【作者】 王磊；

【导师】 任明法；

【作者基本信息】 大连理工大学 ， 工程力学， 2023， 博士

【摘要】 碳纤维增强树脂基复合材料以其轻质高强、耐疲劳、抗腐蚀等优势广泛应用于航天结构中,对降低运载器发射成本、提高运载能力具有重要意义。液氧贮箱,作为航天运载器重要组成部分,采用全复合材料代替传统合金材料能够有效提升航天运载器的轻量化应用和智能化设计水平,已成为未来发展主流。但受推进剂介质自身强氧化性和低温特性的影响,复合材料液氧贮箱用树脂基体容易出现与液氧不相容和低温力学性能差的问题,从而严重影响运载器综合性能和服役安全。当前与液氧相容聚合物的研究工作大多局限于实验手段,需要耗费大量的人/物力成本及较长研制周期。针对上述问题,首先,发展了一种环氧树脂的液氧相容性预测模型,实现了环氧树脂体系的初始筛选和阻燃改性设计;其次,采用阻燃、增韧的改性思路,设计了一种纳米粒子改性含磷环氧树脂的改性方案;然后,基于上述方案合成并制备了改性环氧树脂,验证了改性树脂的热稳定性、改善了其液氧相容性;最后,建立了基于分子动力学的界面性能仿真模型,发展并验证了一种考虑界面相影响的复合材料多尺度渐进损伤分析框架。主要研究结果如下:（1）初始环氧树脂体系筛选与阻燃改性设计。为实现环氧树脂的液氧相容性的定性预测,基于环氧树脂与液氧不相容的本质是一种氧化燃烧现象,采用分子动力学模拟方法,建立了交联环氧树脂与氧气相互作用模型,提出了反映两者反应强度的“峰值温度”和“质量损失”两个判断指标。通过已有实验数据验证了所建立模型的合理性,并对初始环氧树脂材料进行了筛选。进一步地,以初筛材料体系双酚A型环氧树脂为基础,通过前沿轨道和布局电荷分析,确定了将9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物（DOPO）基团引入环氧树脂分子侧链的接枝方式,结果表明:此方式不以消耗树脂的环氧基为代价,在保证交联度的前提下有效提高树脂固化物中阻燃剂DOPO含量,从而提高了树脂的阻燃性能;同时,分子链的空间位阻的进一步增大使得其玻璃化转变温度、刚度和强度分别提高9.8%、2.6%和31.4%,为后续环氧树脂材料设计奠定了基础。（2）阻燃环氧树脂组分比例优化。为保证改性环氧树脂具有高效阻燃性能的同时降低改性成本,针对阻燃基团含量这一影响改性树脂物理性能的主要因素,建立了不同阻燃基团含量的改性环氧树脂模型,探讨了阻燃剂接枝量对环氧树脂的液氧相容性以及力学性能的影响。结果表明,DOPO基团的加入有利于液氧相容性、弹性模量和屈服强度,但会降低断裂韧性,添加2%的磷可以在尽可能不损害机械性能的情况下有效地改善液氧相容性,进一步地,通过对比树脂自身结构状态和化学产物的变化发现,改性树脂可以减少反应过程中的孔隙变化,同时其生成的不可燃气体在树脂的阻燃过程中起到作用。（3）耐低温环氧树脂方案确定。为保证改性环氧树脂的耐低温性能,基于纳米粒子的协同阻燃和增韧特性,针对纳米粒子的易团聚问题,建立了经硅烷偶联剂KH550修饰的nano-SiO₂和GO粒子改性含磷环氧树脂模型,开展了纳米粒子改性含磷环氧树脂的液氧相容性和低温力学性能研究。结果表明:与含磷环氧树脂相比,经nano-SiO₂和GO粒子改性的含磷环氧树脂峰值温度降低了14.8%,剩余质量增加了3.6%,树脂阻燃性进一步提高,液氧相容性得到改善;同时,随着纳米粒子尺寸的增加,改性树脂的液氧相容性能得到了提高;进一步地,纳米粒子分子结构的强稳定性使断裂沿粒子表面延伸以吸收外部能量,使得K_IC增加10%。改性后的环氧树脂能有效地改善液氧相容性和力学性能。（4）改性环氧树脂的合成、制备、表征和验证。为进一步验证基于分子动力学的与液氧相容环氧树脂改性方案的合理性,合成并制备了基于纳米粒子改性的含磷环氧树脂固化物,分析了改性环氧树脂的热性能和液氧相容性。实验结果表明:相比于纯环氧树脂,改性环氧树脂的初始热分解温度、最大热分解温度和残炭率以及玻璃化转变温度均有明显提高,热稳定性得到增强;同时,材料的液氧相容性得到改善。（5）考虑界面相影响的多尺度分析。针对传统的微观力学实验在测量纤维/基体间界面的法向强度方面存在困难的问题,建立了分子尺度的界面法向拉伸和切向剪切模型,研究了改性纤维/基体界面的法向和切向强度。在此基础上,基于纤维/基体/界面三相代表体元,发展了一种考虑界面相影响的复合材料多尺度分析框架,并通过文献中用于间接测量界面法向强度的横向纤维束拉伸（TFBT）实验进行了验证。结果显示:通过新构建的多尺度框架对TFBT试样的预测误差小于2%,而且破坏模式与实验中观察到的相同。实验和模拟结果之间的良好一致性表明,该方法可以为研究纤维增强复合材料的结构分析提供一种途径;进一步地,采用此框架对基于改性树脂的复合材料贮箱进行了渐进损伤分析,相比于纯环氧树脂,贮箱的承载性能得到提高。更多还原

【Abstract】 Carbon fiber reinforced resin matrix composites are widely used in aerospace structures due to their advantages of lightweight,high-strength,fatigue resistance,and corrosion resistance.They are of great significance in reducing launch costs and improving carrier capacity.Liquid oxygen tanks,as an important component of space vehicles,using all composite materials instead of traditional alloy materials can effectively improve the lightweight application and intelligent design level of space vehicles,gradually becoming the mainstream of future development.However,due to the strong oxidation and cryogenic characteristics of the propellant medium itself,the resin matrix used for composite liquid oxygen tanks is prone to problems such as incompatibility with liquid oxygen and poor cryogenic mechanical properties,which seriously affects the comprehensive performance and service safety of the carrier.To address the above issues,a liquid oxygen compatibility prediction model for epoxy resins was developed to achieve initial screening and flame retardant modification design of epoxy resin systems;Then,a modification scheme for phosphorus-containing epoxy resin modified with nanoparticles was designed using flame retardant and toughening modification ideas;Furthermore,modified epoxy resin was synthesized and prepared,verifying its thermal stability and improving its liquid oxygen compatibility;Finally,a molecular dynamics based interface performance simulation model was established,and a multi-scale progressive damage analysis framework for composite materials considering the influence of interface phase was developed and validated.The main research findings are as follows:（1）Initial epoxy resin system screening and flame-retardant modification.To achieve qualitative prediction of the compatibility of epoxy resin with liquid oxygen,based on the fact that the incompatibility between epoxy resin and liquid oxygen is essentially an oxidation combustion phenomenon,a molecular dynamics simulation method was used to establish a model of the interaction between cross-linked epoxy resin and oxygen.Two judgment indicators,"peak temperature"and"mass loss",were proposed to reflect the reaction intensity of the two.The rationality of the established model was verified through existing experimental data,and the initial epoxy resin material was screened.Further,the grafting method of introducing 9,10-dihydro-9-oxa-10-phosphafi-10-oxide（DOPO）groups into the side chains of epoxy resin molecules was determined by frontier orbital and population charge distribution analysis based on the initial screening material system bisphenol A epoxy resin,and the results showed that this method does not consume the epoxy group of the resin,and effectively improves the resin while ensuring the cross-linking degree.At the same time,the further increase of the spatial resistance of the molecular chain increased the glass transition temperature,stiffness and strength by 9.8%,2.6%and 31.4%,respectively,which laid the foundation for the subsequent design of epoxy resin materials.（2）Optimization of the component ratio of flame-retardant epoxy resin.To ensure the efficient flame-retardant performance of modified epoxy resin while reducing modification costs,a model of modified epoxy resin with different flame-retardant group contents was established to explore the influence of flame-retardant grafting amount on the liquid-oxygen compatibility and mechanical properties of the epoxy resin,which is the main factor affecting the physical properties of the modified resin.The results show that the addition of DOPO groups is beneficial to liquid-oxygen compatibility,mechanical stiffness and yield strength,but reduces the fracture toughness,and the addition of 2%phosphorus can effectively improve the liquid-oxygen compatibility without damaging the mechanical properties.Furthermore,by comparing the structural state of the resin itself and the changes in chemical products,it was found that modified resins can reduce pore changes during the reaction process,while the non-combustible gases generated play a role in the flame-retardant process of the resin.（3）Determination of cryogenic resistant epoxy resin scheme.To ensure the cryogenic resistance of the modified epoxy resin,based on the synergistic flame retardancy and toughening properties of nanoparticles,a modified phosphorus containing epoxy resin model was established by grafting nano-SiO₂ and GO particles with silane coupling agent KH550 to address the problem of aggregation of nanoparticles.The liquid oxygen compatibility and cryogenic mechanical properties of phosphorus-containing epoxy resin modified with nanoparticles were studied.The results showed that compared with phosphorus-containing epoxy resin,the peak temperature of phosphorus-containing epoxy resin modified with nano-SiO₂ and GO particles decreased by 14.8%,and the remaining mass increased by 3.6%,which further improved the flame retardancy and liquid-oxygen compatibility;While the liquid-oxygen compatibility of the modified resin was improved with the increase of the nanoparticle size;The modified epoxy resin can effectively improve the liquid-oxygen compatibility and mechanical properties.（4）Synthesis,preparation,characterization,and validation of modified epoxy resin.To further validate the rationality of molecular dynamics based modification schemes for epoxy resin compatible with liquid oxygen,a phosphorus-containing epoxy resin modified with nanoparticles was synthesized and prepared,and the thermal performance and liquid oxygen compatibility of the modified epoxy resin were analyzed.The experimental results show that compared to pure epoxy resin,the initial thermal decomposition temperature,maximum thermal decomposition temperature,char yield,and glass transition temperature of modified epoxy resin are significantly improved,and the thermal stability is enhanced;Meanwhile,the liquid oxygen compatibility of the material has been improved.（5）Multi-scale analysis considering the influence of interfacial phase.In response to the difficulty of traditional micromechanical experiments in measuring the normal strength of the interface between fibers/matrix,a molecular-scale interfacial normal tensile and tangential shear model was established to study the normal and tangential strength of the modified fiber/matrix interface.Based on this,a multiscale analysis framework for composites considering the influence of interface phases was developed based on a three-phase representative volume element of fiber/matrix/interface and validated by transverse fiber bundle stretching（TFBT）experiments used in the literature for indirect measurement of the normal strength of the interface.The results show that the prediction error of the TFBT specimens by the newly constructed multiscale framework is less than 2%and the damage pattern is the same as that observed in the experiments.The good agreement between experimental and simulation results indicates that this method can provide a way to study the structural analysis of fiber-reinforced composites.Further,progressive damage analysis of composite tanks based on modified resins was carried out using this framework,and the load-carrying properties of the tanks were improved compared to pure epoxy resins.更多还原