Experimental and Analytical Investigation of Dynamic Fiber Pull-Out in Composites

*9712291 Geubelle一个实验和分析研究项目，将研究动态载荷条件下纤维增强聚合物和陶瓷基复合材料中的纤维脱粘和拔出过程。虽然在准静态加载条件下这两种破坏机制已经进行了大量的工作，而且所有关于这一主题的初步调查都表明这两个过程强烈地依赖于加载速率，但目前对这些过程在动态加载条件下是如何发生的知之甚少。该联合实验和分析研究项目旨在揭示动态脱粘和拔出过程，并构成耐冲击复合材料结构设计的强制性初步步骤。该项目的实验部分包括利用专门改装的分离式霍普金森杆装置对各种模型复合材料进行的动态推出和推出试验。除了从杆件的弹性动力响应中获得宏观载荷/位移曲线外，还将使用光弹装置和高速摄像机对脱粘和拔出过程进行原位光学观测，提供脱粘长度和速度的独立测量。还将对模型复合材料进行现场热成像测量，并对断口表面进行尸检微观分析，以捕捉局部摩擦加热的可能发生，这在一些初步调查中已被证明对拔出过程有很大影响。*项目的分析部分有两个基本目标：首先，将对实验装置进行详细的有限元模拟，以精确地表征测试期间复合材料试件的动态加载。其次，将使用两种截然不同和互补的数值格式(一种特殊的体积/内聚动态有限元格式和一种谱形式的边界积分方法)来研究现有的内聚和摩擦模型是否足以捕捉观察到的纤维脱粘和拔出过程。

*** 9712291 Geubelle An experimental and analytical research project will investigate the fiber debond and pull-out processes in fiber reinforced polymeric and ceramic matrix composites subjected to dynamic loading conditions. While extensive work has been performed regarding these two failure mechanisms under quasi- static loading conditions, and while all preliminary investigations on that topic indicate a strong dependence on the loading rate, very little is currently known on how these processes take place under dynamic loading conditions. The joint experimental and analytical research project aims at shedding some light on the dynamic debonding and pull-out processes and constitutes a mandatory preliminary step for the design of impact-tolerant composite structures. The experimental part of the project consists of dynamic push-out and pull-out tests performed on various model composites with the aid of a specially adapted Split Hopkinson Bar apparatus. In addition to macroscopic load/displacement curves obtained from the elastodynamic response of the bars, in situ optical observations of the debonding and pull-out processes will be performed using a photoelastic set-up and a high speed camera, providing independent measurements of the debonding length and speed. In situ thermographical measurements on the model composite and post mortem microscopic analyses of the fracture surfaces will also be performed to capture the possible occurrence of localized frictional heating which has been shown in some preliminary investigations to drastically affect the pull-out process.*** The analytical part of the project has two basic objectives: firstly, detailed finite element simulations of the experimental set-up will be performed to characterize with precision the dynamic loading of the composite specimen during the tests. Secondly, two distinct and complementary numerical schemes (a special volumetric/cohesive dynamic finite elemen t scheme and a spectral form of the boundary integral method) will be used to investigate the adequacy of existing cohesive and friction models to capture the observed fiber debond and pull-out processes.***