今日更新:Composite Structures 4 篇
A new mesh-type rail pad with second-order stiffness
Yanbo Bai, Zhenxing He, Nengneng Bao, Peanghao Li
doi:10.1016/j.compstruct.2023.117763
具有二阶刚度的新型网状轨垫
In this paper, a novel mesh-type rail pad with second-order stiffness (MTRPSOS) is proposed, which is comprised of a mesh-type rail pad (MTRP) and multiple filled blocks. By adjusting the height of the filled blocks, the stiffness curves of the MTRPSOS exhibit pronounced second-order stiffness (SOS) characteristics. A finite element (FE) model of the MTRPSOS and a dynamic model were established to investigate the SOS characteristics and their impact on various dynamic indices. The FE calculations reveal that both static and dynamic stiffness of the MTRPSOS increase as the height of the filled blocks decreases. Moreover, as the height of the filled blocks increases, stress distribution becomes more uniform. The dynamic calculations demonstrate that the SOS characteristics of the MTRPSOS significantly affect various dynamic indices. As the SOS of the MTRPSOS decreases, rail displacement correspondingly increases, while vibration acceleration, wheel-rail forces, fastener reaction forces, and derailment coefficient all decrease. This indicates that the MTRPSOS offers superior vibration reduction under the SOS conditions compared to the first-order stiffness conditions. Additionally, a comparative study was conducted to assess the vibration reduction effect of the MTRPSOS in contrast to traditional rail pad, and the results show that the MTRPSOS consistently exhibits lower vibration levels under the same operating conditions, underscoring its superior capacity for vibration reduction.
本文提出了一种具有二阶刚度的新型网状轨道垫(MTRPSOS),它由网状轨道垫(MTRP)和多个填充块组成。通过调整填充块的高度,MTRPSOS 的刚度曲线表现出明显的二阶刚度(SOS)特性。我们建立了 MTRPSOS 的有限元(FE)模型和动态模型,以研究 SOS 特性及其对各种动态指数的影响。有限元计算结果表明,随着填充块高度的降低,MTRPSOS 的静态和动态刚度都会增加。此外,随着填充砌块高度的增加,应力分布也变得更加均匀。动态计算表明,MTRPSOS 的 SOS 特性会显著影响各种动态指数。随着 MTRPSOS 的 SOS 值减小,轨道位移相应增大,而振动加速度、轮轨力、紧固件反作用力和脱轨系数均减小。这表明,与一阶刚度条件相比,MTRPSOS 在 SOS 条件下具有更优越的减振效果。此外,还进行了一项比较研究,以评估 MTRPSOS 与传统轨道垫相比的减振效果,结果表明,在相同的运行条件下,MTRPSOS 始终表现出较低的振动水平,突出了其卓越的减振能力。
Microstructural modeling on electrical conductivities of 3-D carbon/epoxy woven composites along different directions
Zhuodong Liu, Yousong Xue, Baozhong Sun, Bohong Gu, Meiqi Hu
doi:10.1016/j.compstruct.2023.117764
三维碳/环氧编织复合材料不同方向导电性的微观结构建模
Carbon fiber composites have widely been used in aircrafts and high speed vehicles. Electrical conductivity of the carbon fiber composites is critical to electrical safety for the aircrafts and vehicles under high voltage applications. Here we report microstructural modeling on electrical conductivities of three-dimensional (3-D) carbon/epoxy angle-interlock woven composites along on-axis and off-axis directions. A 3-D resistor network model and finite element analysis (FEA) model based on fabric microstructure have been developed to reveal the electric conductivities along different directions. We have found that the conductivity of the woven structure exhibits full anisotropy. The difference of electrical conductivity between in-plane and through-thickness direction decreased due to the existence of through-the-thickness carbon fibers. The electrical conductivity through-thickness direction increases with warp directional length. With increasing off-axis directional length, the conductivity perpendicular to the off-axis direction increases, while the conductivity parallel to the off-axis direction remains basically unchanged. Electric potential distribution and electrical current density are highly related with fabric structure and current directions. Owing to the dependence of mechanical properties are also related with fabric structure and directions, it is expected that both the electrical and mechanical properties of the 3-D woven carbon/epoxy composites could be optimized simultaneously from the composite microstructure designs.
碳纤维复合材料已广泛应用于飞机和高速车辆。碳纤维复合材料的导电性对于高压应用下的飞机和车辆的电气安全至关重要。在此,我们报告了三维(3-D)碳/环氧角交织复合材料沿轴向和离轴向导电性的微观结构模型。我们开发了基于织物微观结构的三维电阻网络模型和有限元分析(FEA)模型,以揭示不同方向的导电率。我们发现,编织结构的电导率表现出完全的各向异性。由于存在穿透厚度的碳纤维,面内和穿透厚度方向的导电率差异减小。厚度方向的导电率随经线方向长度的增加而增加。随着离轴方向长度的增加,垂直于离轴方向的导电率增加,而平行于离轴方向的导电率基本保持不变。电动势分布和电流密度与织物结构和电流方向高度相关。由于力学性能也与织物结构和方向有关,因此预计三维碳/环氧编织复合材料的电气性能和力学性能可以通过复合材料微结构设计同时得到优化。
Experimental and numerical studies on low-velocity impact of laminated C/SiC structures
Bin Liu, Fei Li, Yancheng Liu, Yi Zhang
doi:10.1016/j.compstruct.2023.117765
层状 C/SiC 结构低速冲击的实验和数值研究
Laminated C/SiC(carbon fiber reinforced silicon carbide composites) has the complicated nature of composite failure which include cracks for void defects at the meso and micro scales, complex cracks propagation of tunnel cracks, matrix cracks, delaminations and fiber cracks, orthotropic, and pseudoplastic behavior. It has technical challenge to solve all of them for complicated-mechanics problems by using multi-scale methodology. This paper focused tackling it by a model that lies between macro and meso scales, and proposed a new conceptual 3D FE-PDM(Finite Element - Progressive Damage Method). 3D FE-PDM was validated by the experiments of low-velocity impact of 2D C/SiC and 3D needled C/SiC. Damage initiation and evolution were controlled by strain in order to preventing stress chaos which could occur as cracks leading local stress relief. The multi-linear constitutive relations were adopted in orthotropic directions. The coupled effects of stresses between in-plane and out-of-plane were computed by adding damage coefficients into stiffness matrix. Cohesive Zone Method was used for delamination. The PDM approach was introduced for the 3D elements for intralaminar and cohesive elements for the interfaces. A parametric inversion methodology was put forward to determine the model parameters iteratively by comparing simulation results with the load-time curves, damage CT details of the experiments. Validation implies that, with small number of parameters, 3D FE-PDM is able to predict damage initiation of each phase knee, damage evolution, and load-displacement curve with good convergence for the low-velocity impact case. 2D woven and 3D needled non-woven C/SiC both have impact energy threshold and different damage evolution types.
层状 C/SiC(碳纤维增强碳化硅复合材料)具有复杂的复合材料失效性质,包括中尺度和微尺度的空隙缺陷裂纹、隧道裂纹的复杂裂纹扩展、基体裂纹、分层和纤维裂纹、正交和假塑性行为。使用多尺度方法解决所有这些复杂力学问题是一项技术挑战。本文重点采用介于宏观和中观尺度之间的模型来解决这一问题,并提出了一种新的 3D FE-PDM(有限元渐进损伤法)概念。二维 C/SiC 和三维针 刺 C/SiC 的低速冲击实验验证了 3D FE-PDM。损伤的发生和演变受应变控制,以防止出现应力混乱,导致局部应力释放产生裂纹。在正交方向上采用了多线性组合关系。通过在刚度矩阵中加入损伤系数,计算了平面内和平面外应力的耦合效应。分层采用了内聚区法。层内的三维元素和界面的内聚元素采用了 PDM 方法。通过将模拟结果与实验中的载荷-时间曲线、损伤 CT 细节进行比较,提出了一种参数反演方法来迭代确定模型参数。验证结果表明,在低速冲击情况下,只需少量参数,三维 FE-PDM 就能预测各相膝关节的损伤起始、损伤演变和载荷-位移曲线,且收敛性良好。二维编织和三维针 刺无纺 C/SiC 都具有冲击能量阈值和不同的损伤演变类型。
An adaptive damage monitoring method based on transfer features mapped for advanced composite structures
Yihan Wang, Xiyue Cui, Qijian Liu, Bowen Zhao, Yunlai Liao, Xinlin Qing
doi:10.1016/j.compstruct.2023.117742
基于先进复合材料结构转移特征映射的自适应损伤监测方法
Monitoring damage in advanced composite structures proves challenging due to insufficient transfer and reuse of diagnostic models. Such limitations fail to meet practical monitoring requirements. This paper proposes an innovative method to monitoring damage via Lamb waves based on transfer learning. Firstly, the proposed method utilizes algorithm-centric transfer learning to extract transferable features from the source domain and a limited amount of data from the target domain, using the domain adaptive feature mapping. The aim of this method is to achieve feature adaptation in both the source and target domains by obtaining approximate distribution patterns in the feature space. Subsequently, a fine-tuning method is presented based on data-centric transfer learning for adaptive damage identification. A screening mechanism utilizing a coarse-to-fine strategy is employed to select suitable samples for diagnosing and evaluating damage in the target domain. The proposed method is verified by targeted monitoring cases of advanced composite structures under four monitoring stages, namely, detection of the damage existence, identification of damage types, damage localization and quantification. The results show that the proposed method can present higher monitoring accuracy in general damages for advanced composite structures than nine state-of-the-art methods.
由于诊断模型的转移和再利用不足,监测先进复合材料结构的损坏具有挑战性。这种局限性无法满足实际监测要求。本文提出了一种基于迁移学习的λ波损伤监测创新方法。首先,该方法利用以算法为中心的迁移学习,从源域提取可迁移的特征,并利用域自适应特征映射从目标域提取有限的数据量。这种方法的目的是通过获取特征空间的近似分布模式,实现源域和目标域的特征适应。随后,介绍了一种基于以数据为中心的迁移学习的微调方法,用于自适应损伤识别。利用一种从粗到细的筛选机制,为诊断和评估目标域中的损伤选择合适的样本。在四个监测阶段,即检测损伤是否存在、识别损伤类型、损伤定位和量化阶段,对先进复合材料结构的目标监测案例验证了所提出的方法。结果表明,与九种最先进的方法相比,所提出的方法对先进复合材料结构一般损伤的监测精度更高。