Microscopic Mechanism of the High-Temperature Strength Behaviour of a C/SiC Composite
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Microscopic Mechanism of the High-Temperature Strength Behaviour of a C/SiC Composite Fei Su 1 & Pengfei Huang 2 Received: 18 February 2019 / Accepted: 6 March 2019/ # Springer Nature B.V. 2019
Abstract In this paper, a high-temperature test experimental system is built to investigate the dependence of the strength of a C/SiC composite material on temperature. Unintuitively, the strength increases with temperature. To investigate the microscopic mechanism, scanning electron microscopy (SEM) of an in situ bending test experiment is performed. Our hypothesis is that due to significant residual tensile stress in inter-fibre matrix, external loads reach the ultimate stress first. As the temperature increases, the matrix residual tensile stress decreases, a larger external load needs to be applied for matrix failure, which is exhibited macroscopically as increased strength. To prove this hypothesis, the inter-fibre matrix residual stress and its dependence on temperature are calculated via a finite element method. Next, using a SiC wrapper layer around a single C fibre as an experiment object, the finite element calculation is verified directly via micro-Raman spectroscopy. Keywords C/SiC composite material . Strength . Residual stress . Micro-Raman spectroscopy
1 Introduction C/SiC composites are normally produced under a vacuum at high temperatures of approximately 1000 °C via chemical vapour infiltration (CVI) [1–3]. These materials have advantages such as low density, high strength and a low thermal expansion coefficient [4, 5]. Recently, they have become an important high-temperature structural material in aviation and aerospace [6], where they are commonly used as materials for high-speed aircraft missile stabilizer wings and gas turbine thermal section components [7]. Therefore, understanding the high-temperature mechanical properties and underlying microscopic mechanisms of these materials is greatly important to improving the manufacturing process for this material and fully leveraging its material efficiency.
* Fei Su [email protected]
1
School of Aeronautical Science and Engineering, Beihang University, Beijing, China
2
Chinese Academy of Space Technology(Xi’an), Xi’an, China
Applied Composite Materials
According to some reports, the strength of these materials increased with temperature [8–10]. To explain this unusual phenomenon, some researchers suggested that as the temperature increased, interior residual stress was released, which led to macroscopic strength improvements. However, this explanation was not investigated systematically or proven experimentally. Specifically, under the situation of the material under residual stress and external load, there are no reports of direct stress measurements or any direct observations of internal damage and failure processes. This was primarily due to the lack of an effective test method. In recent years, micro-Raman spectroscopy has made substantial progress in stress testing of crystal materials including C fibre and SiC materials [11–14]. Scanning elec
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