The combined and interactive effects of the bolt-hole fit conditions and the preloads of the fasteners on the load carrying capacity of single-lap composite-to-titanium bolted joints have been investigated both experi...The combined and interactive effects of the bolt-hole fit conditions and the preloads of the fasteners on the load carrying capacity of single-lap composite-to-titanium bolted joints have been investigated both experimentally and numerically. Quasi-static tests of the hybrid joints with different fit conditions are implemented, and a three dimensional finite element progressive failure analysis model is proposed to predict the influences of the bolt-hole fit conditions and fastener＇s pre- loads on the mechanical behaviors of the joints. Based on the experimental validated simulation method, a multi-factor, mixed levels orthogonal design table and the analysis of variance method are used to arrange the simulation conditions and to further study the interactive effects of preloads and fit conditions. Through the analysis of the results, for the researched double bolt, single-lap composite-titanium joints, it is found that： the effects of both the interference fit and the preloads change from positive into negative mode with the increase of the interference fit values or preload values; appropriate bolt-hole fit conditions and preloads can improve the bolt-hole contact conditions of the loaded joints, and then retard the fiber failures around the fastener holes, and increase the load carrying capacity of the joints eventually; the interactive effect of the bolt-hole interference fit conditions and preloads cannot be ignored and the parameters need to be considered together and synthetically as the joints are being optimized.展开更多
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, ...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.展开更多
This paper reports the modeling method and outcomes of mechanical performance and damage evolution of single-lap bolted composite interference-fit joints under extreme temperatures.The anisotropic continuum damage mod...This paper reports the modeling method and outcomes of mechanical performance and damage evolution of single-lap bolted composite interference-fit joints under extreme temperatures.The anisotropic continuum damage model involving thermal effects is established on continuum damage mechanics which integrates the shear nonlinearity constitutive relations characterized by Romberg-Osgood equation.The temperature-induced modification of thermal strains and material properties is incorporated in stress-strain analysis,extended 3 D failure criteria and exponential damage evolution rules.The proposed model is calibrated and employed to simulate behavior of composite joints in interference fitting,bolt preloading,thermal and bearing loading processes,during which the influence of interference-fit sizes,preload levels,laminate layups and service temperatures is thoroughly investigated.The predicated interfacial behavior,bearing response and failure modes are in good agreement with experimental tests.The numerical model is even capable of reflecting some non-intuitive experimental findings such as residual stress relaxation and matrix softening at elevated temperatures.展开更多
This paper focuses on advanced analysis techniques and design considerations of DC interference generated by HVDC electrodes during normal bipolar and temporary monopolar operations on neighboring metallic utilities, ...This paper focuses on advanced analysis techniques and design considerations of DC interference generated by HVDC electrodes during normal bipolar and temporary monopolar operations on neighboring metallic utilities, with a special emphasis on buried gas and oil pipelines. This study examines the level of pipeline corrosion, the safety status in the vicinity of exposed appurtenances and the impact of DC interference on the integrity of insulating flanges and impressed current cathodic protection (ICCP) systems. Computation results obtained for different soil models show that different soils can lead to completely different DC interference effects. The results and conclusions presented here can be used as a reference to analyze the severity of DC interference on pipelines due to proximate HVDC electrodes.展开更多
In clinical practice, dentists sometimes encounter phenomena that cannot be explained by modern western medical concepts;for example, the patient’s medical symptoms improve by bringing medicines or dentures close to ...In clinical practice, dentists sometimes encounter phenomena that cannot be explained by modern western medical concepts;for example, the patient’s medical symptoms improve by bringing medicines or dentures close to the body. Although it seems difficult to completely elucidate the mechanism through modern western medicine, it can be explained using quantum mechanics. The quantum, the smallest unit of matter composition, exhibits wave-particle duality. The fact that symptoms can be improved simply by bringing dentures or medicines closer to the body indicates that the waves emitted by dentures or medicines interfere with the pathological waves emitted by the pathological site. Thus, the pathological waves are deformed and lead to a change in symptoms. In this way, quantum theory can explain phenomena that are difficult to elucidate in conventional medicine, which are encountered in clinical practice. So far, the author has presented a case of difficulty in raising the upper limb where the symptoms improved without the need for dentures in the mouth by adjusting the dentures outside the mouth. This time, the author would like to introduce a case which the patient’s knee pain improved by adjusting the dentures outside the mouth.展开更多
高低轨卫星联合覆盖系统中低轨卫星部署必须无条件规避对高轨卫星的干扰。已有研究采用基于隔离角的空域隔离多波束资源分配,或不满足国际电联的干扰规避要求,或会造成低轨卫星系统服务质量下降。针对以上问题,提出一种高低轨卫星联合...高低轨卫星联合覆盖系统中低轨卫星部署必须无条件规避对高轨卫星的干扰。已有研究采用基于隔离角的空域隔离多波束资源分配,或不满足国际电联的干扰规避要求,或会造成低轨卫星系统服务质量下降。针对以上问题,提出一种高低轨卫星联合覆盖的干扰规避多波束资源分配机制,以等效功率通量密度(Equivalent Power Flux Density,EPFD)为干扰规避约束,以最大化波位服务满意度(Beam Service Satisfaction,BSS)为目标,构建高低轨卫星联合覆盖多波束资源分配优化问题模型,并提出一种联合粒子群和遗传算法的求解算法(BSS Beam Hopping Interference Avoidance with PSO and GA,BBHIA-PG)。在系统忙时和闲时,分别与基于隔离角的联合迭代多星跳波束算法(Joint Iterative Multi-Satellite Beam Hopping,JIMS-BH)和负载均衡及功率控制多星跳波束算法(Load Balancing and Energy-Efficient Beam Hopping,LB-EE-BH)对比。仿真结果表明:基于所选取业务模型,系统最忙时,文中算法较负载均衡及功率控制和多星跳波束算法均满足等效功率通量密度门限要求;波位服务满意度方面,文中算法较负载均衡及功率控制多星跳波束算法提升7.43%,较基于隔离角的联合迭代多星跳波束算法降低3.31%;波位总吞吐量文中算法较负载均衡及功率控制多星跳波束算法提升11.91%,较基于隔离角的联合迭代多星跳波束算法提升2.99%。系统最闲时,3种算法波位服务满意度和波位总吞吐量性能一致,但隔离角的联合迭代多星跳波束资源分配算法不满足等效功率能量密度门限要求。展开更多
To analyze the effect of internal pressure on the connection strength of hydraulically expanded joints,a hydraulic expanding and push-out process of a joint of tube to sleeve was simulated by using FEM and validated b...To analyze the effect of internal pressure on the connection strength of hydraulically expanded joints,a hydraulic expanding and push-out process of a joint of tube to sleeve was simulated by using FEM and validated by experiments at various internal pressure values.The stress and residual stress in the joined pair during the joining process illustrates that the contact pressure on the interface is not uniform along the longitudinal direction.The research reveals that if the sleeve does not experience any plastic deformation,the connection strength increases with the internal pressure linearly.For sleeve material with yield point elongation,if the sleeve experiences some degree of plastic deformation,there is an internal pressure interval in which the connection strength decreases slightly as internal pressure increases.Therefore,the internal pressure should be controlled depending on the deformation of the sleeve,but not as high as possible.The simulated results are in good agreement with those from experiments.展开更多
文摘The combined and interactive effects of the bolt-hole fit conditions and the preloads of the fasteners on the load carrying capacity of single-lap composite-to-titanium bolted joints have been investigated both experimentally and numerically. Quasi-static tests of the hybrid joints with different fit conditions are implemented, and a three dimensional finite element progressive failure analysis model is proposed to predict the influences of the bolt-hole fit conditions and fastener＇s pre- loads on the mechanical behaviors of the joints. Based on the experimental validated simulation method, a multi-factor, mixed levels orthogonal design table and the analysis of variance method are used to arrange the simulation conditions and to further study the interactive effects of preloads and fit conditions. Through the analysis of the results, for the researched double bolt, single-lap composite-titanium joints, it is found that： the effects of both the interference fit and the preloads change from positive into negative mode with the increase of the interference fit values or preload values; appropriate bolt-hole fit conditions and preloads can improve the bolt-hole contact conditions of the loaded joints, and then retard the fiber failures around the fastener holes, and increase the load carrying capacity of the joints eventually; the interactive effect of the bolt-hole interference fit conditions and preloads cannot be ignored and the parameters need to be considered together and synthetically as the joints are being optimized.
基金funded by China Postdoctoral Science Foundation(No.2020M673227)NSAF,China(No.U1830122)Sichuan Science and Technology Program,China(No.2020YFG0109)。
文摘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.
基金finically supported by Joint Found for Equipment Advance Research and Aerospace Science and Technology of China(No.6141B061401)Fund for Distinguished Young Scholars in Shaanxi Province of China(No.2018-JC-009)。
文摘This paper reports the modeling method and outcomes of mechanical performance and damage evolution of single-lap bolted composite interference-fit joints under extreme temperatures.The anisotropic continuum damage model involving thermal effects is established on continuum damage mechanics which integrates the shear nonlinearity constitutive relations characterized by Romberg-Osgood equation.The temperature-induced modification of thermal strains and material properties is incorporated in stress-strain analysis,extended 3 D failure criteria and exponential damage evolution rules.The proposed model is calibrated and employed to simulate behavior of composite joints in interference fitting,bolt preloading,thermal and bearing loading processes,during which the influence of interference-fit sizes,preload levels,laminate layups and service temperatures is thoroughly investigated.The predicated interfacial behavior,bearing response and failure modes are in good agreement with experimental tests.The numerical model is even capable of reflecting some non-intuitive experimental findings such as residual stress relaxation and matrix softening at elevated temperatures.
文摘This paper focuses on advanced analysis techniques and design considerations of DC interference generated by HVDC electrodes during normal bipolar and temporary monopolar operations on neighboring metallic utilities, with a special emphasis on buried gas and oil pipelines. This study examines the level of pipeline corrosion, the safety status in the vicinity of exposed appurtenances and the impact of DC interference on the integrity of insulating flanges and impressed current cathodic protection (ICCP) systems. Computation results obtained for different soil models show that different soils can lead to completely different DC interference effects. The results and conclusions presented here can be used as a reference to analyze the severity of DC interference on pipelines due to proximate HVDC electrodes.
文摘In clinical practice, dentists sometimes encounter phenomena that cannot be explained by modern western medical concepts;for example, the patient’s medical symptoms improve by bringing medicines or dentures close to the body. Although it seems difficult to completely elucidate the mechanism through modern western medicine, it can be explained using quantum mechanics. The quantum, the smallest unit of matter composition, exhibits wave-particle duality. The fact that symptoms can be improved simply by bringing dentures or medicines closer to the body indicates that the waves emitted by dentures or medicines interfere with the pathological waves emitted by the pathological site. Thus, the pathological waves are deformed and lead to a change in symptoms. In this way, quantum theory can explain phenomena that are difficult to elucidate in conventional medicine, which are encountered in clinical practice. So far, the author has presented a case of difficulty in raising the upper limb where the symptoms improved without the need for dentures in the mouth by adjusting the dentures outside the mouth. This time, the author would like to introduce a case which the patient’s knee pain improved by adjusting the dentures outside the mouth.
文摘高低轨卫星联合覆盖系统中低轨卫星部署必须无条件规避对高轨卫星的干扰。已有研究采用基于隔离角的空域隔离多波束资源分配,或不满足国际电联的干扰规避要求,或会造成低轨卫星系统服务质量下降。针对以上问题,提出一种高低轨卫星联合覆盖的干扰规避多波束资源分配机制,以等效功率通量密度(Equivalent Power Flux Density,EPFD)为干扰规避约束,以最大化波位服务满意度(Beam Service Satisfaction,BSS)为目标,构建高低轨卫星联合覆盖多波束资源分配优化问题模型,并提出一种联合粒子群和遗传算法的求解算法(BSS Beam Hopping Interference Avoidance with PSO and GA,BBHIA-PG)。在系统忙时和闲时,分别与基于隔离角的联合迭代多星跳波束算法(Joint Iterative Multi-Satellite Beam Hopping,JIMS-BH)和负载均衡及功率控制多星跳波束算法(Load Balancing and Energy-Efficient Beam Hopping,LB-EE-BH)对比。仿真结果表明:基于所选取业务模型,系统最忙时,文中算法较负载均衡及功率控制和多星跳波束算法均满足等效功率通量密度门限要求;波位服务满意度方面,文中算法较负载均衡及功率控制多星跳波束算法提升7.43%,较基于隔离角的联合迭代多星跳波束算法降低3.31%;波位总吞吐量文中算法较负载均衡及功率控制多星跳波束算法提升11.91%,较基于隔离角的联合迭代多星跳波束算法提升2.99%。系统最闲时,3种算法波位服务满意度和波位总吞吐量性能一致,但隔离角的联合迭代多星跳波束资源分配算法不满足等效功率能量密度门限要求。
文摘To analyze the effect of internal pressure on the connection strength of hydraulically expanded joints,a hydraulic expanding and push-out process of a joint of tube to sleeve was simulated by using FEM and validated by experiments at various internal pressure values.The stress and residual stress in the joined pair during the joining process illustrates that the contact pressure on the interface is not uniform along the longitudinal direction.The research reveals that if the sleeve does not experience any plastic deformation,the connection strength increases with the internal pressure linearly.For sleeve material with yield point elongation,if the sleeve experiences some degree of plastic deformation,there is an internal pressure interval in which the connection strength decreases slightly as internal pressure increases.Therefore,the internal pressure should be controlled depending on the deformation of the sleeve,but not as high as possible.The simulated results are in good agreement with those from experiments.
