Applied Composite Materials最新文献_第10页

Impact and Post-Impact Damage Response of Interlayer Nonwoven Reinforced Hybrid Composites 层间无纺布增强混合复合材料的冲击和冲击后损伤响应

IF 2.3 4区材料科学

Applied Composite Materials Pub Date : 2024-02-14 DOI: 10.1007/s10443-024-10205-4

Tebernuş Tiyek, Gaye Kaya

{"title":"Impact and Post-Impact Damage Response of Interlayer Nonwoven Reinforced Hybrid Composites","authors":"Tebernuş Tiyek, Gaye Kaya","doi":"10.1007/s10443-024-10205-4","DOIUrl":"10.1007/s10443-024-10205-4","url":null,"abstract":"<div><p>This study aims to increase the ductility and the damage tolerance capability of composite structures with interlayer nonwoven reinforcement. The novelty of this study stems from its innovative approach: a comprehensive examination of the arrangement of warp and weft fibres, as well as the preform layer, coupled with both intra-layer and inter-layer hybridization, all while accounting for the incorporation of nonwoven reinforcement. The flexural, compressive, impact and post-impact compressive strengths of unreinforced and interlayer nonwoven reinforced glass/carbon/epoxy hybrid composites are carefully investigated and compared. The nonwoven reinforcement led to a reduction in flexural strength and modulus for composite structures, while enhancing their strain, thus imparting greater ductility to the structure. Both hybridization and interlayer nonwoven reinforcement increased the peak forces of composites while reducing deformations. The cracks occurring in the composite structure under load were arrested by the barrier created by the nonwoven surfaces used between the layers, which was considered an enhancement in the damage tolerance of composite structures.</p></div>","PeriodicalId":468,"journal":{"name":"Applied Composite Materials","volume":"31 3","pages":"1083 - 1107"},"PeriodicalIF":2.3,"publicationDate":"2024-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139752945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Multi-Cellular 3D Flat-Knitted Composite Panels Strengthened by PU-Foam: Manufacturing, Testing and Simulating 由聚氨酯泡沫加固的多孔 3D 扁平针织复合板：制造、测试和模拟

IF 2.3 4区材料科学

Applied Composite Materials Pub Date : 2024-02-14 DOI: 10.1007/s10443-024-10204-5

Atefeh Raji, Hossein Hasani, Sanaz Hassanzadeh

{"title":"Multi-Cellular 3D Flat-Knitted Composite Panels Strengthened by PU-Foam: Manufacturing, Testing and Simulating","authors":"Atefeh Raji, Hossein Hasani, Sanaz Hassanzadeh","doi":"10.1007/s10443-024-10204-5","DOIUrl":"10.1007/s10443-024-10204-5","url":null,"abstract":"<div><p>Composite panels made-up of multi-cellular 3D flat-knitted (M3DFK) fabrics were manufactured in this research and mechanically evaluated in order to analyze their bending functionality after being filled with polyurethane (PU) foam. Using an electronic flat knitting machine, two different groups of M3DFK fabrics varied in their cross-sectional shapes were initially prepared from glass/polyester yarns and then, being molded through vacuum injection method with epoxy resin. A three-point bending test was used to experimentally evaluate the mechanical performance of PU-foam filled composite panels. Also, the composites mechanical behaviors were theoretically investigated using the multi-scale modeling method. The results indicated that the reinforcement structural geometries and foam presence in the composite specimens have a significant impact on their bending properties. The empirical findings revealed that foam injection resulted in a 113.8% and 92.3% increase in energy absorption for double- and single-decker composite structures during the bending process, respectively. According to the results, foam-filled composite structures experience a significant increase in core shear and facing stresses. This increase amounts to 18.4% for the single-decker and 84.7% for the double-decker 3D structure. The results of the simulation method were used to understand the effect of composite structure as well as foam injection on the stress distribution and maximum stress applied during the bending process. Also, no delamination between foam and facing layers was observed.</p></div>","PeriodicalId":468,"journal":{"name":"Applied Composite Materials","volume":"31 3","pages":"1109 - 1130"},"PeriodicalIF":2.3,"publicationDate":"2024-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139752939","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

An Efficient Optimization Method for Stacking Sequence of Composite Pressure Vessels Based on Artificial Neural Network and Genetic Algorithm 基于人工神经网络和遗传算法的复合压力容器堆叠顺序高效优化方法

IF 2.3 4区材料科学

Applied Composite Materials Pub Date : 2024-02-11 DOI: 10.1007/s10443-024-10201-8

Jianguo Liang, Zemin Ning, Yinhui Li, Haifeng Gao, Jianglin Liu, Wang Tian, Xiaodong Zhao, Zhaotun Jia, Yuqin Xue, Chunxiang Miao

{"title":"An Efficient Optimization Method for Stacking Sequence of Composite Pressure Vessels Based on Artificial Neural Network and Genetic Algorithm","authors":"Jianguo Liang, Zemin Ning, Yinhui Li, Haifeng Gao, Jianglin Liu, Wang Tian, Xiaodong Zhao, Zhaotun Jia, Yuqin Xue, Chunxiang Miao","doi":"10.1007/s10443-024-10201-8","DOIUrl":"10.1007/s10443-024-10201-8","url":null,"abstract":"<div><p>This paper proposes an efficient optimization method for the stacking sequence of composite pressure vessels based on the joint application of finite element analysis (FEA), artificial neural network (ANN), and genetic algorithm (GA). The composite pressure vessel has many winding layers and varied angles, and the stacking sequence of the composite pressure vessel affects its performance. It is essential to carry out the optimal design of the stacking sequence. The experimental cost for optimal design of composite pressure vessels is high, and numerical simulation is time-consuming. ANN is used to predict the fiber direction stress of composite pressure vessels, which replaces FEA in the optimization process of GA effectively. In addition, the optimization efficiency of the optimization method proposed in this paper can be improved significantly when the neural network model is employed. The optimization results show that the peak stress in the fiber direction can be reduced by 37.3% with the design burst pressure. The burst pressure of the composite pressure vessel can be increased by 13.4% by optimizing the stacking sequence of composite pressure vessels while keeping the number of plies and the winding angle unchanged. The results imply that the work undertaken in this paper is of great significance for the improvement of the safety performance of composite pressure vessels.</p></div>","PeriodicalId":468,"journal":{"name":"Applied Composite Materials","volume":"31 3","pages":"959 - 982"},"PeriodicalIF":2.3,"publicationDate":"2024-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139773123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Design of Z-fiber Guiding Needle for Composite Material Preform with Large-Thickness and High-Density 用于大厚度和高密度复合材料预成型的 Z 纤维导向针设计

IF 2.3 4区材料科学

Applied Composite Materials Pub Date : 2024-02-04 DOI: 10.1007/s10443-023-10196-8

Rui Jia, Junwei Qi, Yuequan Wang, Jiaqi Shi, Guannan Li

{"title":"Design of Z-fiber Guiding Needle for Composite Material Preform with Large-Thickness and High-Density","authors":"Rui Jia, Junwei Qi, Yuequan Wang, Jiaqi Shi, Guannan Li","doi":"10.1007/s10443-023-10196-8","DOIUrl":"10.1007/s10443-023-10196-8","url":null,"abstract":"<div><p>Traditional carbon fiber reinforced carbon matrix composites are mostly two-dimensional laminated structures with low interlayer properties. Z-fiber reinforcement technology can improve the properties of composites in the thickness direction. However, the low axial modulus of Z-fiber results in insufficient stiffness, and its implanting in large-thickness preforms is susceptible to buckling due to heavy resistance. The existing Z-fiber implantation techniques are challenging to realize the Z-direction reinforcement of large-thickness and high-density preforms. Therefore, this paper proposes a method of using hollow tubes to guide Z-fiber implantation into preforms and puts forward an improved solution for the issue of buckling during the insertion of hollow tube into the preform. A cutting edge was designed for the hollow tube, and a metal rod was utilized to provide support. The enhanced hollow tube was named \"Z-fiber guiding needle.\" A mechanical model of the Z-fiber guiding needle inserted into the preform was established to optimize needle parameters. Then Abaqus software was used to study the strength and stiffness of the needle, as well as analyze its stability. Finally, experimentally verifies the Z-fiber guiding needle. The final results show that the strength, stiffness, and stability of the designed Z-fiber guiding needle can meet the requirements of implantation. This proves the designed method is correct and feasible, and provides a theoretical basis for the design of ultra-long needles used to guide Z-fiber implants into large-thickness, high-density composite material preforms.</p><h3>Graphical Abstract</h3>\u0000<div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":468,"journal":{"name":"Applied Composite Materials","volume":"31 3","pages":"1031 - 1052"},"PeriodicalIF":2.3,"publicationDate":"2024-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139773135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Investigating the Influence of Tufting Parameters on the Lap Joint Strength of Composite Parts Assembled Using Tufting Technology 研究簇绒参数对使用簇绒技术组装的复合材料部件搭接强度的影响

IF 2.3 4区材料科学

Applied Composite Materials Pub Date : 2024-02-01 DOI: 10.1007/s10443-023-10200-1

Jian Hu, Chan Hui, Xavier Legrand, Jue Zhao, Hao Shen, Peng Wang

引用次数: 0

Damage Recognition of Acoustic Emission and Micro-CT Characterization of Bi-adhesive Repaired Composites Based on the Machine Learning Method 基于机器学习方法的声发射损伤识别和双粘合修复复合材料的显微 CT 表征

IF 2.3 4区材料科学

Applied Composite Materials Pub Date : 2024-01-31 DOI: 10.1007/s10443-024-10202-7

Xiao-long Ji, Yu-jiao Liang, Jia-yan Zheng, Lian-hua Ma, Wei Zhou

{"title":"Damage Recognition of Acoustic Emission and Micro-CT Characterization of Bi-adhesive Repaired Composites Based on the Machine Learning Method","authors":"Xiao-long Ji, Yu-jiao Liang, Jia-yan Zheng, Lian-hua Ma, Wei Zhou","doi":"10.1007/s10443-024-10202-7","DOIUrl":"10.1007/s10443-024-10202-7","url":null,"abstract":"<div><p>Bi-adhesive repair method is one of several repair technologies that use the adhesive bonding approach for patch-repaired composites. However, these repairs are subject to matrix-cracking and interface debonding damage. Furthermore, a change in the length ratio (the length of the rigid adhesive region divided by the length of the overall repaired region) also produces a change in the damage modes, which has a significant impact on the repair performance. Hence, this study aims to evaluate the effects of four different length ratios (0, 0.2, 0.5, 1) on the behavior of damage evolution in bi-adhesive repaired composites. The acoustic emission damage identification and micro-CT characterization are carried out based on the machine learning method. A simple prediction method is employed to distinguish damage modes in bi-adhesive repaired composites, achieving a prediction accuracy over 90%. The results demonstrated that the length ratio has a substantial effect on matrix-cracking, fiber-matrix debonding, and their interaction in bi-adhesive repaired composites. These acquired characteristics information of acoustic emission signals provide insights into the impact of length ratio on the progression of damage evolution. Additionally, the visualization of interior damage offers insights into the variations in failure characteristics within distinct bi-adhesive repaired composites, thereby supporting the conclusions gained from acoustic emission studies. This research effectively achieves the real-time monitoring of damage modes in bi-adhesive repaired composites, contributing to the comprehension of the relationship between length ratio and damage mechanism.</p></div>","PeriodicalId":468,"journal":{"name":"Applied Composite Materials","volume":"31 3","pages":"841 - 864"},"PeriodicalIF":2.3,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139649218","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Copper Modified Boron Nitride And Graphene Combined To Self-Assemble Three-Dimensional Thermal Conductivity Framework to Improve the Thermal Conductivity of Epoxy Resin 结合铜改性氮化硼和石墨烯自组装三维导热框架以改善环氧树脂的导热性能

IF 2.3 4区材料科学

Applied Composite Materials Pub Date : 2024-01-22 DOI: 10.1007/s10443-023-10195-9

Shuo Li, Wei Wu, Dietmar Drummer, Florian Tomiak, Yi Wang, Zijian Lu, Xintong Zhao

{"title":"Copper Modified Boron Nitride And Graphene Combined To Self-Assemble Three-Dimensional Thermal Conductivity Framework to Improve the Thermal Conductivity of Epoxy Resin","authors":"Shuo Li, Wei Wu, Dietmar Drummer, Florian Tomiak, Yi Wang, Zijian Lu, Xintong Zhao","doi":"10.1007/s10443-023-10195-9","DOIUrl":"10.1007/s10443-023-10195-9","url":null,"abstract":"<div><p>With the development of integrated circuits and the miniaturization/ integration of electronic devices, heat dissipation solutions have become an increasingly important issue. The thermal conductivity of polymer-based thermal management materials is typically influenced by the amount of incorporated fillers. However, an innovative solution to increase the thermal conductivity without increasing the total filler content is the improvement of the filler connectivity by using specific surface modifications. Surface modifications using thermal conductive submicron particles can reduce the interfiller distances, acting as thermal bridges between the particles. In this paper, copper submicron particles modified BN (BN@CuSMPs) have been prepared by in situ reduction and mixed with graphene oxide (GO). A three-dimensional BN@CuSMPs/rGO aerogel (CBGA) framework with \"point-surface\" connection has been prepared by using the self-assembly mode of GO. CBGA/EP composites were then prepared using epoxy resin (EP) as matrix and a vacuum assisted impregnation method. The thermal conductivity of CBGA/EP composites has been found to be 1.918 W m<sup>−1</sup> K<sup>−1</sup> using a filler content of 19.61%, which was 12.8% higher than that of BN/rGO/EP composites and 909.5% higher than that of pure EP. The thermal resistance of the composites was analyzed using the Foygel model. It was found that the introduction of CuSMPs effectively decreased the thermal resistance between the BN particles, forming a thermal conductive three dimensional network inside the polymer-based material system.</p></div>","PeriodicalId":468,"journal":{"name":"Applied Composite Materials","volume":"31 3","pages":"897 - 910"},"PeriodicalIF":2.3,"publicationDate":"2024-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139551722","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Effects of Energy Director Types on the Interface Morphology and Tensile Properties of Ultrasonically Welded CF/PAEK Joints 能量导向器类型对 CF/PAEK 超声波焊接接头界面形态和拉伸性能的影响

IF 2.3 4区材料科学

Applied Composite Materials Pub Date : 2024-01-18 DOI: 10.1007/s10443-023-10199-5

Li Xiao, Binbin Li, Hengchang Bu, Qiyu Gao, Xiaodong Li, Xiaohong Zhan

{"title":"Effects of Energy Director Types on the Interface Morphology and Tensile Properties of Ultrasonically Welded CF/PAEK Joints","authors":"Li Xiao, Binbin Li, Hengchang Bu, Qiyu Gao, Xiaodong Li, Xiaohong Zhan","doi":"10.1007/s10443-023-10199-5","DOIUrl":"10.1007/s10443-023-10199-5","url":null,"abstract":"<div><p>This study investigates the impact of ultrasonic welding amplitudes and time on the properties of carbon fiber reinforced polyaryletherketone (CF/PAEK) composite joints. To enhance the performance of CF/PAEK ultrasonic welded joints, a hybrid energy director (ED) was proposed, which was composed of the interfacial microgroove and resin film or metal mesh. This study investigated the effect of different types of ED on the forming quality, shear failure load, and fracture interface microstructure of single lap joints made of CF/PAEK. The results indicated that the hybrid ED with resin film offers a distinct effect on enhancing the strength of ultrasonic welded joints. The hybrid ED with resin film essentially improves the tensile properties of the joint, with the strength and toughness increased by 35.8% and 174.3%, respectively. This strengthening effect is primarily attributed to the added resin film providing adequate interfacial resin. Sufficient resin is filled into the interior of the microgroove, ultimately forming a mechanical anchoring structure to strengthen the joint strength.</p></div>","PeriodicalId":468,"journal":{"name":"Applied Composite Materials","volume":"31 3","pages":"865 - 880"},"PeriodicalIF":2.3,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139497593","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Design and Development of 2D Woven Auxetic Fabric and Composites Based on Wave Form Geometry 基于波形几何的二维编织助剂织物和复合材料的设计与开发

IF 2.3 4区材料科学

Applied Composite Materials Pub Date : 2024-01-12 DOI: 10.1007/s10443-023-10197-7

Shivangi Shukla, Jaya Sharma, Shreyansh Jain, B. K. Behera

{"title":"Design and Development of 2D Woven Auxetic Fabric and Composites Based on Wave Form Geometry","authors":"Shivangi Shukla, Jaya Sharma, Shreyansh Jain, B. K. Behera","doi":"10.1007/s10443-023-10197-7","DOIUrl":"10.1007/s10443-023-10197-7","url":null,"abstract":"<div><p>Auxetic materials differ from typical materials in that they expand in the transverse direction when stretched longitudinally, giving them special features. It is possible to weave auxetic fabrics using both auxetic and non-auxetic threads. This study exhibits the semi-empirical modeling of the auxetic woven fabric followed by computational modeling for the prediction of Poisson's ratio. Further, woven fabrics have been developed to test the geometry's potential for producing an auxetic fabric, which can be used for maternity and children's clothing, wound dressing, and protective clothing, providing better comfort and longevity of application. Poisson’s ratio of the developed auxetic samples is measured and compared with experimental results. The effect of thread density and float length on the auxeticity of the fabric based on waveform geometry is also investigated in this study. It was observed that the increase in thread density increases the auxeticity of the fabric, whereas the increase in float length decreases the auxeticity. Auxetic composites were successfully developed using silicon rubber gel as the matrix system.</p></div>","PeriodicalId":468,"journal":{"name":"Applied Composite Materials","volume":"31 3","pages":"1053 - 1068"},"PeriodicalIF":2.3,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139463939","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Preparation of Small-Diameter Phenolic-Based CFRP Rods Using Multi-Die Pultrusion 利用多模拉挤技术制备小直径酚醛基 CFRP 棒材

IF 2.3 4区材料科学

Applied Composite Materials Pub Date : 2024-01-12 DOI: 10.1007/s10443-023-10193-x

Guannan Li, Junwei Qi, Yuequan Wang, Jiaqi Shi, Rui Jia

{"title":"Preparation of Small-Diameter Phenolic-Based CFRP Rods Using Multi-Die Pultrusion","authors":"Guannan Li, Junwei Qi, Yuequan Wang, Jiaqi Shi, Rui Jia","doi":"10.1007/s10443-023-10193-x","DOIUrl":"10.1007/s10443-023-10193-x","url":null,"abstract":"<div><p>This paper introduces a novel multi-die pultrusion system for producing small-diameter phenolic-based CFRP rods. The system consists of multiple short heating dies arranged in series, facilitating the escape of vapor from the die cavities and improving the product quality. The results demonstrate that compared to the traditional dies, the rods produced using the multi-die pultrusion system exhibit higher dimensional stability, and their interlaminar shear strength is mostly above 35 MPa, reaching up to 52 MPa. Compared to the traditional mold, in one instance, its interlaminar shear strength value increased by nearly 71.5%, but in another case, it was only 14.72%. Due to relying solely on one control sample, the results are inconclusive. SEM indicates that the rods produced using the multi-die pultrusion system have fewer voids and better fiber-resin bonding compared to the traditional dies. Additionally, cross-sectional optical microscopy shows that when the pultrusion speed is at or below 0.6 m/min, the impregnation of carbon fibers by phenolic resin is more effective. The proposed multi-die pultrusion system provides a new idea for the production of small-diameter rods.</p><h3>Graphical Abstract</h3>\u0000<div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":468,"journal":{"name":"Applied Composite Materials","volume":"31 3","pages":"1007 - 1029"},"PeriodicalIF":2.3,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139463723","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0