高湿度环境下石墨烯改性加固胶接结构的力学性能表征及机理研究

The deterioration of adhesive in humid environment always results in the ineffective strengthening structure in civil engineering. In view of .the problem, the project intends to study the mechanical properties and the improvement mechanism of the graphene nanoplate modified adhesive and the bonded interface in a high-humidity environment. Firstly, the water absorption, glass transition temperature, tensile and shear properties of graphene nanoplate modified epoxy adhesives in high humidity environment are studied, and the relationship between mechanical properties and moisture content of modified adhesives is established. The mechanism of improving the water absorption, thermal and mechanical properties of the graphene nanoplates under high humidity conditions is revealed. Secondly, the mode I and mode II fracture toughness of the typical strengthening bonded interface in a high humidity environment is studied. With the introduction of the weighted average moisture content, a cohesive constitutive model related to the weighted average moisture content in a high-humidity environment is established. Based on the relationship between the water absorption and the relative humidity of the modified adhesive, and the relationship between the mechanical properties of modified adhesive, interface and moisture content, the ultimate strength and failure mode of the graphene nanoplate modified strengthening adhesive joints under any humidity conditions are analyzed with the aid of numerical calculations. The evolution of long-term performance of strengthening adhesive structures in high-humidity environments is illustrated.

针对土木工程加固结构中胶黏剂材料在潮湿环境下性能退化导致加固无效的问题，本项目拟研究高湿度环境下石墨烯改性胶黏剂及胶接界面的力学性能及改善机理。首先，研究石墨烯纳米片改性环氧胶黏剂在高湿度环境下的吸水性、玻璃化转变温度、拉伸、剪切性能，建立改性胶黏剂力学性能与含水率之间的关系，揭示高湿度环境下石墨烯纳米片对胶黏剂吸水性及热力学性能的改善机理；其次，研究典型加固胶接界面在高湿度环境下的I型和II型断裂韧性，引入加权平均含水率的概念，建立高湿度环境下改性胶接界面与加权平均含水率相关的内聚力本构模型；基于高湿度环境下改性胶黏剂的吸水性与湿度的关系、以及胶黏剂、加固胶接界面的力学性能与含水率之间的关系，借助数值计算，分析任意湿度环境下基于石墨烯改性环氧胶黏剂的加固胶接结构的力学性能、失效模式和极限强度，揭示加固胶接结构在高湿度环境下长期性能的演化规律。

本项目通过溶剂共混法制备了不同含量石墨烯纳米片（GNP）改性环氧胶黏剂，并对改性后胶黏剂的形貌、结构进行了表征。对不同含量石墨烯纳米片改性环氧胶黏剂的力学性能及在潮湿环境下的耐久性进行测试，得到石墨烯纳米片改性前后环氧胶黏剂的力学性能及耐久性的变化规律，阐明石墨烯提高环氧胶黏剂潮湿环境中耐久性的机理。研究结果表明：掺入0.25%、0.5%、0.75%的GNP后，环氧胶黏剂的拉伸、剪切、I型断裂韧性及用于单搭接胶接结构的拉伸剪切性能有明显的提高；对于胶黏剂的拉伸性能，当GNP含量为0.5%时，环氧胶黏剂的拉伸强度较未改性时提高了23.8%，单搭接胶接结构的拉伸剪切性能提高了74.6%；当GNP含量为0.75%时，剪切强度相比于未改性增加了102%。相比于未改性环氧胶黏剂，经过0.75%含量的GNP改性后胶黏剂在潮湿环境中浸泡56d后吸水率下降了15.4%。除了吸水性之外，经过56d潮湿环境处理后，未改性胶黏剂的拉伸性能下降了49.7%，而0.75%GNP改性胶黏剂的拉伸强度较未老化之前仅降低了11.21%，下降幅度减少了77.3%；放入潮湿环境中八周后，未改性胶黏剂的I型断裂韧性值降低了34.4%，0.25% GNP改性后胶黏剂的I型断裂韧性仅降低了18.4%，下降幅度比未改性的减少了46.5%。研究表明在同样的潮湿环境下，经过GNP改性后的环氧胶粘剂力学性能的下降幅度明显减少，可以有效提高在潮湿环境下胶接结构的耐久性。项目对添加GNP后胶黏剂的吸水性及在水环境中力学性能下降的改善机理进行了阐述，加入疏水性的GNP后，有效分散的GNP增加了水分子扩散路径的曲折度；减小了分子链中的自由体积，降低了环氧树脂的可湿性及水分子在环氧树脂中的扩散系数，减少了水分子在环氧树脂表面的吸附，削弱了潮湿环境对胶黏剂力学性的不利影响，提高了环氧树脂胶黏剂在潮湿环境下的防潮能力，本项目对石墨烯纳米片提高胶接结构在潮湿环境中的耐久性，提高胶接结构的使用寿命提供了理论依据。