纤维缠绕复合材料固化过程残余应力/应变的三维数值模拟

采用有限元分析软件ABAQUS,对具有金属内衬的纤维缠绕复合材料圆筒在固化过程中残余应力及应变的变化规律进行了模拟计算。采用FORTRAN语言编制了用以分析固化过程中残余应力的子程序,该子程序考虑了固化过程中复合材料力学性质的变化和由于树脂固化收缩产生的化学收缩应变。算例结果表明：复合材料和金属内衬的残余应力在初始阶段均接近于零,当固化到一定阶段,残余应力迅速增加并且很快达到最大值,在降温阶段释放了部分的残余应力;在整个固化过程中,金属内衬受到压应力,而纤维缠绕层受到拉应力。本文中的三维有限元模型可以得到任意时刻复合材料的温度及固化度分布,通过数值模拟可以有效地优化复合材料固化工艺参数,提高制件的质量。     

复合材料缠绕压力容器的失效风险分析

压力容器的可靠性和安全性将直接影响到空间系统或导弹使命的成败。分析了可能导致复合材料缠绕压力容器失效的危险因素,详细介绍了应力断裂、撞击损伤、内衬泄漏等危险因素的分析和预测方法,并给出了某复合材料缠绕压力容器的失效风险分析结果。     

纤维缠绕聚合物基复合材料压力容器的可靠性设计

为对纤维缠绕聚合物基复合材料( FWRP) 压力容器进行可靠性设计和安全测评, 引入可靠性理论; 应用统计学原理, 以同一失效概率为标准进行FWRP 压力容器结构设计, 以取代目前应用的传统安全系数法设计。根据国家标准制备8 个玻璃纤维缠绕复合材料( GFWRP) 压力容器, 通过实验获得纤维强度、缠绕角、几何尺寸、爆破压力等随机变量特征值。GFWRP 压力容器结构可靠性设计值(纤维缠绕壁厚) 与实验结果基本吻合, 并明显小于传统安全系数法设计值。通过对不同纤维强度随机分布可靠性设计理论计算结果的比较, 确知纤维强度的离散程度是FWRP 压力容器可靠性设计的重要影响因素。传统安全系数设计法只考虑纤维强度(均值) 大小, 而无视纤维强度随机分布特征值对FWRP 压力容器结构抗力的影响, 显然是不合理的。可靠性设计实现了安全性与经济性的有效统一。      

纤维缠绕复合材料压力容器封头厚度预测

本研究的目的是建立一种用来预测纤维缠绕复合材料压力容器封头厚度的方法。针对固化成型的复合材料压力容器封头型面, 基于封头段所有缠绕纱带总体积保持不变条件, 提出了一种采用三次样条函数来预测复合材料压力容器封头厚度的方法。采用该方法对具有不同几何尺寸、 不同缠绕工艺参数的复合材料压力容器进行了封头厚度预测, 并与传统预测方法及实际厚度测量值作了对比分析。算例结果表明, 该方法能够比传统方法更准确地预测纤维缠绕复合材料压力容器的封头厚度, 从而为有限元建模分析提供精确的厚度参数。      

缠绕图型对纤维缠绕复合材料力学性能影响的有限元模拟

针对纤维缠绕复合材料结构中存在纤维束交叉起伏和铺层走向交替的特点,建立了一种分析缠绕图型对缠绕复合材料结构力学性能影响的有限元方法。采用ABAQUS有限元软件,分析了考虑纤维束交叉起伏和铺层走向交替后缠绕复合材料圆柱壳的应力、应变分布规律,并且研究了缠绕图型对缠绕圆柱壳屈曲临界载荷的影响。结果表明:采用层合板模型计算得到的圆柱壳的应力分布比较均匀;考虑纤维束交叉起伏和铺层走向交替后,缠绕复合材料圆柱壳的应力不再均匀分布,应力云图出现规则分布的菱形图案,在菱形区域中纤维交叉起伏和铺层走向交替处的应力有明显的波动。本实验有限元模型中的菱形特征单元可以反映缠绕复合材料纤维交叉起伏和铺层走向交替的实际情况。     

缠绕图型对纤维缠绕复合材料力学性能影响的有限元模拟

针对纤维缠绕复合材料结构中存在纤维束交叉起伏和铺层走向交替的特点,建立了一种分析缠绕图型对缠绕复合材料结构力学性能影响的有限元方法。采用ABAQUS有限元软件,分析了考虑纤维束交叉起伏和铺层走向交替后缠绕复合材料圆柱壳的应力、应变分布规律,并且研究了缠绕图型对缠绕圆柱壳屈曲临界载荷的影响。结果表明:采用层合板模型计算得到的圆柱壳的应力分布比较均匀;考虑纤维束交叉起伏和铺层走向交替后,缠绕复合材料圆柱壳的应力不再均匀分布,应力云图出现规则分布的菱形图案,在菱形区域中纤维交叉起伏和铺层走向交替处的应力有明显的波动。本实验有限元模型中的菱形特征单元可以反映缠绕复合材料纤维交叉起伏和铺层走向交替的实际情况。     

透镜式缠绕肋压扁缠绕过程数值模拟及参数研究

利用ABAQUS 首先建立了透镜式复合材料缠绕肋整体压扁缠绕有限元模型,实现了压扁缠绕非线性数值模拟分析,并得到应力特征。进而对复合材料缠绕肋不同材料参数(铺设角度、层数、厚度)和不同几何参数(卷轴直径、肋圆弧直径、扁平率)下整体缠绕过程进行了数值模拟分析,并比较分析各种情况下的应力特征,得到各种情况下缠绕肋缠绕过程应力、应变及变化规律,以及缠绕弯矩。该文对缠绕肋截面的合理设计及系统样机的研制具有指导和参考价值。     

纤维缠绕复合材料压力容器在内压与非稳定温度场工况下的优化设计

讨论了面内力和法向一维非稳定温度场同时作用下复合材料层合板的优化设计.以层合板的各层铺设角为设计变量,层合板的厚度为目标函数进行优化设计.作为算例,对玻璃纤维缠绕增强塑料压力容器在内压及其内部介质温度突变到稳定温度场全过程逐时刻的不同工况,进行优化设计.     

纤维缠绕复合材料压力容器在内压与非稳定温度场工况下的优化设计

讨论了面内力和法向一维非稳定温度场同时作用下复合材料层合板的优化设计。以层合板的各层铺设角为设计变量, 层合板的厚度为目标函数进行优化设计。作为算例, 对玻璃纤维缠绕增强塑料压力容器在内压及其内部介质温度突变到稳定温度场全过程逐时刻的不同工况, 进行优化设计。      

纤维缠绕复合材料壳体刚度衰减模型数值模拟

应用微分几何理论,推导出纤维缠绕复合材料壳体的非测地线缠绕轨迹、包角方程及绕丝头运动方程,得到缠绕过程的动态仿真模拟数据。将封头处变化的缠绕角、厚度等实际工艺参数直接用于壳体结构的理论分析。采用叠层的增量本构关系,模拟层合板壳结构的损伤过程,建立了损伤后刚度衰减模型及刚度退化准则,并通过实验确定了刚度衰减系数。应用此模型对纤维缠绕复合材料压力容器进行了数值分析。结果表明:纤维缠绕复合材料压力容器封头处损伤会导致其弯曲刚度降低,这是影响轴向变形的重要因素。      

The simultaneous process of filament winding and curing for polymer composites

The simultaneous process of filament winding and curing a composite cylindrical shell is considered. From the macrokinetic point of view it is characterized by the small thickness of the relative effective reaction zone. The thermochemical conditions in manufacturing are governed by the following process variables: speed of winding, initial conversion and temperature of the filament bundle wound, and the heating applied. A thermochemical model is developed for simulation of the temperature and conversion distributions during the process. An approximate solution of the thermochemical model in the form of the constant traveling wave is derived for constant values of process variables and a thermally isolated mandrel. A non-uniform cure stress model of the process is developed for the case of using elastic orthotropic constitutive relations for a composite material. It is found that the thickness of the relative effective reaction zone drastically influences the cure stresses. The dependence of the stress level on the process variables is analyzed.     

The effect of fiber volume fraction on filament wound composite pressure vessel strength

This paper is a continuation of previous research reported in Ref. [1]. The previous paper discussed the relationship between fiber volume fraction in filament wound composite vessels and failure pressure. This research included a design of experiment investigation of manufacturing and design variables that affect composite vessel quality and strength. Statistical analysis of the data shows that composite vessel strength was affected by the manufacturing and design variables. In general, it was found that the laminate stacking sequence, winding tension, winding-tension gradient, winding time, and the interaction between winding-tension gradient and winding time significantly affected composite strength. The mechanism responsible for increases in composite strength was related to the strong correlation between fiber volume fraction in the composite and vessel strength. Cylinders with high-fiber volume in the hoop layers tended to deliver high-fiber strength. This paper further examines the relationship between fiber volume fraction and fiber strain to failure. Data from unidirectional strand tests and additional vessel tests are presented. A computer program that is based on the thermokinetics of the resin and processing conditions is used to calculate the fiber volume fraction distribution in the filament wound vessel. The strand's strength-versus-fiber volume data together with the computer program are used to predict composite vessel burst pressure. In general, good agreement with experimental data is observed.     

Finite element modeling of the filament winding process

A finite element model of the wet filament winding process was developed. In particular, a general purpose software for finite element analysis was used to calculate the fiber volume fraction under different process conditions. Several unique user defined subroutines were developed to modify the commercial code for this specific application, and the numerical result was compared with experimental data for validation. In order to predict the radial distribution of the fiber volume fraction within a wet wound cylinder, three unique user defined subroutines were incorporated into the commercial finite element code: a fiber consolidation/compaction model, a thermochemical model of the resin and a resin mixing model. The fiber consolidation model describes the influence of the external radial compaction pressure of a new layer as it is wound onto the surface of existing layers. The thermochemical model includes both the cure kinetics and viscosity of the resin. This model analyzes the composite properties and tracks the viscosity of the resin, which is a function of the degree of cure of the resin. The resin mixing model describes the mixing of “old” and “new” resin as plies are compacted. Validations were made by comparing image analysis data of fiber volume fraction in each ply for filament wound cylinders with the FEM results. The good agreement of these comparisons demonstrated that the FEM approach has can predict fiber volume fraction over a range of winding conditions. This approach, then, is an invaluable tool for predicting the effects of winding parameters on cylinder structural quality.     

纤维缠绕复合材料壳体原位成型工艺研究

热固型缠绕复合材料壳体以其优异的性能在航空、军事和工业等领域得到了广泛应用.目前,制约其应用和发展的主要瓶颈是壳体的成本和性能,而壳体成型工艺直接决定了其最终性能和成本.由于缠绕壳体为中空结构,因此可以采用加热壳体内部金属芯模或内衬的方法实现缠绕后的或正在缠绕的复合材料的固化成型,即原位成型.本文介绍复合材料壳体原位成型新工艺,建立筒型壳体内加热固化过程的数学模型,利用有限元法对筒体固化过程中的温度和固化度进行了数值模拟分析.该研究为实现壳体高效、优质且低成本成型提供新思路,为原位成型工艺设计、模拟和参数优化提供分析模型和方法.     

Influence of filament winding parameters on composite vessel quality and strength

An experimental design investigation of manufacturing and design variables that affect composite vessel quality, strength, and stiffness was conducted. Eight 20-in. cylinders (with one additional cylinder as a replicate) were manufactured and tested for hoop strength, hoop stiffness, fiber and void volume fraction distribution through thickness, residual stress, and interlaminar shear strength. Material and processing variables were divided into five categories: (a) resin, (b) fiber, (c) fabrication process, (d) design, and (e) equipment. Five variables were selected (from a list of 12) for study using a 1/4 fractional factorial design of experiment setup. The five variables were: (a) winding tension, (b) stacking sequence, (c) winding-tension gradient, (d) winding time, and (e) cut-versus-uncut helicals.

Statistical analysis of the data shows that the composite vessel strength was affected by the manufacturing and design variables. In general, it was found that composite strength was significantly affected by the laminate stacking sequence, winding tension, winding-tension gradient, winding time, and the interaction between winding-tension gradient and winding time. The mechanism that increased composite strength was related to the strong correlation between fiber volume in the composite and vessel strength. Cylinders with high fiber volume in the hoop layers tended to deliver high fiber strength.     

Ar-Kr低温界面传热过程分子动力学模拟

运用非平衡分子动力学原理和LJ势函数仿真研究氩(Ar)与氪(Kr)之间的界面层传热问题,模拟其界面传热的能量变化过程.仿真结果表明,即使界面粗糙度为0,低温固体界面热阻仍然存在.平均温度为40 K,粗糙度为0时,氩(Ar)与氪(Kr)之间界面热阻为0.15～0.18 Wm2/K,相对误差小于17%.     

Modal analysis for filament wound pressure vessels filled with fluid

Filament wound pressure vessels have been extensively used in many engineering fields, especially aerospace industry. Vibration-based damage detection methods have the potential to be employed to monitor the health status of the structures based on the fact that damage occurred in a structure would result in changes in its structural dynamic characteristics. However the presence of fluid will affect the dynamic response of this type of vessel structures. Due to the liquid mass decrease during its service, the whole system is considered a time-variant system in terms of its dynamic response even the structure itself remains free of damage, which cause problems for vibration-based damage detection method that utilized dynamic response change to identify damage. Therefore it is critical to understand how the change of the liquid height level influences the dynamic response of the coupled fluid–structure system. This work describes the FEM analysis and an experimental study on the dynamic response of filament wound pressure vessels filled with liquid of different heights and provides the primary information that can be used for vibration-based damage detection.     

Development of a new generation of filament wound composite pressure cylinders

A new generation of composite pressure vessels for large scale market applications has been studied in this work. The vessels consist on a thermoplastic liner wrapped with a filament winding glass fibre reinforced polymer matrix structure. A high density polyethylene (HDPE) was selected as liner and a thermosetting resin used as matrix in the glass reinforced filament wound laminate.     

Delamination prediction of composite filament wound vessel with metal liner under low velocity impact

Based on low velocity impact kinetic theory and corresponding damage criterion for the composite laminated structures, a 3-D incompatible, geometrically nonlinear finite element method was employed to investigate the impact mechanical behavior of the composite filament cylindrical vessel with metal liner with and without internal pressure and predict their damage distributions during and after impact. A modified Hertzian contact law was used to calculate the contact force between the impact body and impacted cylindrical vessel and a direct integral scheme-Newmark method was applied in time domain during impact analysis process. The damage styles and damage distributions of a typical vessel under different impact velocities are presented. From the numerical results, it is clear that the impact damage extent for composite filament wound vessel with internal pressure is more sever than that without internal pressure under low velocity impact case with same kinetic energy.     

Shape optimization of filament wound articulated pressure vessels based on non-geodesic trajectories

The most important issue for the design of articulated pressure structures reflects on the determination of the optimal meridian profile. In this paper, the optimal design for determining non-geodesics-based meridian profiles is outlined, subjected to geometrical limitations, stability-ensuring winding conditions and the Tsai–Wu failure criterion. The stress field is modeled using classical lamination theory, and the non-geodesic trajectories are employed to enlarge the design space and improve the structural performance. The searched optimal meridian profile is here approximated by cubic splines, which are based on equidistant knots. The objective is to maximize the performance factor using nonlinear optimization techniques. Two design problems are solved: firstly the optimal meridian profile determined using the present method is compared with the geodesic-isotensoid under the given opening radius. Secondly, the different optimal profiles with various slippage coefficients are obtained to demonstrate the effect non-geodesic trajectories have on the geometry and performance of articulated vessels. Results indicate that the articulated structure designed using the present method shows better performance, mainly triggered by increased internal volume as compared to that of the geodesic–isotensoid. Results also show that the structural performance of the articulated pressure vessel can further be improved with increasing slippage coefficients.