【作者】 文思维；

【导师】 肖加余；

【作者基本信息】 国防科学技术大学 ， 材料科学与工程， 2008， 博士

【摘要】 复合材料补片胶接修复技术是一项先进的结构损伤件快速修复技术,已成功应用于军民用飞机铝合金薄板结构件的修复。然而针对铝合金厚板的修复,国外尚处在实验室研究阶段,缺乏必要的实验数据,尤其缺乏有关铝合金厚板修复的疲劳性能实验数据。与碳/环氧复合材料相比,硼/环氧复合材料具有高模量和较大的热膨胀系数等特点,更适于损伤铝合金厚板的修复。我国关于硼/环氧复合材料及其修复铝合金厚板的研究则更少。本文研制出了满足胶接修复用的硼/环氧复合材料补片,研究了硼/环氧复合材料的树脂基体性能、纤维与基体间的界面性能和复合材料力学性能,确定其树脂基体配方和复合材料制备工艺;考察残余热应力、铝合金板厚度、补片材料种类、补片铺层和几何参数及修复工艺等对修复效果的影响,重点考察了试件的热应力、准静态拉伸性能和疲劳性能。采用液体丁腈橡胶（LNBR）改性环氧树脂E-51,考察了其热学、力学和固化反应动力学性能;采用接触角法和改进的单纤维拔出试验方法研究了纤维与基体间的界面性能,同时考察了硼纤维表面处理方法和环氧树脂体系对界面剪切强度的影响;在此基础上,制备出了硼/环氧复合材料,考察了硼/环氧复合材料的力学性能和拉伸破坏模式。结果表明,硼纤维表面采用沸腾乙醇处理、环氧树脂体系为E-51 / 10 wt% LNBR / DDM（DDM为二胺基二苯基甲烷）制备的单向硼/环氧复合材料的力学性能较好,其力学性能为:拉伸强度为1257MPa,拉伸模量为187GPa,断裂延伸率为0.80%;弯曲强度为1606MPa,弯曲模量为187GPa;复合材料层间剪切强度为77.5MPa。分析了厚度为5.20mm和10.20mm两种LC52CS铝合金板的断裂韧度,并分析了这两种铝合金板的应力状态。室温下,5.20mm和10.20mm两种厚度LC52CS铝合金板的断裂韧度KC分别为45.2MPa·m^1/2和42.7MPa·m^1/2。理论分析表明,厚度为5.20mm铝合金板中占主导地位的是平面应力断裂韧度,而厚度为10.20mm铝合金板则是平面应变断裂韧度占主导地位。采用三维有限元模型分析了铝合金厚板修复试件的应力强度因子,考察了残余热应力、铝合金板厚度、补片材料种类和补片参数对修复效果的影响。结果表明,采用硼/环氧补片胶接修复后,铝合金板裂纹尖端应力强度因子显著降低,但其值随铝合金板厚度增大而增大;修复试件的残余热应力降低了修复效果;硼/环氧补片的修复效果好于碳/环氧补片;存在较佳的补片长度、宽度和厚度。分析了铝合金厚板单面修复试件的残余热应力/热应变。结果表明,修复试件中心弯曲挠度随铝合金板厚度增大而减小;修复试件铝合金未修复表面裂纹尖端附近的残余热应力/热应变大于其它区域的残余热应力/热应变,且随铝合金板厚度增大而增大;单向硼/环氧补片单面修复试件的热变形匹配性好于单向碳/环氧补片单面修复试件。分析了铝合金厚板修复试件的准静态拉伸性能。结果表明,相同尺寸的补片,修复试件的承载能力保留率η和承载能力恢复率χ均随铝合金板厚度增大而减小;厚度为10.20mm铝合金板单面修复试件的最大拉伸载荷是完好试件的85.80%,η值比厚度为1.76mm铝合金板单面修复试件的小8.05%,而χ值则只小3.71%;修复试件的最大拉伸载荷提高量随铝合金板厚度增大而增大;修复区域的等效刚度Estiff随铝合金板厚度增大而增大,且均大于相同尺寸完好试件的刚度;临界裂纹中心张开位移δc增大量随铝合金板厚度增大而减小;单向硼/环氧补片单面修复试件的修复效果稍好于单向碳/环氧补片。结果还表明,在本文研究条件下,采用磷酸阳极化表面处理工艺、单向铺层和双面修复等修复方式能较大地提高单向载荷作用下铝合金厚板修复试件的承载能力;采用共固化修复,补片长度为100mm、全宽度和预浸料层数为10层时,单向硼/环氧补片单面修复厚度为5.20mm铝合金板的修复效果较好。研究了铝合金厚板修复试件的疲劳性能。结果表明,在初始裂纹长度为12mm、最大应力为80MPa和应力比为0.1条件下,单向硼/环氧补片单面修复厚度为1.76mm、5.20mm和10.20mm三种铝合金板试件的疲劳寿命分别是未修复试件的22.30倍、12.84倍和8.40倍;单向硼/环氧补片单面修复后,铝合金板的裂纹扩展速率比修复前的裂纹扩展速率小一个数量级,即复合材料补片胶接修复能大大延缓铝合金板疲劳裂纹扩展,且修复试件和未修复试件的裂纹扩展速率均随铝合金板厚度增大而增大;单面修复试件的归一化裂纹长度差Δa随铝合金板厚度增大而增大,说明补片对铝合金板未修复表面裂纹的限制作用随铝合金板厚度增大而减弱;单向硼/环氧补片单面修复试件的疲劳寿命高于单向碳/环氧补片单面修复试件的疲劳寿命。本文同时研究了疲劳破坏模式对修复效果的影响。结果表明,修复试件疲劳破坏由胶粘剂层界面脱粘控制时（厚度为1.76mm铝合金板单面修复试件）,无论铝合金板初始裂纹长度有多大（甚至裂纹完全贯穿铝合金板宽度）,复合材料补片单面修复均能大幅度提高其准静态拉伸和疲劳性能;单面修复试件的最大拉伸载荷能恢复到完好试件的90%左右（铝合金板断裂副修复后也能恢复到完好试件的60%以上）,疲劳寿命（最大应力为80MPa,应力比为0.1）能达到初始裂纹长度为12mm铝合金板的21倍以上;当修复试件疲劳破坏由铝合金板裂纹扩展控制时（厚度为5.20mm和10.20mm铝合金板单面修复试件）,修复试件的准静态拉伸和疲劳性能均随初始裂纹长度增大而降低。本文还采用Paris公式预测了铝合金厚板单面修复试件的疲劳寿命。结果表明,由试验数据拟合得到了不同厚度铝合金板的Paris公式材料常数C和m,材料常数随铝合金板厚度变化而变化;Paris公式能较好地预测疲劳破坏由铝合金板裂纹扩展控制的修复试件疲劳寿命,而对由胶粘剂层界面脱粘控制的修复试件不再适用,建议采用界面脱粘速率与应变能释放率幅值关系式预测其疲劳寿命。更多还原

【Abstract】 The bonded patch repair method is an advanced rapid repair technique for damaged aluminum structures, which has been successfully applied in repairing thin aluminum plates of military and civil aircraft. However, overseas researches are still at the laboratory stage, lacking necessary experimental data, especially the data about the fatigue properties of repaired thick aluminum plates. Compared with carbon fiber reinforced epoxy (Cf / epoxy) composite, boron fiber reinforced epoxy (Bf / epoxy) composite is characterized by high-modulus and bigger coefficient of thermal expansion, which is more suitable for repairing the damaged thick aluminum plates. In China, even fewer studies about Bf / epoxy composite and its application in repairing thick aluminum plates have been carried out.This dissertation studies resin matrix properties of Bf / epoxy composite, interfacial properties of interface between fiber and the matrix, mechanical properties of the composite, then determines the formula of the resin matrix and the preparation technology of the composite to make composite patch according to bonded repair requirements. The study took the Bf / epoxy and Cf / epoxy composite patches to repair center-cracked aluminum plates. The cracked plates were made of LY12CZ aluminum plate with thickness of 1.76 mm and LC52CS aluminum plates with thicknesses of 5.20 mm and 10.20 mm respectively. It aimed to explore the effects on the repair efficiency caused by residual thermal stress, plate thickness, patch material, ply stacking, patch geometry, repair technology, and so on. Study focuses were on the residual thermal stress, quasi-static tensile and fatigue properties of the specimen.Firstly, epoxy resin E-51 was modified by liquid nitrile rubber (LNBR) to explore the thermal properties, stress properties and curing reaction kinetics properties. Contact angle method and developed single fiber pull-out tests were applied to study the interfacial properties of interface between fiber and the matrix, and the effects of boron fiber surface processing method and epoxy resin system on interfacial shear strength were investigated. Based on this experiment, it prepared the Bf / epoxy composite, and studied its mechanical properties and tensile failure mode. The results show that when the boron fiber surface is treated by boiling ethanol, the unidirectional Bf / epoxy composite prepared by epoxy resin of E-51/10 wt% LNBR / 4, 4’-diamino- diphenyl methane (DDM) has good mechanical properties. The indexes of the mechanical properties are as follows: tensile strength is 1257MPa, tensile modulus 187GPa, elongation to fracture 0.80%, bending strength 1606MPa, bending modulus 187GPa, and the interlaminar shear strength 77.5MPa.Secondly, the study analyzed the fracture toughness and the stress state of two types of LC52CS aluminum plates with thicknesses of 5.20mm and 10.20 mm respectively. At the room temperature, the fracture toughness for the plate with thicknesses of 5.20mm and 10.20mm is 45.2MPa·m1/2 and 42.7MPa·m1/2 respectively. Theoretical analysis shows that the plane stress state plays a dominant role in the aluminum plate with thickness of 5.20mm, while the plane strain state plays a dominant role in the aluminum plate with thickness of 10.20mm. Then, three-dimensional finite element model was adopted to calculate Stress Intensity Factor (SIF) of the repaired thick specimens, and the effects of the residual thermal stress, plate thickness, patch material, and ply stacking and patch geometry on the SIF were investigated. It is found that after the bonded repair by Bf / epoxy patch, the SIF of the crack tip of repaired specimens is significantly decreased and the value increases with the increase of the plate thickness. Residual thermal stress of the repaired specimen decreases the repair efficiency. The repair efficiency of Bf / epoxy patch is better than that of Cf / epoxy patch, and there exists better patch length, width, and thickness.Thirdly, the study analyzed residual thermal stress and thermal strain of the single-side repaired thick specimen. The results show that center bending deflection of the repaired specimen, due to mismatching of the coefficient of thermal expansion between the composite patch and aluminum plate, decreases with the increase of the plate thickness. The residual thermal stress and thermal strain near the crack tip of the unrepaired surface are bigger than those around other areas, and they increase with the increase of the plate thickness. The thermal deformation matching ability of single-side repaired specimen of the unidirectional Bf / epoxy patch is better than that of the unidirectional Cf / epoxy patch.Fourthly, quasi-static tensile properties of the repaired specimens were analyzed. The results show that the loading capacity reservations (η), the loading capacity resumption (χ) and the critical crack opening displacement (δc) increment of the repaired specimens decrease with the increase of the plate thickness. The maximum tensile loading for the single-side repaired specimen with thickness of 10.20 mm is 85.80% of the undamaged specimen. Itsηis of 8.05% smaller than the single-side repaired specimen with thickness of 1.76mm. But theχis only of 3.71% smaller. The increase amount of the maximum tensile loading increases with the increase of the plate thickness. The equivalent stiffness (Estiff) of the repaired area increases with the increase of the plate thickness, and both the value of them are bigger than the stiffness of the undamaged plate of the same size. The repair efficiency of single-side repaired specimen of the unidirectional Bf / epoxy patch is better than that of the unidirectional Cf / epoxy patch.The results also show that under the research condition of this study, using anodizing treatment by phosphoric acid to process aluminum plate surface, or taking unidirectional stacking, or double-side repair method could increase the loading capacity of the repaired thick specimen under the unidirectional loading. The repair efficiency of the repaired specimen with thickness of 5.20 mm is the best when the patch width is equal to the plate width, patch length is 100 mm and the number of patch plies is 10.Lastly, it studied the fatigue properties of the repaired thick aluminum plate. The results show that when the initial crack length is 12mm, the maximum stress is 80MPa and the stress ration is 0.1, then the fatigue life of the repaired specimens with thicknesses of 1.76mm, 5.20mm and 10.20mm is 22.30 times, 12.84 times and 8.40 times of those unrepaired specimens respectively. When the unidirectional Bf / epoxy gets single-side repair, the crack growth rate of the aluminum plate is 1 order of magnitude smaller than its growth rate before the repair. That is, bonded patch repair method can greatly delay the fatigue crack growth of aluminum plate, and the crack growth rate of both the repaired specimen and unrepaired specimen increases with the increase of the plate thickness. The normalized crack length difference (Δa ) of the single-side repaired specimen increases with the increase of the plate thickness, which demonstrates that the restriction of patch to the unbonded surface crack growth in single-side repaired specimen decreases with the increase of the plate thickness. The fatigue life of single-side repaired specimen of the unidirectional Bf / epoxy patch is longer than that of the unidirectional Cf / epoxy patch.The dissertation also studied the effect of fatigue failure mode on the repair efficiency. The results show that when the fatigue failure of the repaired specimen with thickness of 1.76mm is controlled by adhesive interfacial debonding, then no matter how long the initial crack of aluminum plate is, the single-side repair of the composite patch can largely increase the quasi-static tensile and fatigue properties. The maximum tensile loading of the single-side repaired specimen can be recovered to 90% of the undamaged specimen, and even the repaired specimen in which the aluminum plate was completely failed can also be recovered up to 60% of the undamaged specimen. The fatigue life, with which the maximum stress is 80 MPa and stress ratio is 0.1, could arrive at 21 times of the repaired specimen with initial crack length of 12mm. However, when the fatigue failure of the repaired specimen with thicknesses of 5.20mm and 10.20mm is controlled by crack growth of aluminum plate, the quasi-static tensile and fatigue properties decrease with the increase of the initial crack length.The dissertation also took Paris law to predict the fatigue life of the single-side repaired thick specimen. The result shows that by matching the experimental data it gets two material constants C and m of the Paris law. The constants in this study have a dependence on the plate thickness. The Paris law can better predict fatigue life of the repaired specimen in which the fatigue failure is controlled by crack growth of aluminum plate, but it is not effective for predicting the repaired specimen controlled by adhesive interfacial debonding. It has been suggested that amplitude formula of interfacial debonding ratio and strain energy release rate range could be used to predict the fatigue life.更多还原