The mechanical interactions between fibers in a dense random-fiber network transmit stress, cause fiber curvature, and influence fiber orientation in the processing of many types of composites. A few theories describe the mechanics of fiber networks, but almost no simulation results are available. Here, we report a direct numerical simulation of the mechanical behavior of random-fiber networks.;The finite element method is used, and each fiber is represented by a small number of 3-D beam elements. The calculations assume a periodic structure to avoid boundary effects, but within the unit cell the fibers are placed randomly. A special algorithm that uses the random sequential adsorption process creates an initial structure of straight, random, non-intersecting fibers, from which a unit cell with periodic boundary conditions is built automatically. The simulation uses an explicit time integration of dynamic equations, with a general contact algorithm (ABAQUS/Explicit).;A typical run involves 5000 fibers with l/d = 100, compressing the network from an initial volume fraction of 5% to a final volume fraction of 25% using 105 time steps. At the final volume fraction, there are 200, 000 fiber-fiber contacts. Results from the simulation are in good agreement with van Wyk's (1946) theory for compaction pressure at low-to-moderate fiber density. They show fair agreement with Toll's (1998) theory for the number of fiber-fiber contacts, and they also show good agreement with a simple slender-body model for fiber orientation, at least during the initial uniaxial compression.;The simulation then extends the uniaxial compression to large shear deformation. A maximum shear strain of about 2.0 is applied. Results from the simulation are shown for the bulk shear stress, the number of fiber-fiber contacts and the fiber orientation. This simulation provides an interesting tool for understanding the mechanics of random-fiber networks, and building models of composite materials processing.
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机译：在致密的随机纤维网络中，纤维之间的机械相互作用传递应力，引起纤维曲率并影响多种类型复合材料的加工过程中的纤维取向。一些理论描述了光纤网络的机制，但是几乎没有仿真结果可用。在此，我们报告了随机光纤网络力学行为的直接数值模拟。；使用了有限元方法，每根光纤都由少量的3-D梁单元表示。计算采用周期性结构以避免边界效应，但是纤维在单元内随机放置。使用随机顺序吸附过程的特殊算法可创建直线，随机，不相交纤维的初始结构，并从中自动构建具有周期性边界条件的晶胞。该模拟使用动态方程式的显式时间积分和一般的接触算法（ABAQUS / Explicit）;;典型的运行涉及l / d = 100的5000根光纤，将网络从初始体积分数的5％压缩到最终使用105个时间步长，体积分数为25％。在最终的体积分数下，有200，000个光纤触点。模拟的结果与van Wyk（1946）关于中低纤维密度下的压实压力的理论非常吻合。它们与Toll（1998）的纤维接触数量理论完全吻合，并且至少在最初的单轴压缩期间，它们与简单的细长纤维取向模型也显示出良好的一致性。单轴压缩使剪切变形大。施加约2.0的最大剪切应变。仿真结果显示了整体剪切应力，纤维与纤维的接触数以及纤维的取向。该模拟提供了一个有趣的工具，可用于理解随机纤维网络的力学以及建立复合材料处理模型。
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