【作者】 尹昌平；

【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， 2009， 博士

【摘要】 对高速飞行器结构的基本要求是轻质高强和防热隔热。已有的主承力与热防护结构的设计和制备方法,大多是将结构承载体与防热体分步成型与制备,不但增加工艺的难度和复杂性,增加制造成本,而且也降低了整体结构的可靠性。本文提出一种称之为“承载/隔热/防热一体化复合材料”的结构,有望将其应用于飞行器主承力/热防护复合结构。在这种一体化复合材料结构中,承载层为碳/环氧复合材料,隔热层为轻质低导热系数材料,防热层即耐烧蚀层为碳/酚醛复合材料,并将采用共注射RTM工艺进行一次整体成型。围绕共注射RTM工艺制备承载/隔热/防热一体化复合材料,本文对多层复合材料及带缝合热通道的一体化复合材料进行了热分析与设计;优选出了能进行共注射的防热层基体的酚醛树脂和承载层基体的环氧树脂;采用共注射RTM工艺分别制备了泡沫夹芯和气凝胶夹芯一体化复合材料,研究了共注射一体化工艺的力学性能并和分步胶接工艺的进行对比;采用缝合-共注射工艺制备了气凝胶夹芯复合材料,考察了缝合承力柱对力学性能的影响以及缝合热通道对热传导性能的影响。建立了多层复合材料和带缝合热通道的一体化复合材料热传导有限元分析（FEA）模型,计算了在峰值温度为912℃的600s全弹道周期内的热载荷条件下的温度分布,结果表明,PMI泡沫不适用于所确定的热载荷条件下的隔热层材料;固定承载层厚度hl-b为2mm、防热层厚度ht-p为3mm,满足给定热载荷条件下SiO₂气凝胶夹芯复合材料各层使用温度要求的最小隔热层厚度hh-i为16mm;湿法缝合热通道的材料可视为SiO₂气凝胶/苯并噁嗪,其平均孔径为3mm,固定hl-b和ht-p,当针距×行距（l×m）为8×8时,满足使用温度要求的最小隔热层厚度hh-i为24mm;干法缝合热通道材料可视为石英/苯并噁嗪复合材料,其平均孔径为0.9mm,固定hl-b和ht-p,当hh-i为17mm时,满足使用温度要求的最小l×m为10×10,当hh-i为18mm时,满足使用温度要求的最小l×m为7×7。研究了氨酚醛、钡酚醛、苯并噁嗪和酚醛型氰酸酯四种酚醛树脂的动态粘度和等温粘度,建立了酚醛树脂的双阿累尼乌斯粘度模型;研究了四种酚醛树脂的耐热性能和力学性能;采用外推法研究了四种酚醛树脂的特征温度,并结合树脂浇铸体的实际制备效果,确定了四种酚醛树脂的最佳固化制度;以氨酚醛、钡酚醛、苯并噁嗪为基体树脂,以碳纤维平纹布为增强材料,采用真空辅助RTM工艺制备了复合材料平板,研究了复合材料的孔隙率、力学性能和烧蚀性能。结果表明,苯并噁嗪是四种酚醛树脂中是满足RTM工艺性能且使用性能最佳的酚醛树脂,在76℃以上可满足注射要求,且低粘度保持时间较长;浇铸体力学性能最佳,1000℃时N₂气氛下的成碳率为47%;碳/苯并噁嗪复合材料的孔隙率为0.85%,质量烧蚀率为0.0435g.s^-1,拉伸强度为445MPa。良好的界面结合和较低的空隙率是碳/苯并噁嗪复合材料的力学性能优于碳/氨酚醛复合材料和碳/钡酚醛复合材料的主要原因。依据和苯并噁嗪进行共注射的环氧体系的工艺要求,研究了几种基体环氧树脂的动态粘度和不同固化剂所构成环氧体系的凝胶特性及浇铸体的力学性能,确定了承载层基体树脂;采用双阿累尼乌斯模型建立所选环氧体系的化学流变模型,确定了苯并噁嗪和所选环氧体系的共注射温度;采用外推法研究了环氧体系的最佳固化温度,并依据不同固化制度下的树脂浇铸体的拉伸强度,确定了苯并噁嗪和环氧体系的最佳共固化制度。结果表明,E-44/GA327是满足和苯并噁嗪进行共注射要求的性能最佳的环氧体系,其最佳质量配比为100∶30,浇铸体的拉伸强度为80.6MPa,拉伸模量为2.98GPa,弯曲强度为138.6MPa,弯曲模量为3.11GPa,断裂延伸率为3.64%,玻璃化转变温度为164℃,拉伸断口表现为韧性断裂;苯并噁嗪和E-44/GA327体系共注射工艺窗口温度为76～90℃,最佳共固化制度85℃/4h+ 130℃/4h+140℃/2h+160℃/1h+180℃/1h。采用共注射RTM工艺制备了承载/PMI泡沫隔热/防热一体化复合材料,研究了主要工艺参数对制备泡沫夹芯复合材料的影响;分别研究了共注射工艺和分步胶接工艺制备的PMI泡沫夹芯复合材料的力学性能,并研究了一体化复合材料的热传导性能。结果表明,共注射工艺制备PMI泡沫夹芯复合材料的最佳工艺参数为承载层和防热层设计纤维体积分数为45%、注射压力1atm、注射温度80℃、注射时采用真空辅助,按此参数制备的泡沫夹芯复合材料制品各层厚度与设计厚度保持一致,泡沫夹芯内部也未被树脂胶液浸渗;共注射工艺的侧压、三点弯曲、界面剪切性能要优于分步胶接工艺的,且数据离散系数也明显减小,两种工艺的平压性能基本一致,各层之间良好的界面结合是共注射工艺的力学性能优于分步胶接工艺的主要原因;建立的多层复合材料热传导FEA模型可以较好地模拟泡沫夹芯一体化复合材料的热传导过程,但在防热层外表面350℃热载荷条件下,PMI泡沫因无法耐受此温度而失效。采用共注射RTM工艺制备了承载/SiO₂气凝胶隔热/防热复合材料,研究了主要工艺参数对制备气凝胶夹芯复合材料的影响;分别研究了共注射工艺和分步胶接工艺制备的SiO₂气凝胶夹芯复合材料的力学性能和热传导性能。结果表明,设计承载层厚度hl-b为2mm、隔热层厚度hh-i为18mm、防热层厚度ht-p为3mm,以降低制品承载层、防热层的孔隙率和减小树脂胶液对夹芯的浸渗深度为目标,优化得到的共注射工艺参数为“承载层和防热层纤维预成型体的设计纤维体积分数V f为45.6%,注射压力为1atm,注射温度为80℃,注射时采用真空辅助”,按此参数制备的SiO₂气凝胶夹芯复合材料的承载层、防热层厚度与设计厚度一致,环氧侧的浸胶深度De poxy为3.4mm,苯并噁嗪侧的浸胶深度Db enzoxazine为2.5mm;共注射工艺的侧压、平压、三点弯曲和界面剪切性能都显著优于分步胶接工艺的。SiO₂气凝胶夹芯复合材料在防热层外表面施加600℃热载荷的条件下的热传导实验结果与FEA计算结果吻合良好。分别采用“湿法缝合-预固化”和“干法缝合-预固化”两种工艺制备缝合SiO₂气凝胶,并以此为隔热层材料,采用共注射RTM工艺制备了承载/SiO₂气凝胶隔热/防热复合材料,研究了缝合方式及l×m对SiO₂气凝胶夹芯复合材料内部结构、密度、力学性能和热传导性能的影响。结果表明,湿法缝合-共注射工艺的缝合热通道（缝合承力柱）由石英/苯并噁嗪复合材料和SiO₂气凝胶/苯并噁嗪复合材料组成,其中石英/苯并噁嗪通道的孔径为0.9mm,SiO₂气凝胶/苯并噁嗪通道孔径为3mm;干法缝合-共注射工艺的缝合热通道由石英/苯并噁嗪复合材料和石英/环氧复合材料组成,两缝合通道直径约为0.9mm,长度都约为隔热层夹芯厚度的一半;两种工艺的侧压、平压、三点弯曲和界面剪切性能都比分步胶接工艺的有了显著提高;两种工艺的力学性能随着l ? m的减小（缝合密度的增大）而提高;当l×m相同时,湿法缝合-共注射工艺的力学性能要优于干法缝合-共注射工艺的;缝合承力柱是缝合-共注射工艺的力学性能提高的主要原因;所建立的带缝合热通道的FEA模型可以较好地模拟缝合一体化复合材料的热传导过程,缝合热通道（尤其是湿法缝合热通道）显著影响着复合材料的热传导性能。更多还原

【Abstract】 The primary requirements for a hypersonic aerocraft structure are low density, high mechanical performance, thermal protection and heat insulation, respectively. Traditionally, the load bearing/thermal protection structure applied in the hypersonic aerocraft was manufactured with the step by step method and then jointing them with glue. It not only makes the manufacturing process more difficulty and complication and more fabrication cost, but also less reliability of the whole structure. A new load bearing/heat insulation/thermal protection integral composite structure which is manufactured by the Co-injection RTM （CIRTM） is developed in this dissertation, which could be used as primary load bearing and thermal protection compound for the hypersonic aerocraft. In the integral composite structure, the load bearing layer materials are carbon fiber reinforced epoxy （carbon/epoxy） composites, the heat insulation layer materials are low density and low thermal conductivity materials such as PMI foams or silica aerogel materials, the thermal protection layer or ablation layer materials are carbon/phenolic composites.In this dissertation, heat transfer analysis and design of multi-layer composites and integral composites with stitching thermal channels are carried out based on finite element analysis （FEA） method. The optimal phenolic resin for the matrix of thermal protection layer, and the optimal epoxy resin for the matrix of load bearing layer are chosen. The multi-layer composites with foam core sandwich and aerogel core sandwich, respectively, are manufactured by CIRTM process, mechanical properties of the multi-layer composites are investigated and compared to that of multi-layer composites manufactured by bonding step by step method. The stitching-CIRTM process is used to manufacture a multi-layer composite with stitching silica aerogel core materials, effects of stitching pillars on mechanical properties and stitching thermal channels on heat transfer properties of the multi-layer composites are investigated, respectively.Heat transfer FEA models for the integral multi-layer composites with and without stitching thermal channels are established, respectively. Applied the thermal load in trajectory which peak temperature is 912℃to outer surface of the thermal protection layer, the temperature distribution in the multi-layer composites is obtained. The results show that PMI foam is not suitable for using as heat insulation layer materials served at the thermal loading. For load bearing layer thickness （hl-b） of 2mm and thermal protection layer thickness （ht-p） 3mm, the least heat insulation layer thickness （hl-b） of silica aerogel core is 16mm. The wet stitching channels materials can be considered as silica aerogel/benzoxazine composites, the average diameter of the stitching is 3mm. For hl-b of 2mm, ht-p 3mm, and needle-distance×row-distance （ l×m） 8×8, the least thickness hh-i of silica aerogel core is 24mm. The dry stitching channels materials can be considered as quartz/benzoxazine composite, the average diameter of the stitching is 0.9mm. For hl-b of 2mm, ht-p 3mm and hh-i 17mm, the least l×m of silica aerogel core is 10×10. For hl-b of 2mm, ht-p 3mm and hh-i 18mm, the least l×m of silica aerogel core is 7×7.Thermal properties, mechanical properties and process parameters of ammonia-phenolic, barium-phenolic, benzoxazine, novolac cyanate ester resins were investigated systematically by experimental and mathematic model, and rheological models based on the dual-Arrhenius equation for the four phenolic resins are established. The curing characteristic temperatures for the four phenolic resins are studied by differential scanning calorimeter （DSC） technique at different heating rates. According to quality of the cured resins, as well as the curing characteristic temperatures, the optimal curing programmes were determined. Using carbon fiber plain cloth as reinforcement, the composite laminates with matrix of ammonia-phenolic, barium-phenolic, benzoxazine, respectively, were manufactured by VARTM process. Porosities, mechanical properties and ablation properties of the composite laminates are investigated. The results show that the benzoxazine matrix composite laminates have better performance which satisfied RTM requirement. Benzoxazine resin maintains the viscosity less than 800mPa·s above 76℃, and has a wide low-viscosity temperature range and a long low-viscosity keeping time. Cured benzoxazine resin has the best mechanical properties among four cured phenolic resin, char yield at 1000℃in nitrogen atmosphere reaches 47%. The features of the carbon/benzoxazine composite laminates can be summarized as following: porosity is 0.85%, tensile strength is 445MPa, mass ablation is 0.0435g.s^-1.According to the co-injection requirements for epoxy resin and benzoxazine, gel characters of the epoxy systems containing different curing agents are studied, and the mechanical properties of the cured products are also investigated. The rheological model based on the dual-Arrhenius equation for the chosen epoxy resin was established, co-injection temperature was determined combined with rheological model of benzoxazine. The curing characteristic temperature for the epoxy resin was studied by differential scanning calorimeter （DSC） technique at different heating rates. The tensile strength of the cured epoxy resin and cured benzoxazine manufactured by different curing programmes was measured, herewith, the optimal co-curing programmes were determined. The results show that E-44/GA327 has the best mechanical properties and thermal properties which is suitable for co-injection with benzoxazine. The weight ratio of E-44 to GA327 is 100:30. The mechanical properties are as follows: tensile strength is 80.6MPa, tensile modulus 2.98GPa, flexural strength 138.6MPa, flexural modulus 3.11GPa, elongation to fracture 3.64%. Glass transition temperature （Tg） is 164℃. The co-injection temperature of benzoxazine and E-44/GA327 system is 76～90℃, the optimal co-curing programme is 85℃/4h+130℃/4h+140℃/2h+160℃/1h+180℃/1h.Load bearing/PMI foam heat insulation/thermal protection multi-layer integral composites was manufactured by the CIRTM, the primary process parameters were investigated. Mechanical properties of the multi-layer composites with PMI foam core manufactured by CIRTM and bonding step by step, respectively, were investigated. The results show that the optimal process parameters for the CIRTM are as follows: fiber volume fraction of load bearing layer and thermal protection layer is about 45%, injection pressure is 1atm, injection temperature is 80℃, with vacuum assisted. Measured thickness of each layer of the multi-layer composites manufactured by CIRTM with the optimal process parameters is agree with designed thickness, and PMI foam wasn’t infiltrated by epoxy resin or benzoxazine. The edgewise compressive,three point flexural and interfacial shear strength of multi-layer composites manufactured by CIRTM is better than that manufactured by bonding step by step, and that, coefficient of variance decreased significantly. The flatwise compressive properties of the multi-layer composites manufactured by two processes are identical. The multi-layer composites have better interface between each layer manufactured by CIRTM than by bonding step by step. The heat transfer experimental result agrees well with that of the FEA calculation. PMI foam is disabled under the thermal load of 350℃on the outer surface of thermal protection layer.Primary process parameters for load bearing/silica aerogel heat insulation/thermal protection multi-layer integral composites manufactured by CIRTM, were investigated. Mechanical properties and thermal properties of the multi-layer integral composites with silica aerogel core manufactured by the CIRTM and by the bonding step by step are studied, respectively. The results show that when the designed thickness of load bearing layer, heat insulation layer and thermal protection layer is 2mm, 18mm and 3mm, aimed at reducing the porosities of load bearing layer, thermal protection and the thickness of the resin layer infiltrated to the aerogel, the optimized process parameters for the CIRTM are as follows: fiber volume fractions of load bearing layer and thermal protection layer are about 45%, injection pressure is 1atm, injection temperature is 80℃, with vacuum assisted. The final thicknesses of load bearing layer and thermal protection layer of the multi-layer composites with silica aerogel core manufactured by the CIRTM are agree with the designed thickness, exception of the thickness of the heat insulation layer. The depth of the epoxy resin infiltrated to the aerogel core （ De poxy） is 3.4mm, and the depth of benzoxazine resin infiltrated to the aerogel core （ Db enzoxazine） is 2.5mm. The edgewise compressive, flatwise compressive, three point flexural and interfacial shear properties of the multi-layer composites with silica aerogel core manufactured by the CIRTM is better than that manufactured by bonding step by step. The multi-layer composites with silica aerogel core manufactured by the CIRTM has better interface than the one manufactured by bonding step by step. The heat transfer experimental results for of the multi-layer somposites with silica aerogel core under the thermal loading of 600℃on the outer surface of the thermal protection layer agrees well with FEA calculation.Wet stitching-pre-curing process and dry stitching-pre-curing process were used to manufacture stitched silica aerogel core, respectively, and then used as heat insulation layer materials, load bearing/stitched silica aerogel heat insulation/thermal protection multi-layer integral composites were manufactured by the CIRTM. The effects of stitching methods and l×m on inner configuration, densities, mechanical properties and thermal properties were investigated. The stitching thermal channels （stitching pillars） by wet stitching-CIRTM process include quartz/benzoxazine composites and silica aerogel/benzoxazine composites, the diameters of the channels are 0.9mm and 3mm, respectively. The stitching thermal channels by dry stitching-CIRTM process include quartz/benzoxazine composites and quartz/epoxy composites, the diameters of the channels are all 0.9mm. The edgewise compressive, flatwise compressive, three point flexural and interfacial shear properties of the sandwich composites manufactured by wet stitching-CIRTM process and dry stitching-CIRTM process increased significantly, compared to the composites by bonding step by step and CIRTM. However, mechanical properties of the sandwich composites by two processes increased with the decrease of l×m （the increase of stitching density）. For the same l ? m, the mechanical properties of sandwich composite by wet stitching-CIRTM is much higher than those of the sandwich composite by dry stitching-CIRTM. The improvements of mechanical properties of the sandwich composites by stitching-CIRTM are due to the stitching pillars. The calculated results by FEA model show that the stitching thermal channels have significant effects of the heat transfer of, the multi-layer composites with stitched core, especially to the wet stitching channels.更多还原