不同芯材增强材料抗压性能比较的有限元计算

为了分析不同芯材对"O"形芯材增强复合材料抗压能力的影响,通过有限元计算,比较树脂、玻璃纤维、铁质3种芯材增强复合材料在相同压力作用下的力学行为。通过对比与分析材料挠度随时间的变化曲线、质量大小、应力分布及受力均衡性等指标发现:应力分布的对称性与承力均衡性对材料抵抗外力有利,即使其能够吸收较多的能量并产生较小的变形。此外,综合考虑抗压能力、承力均衡性以及轻质化等方面的要求,不应选用树脂或铁质芯材增强复合材料,而应选用玻璃纤维芯材增强复合材料。     

碳纤维/环氧树脂基中空夹芯复合材料压缩性能的有限元法研究

在已有研究的基础上,利用有限元软件ANSYS Workbench,建立了三维中空夹芯复合材料结构模型,进行三维中空夹芯复合材料的压缩性能研究。利用该模型,探讨了材料在2 mm压缩位移载荷作用下纤维、树脂和复合材料的应力、应变分布。结果表明:三维中空夹芯复合材料在压缩载荷作用下,芯材交叉处应力最大,最容易发生压缩破坏;上下面板应力最小,最不容易发生压缩破坏;复合材料在承受压缩载荷作用时,纤维起主要承载作用,树脂起次要作用;材料的破坏模式主要为树脂破裂。     

基于有限元的芯材增强材料抗冲击性能分析

为研究"O"形中空芯材增强复合材料的抗冲击性能,通过有限元建模分析的方法,计算芯材增强材料在具有不同入射速度弹体冲击下的结构动态响应。通过对比分析各种冲击情况下弹体的速度随时间的变化曲线、加速度随时间的变化曲线、材料结构破坏形态与模式以及纤维体积分数对材料抗冲击性能的影响发现:在具有一定初速度的弹体冲击复合材料靶体的过程中,其速度变化一般经历3个阶段;弹体加速度的波动规律可直接反映弹体承受靶体反作用力的变化情况;材料靶体的破坏程度还因弹速的不同而呈现出一定的规律,这与靶体吸收与耗散冲击能量的多少有关;此外,在一般情况下,纤维体积分数越大,材料的抗冲击性能越佳。     

蜂窝夹层结构消音板平压试验研究

通过对蜂窝夹层结构消音板压缩试验研究,建立蜂窝结构压缩应力随压缩应变变化曲线,得到不同位移载荷下芯材的变形特点,试验结果曲线验证了蜂窝纸板压缩过程经历的4个阶段,与理论曲线吻合。从试验结果来看,该芳纶纤维增强蜂窝夹层结构复合材料作为某新机用风扇消音板材料满足力学性能要求。     

玻璃纤维/环氧树脂基夹芯材料侧压性能数值模拟

为分析材料在侧压载荷下的失效机制及破坏模式,采用有限元软件ANSYS,建立了材料的细观结构模型,并进行侧压性能的数值模拟,探讨了材料在3 mm侧压位移载荷作用下复合材料、纤维和树脂基体的应力、应变分布情况。结果表明:玻璃纤维/环氧树脂基夹芯材料在侧压载荷作用下,从宏观角度分析发现,上下面板应力最大,最易发生压缩破坏;芯材应力最小,最不易被破坏;2排芯材间的面板最易发生失稳破坏,这是导致材料失效的最主要原因。从微观角度分析发现,纤维起主要承载作用,树脂起次要作用,当侧压位移载荷达到3 mm时,材料的破坏模式主要为树脂破裂、纤维与树脂严重脱黏等。     

三维夹芯复合材料低速冲击性能有限元法研究

借助有限元软件ANSYS建立了三维夹芯复合材料细观结构模型,重点研究了在低速冲击载荷作用下材料、纤维和树脂的应力、应变分布,并分析了树脂种类对材料抗低速冲击性能的影响。结果表明,在低速冲击载荷下,从宏观角度来看,冲击点处、芯材圆弧中心处应力较大,最易发生破坏,而下面板边缘处应力最小,不易被损坏;从细观角度来看,纤维是承载的主体,树脂起次要作用;环氧树脂基复合材料抗低速冲击性能更优。     

结构参数对三维中空夹芯复合材料平压性能的影响

三维中空夹芯复合材料是一种新型夹芯结构材料,具有轻质、高强、高模、抗冲击、隔音、保温等特性,可广泛用于航空航天、汽车、储油罐、船舶、建筑、能源等领域。本文选取芯材高度分别为2、4、6和8mm,以及芯材间距分别为4、6和8 mm的两组三维中空夹芯复合材料为样品,测试其平压性能,重点研究芯材高度、芯材间距等结构参数对三维中空夹芯复合材料平压性能的影响,并分析材料的压缩特性及损伤机理。结果表明,三维中空夹芯复合材料受到平压载荷时的破坏模式为明显的脆性破坏,同时,材料破坏形式主要表现为树脂开裂、纤维断裂、界面脱粘等特征。三维中空夹芯复合材料的平压性能随着芯材高度、芯材间距的增加而下降。研究结果将为该材料的结构优化设计和性能分析奠定理论基础。     

锦纶对纺织废胶-受阻酚微观形态与性能的影响

为开发一种集阻尼、吸声性能为一体的多功能复合材料,利用纺织工业废胶粉（TWRP）、受阻酚（AO 2246）和单孔中空锦纶（PF） 制备了一系列的PF/TWRP-AO246 三元阻尼吸声复合材料。通过动态热分析、扫描电子显微镜、吸声测试、织物强力测试等表征手段对复合材料的微观形态和性能进行分析。结果表明：锦纶充当了AO 2246的结晶诱导核,使AO 2246形成包覆于纤维表面的结晶,从而在复合材料中出现了结晶纤维网络结构,形成“贯穿的空气层”,改善了复合材料的吸声性能;加入锦纶使复合材料的阻尼损耗下降;结晶纤维网络结构充当了复合材料中的骨架,起到了增强作用。当纤维含量从10%增加到50%时,其最大断裂应力从62.8 MPa增至129.8 MPa,断裂应变从363.6%降至19%。     

不同芯材高度三维夹芯复合材料抗低速冲击响应的数值模拟

为研究三维夹芯复合材料低速冲击力学响应及损伤机制,借助ANSYS有限元软件,建立不同芯材高度的三维夹芯复合材料细观结构模型进行低速冲击响应模拟,并将模拟值与实验值进行对比分析。结果表明:从宏观角度分析,三维夹芯复合材料抗低速冲击性能随着芯材高度的增加而增加,在上面板均已损坏的情况下,芯材高度为5 mm的材料芯材破坏情况更严重,模拟结果与实验结果具有较好的一致性;从细观角度分析,材料中的经纱、纬纱、接结经纱是承载的主体,树脂基体起次要作用;在5 J能量冲击作用下,材料的破坏模式主要是树脂形变、碎裂,纤维与树脂脱黏。     

亚麻增强复合材料/蜂窝夹芯结构冲击响应

文章研究了亚麻增强复合材料/蜂窝夹芯结构的冲击响应。所用的夹芯结构的芯材是蜂窝材料,面板使用不同规格的亚麻纤维增强/酚醛树脂复合材料。研究了不同冲击能量下,面板厚度对冲击响应及破坏模式的影响。面板厚度小的夹芯结构主要由面板的拉伸破坏主导,而面板厚度大的夹芯结构则主要由面板的分层破坏主导,并且能够吸收更多冲击能量。     

Mechanical properties and microstructure of 3D sinking woven quartz fiber-reinforced silica composites by silicasol-infiltration-sintering

Three-dimensional (3D) sinking woven quartz fiber-reinforced silica composites were successfully prepared by silicasol-infiltration-sintering process at a low temperature of 450°C. The density of the composites was 1.74?g/cm³. The characteristics of 3D sinking woven structure were determined. Flexural strength and shear strength of the composites were investigated along the warp and weft directions. Both flexural stress–displacement curves in warp and weft directions had two fractural points, e.g. matrix fracture point and fiber fracture point. The shear stress–displacement curves exhibited mostly nonlinear behavior. The composite in warp and weft direction reflects different shear behavior. Microstructural observations revealed that the adhesion strength between the fibers and the matrix was weak. There was a good state without serious degradation of quartz fibers during the preparation. Apart from these, the composites exhibited an extensive and long fiber pullout in the fracture surface. Crack deflection and fiber pullout contributed to the good toughness of the composites under the loading.     

Mechanical,morphological, and thermogravimetric analysis of alkali-treated Cordia-Dichotoma natural fiber composites

ABSTRACT

Usage of composites with natural fiber reinforcement is drastically increasing in recent times because of their low density, biodegradable nature, and low cost. However, natural fibers have certain core problems such as poor adhesion between the fiber and matrix and a relatively high degree of moisture absorption. Alkaline treatment of natural fibers is aimed at improving the adhesive strength so that effective stress transferability takes place in the composite. In the present work, Cordia-Dichotoma fibers were treated with sodium hydroxide (NaOH) and composites were prepared with different weight ratios of these fibers reinforced with epoxy. The prepared composites were tested for their tensile and flexural strengths (mechanical properties). Besides, for a comprehensive material characterization, IR spectroscopy (FT-IR), scanning electron microscope, and thermogravimetric analysis were carried out. This work investigates the influence of aforementioned NaOH treatment on thermal, mechanical, and morphological properties of the composite material.     

3D woven green composites from textile waste: mechanical performance

Application of textile waste for development of value added green composites has been carried out in this work. Textile fabric waste is collected from various sources. These waste materials are garneted, so as to produce loose fibrous material, subsequently this fibrous material was converted into twisted strand for manufacturing of 3D woven preforms for production of composites. Twisted strands are converted into orthogonal 3D woven structure. The fibers extracted from waste material are combined with polypropylene in 60/40 proportion. Composites of various specifications are developed to examine their end-use applications. These composite materials are characterized for their mechanical behavior to find out the response against tensile loading, flexural stress, and impact force. The effects of moisture absorption on mechanical properties of composites are investigated. 3D woven fabric reinforced composites produced by using waste fiber yarn and normal cotton OE yarn do not exhibit any significant difference in the mechanical behavior of composite. This result confirmed that waste material can be safely used as reinforcing structure in green composite manufacturing.     

不同结构厚截面三维机织碳纤维复合材料的弯曲性能对比

为准确分析不同结构厚截面复合材料不同方向上的弯曲性能差异,通过设计织造三向正交、浅交直联、浅交弯联3种典型机织结构的厚截面碳纤维三维机织物,并采用真空辅助树脂成型工艺制备了近似纤维体积含量的碳纤维复合材料板,对其进行了XYZ方向的弯曲实验。结果表明:三向正交结构由于内部纤维束近似平直,碳纤维束自身性能得到最大利用,对应复合材料经向弯曲强度最好;浅交直联结构复合材料的Z经和Z纬弯曲强度累加值最大,其厚度截面上的综合弯曲性能最好,且其他各方向的弯曲强度较为均衡;浅交弯联结构内部纱线交织摩擦损伤严重,且经纱屈曲程度最大,对应复合材料经纬向弯曲性能均为最差。     

Investigation of mechanical behavior of woven/knitted hybrid composites

The objective of this research is to develop the woven/knitted hybrid composites for improved in plane as well as out of plane mechanical properties. Two different type of structures and two different materials were used in this study. Firstly, the woven and knitted fabrics were developed with glass and Kevlar yarn. Secondly, the laminated composite samples were fabricated with different stacking sequence of fabric plies. The epoxy resin was used as matrix. The cured samples were characterized for impact, tensile and dynamic mechanical properties. The behavior of composite materials was then analyzed with percentages of different fiber and fabric types. The samples with higher percentages of knitted reinforcement gave better impact strength but failed to provide better tensile properties. Moreover, the samples with higher percentages of woven structure and glass materials gives better modulus values.     

单向不连续碳纤维增强复合材料有限元分析

采用有限元法建立了有关的单胞模型和相关的边界条件。着重研究了复合材料的结构参数与单向不连续碳纤维增强聚醚醚酮（CF/PEEK）复合材料的细观弹塑性应力应变的关系，分析了纤维重叠比、纤维端部的不连续性对复合材料中纤维与纤维、纤维与周围基体相互作用以及应力场变化的影响。此外利用体积平均法预测了在外载荷作用下不同结构参数的单向不连续碳纤维增强复合材料的弹塑性应力-应变关系。     

Effect of variation of root post in different layers of tooth: linear vs nonlinear finite element stress analysis

The objective of this study was to obtain an accurate stress distribution pattern on different domains of a post- and core-treated tooth, taking into account the nonlinear properties of the periodontal ligament (PDL). Linear stress and deformation analysis was carried out using four posts, different in constitution and shape. Accurate three-dimensional models of a restored tooth with different layers were prepared using CAD modeling software. The study was carried out using a cast metal post and core assembly, a glass fiber, a carbon fiber, and a titanium post with a composite resin core. For each restoration, parallel, tapered and threaded posts were modeled. However, PDL exhibits nonlinear properties ensuring a uniform stress distribution in the tooth structure. Hence, accurate results could be expected by simulating the model for the nonlinear properties of PDL. Owing to computational difficulties, a simplified model was prepared in the ANSYS environment and nonlinear stress analysis was carried out. The results indicate that for optimum strength, rigidity and flexibility, tapered fiber posts with a composite resin core cemented to the root are desirable. Under similar loading conditions, in the case of nonlinear analysis, the stresses decreased by approximately 25% and the deformation increased by approximately 50% as compared with those in case of linear static analysis for an endodontically treated maxillary central incisor. Thus, stress distribution within the restored tooth and surrounding tissues can be better anticipated by a dentist. From the results of this study, the dimensions of a post could be modified, to further reduce stress in the oral cavity and thereby reduce the risk of root and post fractures.     

三维角联锁机织复合材料三点弯曲破坏的有限元计算

为了说明一种层层接结三维角联锁机织复合材料在三点弯曲载荷下的动态响应以及结构破坏行为,运用有限元分析软件ABAQUS,在纱线、基体细观结构尺度上计算与考察材料在一恒速弯曲应力作用下的挠度随时间的变化历程、渐进破坏过程、应力分布以及应力集中区域的结构效应。通过分析计算结果发现：三维角联锁机织复合材料的三点弯曲破坏与其结构特征密切相关,破坏由结构中的应力集中区域萌发。此外,应力集中部位主要位于屈曲波浪状的经纱上,且处于各根经纱的弯折部位。这种结构特征使其在材料承载过程中受到的载荷最大,从而导致破坏的进一步扩展。     

Hybrid Yarns and Textile Preforming for Thermoplastic Composites

In the recent years, the use of textile structures made from high performance fibers is finding increasing importance in composites applications. In textile process, there is direct control over fiber placements and ease of handling of fibers. Besides economical advantages, textile technologies also provide homogenous distribution of matrix and reinforcing fiber. Thus textile performs are considered to be the structural backbone of composite structures. Textile technology is of particular importance in the context of improving certain properties of composites like inter-laminar shear and damage tolerance apart from reducing the cost of manufacturing. Textile industry has the necessary technology to weave high performance multifilament fibers such as glass, aramid and carbon, which have high tensile strength, modulus, and resistance to chemicals and heat into various types of preforms. Depending upon textile preforming method the range of fiber orientation and fiber volume fraction of preform will vary, subsequently affecting matrix infiltration and consolidation. As a route to mass production of textile composites, the production speed, material handling, and material design flexibility are major factors responsible for selection of textile reinforcement production. This opens a new field of technical applications with a new type of semifinished material produced by textile industry. Various types of hybrid yarns for thermoplastic composites and textile preforming methods have been discussed in detail in this issue. Information on manufacturing methods, structural details and properties of different hybrid yarns are presented and critically analyzed. Characterization methods used for these hybrid yarns have been discussed along with the influence of different processing parameters on the properties being characterized. The developments in all areas of textile preforming including weaving, knitting, braiding, stitching and nonwovens techniques are presented and discussed along with the characterization techniques for these preforms. The techniques used for manufacturing composites using hybrid yarns and textile preforms are discussed along with the details on compaction behavior of these structures during consolidation process. The structure of hybrid yarns and the textile preforms have direct influence on the properties of the composite made from them. The reported literature in this aspect is discussed in detail. In the end, the potential application areas and their trends for thermoplastic composites are discussed and analyzed.