【作者】 刘伟先；

【导师】 周光明；

【作者基本信息】 南京航空航天大学 ， 工程力学， 2013， 博士

【摘要】 随着航空航天、风力发电、高速列车、船舶工业、汽车工业等行业快速发展的需要，具有比强度、比刚度高，可设计性强，抗疲劳优良等特点的复合材料层合板，得到了越来越广泛的应用。但复合材料层合板在制造、运输以及使用过程中难免产生各种损伤，从而影响复合材料结构件的安全性能。因此对损伤后的复合材料层合板进行修理以达到结构使用的刚度以及强度要求，具有重大的实用价值。本文主要研究了复合材料层合板真空辅助湿铺贴挖补修理的分析方法。首先发展了用于模拟此类挖补修理结构中复合材料单层破坏的各向异性连续损伤本构模型，其中综合考虑了纤维拉伸压缩破坏、基体拉伸压缩破坏、厚度方向拉伸压缩破坏以及1-2平面和1-3平面内的剪切非线性现象，通过采用基于应变的Hashin准则解决了损伤前后应力准则不连续问题；同时本文在充分考虑二次固化界面无厚度特征后，假设复合材料母板和补片通过接触相互粘接在一起，采用双线性cohesive损伤模型模拟粘接属性，分别描述了纯模式及混合模式下其损伤状态变量的计算公式。采用双线性cohesive损伤模型对双悬臂梁(DCB)和端部缺口弯曲(ENF)试件进行了裂纹扩展理论分析，通过与梁理论、修正梁理论以及弹性地基梁模型结果进行对比验证了此理论分析的准确性，探讨了双线性损伤模型中参数变化对试验载荷-位移曲线和黏聚区长度的影响，为双线性cohesive损伤模型参数的选取提供了理论指导。基于遗传算法建立了力学问题中本构模型参数的识别方法，基于试验测量和参数识别模型正分析所得载荷-位移曲线之间的误差平方和定义了适应度函数，编写了MATLAB程序实现了此参数识别方法。采用铺层结构为(00,900,450,-450)s的ASTM标准开孔拉伸试件作为复合材料单层损伤本构模型中剪切非线性因子和损伤速率影响因子的参数识别模型；选用DCB和ENF试件作为二次固化界面双线性损伤参数识别模型，用于界面刚度、界面点强度、界面断裂韧性的取值。通过假设“真实值”进行数值仿真分析验证了参数识别模型的可靠性和有效性。根据复合材料层合板真空辅助湿铺贴挖补修理工艺流程分别制作了三种不同打磨角度和不同阶梯宽厚比的斜面形和阶梯形修理试验件，通过试验研究获得了各试验件指定点弹性应变值以及拉伸极限载荷，对试验过程观察获得了两种挖补修理方式的破坏过程，并得到了最终破坏模式。通过对真空辅助湿铺贴挖补修理结构中母板和补片构型进行微观分析，进行适当简化建立了合理的斜面形和阶梯形挖补修理截面模型。分别对两种修理方式试验件建立了三维有限元模型，采用复合材料连续损伤本构模型模拟层合板单层破坏、采用基于双线性cohesive损伤模型的接触分析模拟二次固化界面破坏，分别对两种挖补修理方式的破坏过程进行了模拟研究，通过与试验结果进行对比验证了此模型的有效性，最后研究了修理参数(打磨角度、阶梯宽厚比)变化对挖补修理结果的影响。更多还原

【Abstract】 With the rapid development of aerospace, wind power generation, high-speed train, shipindustry, automobile industry, the composite laminates, which possess high specific strength,high specific stiffness, outstanding designability, excellent fatigue resistance and otheradvantages, have been more and more widely used. However, damages that may affect the safetyperformance of composite structures will inevitably produce in composite laminates during theprocess of the manufacturing, transportation and use, thus affects the safety performance ofcomposite structures. Therefore, the repairs for damaged composite laminates has a great valuein practicality. Once repaired, the structure shall satisfy the structural stiffness and strengthrequirements. This paper mainly studies the assessment of the vacuum-assisted wet-layupscarf-patch and stepped-patch repaired composite laminates.The study started from the continuum damage constitutive model for composites of each ply,which took into account the fiber tensile and compressive failure, the matrix tensile andcompression damage, tensile and compression failure in the thickness direction and the shearnonlinear phenomena in1-2plane and1-3plane. The stress discontinuity problem before andafter damage was solved by using the Hashin criterion based on strain. At the same time,considering the zero thickness characteristics of secondary curing interface, the motherboard andthe composite patch are bonded to each other through the contact. The bilinear cohesive damagemodel was used to simulate this adhesive contact property. The pure mode and mixed mode ofthe damage variable formula were described, respectively.Following a crack extension theoretical analysis on the double cantilever beam (DCB) andend notched flexure (ENF) specimens using bilinear cohesive damage model, the accuracy ofthis theoretical analysis was verified by comparing results to data obtained by the beam theory,modified beam theory and elastic foundation beam model. The influence of the changes of thedamage model parameters on the test load displacement curve and the length of the cohesivezone is discussed, This provides a theoretical guidance for the selection of parameters of bilinearcohesive damage model.Based on genetic algorithm, the identification method of constitutive model parameter for amechanical problem was established. The fitness function was defined by using the errorbetween the load displacement curves, obtained by the experiment and analysis using theparameter identification model. This parameter identification method was implemented byMATLAB program. The open hole tensile testing specimens as specified in ASTM, whose layupwere (00,900,450,-450)s, were used for parameter identification of the shear nonlinear factors and the damage rate impact factors in the single-layer composite damage constitutive model. TheDCB and ENF specimens were selected as the bilinear damage parameter identification model ofsecondary curing interface for the interface stiffness, the interface point strength, interfacialfracture toughness values. Numerical simulation analysis were carried out by assuming the ’realvalue’ to verify the reliability and validity of the parameter identification model.According to the process of the vacuum-assisted wet-layup flush repaired compositelaminates, three different grinding angles of scarf repaired and different step width to thicknessratioe of stepped repaired specimens were produced. The elastic strain at specified points and theultimate tensile load were obtained by experiment. The failure process and the final failure modeof these two kinds of repaired method were obtained by observation during the trial process.Through the microscopic analysis of the configurations of the parent material and the patchin the vacuum-assisted wet-layup flush repaired laminates, the models of the section for the scarfand stepped repair were established reasonably. And three-dimensional finite element models ofthese two kinds of repaired mode were built respectively. The composite continuous damageconstitutive model is used to simulate layer destruction, and the contact analysis is based onbilinear cohesive damage model to simulate the failure of secondary curing interface. The failureprocess of each method was studied. These models were verified by comparing with theexperimental results. Finally the effect of the repair parameters, such as grinding angle, stepwidth to thickness ratio, on the repair result were studied.更多还原