Compressive and shear performance of three-dimensional rigid stochastic fibrous networks: Experiment,finite element simulation,and factor analysis

The macro-mechanical behaviors of stochastic fibrous materials are strongly affected by their architecture and the properties of the component fibers. In this study, a three-dimensional finite element model was constructed to study the through-the-thickness compressive and interfacial shear performance of rigid SiO₂ ceramic fibrous tiles and some of the factors affecting them. The simulation consists with the experiments. The failure mechanisms of the model show fiber damage is dominant while the effect of the connections on the shear performance is stronger. We analyzed the factors affecting the mechanical performance of the structure, including the size effects of the model and the distribution and performance of the fibers. Among them, the effect of the degree of preferred orientation of the meso-architecture is the most significant and statistically satisfies the logistic regression model. Other factors, like the diameter and strength fluctuation of fibers, also result in noticeable changes in the mechanical performance.     

High‐temperature short‐range compressive responses and contact effect of ultrahigh porosity 3D random fibrous materials

Through experiments and finite element modeling (FEM) of contacting fibers, we study the compressive responses of a 3‐dimensional (3D) random fibrous (RF) material of ultrahigh porosity (89%) in the through‐the‐thickness (TTT) and in‐plane (IP) directions from 299 (room temperature) to 1273 K. The experimental results indicate that localized failure and overall compressive deformation dominate the deformation process of RF materials loaded in the TTT direction at low and high temperatures, respectively. On the other hand, only localized failure is observed in the IP direction upon loading. Based on its morphological characteristics, a FE model that considers contact between the fibers is developed to simulate the compressive responses of the tested 3D RF material. In this model, the contact mechanism between the fibers is simulated based on a user‐defined nonlinear spring element. The simulated strength and elastic modulus agree well with the observations from the compressive experiments.     

Behavior of beams in bolted column‐tree frames at elevated temperature

Column‐tree moment resisting frames, as the efficient shop‐welded and field‐bolted structural systems, are used in many countries. Very limited research has been carried out on such systems under fire conditions. This paper presents experimental and numerical investigations of the behavior of beam and bolted splice connections in steel column‐tree moment resisting frames exposed to fire. Two full‐scale steel sub‐frames with different splice connections were tested under International Organization for Standardization (ISO 834) fire. The observation of thermal and structural fire behaviors including temperature histories, temperature deflection of the beam, temperature rotation of splice connections, and failure modes was investigated. The beam splice connection failed because of shear fracture of top bolts at temperatures beyond 750 °C, while beam underwent large deflections of more than span/20. In addition, detailed 3‐D finite element models were developed to simulate the structural behavior of the specimens in fire. Obtained numerical results from the finite element analysis successfully simulated the experimental fire test results. Copyright © 2015 John Wiley & Sons, Ltd.     

Multiscale mechanical phenomena in electrospun carbon nanotube composites

The carbon nanotube (CNT) structure is a promising building block for future nanocomposite structures. Mechanical properties of the electrospun butadiene elastomer reinforced with CNT are analyzed by multiscale method. Nanofiber diameter dependence on electric field and solution concentration is estimated from experimental data. The fiber microscale effective properties are determined by homogenization procedure using modified shear‐lag model, while the point‐bonded stochastic fibrous network on the mesoscale replaced by continuum effective sheet. Random fibrous network was generated according experimentally determined stochastic quantifiers. The influence of CNT reinforcement on elastic modulus of electrospun sheet on macroscopic level is determined by finite element method. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

On the Effect of Fiber Shape and Packing Array on Elastic Properties of Fiber-Polymer-Matrix Composites

Abstract

In this study, three-dimensional finite element simulations on the base of the cell model and micromechanics are made to predict effective elastic properties of fibrous composites. The effects of fiber shape, packing array and volume fraction on the overall elastic behavior of an epoxy resin containing unidirectional glass fibers are examined. The geometrical structure includes three types of periodic fiber arrangements in cubic, hexagonal and rectangular cells. The fibers are assumed to be of four shapes; square, circular, elliptic and rectangular. The numerical results indicate that the overall transverse elastic properties are rather sensitive to both fiber shape and packing array while fiber geometry has no effect on the apparent overall Young's modulus in the longitudinal direction of the fibrous composite.     

Numerical/experimental assessment of 3D-printed shape-memory polymeric beams

The main objective of this article is to present different computational tools to replicate thermomechanical shape-memory responses of beam-like structures fabricated by three-dimensional (3D) printing technology. To simulate thermomechanical behaviors of shape-memory polymer (SMP) beams, one-dimensional (1D) finite element model (FEM) building with MATLAB and 3D FEM by means of COMSOL Multiphysics are established. All governing equations are developed based on a 3D thermomechanical SMP constitutive model. 1D FEM is derived on the basis of the Euler–Bernoulli beam theory and linear geometrical assumption. The 3D SMP constitutive model is implemented into geometrically nonlinear COMSOL Multiphysics software through a user-defined material subroutine to provide a powerful 3D simulation tool. Comparative studies on FEMs of MATLAB and COMSOL Multiphysics reveal that geometrically linear assumption is appropriate for models in large/small deformation under tension/bending. 1D analytical solution for deflection of an SMP beam employing Euler–Bernoulli beam theory is also developed. An experiment is conducted to demonstrate a full shape-memory cycle of SMPs. It is experimentally shown that a 3D-printed beam recovers the deformation incurred by external loads upon heating over the transition temperature. The accuracy of the 3D FEM in COMSOL Multiphysics is checked with analytical solutions and experimental data. It is found that simulation results of the program are in good agreement with characteristics observed in the experiment and analytical solutions. The developed computational tools are expected to be instrumental in the design of simple/complicated SMP structures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47422.     

基于有限元形状优化方法实现等强度梁的探讨

为了应用有限元形状优化方法,获得材料力学中简支梁的等强度梁结构,我们首先建立简支梁的平面有限元模型,进行形状优化,得到了平面等强度梁的结果;然后建立三维简支梁的有限元模型,计算得到形状优化的三维等强度梁结果.将材料力学中等强度梁与有限元形状优化结果比较可知,两者结论一致.进而,如果选择不同的优化区域则可以得到不同的结果.这说明应用有限元形状优化方法建立等强度梁,可以方便学生理解材料力学等强度梁的内容,激发学习兴趣.     

Numerical and experimental study on the nonlinear dynamic response of a ceramic matrix composites beam

In this paper, nonlinear dynamic responses of a unidirectional ceramic matrix composite (CMC) beam are studied both experimentally and numerically. Frequency-sweep tests are performed to study the dynamic response of a CMC beam under swept harmonic loads. Constitutive tests, which include axial loading and unloading, were performed to study the constitutive response of a unidirectional CMC under a complicated load history. The shear-lag model is extended to three-dimension (3D) and the values of parameters in this model are certificated by experimental result. The finite element method combined with the shear-lag model is used to simulate the dynamic response of CMC beams under swept harmonic loads. The experimental and numerical results revealed that the variable stiffness of the CMC leads to amplitude saltation under swept harmonic load. The natural frequency of the CMC beams changed with the magnitudes of the external load. Based on the dynamic simulation model, the effects of parameters in constitutive model on the dynamic response of CMC beam are also discussed.     

Homogenized tensile and bending properties of plain weave single‐Ply E‐glass/epoxy

This study empirically, numerically, and analytically analyzes the tensile and bending behavior of a plain weave single‐ply E‐glass/epoxy composite. In the empirical part of the study, tensile and simple bending experiments are conducted. Finite element method is used in the modeling part of the numerical study. Transverse and longitudinal fibers of the plain woven composite are modeled in one and three dimensions by using the ABAQUS software. Finally, mixture ratio approach and composite beam approach are considered in the analytical part of the study. Elastic modulus, Poisson's ratio, bending stiffness, and critical bending radius are obtained experimentally and are compared with the results of the finite element analyses and the results of the analytical study where applicable. The results closest to the empirically obtained ones are obtained by three‐dimensional (3D) finite elements analysis. Moreover, the mechanical characteristics obtained by the composite beam approach used in the analytical study are also very close to the values obtained by 3D finite elements analysis. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Metabolic network modelling: Including stochastic effects

We propose to model the dynamics of metabolic networks from a systems biology point of view by four dynamical structure elements: potential function, translocation matrix, degradation matrix, and stochastic force. These four elements are balanced to determine the network dynamics, which gives arise to a special stochastic differential equation supplemented by a relationship between the stochastic force and the degradation matrix. Important network behaviors can be obtained from the potential function without explicitly solving for the time-dependent solution. The existence of such a potential function suggests a global optimization principle. The existence stochastic force corresponds naturally to the hierarchical structure in metabolic networks. We provide theoretical evidences to justify our proposal by discussing its connections to others large-scale biochemical systems approaches, such as the network thermodynamics theory, biochemical systems theory, metabolic control analysis, and flux balance analysis. Experimental data displaying stochasticity which carries important biological information are also pointed out.     

Multi‐scale modelling of the tensile behavior of lithium ion battery cellulose separator

As a satisfactory green material for a lithium ion battery separator, cellulose possesses better wettability and superior thermal and chemical stability compared to commercial polyolefin separators. The macroscopic mechanical properties of the separator are determined by structural parameters on different dimensional scales. In this paper, a two‐scale modelling method is proposed for a cellulose separator. At micro‐scale, a single fiber structural model was established with a cross‐sectional profile extracted through image processing, combined with the fiber helix angle. At meso‐scale, a representative volumetric element model and a two‐dimensional random fibrous model for the fibrous network of the cellulose separator were developed. The elastic modulus in the machining direction (MD) and transverse direction (TD) of the two models were calculated by finite element simulation and compared with experimental data. The results show that the elastic modulus of the models is slightly larger than that from experiments. Compared to experiments, the relative errors in the MD and TD of the representative volumetric element model are 2.80% and 6.78%, respectively. The relative errors in the MD and TD of the two‐dimensional random fibrous model are 6.70% and 8.47%, respectively. Consequently, multi‐scale modelling is proven to have considerable value in investigating the properties of fibrous materials. © 2019 Society of Chemical Industry     

Modeling of the impregnation process during resin transfer molding

A model has developed for simulating isothermal mold filling during resin transfer molding (RTM) of polymeric composites. The model takes into account the anisotropic nature of the fibrous reinforcement and change in viscosity of the polymer resin as a result of chemical reaction. The flow of impregnating resin through the fibrous network is described in terms of Darcy's law. The differential equations in the model are solved numerically using the finite element technique. The Galerkin finite element method is used for obtaining the pressure distribution. A characteristics based method is used to solve the non-linear hyperbolic mass balance equation. The finite element formulation facilitates computations involving the motion of the polymer resin front characterized by a free surface flow phenomenon.     

Three-dimensional sintering morphology simulation of silica fibrous insulator and its quantitative description

Silica fibrous insulator possessing excellent thermal properties is widely used in the aerospace engineering field. A finite element model is developed for simulating the solid-state sintering process in the preparation process of the fibrous insulator. The model is capable of simulating initial surfaces with complex geometric features. The model is validated by using the classic double-sphere diffusion model and comparing the simulation results with the experimental results in the reference. Results suggest sintered morphology is strongly controlled by the highest holding temperature and has little relationship with the heating rate. The detailed simulation parameters for sintering fibrous silica are determined by the experiment of sintering parallel fibers. Comparison between the simulation results of planar simplification model, double-sphere model, and double-cylinder model reveals the significance of neighborhood diffusion on the sintering of parallel fibers. We found the morphological geometric feature of the sintered fibrous body is consistent and accordingly the Feature Neck Ratio (FNR) is defined to quantitatively describe the degree of sintering and the morphology feature of the sintered fibers. From the perspective of the sintering morphology, when FNR reaches about 0.7–1 no matter how the sintering route is, the fibers are considered to be fully sintered together.     

油气管道长腐蚀缺陷的非线性有限元分析

利用有限元分析软件ANSYS对长腐蚀缺陷管道进行了非线性有限元分析,发现对于长度超过1 200 mm的长腐蚀缺陷,可以采用简化的二维模型代替三维模型来进行计算;腐蚀缺陷深度对腐蚀管道极限载荷的影响比较大;腐蚀缺陷宽度的影响不明显,可以忽略不计。     

基于ABAQUS的轮胎滑水仿真分析

通过SolidWorks建立12种花纹轮胎的三维模型,导入ABAQUS中生成有限元模型,然后使用ABAQUS CEL方法进行轮胎滑水仿真分析,对不同类型花纹轮胎的滑水性能分别进行比较。结果表明:对于横沟花纹轮胎,采用带有倾斜的横向沟槽花纹有利于轮胎排水;对于纵沟花纹轮胎,纵沟条数越多,滑水性能越好,无弯折花纹沟轮胎的滑水性能较好;对于混合花纹轮胎,纵沟为无弯折花纹沟、横沟为斜横沟且纵横相连的花纹可明显优化轮胎的滑水性能。     

三维机织复合材料单胞模型各向异性的有限元分析

使用三维绘图软件Pro/E绘制出三维浅交弯联机织复合材料数字化结构模型,借助大型有限元分析软件ANSYS模拟单胞模型承受不同方向压缩载荷作用下的力学性能。探究在不同方向的压缩载荷作用下复合材料单胞模型的应力分布情况,并借此分析复合材料单胞模型的各向性能;以承受X方向压缩载荷的单胞模型为例,分析复合材料中纤维与树脂的受力情况。结果表明:三维机织复合材料受到压缩载荷时,表现出明显的各向异性,表现为X方向压缩性能最好,Z方向压缩性能最差;纤维作为主要承载体,承担较多载荷作用,树脂作为次要承载体,承担较少载荷作用。     

三维四步法纱线不同运动式样编织复合材料力学性能分析

通过对三维四步法1×3式样、1×5式样编织复合材料几何细观结构的研究,采用六边形纤维束截面假设,建立了一种三维四步法1×3式样、1×5式样编织复合材料有限元3D模型,对其拉伸、压缩和剪切力学性能进行了理论分析,并与试验结果进行了对比,验证了有限元3D模型的准确性。     

陶瓷全自动液压压机接触有限元分析

利用有限元接触分析法对６００吨陶瓷全自动液压压机立柱的预紧进行了研究。传统的压机有限元分析是将上梁、立柱、底腐和为单独部分进行的,在整机分析中将各部件作为固连的整体,忽略了接触的非线性特性;本文还分别按传统的有限元方法和接触有限元方法对压机计算结果进行对比,分析结果表明,两者计算结果有较大的差异,考虑接触科技司的压机有限元分析更接近实际工况。本文采用的分析方法对其它立柱式压机同样适用。     

Scalable Numerical Tools for Flow and Pressure Drop Computation in Fibrous Filter Media

The prediction of flow behavior and pressure drop in fibrous filter media is challenging due to the complexity of the nonuniform fiber structure. Numerical calculation tools can considerably contribute to pressure drop determination for inhomogeneous filter structures. A numerical solution approach based on the finite element method to simulate 2D and 3D filter structures is considered. As numerical examples, computer designed homogeneous and inhomogeneous 2D cases where the numerical approach is validated by analytical models are investigated. Furthermore, the capability of the numerical method to simulate real 3D structures corresponding to more than 25 million degrees of freedom of the related algebraic system is demonstrated. The large systems involved require the use of dedicated techniques related to high performance computing.