Damage detection and localisation of CMCs by means of electrical health monitoring
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ORIGINAL PAPER
Damage detection and localisation of CMCs by means of electrical health monitoring Tina Staebler1 · Hannah Boehrk1 · Heinz Voggenreiter1 Received: 31 August 2019 / Revised: 5 June 2020 / Accepted: 12 July 2020 © The Author(s) 2020
Abstract Carbon-based composites such as C/C-SiC are used in thermal protection systems for atmospheric re-entry. The electrical properties of this semiconductor material can be used for health monitoring, as electrical resistivity changes with damage, strain, and temperature. In this work, electrical resistance measurements are used to detect damage in a thermal protection system made of C/C-SiC. This can be done in-situ. Damage experiments with 320 mm × 120 mm × 3 mm panel shaped samples were conducted with a multiplexer switching unit to determine up to 288 electrical resistance and voltage measurements per cycle time and spatially resolved. The change in resistance is an indicator for damage, and with the use of post-processing algorithms, the location of the damage can be determined. With these data, inhomogeneous temperatures can be accorded for and damage can be detected. This method reacts even to small damages where less than 0.02% of the monitored surface is damaged. A localisation with a deviation from the real defect of less than 8% in sample width and 17% in sample length is presented. Keywords Health monitoring · Electrical resistance measurements · CMC
1 Introduction Building and optimizing space vehicles are a complex problem, as, depending on the flight trajectory, temperatures of over to 2000 K may occur. Damage to the thermal protection system of a space vehicle during atmospheric re-entry is a serious safety issue, especially when considering re-usability of space transportation systems. The need for structural health monitoring systems and non-destructive inspection methods is obvious; since then, minor or major defects can be detected which makes an intervention possible, potentially saving a spacecraft and also human lives. Damages occur often undetected or not correctly detected already as early as during launch of the spacecraft [1, 2]. It is a crucial challenge for scientists to develop materials and sensors which can withstand the extreme conditions of re-entry. For gaining better knowledge of the re-entry phase and for subsequently optimizing structural safety margins, sensors are needed which can collect data and monitor the
* Tina Staebler [email protected] 1
Pfaffenwaldring 38‑40, 70569 Stuttgart, Germany
heat shield before and during an actual re-entry flight. This is not only important for developing better thermal protection systems, but also for detecting defects which occurred any time between launch and re-entry. There are different concepts of electrical monitoring of defects in ceramic matrix composites. Todoroki et al. [3–5] use contacts in regular distances on a sample surface to monitor delamination in the sample. They measure the voltage drop between two neighbouring contacts. With this, they determine the depth and
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