Modeling the response,strength and degradation of 3D woven composites subjected to high rate loading

Experimental results which were obtained using a split Hopkinson pressure bar (SHPB) apparatus to determine rate dependent effects, and reported by the authors in [1] are used as the basis to perform dynamic simulations of 3D woven composites (3DWCs) using representative unit cells (RUCs). The input material properties for the RUC simulations were determined from the concentric cylinder model (CCM) in conjunction with the geometry of the textile architecture, mechanical properties of pure epoxy samples and fiber mechanical properties. The RUC model incorporates rate dependent plasticity. Additionally, linear-eigen perturbations that correspond to buckling modes are used to seed imperfections in the RUC model to capture buckling and subsequent failure that was observed in experiments. The RUC model results showed good agreement with experiment and correctly captured the observed modes of failure while pointing to transitions in failure modes.     

三维机织夹芯复合材料的制备与压缩性能研究

以玻璃纤维为原料,采用2个系统经纱(一个为上下表层经纱,另一个为夹芯层经纱)、1个系统纬纱,在SU111型全自动剑杆织机上制织经向截面为“口”字形的新型三维夹芯织物.以环氧树脂E-44与9055型固化剂为基体体系,采用手糊成型工艺将上述机织物复合制成三维机织夹芯复合材料.研究三维机织夹芯复合材料的压缩性能,分析材料结构与压缩性能之间的关系,并与“8”字形中空复合材料进行比较.结果表明,芯材间距为5mm的“8”字形中空复合材料的压缩强度高于芯材间距为25 mm的三维机织夹芯复合材料,但是后者的弹性模量高于前者.实验结果对该类结构材料的优化设计与力学性能研究具有极其重要的指导价值.     

In-plane Compressive Behaviors of 3-D Textile Composites at Various Strain Rates

The in-plane compressive behaviors of 3-D textile composites, which including 3-D woven composite, multi-axial multi-layer warp knitted (MMWK) composite and 3-D braided composite, were studied at quasi-static and high strain rate compression loading. The compression behaviors at high strain rates (600∼2,500/s) were tested with split Hopkinson pressure bar (SHPB). The quasi-static compressive tests were conducted on a MTS 810.23 tester and compared with the results at high strain rates. The comparisons indicate that the compression stiffness, failure stress and failure strain for the three kinds of 3-D textile composites are sensitive to strain rate. The MMWK composite has higher failure stress than the 3-D woven composite and 3-D braided composite at the same strain rate; however, the failure strain of the 3-D braided composites is higher than that of the 3-D woven composite and 3-D knitted composite at quasi-static compression because of the quasi-isotropic structure feature in the 3-D braided composite. The compressive failure modes of the 3-D woven composite, MMWK composite and 3-D braided composite are totally different because of the different preform structure.     

Modeling strategies of 3D woven composites: A review

Due to advancements made in 3D weaving process, 3D woven composites have evolved as an attractive structural material for multi-directional load bearing and impact applications, due to their unique transverse properties such as stiffness, strength, fracture toughness and damage resistance. Substantial progress has been made in recent years for the development of new modeling techniques in design and analysis to understand the unique mechanical behavior of 3D woven composites. This paper systematically reviews the modeling techniques along with their capabilities and limitations for characterization of the micro-geometry, mechanical/thermo-mechanical behavior and impact behavior of 3D woven composites. Advantages, disadvantages and applications of 3D woven composites have also been delineated. In addition, this reference list provides a good database for future research on 3D woven composites.     

3D打印发展背景下三维建模软件变革趋势分析

目的作为3D打印重要的辅助工具,现有三维建模软件针对专业用户开发设计,并不适用于普通用户。分析三维建模软件的变革趋势,目的在于让普通用户更方便地使用3D打印设备。方法采用实例分析方法,对具有代表性的三维建模软件进行分析。结论提出面向普通用户的三维建模软件开发思路,包括操作界面图形符号化、信息架构扁平化、建模功能智能化以及基于浏览器的三维建模软件服务平台。     

3D纤维增强复合材料的结构对力学性能的影响

研究了树脂基镀镍碳纤维3D复合材料的不同结构,包括三维五向、正交三向结构对3D复合材料拉伸性能和冲击性能的影响。进行了两种试件力学性能的测定,结果表明,三维五向3D复合材料和正交三向3D复合材料都能达到高的力学性能,在纤维体积含量相近的情况下,三维五向3D复合材料的拉伸强度和冲击强度较正交三向3D复合材料高,拉伸强度可达920 MPa、冲击强度达150 KJ/m2。通过对编织结构的设计,可以设计3D复合材料的性能。     

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.     

爆破荷载作用下岩石边坡动态响应的FLAC3D模拟研究

已有的岩石边坡爆破动力响应分析多用有限单元法.作者尝试运用FLAC3D的动力分析模块进行岩石边坡爆破动力响应分析.建立了能够反映主要地质构造的三维岩石边坡数值模型.介绍了三维有限差分程序FLAC3D动力分析的理论基础,包括边界条件的设定、动力荷载的输入、阻尼的选取以及岩体本构模型的选择.采用FLAC3D模拟了该岩石边坡在爆破荷载作用下的动态响应.分析了爆破结束后边坡体内位移场、应力场、速度场以及塑性区的分布情况,并与爆破前进行对比.将计算结果与实测数据进行了比较,结果表明FLAC3D用于爆破荷载作用下岩石边坡动态响应的数值模拟是可行的.     

三维编织复合材料理论研究进展

有关三维编织复合材料的理论分析研究归纳为:基于细观结构几何模型的物理性能研究和力学性能研究两部分.纤维体积分数是物理性能研究的最主要参数,力学分析以复合材料的弹性性能为主.合理的几何模型决定了力学性能分析与试验结果的一致性.建立在代表性体积单元尺度的几何模型应用最为广泛,得到了力学性能的试验验证.三维编织复合材料的力学性能的数值仿真主要以有限元方法为主,然而仅仅依赖于对其弹性性能的研究结果还远远不能满足三维编织复合材料作为关键结构部件的使用要求,建立完善的断裂准则是编织复合材料大量使用的理论依据.特殊形状的一次性编织复合材料的力学性能研究有待进一步深入.     

OpenGL环境下的模型数据库管理与复杂三维建模

OpenGL作为一个图形标准具有强大的三维图形处理功能,但建模功能较弱,而专业的三维建模软件却有着很强的建模功能.因此,将OpenGL与三维建模软件相结合,对三维建模软件所创建的模型采用Oracle数据库进行管理,再通过构建不同模型类别的转换模块,实现对最常用的三维模型格式转换的支持.读取模型数据,经转换后在OpenGL环境中重新构建三维模型,由此,解决了OpenGL中的复杂三维建模问题.     

石墨烯基复合材料的三维组装与应用研究进展

三维石墨烯结构体不仅继承了二维石墨烯片完美的碳晶体结构,还展现出超低的密度、极高的孔隙率和较大的比表面积等特点,具有导电、导热、吸附等优异性能,是近年来石墨烯功能材料中的一颗新星。目前,石墨烯与聚合物、无机纳米材料组装成三维结构复合材料的研究已经取得了实质性进展,研究者通过丰富的化学和物理路径实现了石墨烯与功能组分的三维有序组装,并赋予该材料奇特的结构特点和性能优势。这些特性使材料在能量储存、环境保护、传感器等研究领域表现出不错的应用前景。根据当前研究热点,综述了石墨烯基复合材料的三维组装与应用的研究进展,包括三维石墨烯/聚合物复合材料与三维石墨烯/无机纳米复合材料两种体系。重点总结了两种体系的三维组装方法,并分析了复合材料中石墨烯与功能组分的结构特点,简要概括了当前三维石墨烯基复合材料在环境保护、超级电容器等不同领域的应用进展,并对三维石墨烯基复合材料的三维结构设计与多样化应用进行了展望。     

Microstructural Modeling and Second-Order Two-Scale Computation for Mechanical Properties of 3D 4-Directional Braided Composites

This study is concerned with the microstructural modeling and mechanical properties computation of three-dimensional (3D) 4-directional braided composites. Microstructure of the braided composite determines its mechanical properties and a precise geometry modeling of the composite is essential to predict the material properties. On the basis of microscopic observation, a new parameterized microstructural unit cell model is established in this paper. And this model truly simulates the microstructure of the braided composites. Furthermore, the mathematical relationships among the structural parameters, including the braiding angle, fiber volume fraction and braiding bitch, are derived. By using the unit cell model, the second-order two-scale (SOTS) method is applied to predict the mechanical properties of 3D 4-directional braided composites, including stiffness parameters and strength parameters. Besides, the effects of the braiding angle and fiber volume fraction on the elastic constants are investigated in detail. Numerical results show that the predictive stiffness and strength parameters are in good agreement with the available experimental data, which demonstrate that the established unit cell model is applicable and the second-order two-scale method is valid to predict the mechanical properties of 3D 4-directional braided composites.     

Analytical and numerical modeling of mechanical properties of orthogonal 3D CFRP

This study proposes an analytical and numerical model, for the prediction of mechanical properties of orthogonal 3D reinforcement composite materials, taking into account their structural parameters (mechanical properties of the components and geometrical architecture). This first step of this work requires the definition of the composite representative elementary volume (REV). Microscope studies made possible to visualize the architectural aspect of the internal structure. From these observations two types of REV, adapted to the types of modeling (analytical and by finite elements FE), were defined. The first one takes into account the whole of material in its thickness thus integrating the characteristics of the layers and the vertical reinforcements. The second one, strongly simplified in order to minimize the costs of calculations, is used in the FE approach. Moreover the analytical model is extended to the prediction of the ultimate properties by using the tonsorial criterion 3D of Tsai. The results obtaining from these modeling are compared with experimental results. This comparison highlights the interest and the limits of each approach according to the effect of the choice of the REV.     

2.5D机织复合材料冲击后剩余强度研究

本文主要对2.5D机织复合材料冲击后的剩余拉伸强度进行研究。采用落锤法预制冲击损伤,并进行剩余拉伸试验。用了基于层合板理论的软化夹杂法对冲击后试样进行刚度衰减的模拟,用有限元软件根据点应力破坏准则计算得到剩余强度,并与剩余拉伸试验结果进行比较,验证了模型的有效性。为便于对比,对平面机织斜纹布铺设的层合板进行了同种计算和实验,得到了在相同冲击能量下2.5D机织复合材料剩余拉伸强度衰减比例小于层合材料的结论,证明2.5D机织复合材料由于Z方向经纱的存在因而具有良好的抗冲击性。     

A Two-Scale Approach to Numerically Predict the Strength and Degradation of Composites

Regarding the composite structure firstly as a composite on the macro-scale and then as the fiber phase and matrix phase on the meso scale, a two-scale approach is proposed to numerically predict the strength of fiber-reinforced composites. As the first step, the stress field is calculated by combining the macro-scale and meso-scale analysis together. With the stress field, the strength index is defined and the initial strength is then predicted. As the second step, the damage is defined and the degradation strength is then predicted. The two-scale approach is validated by analyzing a woven fiber reinforced composite under compression after impact (CAI) loading. Compared with the conventional homogenization approach, the present two-scale approach can not only calculate the stress and the damage of constituent phases on the meso scale, but obtain well correlated CAI strengths with the experimental test.