Experimental Study On Fiber Interfacial Micromechanics By Raman Spectroscopy

Based on fiber composite materials widely-used in aerospace and national demand background, the research status and faced task for the fiber interface micromechanics were firstly given in this article, such as the composition and performance of fiber composites, microstructure and mechanics model of the interface, interface optimization roadmap. The ultimate goal of the design and optimization of composite interface is to obtain the excellent performance of interfacial stress transfer, which has important scientific significance. The main work of this paper is the characterizing of fiber interface micro-mechanical behavior and the establishment of micro-mechanics model from the microscale experiments. The work is funded by the project of NSFC (The study of microscale experimental mechanics on interfacial stress transfer and debonding in polymer-matrix fibrous composite,10972047,2009-2012).The most difficult and crucial stage for the fiber interface optimization is the mechanical characterization of microscale experiments. A preferred research means for interface micromechanics study is micro-Raman spectroscopy (MRS). Its microscopic basis for stress measurement is that Raman shift reflects the changes in the interatomic distance, also reflects the strain. The basic principles, instrument and measurement aspects of MRS were introduced. Raman spectra of some resins and fibers were given to explain the phenomenon of Raman blue shift related to strain. The calibration schemes for Raman shift vs. stress were given. The various test methods and their mechanics models of fiber interface were summarized. The fiber interface failure models and its strength standards, including the elastic stress transfer model and the partially-debonded stress transfer model were given. Single fiber tensile test was used to obtain the mechanical properties of the fibers used in this article. Microbond test was performed to give the interfacial strength of fiber/resin system. Those basic data are provided to the next study of fiber-matrix stress transfer and crack-fiber interaction.Two types of aramid fiber pullout tests were conducted to study the stress transfer behavior of the fiber interface. Sample preparation, optical observation, Raman test scheme design, testing process and analysis methods were described in details. Using fine experiment data to explain the process of interfacial stress transfer, it gets well with the prediction of shear lag model. The interface debonding phenomenon reflected from fiber stress distribution gives the friction shear stress levels of the debonded fiber. A new method of fiber/droplet tension test was developed to study the stress transfer behavior of the fiber interface, especially fiber coating stress transfer. Based on the introduction of the fiber surface modification, specimen preparation of carbon fibers, the preparation of PVC coating and uncoated aramid fiber, optical observation, single fiber deformation measurement, Raman test scheme design, testing process, residual stress, fiber stress and interfacial shear stress were described in details. Using fine experiment data to explain the process of interfacial stress transfer, the effect of the flexible coating on the stress transfer mechanism was discussed.A new sample preparation method was developed to study the fiber-crack interaction with advantages of multiple loading and repeated experiments. Specimen preparation, testing methods, well-bonded fiber, bridging fiber, broken fiber, residual stress, stress transfer, interface slip and friction shear stress were described in details. By observing the bridging fiber and broken fiber on the same sample, the stress transfer models and strength standards were given. Interface friction slipping and re-bearing mechanisms in the process of fiber bridging and fiber breaking were analyzed and modeled to explain the interface debonding and frctional sliding mechanism at microscale.