An automated testing machine for monitoring the evolution of fiber breaks

A cooperative agreement between the National Institute of Standards and Technology (NIST) and the Textile Research Institute/Princeton (TRI/Princeton) has resulted in the development of an automated tensile testing machine for determining the interfacial shear strength (IFSS) as determined by the single fiber fragmentation (SFF) test. The imaging capability of this new machine permits the archiving of data for additional analyses as new data reduction methods are developed and provides a framework for the sharing of fragmentation data among researchers. To keep pace with the changing directions of composite micromechanics research, the new machine was extended to obtaining archival data on fiber fragmentation in 2D multifiber arrays by utilizing a new fiber placement device that allows for the precise placement of these arrays within the dogbone specimen. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

---

考虑纤维方向分布的玻纤增强PP复合材料拉伸性能

纤维方向及其分布对玻纤增强PP复合材料的力学特性具有至为关键的影响.提出了一种快速获取纤维数量及每根纤维方向的方法.通过引入方向张量,利用Moldflow软件进行玻纤增强PP树脂注塑成型模拟获得纤维方向的平均分布,结合显微方法观察判断特定点的纤维沿厚度方向的分层情况及定量判断纤维方向的分布.对轿车玻璃纤维增强注塑仪表板的纤维方向相对一致处取与纤维方向呈0°、45°、90°的样条,通过拉伸实验测得拉伸模量,利用所提出的方法研究了仪表板内玻纤方向的分布及其对拉伸模量的影响.研究结果表明:玻纤增强注塑仪表板的力学性能是各向异性的,其沿厚度方向纤维按方向大致可分为三层.     

考虑纤维方向分布的玻纤增强PP复合材料拉伸性能

纤维方向及其分布对玻纤增强PP复合材料的力学特性具有至为关键的影响。提出了一种快速获取纤维数量及每根纤维方向的方法。通过引入方向张量, 利用Moldflow软件进行玻纤增强PP树脂注塑成型模拟获得纤维方向的平均分布, 结合显微方法观察判断特定点的纤维沿厚度方向的分层情况及定量判断纤维方向的分布。对轿车玻璃纤维增强注塑仪表板的纤维方向相对一致处取与纤维方向呈0°、45°、90°的样条, 通过拉伸实验测得拉伸模量, 利用所提出的方法研究了仪表板内玻纤方向的分布及其对拉伸模量的影响。研究结果表明: 玻纤增强注塑仪表板的力学性能是各向异性的, 其沿厚度方向纤维按方向大致可分为三层。     

Implicit scheme of RVE calculation for FCC polycrystals

Considering the coupling effect between the nodal force equilibrium and internal variables evolution, an implicit scheme of solving the non-linear FEM problem is presented to modelling the texture evolution and the anisotropic behaviour of polycrystals for large deformation. This algorithm is based on the isomorphism theory that the current elastic law can be achieved through transferring the reference elastic law by a plastic transformation. Different time steps have been adopted with respect to the global and local iteration systems and the consistent tangent module is also calculated to construct a high speed integration algorithm.     

Choosing a calculation scheme for the temperature field in pulse microwelding

Thermal processes in pulsed methods of microwelding in a solid phase during semiconductor assembly are investigated. Expressions determining the choice of the temperature-field calculational scheme are subjected to numerical analysis. It is shown that the calculated and experimental data are in qualitative agreement.     

An automated design scheme: Weight minimization of a single hulled ship compartment

This paper describes the stages of development of an optimum structural design scheme. Any attempt to generate the optimum scantlings of a structure of even moderate complexity usually poses nonlinear programming problems for which there exist no universally accepted solution method. The structure considered here is a complete compartment of a single-hulled ship acted upon by multiple load cases. The elastic responses under four different load types are obtained by a quasi finite element analysis routine developed specifically for this purpose. Sequential linear programming (SLP) with appropriate artifices to achieve rapid convergence has been successfully employed as an optimization routine to minimize the object function, which in this case was the total weight of the major structural members. The test problem has 490 basic degrees-of-freedom, 21 free design variables and more than 100 mixed constraints, the majority of which are nonlinear implicit stress functions. The method is then applied to a number of cases representative of small warship designs. Suggestions for future extensions and general conclusions are included at the end of the paper.     

An algorithmic approach to the optimization of process cogeneration

In most industrial processes, there is a significant need for electric power and for heating. Process cogeneration is aimed at the simultaneous provision of combined heat and power. The net result is usually a reduction in the overall cost and emissions of greenhouse gases. Therefore, there is a significant need for the optimal design of process cogeneration systems. This objective of this paper is to introduce an algorithmic approach to the optimal design of process cogeneration systems. Focus is given to the interaction of the power cycle with the process heat requirements. Because of the need for explicit thermodynamic expressions, a new set of thermodynamic correlations of steam properties is developed for proper inclusion within a mathematical-programming approach. An optimization formulation is developed to provide a generally applicable tool for integrating the process and the power cycle and for identifying the optimum equipment size, operating parameters (such as boiler pressure, superheat temperature and steam load). The objective can be chosen as minimizing the cost, satisfying the heat requirement of the process, or producing the maximum possible of power. A case study is solved to illustrate the applicability of the devised approach and associated thermodynamic correlations.     

Hyperelastic modelling of arterial layers with distributed collagen fibre orientations.

Constitutive relations are fundamental to the solution of problems in continuum mechanics, and are required in the study of, for example, mechanically dominated clinical interventions involving soft biological tissues. Structural continuum constitutive models of arterial layers integrate information about the tissue morphology and therefore allow investigation of the interrelation between structure and function in response to mechanical loading. Collagen fibres are key ingredients in the structure of arteries. In the media (the middle layer of the artery wall) they are arranged in two helically distributed families with a small pitch and very little dispersion in their orientation (i.e. they are aligned quite close to the circumferential direction). By contrast, in the adventitial and intimal layers, the orientation of the collagen fibres is dispersed, as shown by polarized light microscopy of stained arterial tissue. As a result, continuum models that do not account for the dispersion are not able to capture accurately the stress-strain response of these layers. The purpose of this paper, therefore, is to develop a structural continuum framework that is able to represent the dispersion of the collagen fibre orientation. This then allows the development of a new hyperelastic free-energy function that is particularly suited for representing the anisotropic elastic properties of adventitial and intimal layers of arterial walls, and is a generalization of the fibre-reinforced structural model introduced by Holzapfel & Gasser (Holzapfel & Gasser 2001 Comput. Meth. Appl. Mech. Eng. 190, 4379-4403) and Holzapfel et al. (Holzapfel et al. 2000 J. Elast. 61, 1-48). The model incorporates an additional scalar structure parameter that characterizes the dispersed collagen orientation. An efficient finite element implementation of the model is then presented and numerical examples show that the dispersion of the orientation of collagen fibres in the adventitia of human iliac arteries has a significant effect on their mechanical response.     

密肋复合墙板支撑框架结构自振周期计算方法

密肋复合墙板支撑框架结构是由框架与其内部嵌入的密肋复合墙板组成的一种双重抗震结构,框架内部嵌入复合墙板所组成的受力构件,其变形特征不同于普通框架和剪力墙,由此导致结构的自振周期计算方法不能直接按照一般框架-剪力墙结构进行计算。本文以Timoshenko双变量梁理论及协同工作模型为基础,建立了复合墙板支撑框架结构的频率方程,结合边界条件导出了结构的自振周期计算公式,并给出了基本自振周期的近似计算方法。算例分析表明：复合墙板支撑框架结构自振周期受复合板抗剪刚度影响较大,且影响随着振型的增加而增大,高振型时复合墙板剪切变形的影响不可忽略;采用似计算方法计算基本自振周期的误差不大,可以满足工程计算精度要求。     

纤维复合材料电磁屏蔽效能分层多尺度计算

为建立复合材料宏细观尺度之间电磁响应的关联性,将分层多尺度计算方法应用于纤维复合材料电磁屏蔽效能计算。为准确描述复合材料宏细观之间的联系,以电磁屏蔽效能为衡量标准,确定了复合材料细观结构的代表性体积单元(RVE)。根据电磁场媒质本构方程计算了RVE的等效电磁参数。采用分层多尺度方法计算复合材料宏观构件的电磁屏蔽效能。结果表明工作频率越高则复合材料的RVE越小;所设计的纤维复合材料结构在工作频率2～18GHz范围内具有38dB以上的电磁屏蔽效能,且电磁屏蔽效能随工作频率增加而下降。研究方法适用于求解细观结构相分散均匀或分布有规律的任意形状复合材料宏观构件电磁屏蔽效能。     

热塑性复合材料自动铺放工艺参数分析与优化

热塑性复合材料自动铺放原位成型（AFP）技术是高效低成本制造大型复合材料构件的关键,而自动铺放过程中工艺参数的选取及控制精度对成型构件的性能有较大影响,因此为保证原位成型后成型构件的性能,需分析自动铺放工艺参数对成型构件性能的影响并对其进行优化。本文基于热塑性复合材料自动铺放平台,以连续玻璃纤维增强聚丙烯（GF/PP）预浸纱为原料制备复合材料层合板,以层合板的力学性能为优化目标,根据响应曲面法原理设计试验,分析热气温度、热压辊压力及冷压辊压力各工艺参数及其耦合作用对层合板力学性能的影响,建立各工艺参数与层合板力学性能的二次多项式回归方程预测模型,通过预测值与实际值对比等检验分析,验证回归模型的有效性和可靠性,进而获得热塑性复合材料AFP最优工艺参数组合为热气温度为385℃、热压辊压力为0.3 MPa、冷压辊压力为1.1 MPa。     

Dry fiber automated placement of carbon fibrous preforms

The superior material properties of carbon fiber-reinforced composites make them especially attractive for applications in aeronautics and aerospace industries. Cost reduction and time saving are continuously driving industry, leading to new industrial challenges which include manufacturing composite structures with optimal mechanical performances using the potential of advanced processes using robotics.To produce complex part shapes, technologies implying fabric draping in a mold imply large waste amount, fabric structure variability and uncertainties concerning local fiber volume fraction amount and thus final mechanical properties. To overcome such issues and comply with cost and time efficiency, automated dry fiber placement for preform manufacturing is proposed. This approach allows to integrate many functions in a complex part thank to the ability of the robot to steer fiber tows at specific locations. The final composite part is obtained by injecting the produced preform with resin using RTM (Resin Transfer Molding) or infusion process.The presented project aims to define the influence of the process driving parameters during fiber placement on the final preform properties range. Preforms were produced using a lab-scale automated placement demonstrator. Three preforms configurations were tested to highlight the influence of the preform structure on permeability and mechanical parameters through characterization of the compression behavior and permeability of the produced preforms. Choice of configuration will affect mechanical properties on the manufactured preforms, whereas creation of open channels to enhance the flow propagation during manufacturing does not necessarily increase the preform permeability.     

热塑性复合材料自动铺放过程中红外加热技术研究

为保证热塑性预浸料树脂基体在自动铺放(automated fiber placement, AFP)过程中充分熔融,实现热塑性复合材料(thermoplastic composites,TPC)逐层"原位固结"成型,自动铺放成型过程中需精确控制预浸料的加热温度。针对自动铺放过程中铺放速率会在较大范围内变动的特点,本工作提出一种高速率响应的红外线辐射加热技术。通过对红外热源与铺层间能量传输过程的分析,提出红外加热过程中动态恒温控制方程,建立热源辐射强度与铺放速率之间的匹配关系。基于热塑性复合材料自动铺放实验平台,构建红外加热恒温控制系统,该系统采用前馈控制方式,根据动态恒温控制方程,制定相应控制策略,实现对预浸料加热过程中温度的精确控制。实验结果表明自动铺放过程中使用红外加热恒温控制系统满足变速工况下恒温加热要求,且铺放成型实验件的压缩强度及层间剪切强度均接近模压成型实验件。     

碳纤维增强聚苯硫醚复合材料激光加热原位成型过程中的温度场

连续纤维增强热塑性复合材料（Thermoplastic Composite,TPC）自动铺放（Automated Fiber Placement,AFP）可以实现铺层原位成型,因此在制造大型结构件、降低加工成本及提升生产效率方面潜力巨大。原位成型过程中铺层温度场分布对复合材料构件成型质量具有较大影响,且激光加热过程中又涉及激光能量场与预浸料吸收光能后产生的温度场之间相互耦联,机理复杂,因此结合传热模型,通过有限元模拟仿真研究激光辅助加热自动铺放成型连续碳纤维增强聚苯硫醚（CF/PPS）复合材料过程中铺层经历的温度历程。同时构建铺层温度场测量系统,对铺层经历的温度历程进行实时采集和存储。研究结果表明,铺放过程中黏合区域前方存在激光辐照阴影区,使压辊下方黏合区域的温度急剧下降;随着铺放速度的增加,黏合区域峰值温度逐渐降低,且成型速度越快,铺层间黏合区域峰值温度差越小,而热电偶测量结果与仿真结果相差越大;随着激光输出功率的增大,铺层峰值温度逐渐升高;为提高原位成型效率,当激光输出功率选择最大6kW时,最大铺放速度为0.75 m/s。通过对比,试验结果中的峰值温度与仿真模拟结果变化趋势相近,证明了有限元仿真模型的正确性。      

Method of determining temperature and calculation of thermal stresses in porous permeable walls

The article suggests a method of determining temperature and of calculating thermal stresses in the range of elastic deformations and of the boundaries of the plastic zones in elastoplastic deformation of the material of a permeable cylindrical wall with porous cooling in steady-state heating.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 5, pp. 814–818, November, 1985.     

Shear strength of concrete filled glass fiber reinforced gypsum walls

Glass fiber reinforced gypsum (GFRG) walls, known as a green product that helps to save energy and protect the environment, are promising new building materials developed in Australia in the early 1990s. Driven by the wide-spread interest from the construction industry and the research community, substantial research has been carried out in Australia and a few Asian countries such as China, Malaysia and India to investigate its performance, including the structural behavior for building construction. This paper investigates the shear strength of GFRG walls fully or partially filled with concrete in the hollow cores. Eight full scale GFRG walls were tested under cyclic loadings. The shear performance of the tested walls, including the shear failure mode, hysteresis responses, the ultimate shear strength and the axial load effect, were studied in the paper. With the aid of nonlinear finite element analyses, a design procedure for the shear strength of the concrete filled GFRG walls is developed.     

Boundary layer calculation on the insulated walls of a MHD generator channel with allowance for hall current

An examination is made of the laminar boundary layer of low-temperature plasma on the insulated walls of a MHD generator channel with arbitrary magnetic field along the channel, perpendicular to the wall. An example of a boundary layer calculation by this method is given.     

An enrichment scheme for solidification problems

A new enriched finite element formulation for solving isothermal phase change problems is presented. We propose a fixed mesh method, where the discontinuity in the temperature gradient is represented by enriching the finite element space through a function whose definition includes a gradient discontinuity. Generally, in these types of formulations, the enrichment location (the location of the solidification front) is determined through a level set auxiliary scheme. In this work, this position is determined implicitly by constraining the temperature at the phase change boundary to be equal to the melting temperature. Several numerical examples are presented to show the application of the method.     

聚氨酯弹性体隔板夹层结构的等效参数计算

针对聚氨酯弹性体的隔板夹层结构,阐述了多种不同的等效参数计算方法,并对等效参数进行计算。首先讨论和计算了不考虑结构剪切变形时的整体结构等效参数计算方法,将整体夹层结构等效为正交各向异性薄板,给出了考虑夹芯抗弯刚度的整体刚度系数表达式。其次,在考虑夹层结构夹芯存在剪切变形的情况下,推导了由分隔隔板和聚氨酯弹性体组成的夹芯胞元的等效弹性常数;最后,使用基于应变能密度等效分析的有限元方法对夹芯胞元等效弹性常数进行计算,并与理论分析结果进行对比,二者误差在10%以内。