玻纤复合材料多尺度本构建模及其应用研究

本构模型对复合材料结构设计及分析具有十分重要的作用,在本构模型中应用最广泛的强度准则之一就是蔡-吴(Tsai-Wu)准则。在蔡-吴准则中,交叉项参数需要通过双轴试验确定。工程中常以经验值代替交叉项参数,但是这会影响本构模型的精度。本研究基于玻纤增强复合材料,建立了材料多尺度模型,通过仿真研究材料在双轴加载下的力学性能,确定蔡吴准则中的交叉项参数。在此基础上,建立了玻纤复合材料多尺度本构模型,通过三点弯曲仿真和试验验证本构模型精度,结果表明计算误差小于5%。最后,将建立的本构模型应用于某款车型的玻纤复合材料板簧的设计和分析中,结果满足设计要求。     

层合板在冲击载荷作用下本构方程的研究

纤维增强复合材料层合板的冲击响应是一个兼有几何非线性、材料非线性、接触非线性的复杂过程。本文采用连续介质力学,对层合板的运动、变形进行描述,给出了冲击系统的有限元列式。并一步分析研究层合板在低速冲击作用下的极限承载能力,最后导出有限应变低阶壳单元在显式分析中的应力更新方法,便于在有限元程序中加入复合材料的弹塑性本构模型。     

VARTM工艺铺层取向对复合材料力学性能的影响

采用真空辅助树脂传递模塑(VARTM)工艺制作了玻璃纤维增强不饱和聚酯复合材料层合板,对其进行了拉伸、弯曲、冲击性能测试,并对铺层取向与玻璃纤维复合材料层合板力学性能的影响关系进行了实验研究。实验结果表明,0°取向玻纤增强复合材料在单一方向上的力学性能最佳,±θ取向比θ取向玻纤增强复合材料有更好的力学性能;θ单向铺层复合材料在外载荷作用下发生破坏,其断口破坏的角度与铺层角度一致,而在±θ多向铺层复合材料的断口形貌更复杂。通过合理的铺层设计可获得满足工程需要的复合材料制品。     

玻璃纤维／环氧复合材料双轴非线性分析

本文用玻璃纤雄/环氧复合材料主轴方向上的简单实验结果,建立了基于Hahn—Tsai模型和Jones-Nelson模型的非线性本构方程,并进行了双轴非线性分析。对于Jones—Nelson模型,提出了较之Jones方法更为合理有效的参数确定方法;在双轴非线性分析中,成功地引入应力叠加原理,解决了模型的扩充使用问题,从而保证了模型在整个应力空间的连续性和适用性。为了进一步表征双轴非线性,笔者还提出了双轴硬化系数的概念,并给出了一系列有参考价值的理论预测结果。     

基于非线性本构关系的有限元计算复合材料层合板的强度

复合材料的桥联模型本构理论考虑了基体材料的非线性特性.本文根据联模型理论编制出用户自定义材料库程序,与有限元软件ABAQUS实现接口,以方便地分析计算复合材料层合板结构的非线性响应与极限强度问题.在限元计算中荷载采用逐步加载的方式施加,最终得到复合材料层合板极限坏时的内力包罗图和应力应变曲线.有限元模拟的结果与桥联模型解析解结果吻合得很好,并且与实验结果相一致.     

层合板切口强度和切口敏感性的试验研究

提出了在复合材料板中人工预制尖锐切口的方法。进行了切口呼无切口试样在载荷方向垂直于和平行于纤维面的三点弯曲破坏试验。测定了玻纤／环氧层合板的切口强发口敏感度。探讨了玻纤／环氧层合板的线弹性断裂力学的适用性，借助复合材料的ＷＥＫ断裂模型估计层合板在尖切口前沿的损伤区尺寸。预测了切口强度。结果表明：对于玻纤／环氧层合板，若根据平面应变和小范围屈服的力不条件选择试样尺寸，则其三点弯曲的断裂应力、等效尖     

玻纤增强热塑性复合材料多尺度建模与各向同性曲线拟合

基于玻纤增强复合材料玻纤取向3D计算的Moldflow旋转扩散(MRD)模型对玻纤增强热塑性复合材料(PA66-G30)的标准1BA样条注塑填充过程中的玻纤取向张量进行计算。以14层玻纤取向张量分布和厚度数据为基础,建立该复合材料多层微观代表性体积元(RVE)模型,采用J2幂乘硬化弹塑性模型来拟合实验测试应力-应变曲线,完成该玻纤增强热塑性复合材料多尺度模型的构建。基于该材料模型生成的45°取向的应力-应变曲线与实验结果吻合良好,验证了本实验材料模型的准确性。基于该模型生成了PA66-G30材料的各向同性应力-应变曲线,用于提高注塑产品力学仿真计算的精度。     

纤维复合材料层合板在四点弯曲载荷下的损伤分析

实验测试了T300/7901碳纤维复合材料[0/90]_(8s)层合板在四点弯曲静载下的载荷-位移响应及破坏载荷。基于桥联模型,在商用软件Abaqus/CAE中实现对该层合板在四点弯曲静载条件下的层内以及层间损伤破坏进行模拟分析。分析方法分为四个部分:仅利用组分材料数据,基于桥联模型对单向复合材料层的本构关系建模;利用考虑三维应力的Hashin判据预报复合材料层的纤维拉伸、压缩损伤及基体拉伸、压缩损伤;出现组分材料损伤后对相应材料点采用Camando方法进行刚度退化;在复合材料单层中间插入薄的纯树脂层,通过树脂层的损伤破坏分析层间分层。在Abaqus/Explicit模块中,利用子程序VUMAT完成以上材料建模分析;将模拟结果与实验数据进行对比。结果表明,模拟得到的载荷-位移曲线及破坏载荷与实验结果吻合很好,所提出的材料模型能有效预报纤维复合材料层合板的层内及层间损伤破坏情况。     

环氧改性聚碳酸酯单向纤维复合材料研究

采用Ｅ－５１环氧树脂改性聚碳酸酯，研究其单向Ｅ－玻璃纤维、单向碳纤维Ｔ３００、Ｍ４０复合材料。结果表明，改性后的聚碳酸酯复合材料（ＰＣＣＭ）的层间剪切强度等性能明显提高，玻纤复合材料提高幅度最大。纤维－基体界面粘接良好。     

风电叶片用高模玻纤的开发与应用分析

以风电叶片专用高模量玻璃纤维为研究对象,将其与E玻纤进行了纤维性能差异对比,并利用相应的玻纤单向布制备层合板,对比了层合板的力学性能和单向布的工艺性能,选取3个型号的风电叶片进行了等刚度换算。结果表明,高模玻纤具有更高的抗拉强度、弹性模量、耐化学腐蚀性以及耐疲劳强度;在特征单层厚度和垂直渗透性能相当的情况下,高模玻纤层合板的力学性能均有不同程度的提升;高模玻纤在风电叶片主梁帽中的应用使得风电叶片的质量减轻和成本降低。     

Constitutive modeling for mechanical behavior of PMMA microcellular foams

Constitutive equations for nonlinear tensile behavior of PMMA foams were studied. Five viscoelastic models composed of elastic and viscous components were accounted for the modeling of the constitutive equations. The developed constitutive equations are expressed in terms of material properties and foam properties such as strain, strain rate, elastic modulus, relative density of foam, and relaxation time constant. It was found that the stress-strain behaviors by Generalized Maxwell model, Three Element model and Burgers model could be described by the constitutive equation obtained from the Maxwell model. For the verification of the constitutive model, poly(methyl methacrylate) (PMMA) microcellular foams were manufactured using batch process method, and then uniaxial tensile tests were performed. The stress-strain curves by experiment were compared with the theoretical results by the constitutive equation. It was demonstrated that nonlinear tensile stress-strain behaviors of PMMA foams were well described by the constitutive equation.     

Analysis of nonlinearly elastic cantilever snap beams for assembly of plastic parts

Accounting for the nonlinear stress-strain behavior of plastics is important for good design of a snap joint. A constitutive equation for approximating the nonlinear stress-strain behavior of plastics is introduced in this paper. The equations for the stress, strain, and deflection of a cantilever beam, based upon the newly introduced constitutive equation are presented. In comparison with the experimental results, the cantilever deflection predicted from the nonlinear analysis is found to be about 50% more accurate than the corresponding predictions from the linear analysis.     

A practical approach to modeling time‐dependent nonlinear creep behavior of polyethylene for structural applications

The purpose of this work is to develop a practical method for constitutive modeling of polyethylene, based on a phenomenological approach, which can be applied for structural analysis. Polyethylene is increasingly used as a structural material, for example, in pipes installed by trenchless methods, where the relatively low stiffness of polyethylene reduces the required installation forces, chemical inertness makes it applicable for corrosive environments, and adequate strength allows its use in sewer, gas, and water lines. Polyethylene exhibits time‐dependent constitutive behavior which is also dependent on the applied stress level resulting in nonlinear stress–strain relationships. Nonlinear viscoelastic theory has been well established and a variety of modeling approaches have been derived from it. To realistically utilize the nonlinear modeling approaches in design, a simple method is needed for finding a constitutive formulation for a specific polyethylene type. This paper presents such a practical approach to nonlinear viscoelastic modeling utilizing both the multi‐Kelvin element theory and the power law functions to model creep compliance. Creep tests are used to determine material parameters and models are generated for four different polyethylene materials. The corroboration of the models is completed by comparisons with results from different tensile creep, step‐loading creep, and load‐rate tests. POLYM. ENG. SCI., 48:159–167, 2008. © 2007 Society of Plastics Engineers     

Nonlinear model reduction for dynamic analysis of cell population models

Transient cell population balance models consist of nonlinear partial differential-integro equations. An accurate discretized approximation typically requires a large number of nonlinear ordinary differential equations that are not well suited for dynamic analysis and model based controller design. In this paper, proper orthogonal decomposition (also known as the method of empirical orthogonal eigenfunctions and Karhunen Loéve expansion) is used to construct nonlinear reduced-order models from spatiotemporal data sets obtained via simulations of an accurate discretized yeast cell population model. The short-term and long-term behavior of the reduced-order models are evaluated by comparison to the full-order model. Dynamic simulation and bifurcation analysis results demonstrate that reduced-order models with a comparatively small number of differential equations yield accurate predictions over a wide range of operating conditions.     

Biaxial elastic-viscoplastic behavior of Nafion membranes

Durability is a major limitation of current proton exchange membrane fuel cells. Mechanical stress due to hygro-thermal cycling is one failure mechanism of the polymer electrolyte membrane (PEM). In a fuel cell the PEM is highly constrained in the membrane plane and relatively unconstrained in the through-thickness direction, leading to primarily biaxial loading upon hygro-thermal cycling. The rate, temperature, and hydration dependent elastic-viscoplastic mechanical behavior of Nafion, the benchmark PEM, has been extensively investigated in uniaxial tension in prior work which also served as a data basis for a three dimensional constitutive model. Here, the important effects of the biaxiality of the loading conditions on the elastic-viscoplastic Nafion stress-strain behavior are investigated for the first time via experiments and simulation. Biaxial stress-strain behaviors were shown to exhibit similar features to uniaxial behavior including linear elasticity followed by a highly non-linear transition to yield followed by post-yield strain hardening with highly non-linear unloading and reloading; these features were each quantitatively dependent on the biaxiality of the loading conditions. The constitutive model was found to successfully quantitatively predict the loading behavior and its dependence on biaxiality. The constitutive model was also found to predict the magnitude of the yield shoulder during unloading and reloading, but to underestimate the gradual nature of both the forward and reverse plastic deformation processes as well as the strain recovery at zero load. These errors are consistent with those seen in the uniaxial model indicating that the framework used to incorporate the uniaxial behavior into a three dimensional model is capable of predicting the biaxial deformation response of the membrane.     

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.     

Airbag fabric material modeling of nylon and polyester fabrics using a very simple neural network architecture

The material properties of engineering fabrics that are used to manufacture airbags can not be modeled easily by the available nonlinear elastic–plastic shell elements. A nonlinear membrane element that incorporates an elaborate tissue material model has been widely used by the auto industry for the airbag simulation studies. This model is highly computation intensive and does not differentiate between the various physical properties of the fabrics like fiber denier, the polymer fiber, and weave pattern. This paper introduces a new modeling technique that uses artificial neural networks. Experimental permeability data for fabrics under biaxial strain conditions were obtained through a blister-inflation technique and were used to train the proposed network architecture. In this training environment, various properties of the fabric can be incorporated and the network can be trained to generalize relative to the environment. Once trained, the cause–effect pattern is assimilated by the network with approprate weights to produce a desired output. Fabrics tested in this study included nylon 66 fabrics with three different fabric deniers: 420, 630, & 840 and two types of weave, and two 650-denier polyster fabrics having different calendering effects. The predictions obtained from this neural network model agreed very well with the experimental data. This indicates that neural nets can be considered as a serious design tool use in determining permeability and biaxial stress–strain relationships for textile fabrics used in airbags. © 1996 John Wiley & Sons, Inc.     

连续环状色谱柱分离性能的模拟

连续环状色谱柱是有机物稀溶液及生物制品纯化的重要制备手段,为深入认识连续环状色谱柱的性能,开展了连续环状色谱柱分离性能模拟计算的研究。提出了二维空间网格差分的模拟计算方法,并采用文献报道的木糖-山梨糖分离的实验结果进行验证,模拟计算结果与实验数据基本吻合,证明了模拟计算方法的可行性。同时考察了单组分体系下进料流量、床层旋转速度、相间总传质系数、吸附平衡常数对流出曲线的影响;以木糖为分离关键组分,以木糖的收率和纯度为目标函数,对双组分体系下进料流量、床层旋转速度、床层高度、选择性系数对分离效果的影响进行了计算和讨论,结果表明,选择性系数是决定性因素,适当提高床层旋转速度或床层高度可以增大木糖的纯度。     

Targeting optimum resource allocation using reverse problem formulations and property clustering techniques

Decoupling the constitutive equations from the balance and constraint equations allows for reformulating a conventional forward problem into two reverse problems. The first reverse problem is the reverse of a simulation problem, where the process model is solved in terms of the constitutive (synthesis/design) variables instead of the process variables, thus providing the synthesis/design targets. The second reverse problem (reverse property prediction) solves the constitutive equations to identify unit operations, operating conditions and/or products by matching the synthesis/design targets. Visualization of the problem is achieved by employing recently developed property clustering techniques, which allows a high-dimensional problem to be visualized in two or three dimensions. The clusters by definition satisfy intra-stream and inter-stream conservation through linear “mixing” rules, which allows for the development of consistent additive rules along with their ternary representation.     

Targeting optimum resource allocation using reverse problem formulations and property clustering techniques

Decoupling the constitutive equations from the balance and constraint equations allows for reformulating a conventional forward problem into two reverse problems. The first reverse problem is the reverse of a simulation problem, where the process model is solved in terms of the constitutive (synthesis/design) variables instead of the process variables, thus providing the synthesis/design targets. The second reverse problem (reverse property prediction) solves the constitutive equations to identify unit operations, operating conditions and/or products by matching the synthesis/design targets. Visualization of the problem is achieved by employing recently developed property clustering techniques, which allows a high-dimensional problem to be visualized in two or three dimensions. The clusters by definition satisfy intra-stream and inter-stream conservation through linear “mixing” rules, which allows for the development of consistent additive rules along with their ternary representation.