Mechanical characterisation of the shear,bending and friction behaviour of bindered woven fabrics during the forming process

A critical process step within the liquid composite moulding constitutes in the preforming of two‐dimensional textile material into a near‐net‐shape and load‐capable fibre structure by stamp forming. This paper presents fundamental material experiments on the shearing behaviour, bending properties and friction behaviour considering the binder quantity and forming temperature. In addition, the influence of the process time on the resulting stability of the preform is examined. The findings indicate that the quantity of the binder as well as the forming temperature and the process time have a great influence on the preform quality.     

基于灰色关联分析的空调工程设计方缘的综合评价及优化选择

利用灰色关联分析方法建立了空调工程设计方案优化选择的数学模型,同时进行了实例的研究工作.该方法简便易行,评价较全面、准确,是一种较理想、有效的决策方法.     

Computational modeling of the probabilistic impact response of flexible fabrics

The impact response of flexible woven fabrics is probabilistic in nature and described through a probabilistic velocity response curve or V₀–V₁₀₀ curve. Computational impact analyses based on deterministic methods are incapable of predicting the experimentally observed probabilistic fabric impact response. To overcome this limitation we have developed a probabilistic computational framework within a finite element analysis to predict the V₀–V₁₀₀ response. The finite element model is a yarn-based representation of the fabric architecture, with a principal stress based failure criterion implemented uniformly within each yarn, but varying for each yarn within the fabric. For each impact simulation, individual yarn strengths are mapped from experimentally obtained yarn strength distributions, resulting in fabric models with spatially non-uniform failure conditions. Impact simulations are run for the case of a spherical projectile of diameter 5.556 mm impacting a single layer of 50.8 × 50.8 mm, edge-clamped, unbacked, aramid fabric. Three different yarn strength models are implemented, representing spool yarns, and yarns extracted from greige and scoured woven fabrics. Decreases in yarn strength are found to correlate to decreases in the V₁, V₅₀, and V₉₉ velocities predicted by the simulations. The relationships between yarn strength distribution and probabilistic fabric impact response are discussed.     

Investigation of mechanical properties of auxetic woven polymer composite material

Contrary to normal materials, the auxetic/meta‐materials expand transversally as well as longitudinally when subjected to longitudinal load and contract in both directions on compression. In this work, auxeticity is obtained in composites reinforced with carbon woven fabrics placed at certain angles. The auxetic effect on the mechanical properties of the prepared carbon/epoxy composites was investigated. The mechanical properties include the tensile, flexural and impact properties. It is found that the tensile properties are not affected by the auxetic effect; however, the flexural and impact properties are significantly enhanced by the auxetic effect.     

苎麻织物表面改性对其增强热固性聚乳酸复合材料力学及阻燃性能的影响

采用碱处理、硅烷偶联剂处理、碱+硅烷偶联剂复合处理、碱+阻燃剂+硅烷偶联剂复合处理对苎麻织物进行表面改性,采用模压工艺制备了苎麻织物增强热固性聚乳酸(PLA)复合材料。研究了4种表面改性方法对苎麻织物/PLA复合材料弯曲性能的影响,采用SEM研究了苎麻纤维与PLA基体之间的界面结合状况。结果表明:经过4种表面改性处理后苎麻织物/PLA复合材料的弯曲性能均有所提高,其中碱+硅烷偶联剂复合处理后提高幅度最大,苎麻织物/PLA复合材料的弯曲强度、模量分别提高了59.5%、51.9%。碱+阻燃剂+硅烷偶联剂复合处理后苎麻织物/PLA复合材料的弯曲强度、模量较未处理时分别提高了38.0%、66.8%;且苎麻织物/PLA复合材料60s点火时间的损毁长度为8.25cm,达到了美国DOT/FAA/AR-00/12要求的标准。SEM结果表明:改性处理后苎麻织物/PLA复合材料中纤维与树脂之间的界面结合更好。     

Effect of statistical yarn tensile strength on the probabilistic impact response of woven fabrics

The probabilistic impact response of flexible woven fabrics can be described through the V₀–V₁₀₀ or probabilistic velocity response (PVR) curve which describes the probability of fabric penetration as a function of projectile impact velocity. One source of variability that affects the probabilistic nature of fabric impact performance is the statistical distribution of yarn tensile strengths. In this paper the effects of the statistical yarn strength distribution characteristics on the probabilistic fabric impact response are computationally studied using five different strength distributions with differing mean strengths and distribution widths. Corresponding fabric PVR curves are generated for each strength distribution using a probabilistic computational framework that involves randomly mapping yarn strengths onto the individual woven yarns of a fabric finite element model and then running a series of impact simulations for the case of a four-sided clamped fabric impacted at the center by a spherical projectile.     

Analysis of the mechanical response of a woven polymeric fabric with locally induced damage

Local variation of appearance and degradation of mechanical properties affect the performance of textile polymeric materials. In this paper controlled ultraviolet light exposure is used to degrade a nylon66/polyester fabric. Preliminary tensile tests quantify the influence of exposure time on the mechanical response of the material and are used to define constitutive laws of the unexposed and exposed materials. Such constitutive laws of the fabric are implemented within a finite element code. The role of local degradation on the bias extension test is investigated computationally with the macroscopic approach and experimentally using image processing and digital image correlation. The experimental test results apparently support the FEM modeling approach and results.     

基于灰色关联分析法的空调冷热源优化选择

利用灰色关联分析方法建立了空调工程设计方案优化选择的数学模型,以某建筑物空调冷热源方案为例进行分析,得出了优化方案。     

基于灰色关联分析与回归分析WC-12Co涂层工艺参数的多目标优化

以Q235钢为基体,采用等离子喷涂法制备了高质量WC-12Co涂层,对WC-12Co涂层显微硬度、沉积厚度和结合强度进行综合评价。基于主气流量、电流和喷涂距离工艺参数设计了Box-Behnken实验模型,利用层次分析确定评价指标的权重,用灰色关联分析和回归分析对工艺参数进行优化。研究结果表明,层次分析后评价指标的权重矩阵为W_j=[0.44,0.17,0.39]。通过灰色关联分析法得到最优参数为气流量2 500L/h、电流350A、喷涂距离130mm,回归分析得到最优参数为主气流量2 500L/h、电流349.08A、喷涂距离129.18mm。两种方法优化结果基本一致,可以应用于工艺参数的多目标优化。     

Experimental and numerical study of oblique impact on woven composite sandwich structure: Influence of the firing axis orientation

During flight, aircrafts can be submitted to complex loadings. The reliability of their structure is an essential aspect in ensuring passenger safety. In the specific case of helicopters, blades are subjected to impact loading. The following work will focus on the experimental and numerical study of an oblique impact on the skin of the blade. It is equivalent in a first approach to an impact on a sandwich panel comprising a foam core and a thin woven composite skin. This study aims to identify the mechanisms of damage to the skin for different orientations of the firing axis, and to develop a representative model of the damage kinetics adapted to the modeling of the complete structure. Thus, an F.E. semi-continuous explicit model has been developed. It relies on the development of a specific damageable element at the woven mesh scale. Numerical results obtained are accurate, allowing the identification of the damage mechanism of the woven skin for different firing orientations.     

Improved analytical model to predict the effective elastic properties of 2.5D interlock woven fabrics composite

An improved analytical modeling, three stages homogenization method “3SHM”, of a 2.5D interlock woven composite is proposed. The development of the analytical model based on mixed iso-strain and iso-stress assembling models (the stiffness and the compliance averaging models) is presented. A finite element (FE) modeling is carried out in order to use its results in the development of the analytical model. It is proved that a model based only on an iso-strain condition could not give accurate results, while a mixed iso-strain and iso-stress model yields more accurate estimations. the developed homogenization method as well as the geometrical modeling, that takes into account the real geometry of undulated yarns, proposed by the analytical model leads to very good agreement in comparing with results obtained from FE models and available experimental data from the literature.     

综合利用率评估的民机结构维修间隔确定方法

确定结构维修间隔是民机结构维修大纲中的关键内容之一,民机利用率对维修间隔制定的合理性有很大影响。基于环境损伤条件下的民机结构,通过分析不同利用率下影响金属结构环境损伤的指标的敏感性,提出了民机结构维修间隔与利用率匹配模型。在该模型中,应用序关系分析法-属性重要度相结合的组合赋权方法,对不同利用率下影响金属结构环境损伤的指标进行组合权重评估,确定金属结构环境损伤的总等级,并根据环境损伤等级-维修间隔回归方程确定了不同利用率下的民机结构维修间隔,最后采用灰色关联分析法验证了不同利用率下各指标评价值与理想值的关联度。以某型飞机中央盒段上壁板内表面维修间隔确定为例,对所提出的模型进行验证分析,利用模型得到的维修间隔与维修审查委员会报告（maintenance review board report,MRBR）规定相比偏小,鉴于该文件规定的为最低工程要求,从而确定该维修间隔满足要求,证明了模型的有效性。研究成果表明,建立的民机结构维修间隔与利用率匹配模型的适用性较强,可以有效解决国产飞机结构维修大纲中维修间隔确定时利用率考虑不足的问题,具有较高的工程应用价值。     

确定供应商评价指标权重的一种方法

首先分析了供应链管理中供应商选择和评价的重要意义,然后对选择供应商的评价指标及权重的确定问题进行了分析;根据已有的评价方法中确定指标权重方法的某些不足,提出一个灰关联分析模型,试图从灰色系统理论角度来探讨这个问题,最后,选择了质量、成本、交货期3个常用指标,建立起了供应商选择和评价的指标权重灰关联分析模型,给出了一个数据计算过程示例,并对计算结果进行了分析和讨论。     

结构参数对自相似多级蜂窝力学性能的影响

对蜂窝的代表性体积单元(RVE)研究发现,相比于均匀化边界条件,周期性边界条件能更好地预测蜂窝的等效力学性能。基于周期性边界条件,对自相似多级蜂窝进行面内不同方向的拉伸模拟,重点分析了蜂窝孔隙率与多级长度比对拉伸性能的影响。结果表明:自相似多级蜂窝在拉伸过程中会呈现面内各向异性,沿扶手椅方向拉伸时,会在节点六边形的水平连接边处发生断裂;沿锯齿形方向拉伸时,当节点六边形的边长大于壁厚和节点六边形的连接斜边的边长较长的情况下,蜂窝会出现两次拉伸破坏,分别在节点六边形边与节点六边形的连接斜边处,而在其他情况下,则只会在节点六边形连接斜边处发生一次破坏。并且自相似多级蜂窝随着孔隙率或长度比的增大,蜂窝拉伸强度呈现减小的趋势。     

Controlled growth of CuO nanowires on woven carbon fibers and effects on the mechanical properties of woven carbon fiber/polyester composites

The effect of CuO nanowires on the improvement of the mechanical properties of woven carbon fiber (WCF)-based polyester resin composite was studied. The composite was manufactured by the vacuum-assisted resin transfer molding (VARTM) process. CuO nanowires were grown on woven carbon fiber sheets in subsequent steps of seeding followed by growth. Scanning electron microscopy (SEM) showed the growth of CuO nanowires on the surface of the carbon fibers; this growth increased with the number of seeding cycles and the length of the growth time. The concentration of the growth solution did not have a significant effect. The maximum amount of growth occurred for 8 seeding cycles with a 60 mM growth solution and a growth time of 8 h. An analysis of the percent weight change, along with X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, supported the above findings. The crystalline peak height of the CuO nanowires increased with the nanowire growth. The new absorption peaks arising in the FTIR spectra also indicated growth of CuO nanowires on the WCF. The mechanical properties in terms of tensile strength, modulus, and impact resistance improved significantly after the growth of nanowires on the carbon fibers: the modulus and strength improved by up to 33.1% and 42.8%, while the impact energy absorption increased by 136.8% relative to bare WCF.     

定型剂对单轴向经编织物复合材料力学性能影响的试验研究

研究了真空辅助树脂注射（VARI）工艺中定型剂对环氧树脂的影响及其在织物表面的分布形式,以及定型剂用量对单轴向经编织物复合材料力学性能的影响,以确定最优的定型参数。采用示差扫描量热法（DSC）和扫描电镜（SEM）分别对加入不同用量定型剂的环氧树脂的玻璃化转变温度和相形貌进行分析,并测试了加入不同用量定型剂后复合材料的力学性能。结果表明：随着定型剂用量的增加,环氧树脂的玻璃化转变温度逐渐降低,且其相形貌逐渐由海岛结构经过双连续相结构到最后的相反转结构;室温下,随着定型剂用量的增加,织物表面定型剂的厚度及不均匀性增加,经过高温处理后,定型剂均匀分布在织物表面。定型剂用量对单轴向经编织物复合材料力学性能有较大影响,用量为20 g/m²时,复合材料体系的综合力学性能最优。     

三维机织碳/碳复合材料双轴压缩载荷下的力学行为

基于三维机织碳/碳复合材料的细观结构特征, 设计平板十字形试样, 在材料双轴力学性能试验机上开展了复合材料单轴、 双轴加载压缩试验, 对比分析了三维机织碳/碳复合材料在双轴压缩载荷下的力学行为。研究表明: 三维机织碳/碳复合材料的压缩行为表现为非线性、 脆性断裂; 双轴载荷作用下非线性特征更为显著, 压缩模量随应力的增加而增大, 强度与模量相较于单轴有较大幅度增加, 双轴压缩载荷作用下材料的强化效应显著; 试样破坏位置并未出现在试样中心区, 而是发生在试样的加载端部或十字形试样的加载分枝根部, 主要表现为基体开裂、 纤维断裂和层间脱粘, 碳布及其层间界面剪切强度的强弱直接影响材料的压缩强度。     

全地形移动机器人车身结构分析与优化

为了提高全地形移动机器人车身结构的力学性能,提出了一种结合多体动力学、有限元分析与正交试验的优化方法.针对全地形移动机器人的满载弯曲和扭转工况,利用多体动力学分析获得了该移动机器人车身在运动中所受的外部载荷,并结合有限元分析获得了车身结构的动态力学性能参数,以验证极限工况下车身结构的力学性能.基于四因素三水平正交试验,...     

基于粒子群算法与连续型深度信念网络的水泥熟料游离氧化钙预测

针对水泥熟料质量指标游离氧化钙含量难以实时检测的问题,提出一种基于连续型深度信念网络建模的预测方法。首先根据水泥熟料生产工艺选取影响烧成系统的主要变量,利用灰关联分析得出各变量灰色关联度并去除关联度小的变量,建立水泥熟料游离钙预测的辅助变量集合。其次采用粒子群算法对连续型深度信念网络进行优化,建立水泥熟料游离钙预测模型。最后与最小二乘支持向量机、反向传播算法网络和连续型深度信念网络预测效果进行对比。结果表明,基于粒子群寻优的连续型深度信念网络水泥熟料游离钙含量的预测方法精度高、泛化能力强。     

The use of a grey-based Taguchi method for optimizing multi-response simulation problems

Simulation modelling is a widely accepted tool in system design and analysis, particularly when the system or environment has stochastic and nonlinear behaviour. However, it does not provide a method for optimization. In general, problems contain more than one response, which are often in conflict with each other. This article proposes a grey-based Taguchi method to solve the multi-response simulation problem. The grey-based Taguchi method is based on the optimizing procedure of the Taguchi method, and adopts grey relational analysis (GRA) to transfer multi-response problems into single-response problems. A practical case study from an integrated-circuit packaging company illustrates that differences in performance of the proposed grey-based Taguchi method and other methods found in the literature were not significant. The grey-based Taguchi method thus provides a new option when solving a multi-response simulation-optimization problem.