Degradation at the fiber-matrix interphase and effects on long-term performance of composites

摘要：复合材料的长期降解对提高复合材料的可靠性和使用寿命具有重要意义。在这个建议中，复合材料的力学性能是通过定量测量纳米力学纤维-基质界面性能作为降解的函数来评估的。碳纤维增强复合材料受纤维增强材料与基体材料界面的控制，并在界面处失效。该区域通常被称为纤维和基体之间的界面，并包含独特的微力学性能，这些性能已被证明对整体复合材料性能有影响。定量测量间相性能的能力对复合材料的长期性能至关重要，但由于间相的典型长度尺度在微米量级，对各种复合材料的间相力学性能的定量测量一直很困难。使用仪器压痕技术来探测机械性能，这种技术已被证明在亚微米厚度的涂层材料上是可行的，但不能获得定量间相测量所需的横向空间分辨率。为了获得必要的横向分辨率，原子力显微镜（AFM）已经被用来测量定量和评估纤维基质界面的定性力学性能（即刚度），尽管迄今为止使用的基于原子力显微镜的定量技术（即纳米压痕）依赖于表面的离散点分析，不能提供连续的刚度映射。原子力声学显微镜（AFAM）作为原子力声学显微镜技术定量测量材料力学性能的一种可行方法，在过去的几年里得到了广泛的关注。该技术涉及到样品的超声波转导和利用AFM悬臂振动测量样品-AFM尖端接触刚度。然而，目前还没有使用任何基于原子力显微镜的技术来研究复合纤维-基体界面力学性能作为降解的函数，以达到亚微米尺度的分辨率。这将在这里通过使用AFAM定量地完成。此外，界面区域的断裂韧性对整体复合材料的性能也很重要，因为它与纤维-基体界面上发生的断裂有关。已经尝试使用常规仪器压痕进行测量，但不能提供仅对间相区域进行充分分析所需的横向分辨率。在这项工作中，断裂韧性将利用一种新的仪器划痕测试技术作为退化的函数来测量，该技术的分辨率在界面长度的数量级上。刚度和断裂韧性的微力学性能将用于现有的体复合材料力学性能的微力学模型，并与现有数据作为退化函数进行比较。

Abstract: CMS-0626025 Long-term degradation of composites is important for the reliability and improvement of composite material life-times. In this proposal, mechanical performance of composites is assessed with respect to quantitative measurements of nanomechanical fiber-matrix interphase properties performed as a function of degradation. Carbon-fiber reinforced composites are governed by and have been shown to fail at the interface between the fiber-reinforcements and the matrix material. The region is characteristically called the interphase between the fiber and the matrix and contains unique micromechanical properties that have demonstrated effects on bulk composite properties. The ability to quantitatively measure the interphase properties is critical to the long-term performance of composite materials, but due to the typical length-scale of the interphase being on the order of micrometers, the quantitative measurement of the interphase mechanical properties of various composites has been difficult. The use of instrumented-indentation techniques to probe mechanical properties, which have been proven viable on coating materials with sub-micrometer thicknesses, does not garner the lateral spatial resolution necessary for quantitative interphase measurements. To achieve the lateral resolution necessary, Atomic Force Microscopy (AFM) has been utilized to measure quantitative and assess qualitative mechanical properties of the fiber-matrix interphase (namely stiffness), though quantitative AFM-based techniques so far used (i.e. nanoindentation) rely on discrete point analysis of the surface and cannot provide continuous stiffness mapping. The use of Atomic Force Acoustic Microscopy (AFAM) has gained attention in the past few years as a viable method for quantitative mechanical property measurement using AFM technology. The technique involves ultrasonic acoustic transduction of the sample and measurement of the sample-AFM tip contact stiffness by means of the AFM cantilever vibrations. Nevertheless, the use of any AFM-based techniques has not been employed to study the composite fiber-matrix interphase mechanical properties as a function of degradation to achieve resolution on the sub-micrometer scale. This will be accomplished here quantitatively by using AFAM. In addition, the fracture toughness of the interphase region is of interest to bulk composite properties since it is related to cracking that occurs along the fiber-matrix interface. Measurement using normal instrumented-indentation has been attempted, but does not provide the lateral resolution necessary for adequate analysis of the interphase region only. In this work, the fracture toughness will be measured as a function of degradation utilizing a novel instrumented-scratch testing technique that has resolution on the order of the interphase length. The micromechanical properties of stiffness and fracture toughness will be used in existing micromechanical models for bulk composite mechanical properties and compared with existing data as a function of degradation.