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

摘要：CMS-0626025复合材料的长期老化对提高复合材料的可靠性和使用寿命具有重要意义。在这项建议中，复合材料的机械性能是通过定量测量纳米机械纤维-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制于纤维增强材料和基质材料之间的界面，并且已被证明在界面处失效。该区域通常被称为纤维和基质之间的界面，并包含独特的微观机械性能，这些性能已显示出对块体复合材料性能的影响。定量测量界面性能对复合材料的长期性能至关重要，但由于界面的典型长度尺度在微米量级，各种复合材料的界面力学性能的定量测量一直是困难的。使用仪器压痕技术来探测机械性能，这已被证明在亚微米厚度的涂层材料上是可行的，但无法获得定量相间测量所需的横向空间分辨率。为了获得所需的横向分辨率，原子力显微镜(AFM)被用来测量和评估纤维-基质界面的定量机械性能(即硬度)，尽管迄今使用的基于AFM的定量技术(即纳米压痕)依赖于表面的离散点分析，不能提供连续的硬度图。原子力声学显微镜(AFAM)作为一种利用原子力显微镜(AFM)技术进行力学性能定量测量的可行方法，在过去的几年里受到了广泛的关注。该技术包括样品的超声波换能器和利用原子力显微镜悬臂振动测量样品-原子力显微镜针尖接触刚度。然而，使用任何基于AFM的技术来研究复合纤维-基质界面的力学性能作为降解的函数以达到亚微米级的分辨率还没有被使用。这将通过使用AFAM在这里定量地完成。此外，界面区域的断裂韧性与块体复合材料的性能有关，因为它与沿纤维-基质界面发生的裂纹有关。已尝试使用常规仪器压痕进行测量，但不能提供仅对相界面区进行充分分析所需的横向分辨率。在这项工作中，将使用一种新的仪器划痕测试技术来测量断裂韧性作为退化的函数，该技术具有相间长度量级的分辨率。将在现有的块体复合材料力学性能的细观力学模型中使用刚度和断裂韧性的细观力学特性，并将其作为退化的函数与现有数据进行比较。

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.