纤维缠绕壳体材料非线性及大变形分析计算

论述了Jones-N elson-Morgan 模型的构成原理及其参数的确定方法, 利用这个模型研究了纤维缠绕复合材料的非线性本构关系。推导和建立了纤维缠绕壳体大变形有限元公式和有限元模型。在同时考虑材料非线性和大变形情况下对纤维缠绕壳体内压进行了有限元分析计算, 获得了与实验结果符合较好的理论预报结果。      

纤维缠绕固体火箭发动机壳体的应力及强度分析

纤维增强复合材料在许多领域得到广泛应用,固体火箭发动机壳体就是一例。因此,分析其不同内压下的应力及预报爆破压力是十分重要的。复合材料结构承载过程的应力分析,需进行单元失效判断,许引入失效单元的刚度衰退,这种方法是最合理的。本文采用该方法并结合大变形有限元分析理论,计算了某一纤维缠绕固体火箭发动机壳体的应力和爆破压力,数值计算结果与实测数据吻合,证明该方法可用于纤维缠绕复合材料结构的应力及强度分析,值得重视。     

固体火箭发动机纤维壳体缠绕张力校准系统设计

通过对某厂固体火箭发动机纤维壳体缠绕成型生产过程的实地调研和分析,结合生产现状介绍了固体火箭发动机壳体成型工艺中的工艺指标、参数的制定及控制方法,提出了固体火箭发动机纤维壳体缠绕过程中的张力校准解决方案。主要通过检测到的张力数据计算张力静差率和张力波动率,以便更好地了解缠绕机的实际工作情况,进一步对缠绕工艺进行分析。     

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。      

不等开口纤维增强树脂复合材料缠绕壳体非测地线线型设计

线型设计是纤维增强树脂（FRP）复合材料缠绕壳体设计的一项重要研究内容,它对壳体FRP复合材料缠绕制品的质量起关键作用。本文针对不等开口极孔或不同形状封头的FRP复合材料压力容器壳体,基于非测地线缠绕方程,提出了一套非测地线缠绕线型设计方法,建立了根据已知缠绕线型和芯模转角来确定相应的切点数和纱片宽度的计算模型,开发出了一套FRP复合材料缠绕壳体仿真软件系统,对非测地线缠绕线型进行了计算机图像仿真与检验。结果表明:各个设计区间的仿真结果满足设计要求,没有出现缠绕角突变、纤维分布不规律和纤维在局部严重重叠等异常现象。该仿真软件系统可以为工程人员在实际壳体缠绕之前提供参考,缩短缠绕线型迭代试错周期,同时也为后续缠绕角及缠绕顺序等缠绕参数的优化奠定了基础。      

固体火箭发动机复合材料壳体承载力分析

为了提高固体火箭发动机(SRM)的外载荷承载能力,研究了其复合材料壳体的失效机制,提出了复合材料壳体的增强改进结构形式。通过提高复合材料外缠绕层的轴向刚度和横向弯曲刚度,使得连接区域内的内、外缠绕层的轴向变形相协调,改善了内、外缠绕层的轴向承载分配,使增强改进后的复合材料壳体结构的承载能力提高了124%,而结构质量增加低于10%。研究结果表明: SRM复合材料壳体承载能力的关键因素是连接区域内复合材料内、外缠绕层的刚度匹配设计,只有保证连接区域内的刚度匹配和位移变形相协调,才能充分发挥复合材料壳体的承载能力。     

复合材料干纤维增强回转体结构缠绕线型设计

复合材料干纤维缠绕增强结构可解决纤维缠绕树脂基复合材料结构耐冲击性差、低温环境树脂易失效等问题。干纤维增强结构缠绕过程中,纤维束重叠、压缩导致干纤维缠绕增强层各处厚度不一,会对缠绕线型稳定性产生影响。为满足缠绕线型稳定,研究了测地线干纤维缠绕增强层厚度变化及分布规律,分析了纱带宽度、极孔尺寸及芯模结构等参数对增强层厚度的影响,考虑芯模厚度的变化,逐层更新干纤维缠绕增强结构数学模型,进行了缠绕轨迹计算,获得测地线缠绕线型。缠绕实验表明：理论仿真获得的复合材料干纤维缠绕增强容器增强层厚度准确,缠绕线型稳定,无滑纱现象,验证了纤维厚度与缠绕轨迹计算方法的可行性和干纤维增强层厚度仿真的正确性。     

考虑纤维体积含量变化的纤维缠绕厚壁柱形结构的等强度设计

纤维缠绕厚壁柱形管道或容器在缠绕张力作用下会使缠绕纤维层的应力状态不断变化,形成沿壁厚力学性能非均匀的结构。依据缠绕过程中的纤维束应力状态分析和纤维束本构关系,获得了纤维体积含量与所受应力状态的关系。基于正交各向异性本构关系和双层筒模型的离散叠加法,建立了给定缠绕张力确定纤维缠绕厚壁柱形结构剩余张力的计算方法,并计算了等张力缠绕纤维层的纤维体积含量沿壁厚的分布。利用Tsai-Wu失效准则研究了纤维体积含量非均匀的厚壁柱形结构的纤维层强度。研究表明:缠绕工艺使内层纤维体积含量和强度均略高于外层,纤维缠绕厚壁柱形结构的强度分析和设计时应考虑这种影响;利用变化的缠绕张力设计可以实现强度比沿壁厚的均匀分布。     

基于爆破试验的CFRP固体火箭发动机壳体的可靠性设计

根据GJB 1878-94制备了8个碳纤维缠绕复合材料压力容器，通过试验获得壳体的纤维强度、缠绕角、几何尺寸、爆破压强等随机变量特征值，利用这些实验数据对固体火箭发动机壳体进行可靠性设计，并与传统的安全系数法设计进行比较。结果表明，使用可靠性安全系数法设计可以实现安全性和经济性的统一。分析了材料的力学性能参数及壳体的几何参数等随机变量的变异系数对CFRP固体火箭发动机壳体爆破压强分散程度的影响。纤维应力、壳体纤维层厚度和壳体半径的变异系数的大小直接影响了爆破压强的分散程度；而纤维缠绕角除其变异系数的大小直接影响爆破压强的分散程度外，其参数均值也对爆破压强的分散程度有影响。     

用加权残数法分析正交异性扁薄壳体的大变形问题

本文用加权残数法对正交异性扁薄壳体的大变形问题进行了计算分析，首先，本文推导了正交异性扁薄壳体出中曲面挠度Ｗ和应力函数Φ表示的微分方程，其次，本文用加权残数法中的离散最小二乘法编写了计算程序，对四种支承情况下的正交异性扁薄壳体在均布荷载下的变形问题进行了计算，最后，本文进行了其中一种情况的验证试验，结果与计算吻合。     

缠绕线型对缠绕复合材料圆管轴向拉伸失效的影响

采用细观刚度模型的有限元分析（FEA）与改进的逐渐累积损伤方法相结合,建立了缠绕复合材料圆管轴向拉伸失效的分析方法与流程,以揭示缠绕线型对缠绕复合材料损伤失效的影响。对沿圆周方向分布有1个、3个和5个单胞的3种不同线型的缠绕复合材料圆管试件进行轴向拉伸破坏实验,获得其失效形式、平均拉伸强度及其随缠绕线型的变化规律。研究表明：缠绕复合材料圆管轴向拉伸失效主要以丧失承载能力的功能失效为主,缠绕线型对其拉伸强度有一定的影响;数值分析结果表明,轴向拉伸过程中,主要损伤为基体开裂与基纤剪切,纤维交叉容易引起损伤起始与扩展。     

Experimental dynamic characterization of an FRP composite bridge superstructure assembly

A system comprised of concrete filled, filament wound, circular carbon/epoxy girders and an E-glass/polyester deck, representative of a bridge section in the positive moment region was tested at large scale to assess the overall and component structural response. The system was characterized for stiffness and overall response under monotonic and cyclic fatigue loads. Forced vibration testing was conducted as part of a level I non-destructive evaluation (NDE) procedure at each of the test stages, including after failure. Experimental results from the tests were seen to correspond well with analytical results for mode shapes and frequencies obtained through an eigenvalue analysis of a plane-grillage finite element model. The test method was shown to be effective in indicating changes in response as a function of load level and damage accumulation, and is expected to have significant potential for eventual routine health monitoring and damage detection of such structural systems in the field.     

考虑纤维缠绕形态的复合材料结构拉伸承载行为

纤维缠绕复合材料的纤维束具有交叉起伏形态特征,该形态对复合材料结构的力学行为有显著的影响。本文采用数值仿真和实验手段研究了纤维缠绕复合材料平板结构的拉伸力学行为。实验方面,开展纤维缠绕复合材料平板的准静态拉伸实验,通过数字图像相关技术(DIC)监测其表面应变场的演化过程,研究交叉起伏特征对载荷-位移曲线和应变分布特征的影响;数值分析方面,构建包含纤维缠绕形态的介观有限元模型,基于3D Hashin失效准则开展渐进损伤过程模拟,并引入了复合材料的剪切非线性行为。选取层合板结构为参照组,同时开展实验和数值分析。实验结果表明:对于层合结构,缠绕结构的整体刚度更低,失效位移更大,失效载荷基本相同,且缠绕结构菱形特征单元中部纤维交叉起伏区域存在明显的应变集中现象。所构建的有限元模型和实验结果吻合较好,呈现出纤维起伏区域的应变集中、失效起始和扩展行为。      

Advances in the development of built-in diagnostic system for filament wound composite structures

Monitoring the structural integrity of filament wound composite structures such as solid rocket motor cases and liquid fuel bottles can help prevent catastrophic failures and prolong their service life. An integrated structural health monitoring system has been developed by Acellent as a non-destructive evaluation tool for detecting hidden damage in filament wound composite structures. The system includes a built-in sensor network, supporting diagnostic hardware and data processing/analysis software. A prototype of a filament wound composite bottle with embedded SMART Layers has been fabricated successfully at NASA Marshall Space and Flight Center. This demonstrated the compatibility of the SMART Layer to filament winding process. Impact tests were performed on the prototype bottle to generate damage. A scan of the entire bottle by the distributed network of sensors using Acellent’s diagnostic system was able to locate the damage. The built-in signal processing and imaging techniques employed by the software demonstrated the ability of the software to display the impact damage with relative ease in the face of temperature change.     

Residual Stress Assessment in Thin Angle Ply Tubes

This preliminary study aims to investigate the residual stresses developed in hot cured thin-walled angle-ply filament wound tubes made of E-glass/epoxy, Kevlar/epoxy and carbon/epoxy materials. The residual stresses were estimated from change in geometry of these tubes when axially slitted at ambient temperature. Three basic deformation modes; namely opening up, closing-in and twisting, were observed and these depended on the winding angle, material and wall thickness. The residual stresses were also determined from hoop and axial strain gauges mounted on both the inner and outer surfaces at various locations around the tube. The stresses were compared with theoretical prediction based upon a linear thermo-elastic analysis. Both the predicted and measured values were found to increase with increasing hoop stiffness but there was a large discrepancy between the predicted and measured data, reaching a factor of 5 for the thinnest case. When compared with predicted failure stresses, the experimentally determined stresses were some 15% of the computed compressive strength.     

The effect of stress ratio on the fracture morphology of filament wound composite tubes

A comparative study was done between two typical loading conditions (closed-end and restrained-end condition) in the pipeline and piping systems manufactured by filament wound composite tubes with the objective of studying the influence of loading condition on fracture morphology. Four thin-walled E-glass fiber epoxy tubes with different wind angles were produced to perform hydrostatic tests under restrained-end condition. The results were compared with composite tubes tested under closed-end condition in previous work. Unlined tubes were first tested to obtain the leakage failure and then tubes lined with PVC were tested for burst failure pressure under restrained-end condition. The results showed that the fracture morphology of filament wound composite tubes hold a direct relationship to the stress ratio (σ_Hoop:σ_Axial).     

Strength of composite laminates under biaxial loads

Five well known failure criteria and one simple progressive model have been used in conjunction with laminate theory, which allows for nonlinear lamina shear behaviour, to predict the initial and final failure strengths of filament wound composite tubes. The predictions have been compared with experimental leakage and fracture stresses for ±75°, ±55° and ±45° filament wound GRP tubes subjected to a wide range of biaxial stress systems including biaxial compression. In some cases the fracture strengths were a factor of 10 higher than the initial failure predictions. The simple progressive failure theory predictions gave the best agreement with the experimental results.©British Crown Copyright 1996, Defence Evaluation and Research Agency published by Kluwer Academic Publishers with permission.