冲击荷载下FRP-混凝土界面剥离机理研究

Interfacial debonding phenomenon always happens in FRP reinforced concrete structures under generalized loading because of the insufficient strength of interface. The process of interfacial debonding is extremely complicated, thus it is hard to be observed by experiments. Numerical Methods such as Finite Element Method(FEM) have obstacles in modeling interfacial debonding, such as constitutive law of cohesive interface，accuracy of solution, remeshing and mesh mapping, solution of large-scale nonlinear equations, stability and convergence of algorithm. Furthermore, currently most of the studies focus on interfacial debonding phenomenon under static loading, while the mechanism of interfacial debonding under dynamic loadings, such as impact, collision and explosion, are not clear yet. This project intends to deduce and verify a universal elastic-plastic fracture criterion based on Griffith strain energy release rate, establish a reasonable rate-dependent interfacial constitutive model combined with in-plane shear test, and explicitly model the whole process of FRP-concrete interfacial dynamic debonding under impact loading based on FEM - SBFEM coupled method, local arc-length algorithm and effective remeshing and mesh mapping technology, and then verify the algorithm by fine-mesh FEM and impact experiments,in order to reveal the influence of strain rate effect,inertial effect, loading rate and paste material properties on the macro regularity and micro representation of interfacial debonding based on parameter analysis, and lay an important foundation for the safety study of FRP reinforced concrete.

广义荷载下，纤维增强复合材料（FRP）加固混凝土结构往往因界面强度不足而发生界面剥离破坏。界面剥离过程复杂，试验观测难度大。有限元法等数值模拟方法在粘结界面本构模型、求解精度、网格重分和映射、大型非线性方程组求解、算法稳定性和收敛性等方面尚存不足。目前大部分研究针对静载下的界面剥离问题，冲击、碰撞和爆炸等动载作用下的界面剥离机理尚不明确。本项目拟基于Griffith应变能释放率推导和验证一种普适的弹塑性复合型裂缝扩展准则，结合面内剪切试验建立合理的率相关界面单元本构模型，在FEM-SBFEM耦合技术、局部弧长法、高效的网格重分和映射技术的基础上实现冲击荷载下FRP-混凝土界面动态剥离全过程的快速显式模拟，并与精细有限元和冲击试验相互验证。通过参数分析揭示应变率效应、惯性效应、加载速率和粘结材料特性等因素对界面剥离宏观规律和微观表征的影响，为FRP加固混凝土结构的安全性研究奠定重要基础。

广义荷载下， FRP加固混凝土结构往往因界面强度不足而发生界面剥离破坏。界面剥离过程复杂，试验观测难度大。有限元法等数值模拟方法在粘结界面本构模型、求解精度、网格重分和映射、大型非线性方程组求解、算法稳定性和收敛性等方面尚存不足。本项目完成了冲击荷载下FRP-混凝土界面正拉粘结破坏试验、冲击荷载下FRP-混凝土界面剪切剥离试验、基于随机游走法的二维/三维混凝土细观模型生成方法、基于自适应多边形比例边界元法的弹性动力问题快速求解、基于四叉树（二维）和八叉树（三维）比例边界元的混凝土损伤模拟、基于细观模型和比例边界元法的混凝土损伤模拟等研究内容。系统总结了FRP-混凝土界面断裂能、界面承载力、应力应变分布的影响因素。通过参数拟合获得了考虑应变率效应的FRP-混凝土界面正拉强度计算公式和粘结滑移曲线，为FRP加固混凝土结构的设计提供了参考。