties of DCE method, and the corresponding static cold expansion (SCE) method was also investigated as comparison. The expansion resistance was evaluated. The geometric dimension varieties of holes after cold expansion were measured. Moreover, the fatigue life of specimens after DCE and SCE were assessed, and the fatigue failure mechanism was discussed. Results showed that DCE method can obviously reduce expansion resistance compared with SCE method and generate more uniform hole diameter distribution along the hole axial direction after cold expansion. In fatigue tests, specimens worked by DCE exhibited the higher fatigue life than that worked by SCE, especially under high load level. Furthermore, DCE method was also observed to have significant effects on fatigue crack initiation and propagation of specimens.
In this study, experiments and finite element analysis (FEA) were used to evaluate the impact of interference-fit sizes on CFRP hybrid bonded-bolted (HBB) joint damage during bolt insertion. The ...specimens were designed in accordance with the ASTM D5961 standard and bolt insertion tests were performed at selected interference-fit sizes (0.4%, 0.6%, 0.8%, and 1%). Damage to composite laminates was predicted using the Shokrieh-Hashin criterion and Tan's degradation rule via the user subroutine USDFLD, while damage to the adhesive layer was simulated by the Cohesive Zone Model (CZM). The corresponding bolt insertion tests were performed. The variation of insertion force with interference-fit size was discussed. The results showed that matrix compressive failure was the main failure mode. With the growth of the interference-fit size, more failure modes appeared, and the failure region expanded. Regarding the adhesive layer, it did not completely fail at the four interference-fit sizes. This paper will be helpful in designing composite joint structures and especially for understanding CFRP HBB joint damage and failure mechanisms.
CFRP/Ti bolted joints are increasingly used in aircraft structures. Optimizing the joint design is vital for overall composite structure designs. Therefore, a progressive damage model was developed ...for investigating the effects of clearance and interference sizes on the damage and failure of CFRP/Ti double-lap, single-bolt joints under quasi-static loads, in which the improved three dimensional Hashin failure criterion and Tan degradation rules were used through an ABAQUS user-define-field (USDFLD) subroutine. The corresponding quasi-static tensile tests and fatigue tests were also conducted. Joints strength were evaluated and failure mechanism was discussed. Numerical results showed that the matrix compression failure dominated the joint failure mode. Joint ultimate strength decreased gradually with the increase of clearance sizes, while joint bearing strength and stiffness exhibited an increase with interference sizes at first and then decreased rapidly due to the initial installation damage. Moreover, the maximum strength was achieved at the interference size of 0.5%. Those results were in well agreement with corresponding experimental results. In addition, interference sizes were also revealed a correlation with the fatigue life of the joints. The study presented here will be useful for optimization of composite structure designs.
CFRP/Ti pinned joints are widely applied on main load-bearing structures of aircrafts. Understanding the dynamic behavior of the joints is important for optimal joint designs. Therefore, a dynamic ...test platform based on electromagnetic loading method was developed to investigate the dynamic behavior of CFRP/Ti single-lap pinned joints under tensile dynamic loading. Bearing and failure loads of the joints were evaluated, and the dynamic failure mechanism was discussed. The test results demonstrated that both bearing and failure loads decreased with impact velocity, which is consistent with the literature. Failure modes of the joints were dominated by CFRP failure. High-rate joints failed first in bearing failure mode, but ultimately experienced tearing-out failure. Moreover, much fiber and matrix fracture was observed during dynamic loading progress. A study of interference size also revealed a correlation with the dynamic behavior of the joints, which will help to optimize joint designs.
Interference fit has advantages in improving fatigue behaviors of composite bolted joints; however, interference fit bolt insertion tends to cause damages in laminates weakening joint mechanical ...properties. Therefore, an experimental study was conducted to investigate bolt insertion damages of Carbon Fiber Reinforced Polymer (CFRP)/CFRP interference fit bolted joints. Mechanical behaviors of joints were also evaluated experimentally under both quasi-static loads and cyclic loads. Scanning Electron Microscope (SEM) and high-resolution X-ray micro-CT scan were used to examine micro damages in laminates. Damage and failure behaviors of joints were characterized. The results demonstrated that the hole entrance in upper laminate and the laminate boundary near the hole wall were the most critical regions for damages during bolt insertions. However, the influence of those damages on quasi-static failure loads and fatigue failure modes of joints was minimal. Delamination and matrix cracking occurred first in laminates following fiber and matrix fracture in quasi-static tensile tests. Interference fit could improve the fatigue resistance of the laminate hole; however, the bolt seemed to suffer a more critical local fatigue loading condition. This paper can contribute to composite structure designs, especially in understanding damage and failure behaviors of composite bolted joints.
Foams are widely used in protective applications requiring high energy absorption under impact, and evaluating impact properties of foams is vital. Therefore, a novel test method based on a shock ...tube was developed to investigate the impact properties of closed-cell polyethylene (PE) foams at strain rates over 6000 s−1, and the test theory is presented. Based on the test method, the failure progress and final failure modes of PE foams are discussed. Moreover, energy absorption capabilities of PE foams were assessed under both quasi-static and high strain rate loading conditions. The results showed that the foam exhibited a nonuniform deformation along the specimen length under high strain rates. The energy absorption rate of PE foam increased with the increasing of strain rates. The specimen energy absorption varied linearly in the early stage and then increased rapidly, corresponding to a uniform compression process. However, in the shock wave deformation process, the energy absorption capacity of the foam maintained a good stability and exhibited the best energy absorption state when the speed was higher than 26 m/s. This stable energy absorption state disappeared until the speed was lower than 1.3 m/s. The loading speed exhibited an obvious influence on energy density.
To mitigate the challenges pertaining to coating damage and processing defects arising from the utilization of ultrafast laser drilling for microhole creation in thermal barrier coatings (TBCs), ...thereby exerting substantial influence on the long-term durability of these microholes, the investigation proposes a comprehensive methodology. It encompasses the design of a two-factor four-level full factorial experiment and the execution of experimental research on picosecond laser drilling of TBC microholes. By meticulously analyzing the morphology of the microholes and the coating interface, the damage mechanisms associated with picosecond laser drilling of TBC microholes, as well as the influence of laser process parameters on coating damage, are revealed. The findings reveal that the optimal microhole entrance quality and the lowest roughness along the hole perimeter are attained at a laser power of 12 W and a scanning speed of 320 mm/s. Moreover, at a laser power of 30 W and a scanning speed of 320 mm/s, the minimal crack length on the blunt angle side of the hole and the highest machining quality are observed.
Carbon fiber reinforced composites (CFRP) are prone to occur riveting damage. Therefore, the damage behaviors and mechanical properties of CFRP/CFRP washer-bushing riveted joints were investigated ...experimentally in this paper. Results showed that due to the uneven expansion of rivet shank and local pressure caused by upsetting head, CFRP/CFRP riveted joints occurred multiple damage modes by using net riveting method and bushing method. The damage was mainly located in the layer around the CFRP hole near the upsetting head. However, washer-bushing riveting method effectively limited the uneven expansion and the local pressure of upsetting head, and no obvious damage was observed. Load-displacement curves of direct riveted joints and washer-bushing riveted joints exhibited obvious linear stage, progressive damage stage and final failure stage in both tensile shear and pull-off tests. However, the bushing reduced the effective fastening area of upsetting head, and load-displacement curves of bushing riveted joints only included linear and failure stages. Besides, the tensile shear and pull-off peak load were also the lowest. Tensile failure modes of both net riveted joints and washer-bushing riveted joints were dominated by the coupling failure mode of shear failure and rivet pull-off. The CFRP connecting hole was observed with obvious shear damage and extrusion deformation area. Besides, pull-off failure modes were laminate fracture and ply delamination, and also accompanied by laminate bending deformation. In contrast, bushing riveted joints failed by rivet pull-off in both tensile shear and pull-off tests.
碳纤维增强复合材料(CFRP)易发生铆接损伤, 通过试验方法开展垫圈/衬套铆接损伤行为及其拉剪性能研究, 研究结果表明: 镦头不均匀膨胀及下压会导致净铆接和衬套铆接出现不同程度、多损伤模式铆接损伤, 而垫圈/衬套铆接后并未出现明显损伤。净铆接试件与垫圈/衬套铆接试件的拉剪力-位移响应呈现出明显的线性、渐进损伤和失效破坏的特征, 而衬套铆接由于减小了镦头与层板的有效紧固面积, 衬套铆接试件拉剪力-位移响应仅包含线性和失效破坏阶段, 其拉剪峰值载荷亦最低。净铆接试件和垫圈/衬套铆接试件的拉伸失效模式均为层板剪切与铆钉拉脱耦合失效, 拉脱失效模式为层板铺层断裂和分层, 且伴有层板弯曲变形; 衬套铆接试件拉剪过程中均发生铆钉直接拉脱破坏。
Vascular embolic diseases are associated with blockage of blood supply to vital organs and thus are lethal. Aspiration thrombectomy is becoming the primary choice for revascularization in the ...treatment of vascular occlusions condition. As the power source in the aspiration thrombectomy procedure, the aspiration pump directly influences the outcome of the operation. This research surveyed the current technical developments of the aspiration pump in China through reviewing information obtained from the patent database and technical literatures, commented on the issues in the current patent designs, and gave suggestions for future design improvement. This study can be used as a reference for researchers and developers of medical devices besides the neurosurgeons.
•Summarized the concurrent development of aspiration pump used in thrombectomy.•Commented on the problems in the current patent designs in the area.•Suggested directions for future design improvement of the aspiration pump.
With the increasing applications of novel materials and structures in new-generation aircraft, conventional joining techniques in aircraft component assembly are greatly challenged. To meet those ...challenges, the electromagnetic riveting (EMR) technique was developed as an advanced joining tool, which exhibits obvious advantages in the assembly of new-generation aircraft. In this paper, the riveting principle of EMR was analyzed, and its development history and status were presented in detail. Then, equipment features of three typical EMR systems were given. Moreover, three important applications of EMR were covered, i.e., composite structure riveting, titanium rivet and large-size aluminum rivet riveting, and interference fit bolt installation. Specially, a novel strengthening method for mechanical linking holes based on EMR was also presented, which can significantly improve the fatigue behaviors of mechanical joints. Finally, open questions in the EMR field were discussed, and some recommendations for future work were also made. This paper can be useful for optimizing the joint designs of aircraft components and improving the level of aircraft maintenance.
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