Monitoring damage accumulation in ceramic matrix composites using electrical resistivity

Abstract

The electric resistance of woven SiC fiber reinforced SiC matrix composites were measured under tensile loading conditions. The results show that the electrical resistance is closely related to damage and that real-time information about the damage state can be obtained through monitoring of the resistance. Such self-sensing capability provides the possibility of on-board/in-situ damage detection and accurate life prediction for hightemperature ceramic matrix composites.Woven silicon carbide fiber-reinforced silicon carbide (SiC/SiC) ceramic matrix composites (CMC) possess unique properties such as high thermal conductivity, excellent creep resistance, improved toughness, and good environmental stability (oxidation resistance), making them particularly suitable for hot structure applications. In specific, CMCs could be applied to hot section components of gas turbines [1], aerojet engines [2], thermal protection systems [3], and hot control surfaces [4]. The benefits of implementing these materials include reduced cooling air requirements, lower weight, simpler component design, longer service life, and higher thrust [5]. It has been identified in NASA High Speed Research (HSR) program that the SiC/SiC CMC has the most promise for high temperature, high oxidation applications [6].One of the critical issues in the successful application of CMCs is on-board or insitu assessment of the damage state and an accurate prediction of the remaining service life of a particular component. This is of great concern, since most CMC components envisioned for aerospace applications will be exposed to harsh environments and play a key role in the vehicle's safety. On-line health monitoring can enable prediction of remaining life; thus resulting in improved safety and reliability of structural components. Monitoring can also allow for appropriate corrections to be made in real time, therefore leading to the prevention of catastrophic failures. Most conventional nondestructive evaluation (NDE) techniques such as ultrasonic C-scan, x-ray, thermography, and eddy current are limited since they require structural components of complex geometry to be taken out of service for a substantial length of time for post-damage inspection and assessment. Furthermore, the typical NDE techniques are useful for identifying large interlaminar flaws, but insensitive to CMC materials flaws developed perpendicular to the surface under tensile creep conditions. There are techniques such as piezoelectric sensor [7,8], and optical fiber [9,10] that could be used for on-line health monitoring of CMC structures. However, these systems involve attaching an external sensor or putting special fibers in CMC composites, which would be problematic at high temperature applications.https://ntrs.nasa.gov/search.jsp?R=20080047468 2018-05-11T18:03:58+00:00Z Most composite materials are multifunctional materials in which the damage is coupled with the material electrical resistance, providing the possibility of real-time information about the damage state thro...

Detecting cracks in ceramic matrix composites by electrical resistance

“…At that point, the resistance increased linearly (the AE events also resumed). Unlike the CVI material tested previously 23 , the cyclic loading resulted in a higher resistance for each cycle. That is to say, after unloading and then re-loading to the same stress, the resistance was higher than before.…”

“…Previous work with chemical vapor infiltrated (CVI) SiC/SiC composites has shown a direct relationship between matrix crack density and resistance change for samples subjected to creep conditions 22 . Room temperature monotonic tensile tests have also been conducted concerning this material 23 . Typically, the resistance changes were on the order of 50% for both test conditions.…”

Mechanical properties and real-time damage evaluations of environmental barrier coated SiC/SiC CMCs subjected to tensile loading under thermal gradients

“…The coated and uncoated samples show increases in electrical resistance of 220% and 180% over the entire specimen length, with measured increases in gage-section strain of 0.371% and 0.134% respectively. As is the case of room temperature tensile loading of SiC/SiC composite systems [22][23], the ER increase in these tests appears to be strongly related to damage accumulation. In the case of room temperature tests, the high volume fraction of free bonded composites segments, debonded fiber/matrix regions and matrix cracks bridged solely by the reinforcing fibers [23].…”

“…Ideally, such techniques would be simple to implement on a material level as well as a structural testing scale. Recent studies have shown the viability of using in-situ modal acoustic emission (AE) and electrical resistance (ER) monitoring of SiC/SiC CMC specimens during room temperature monotonic tensile loading in order to detect damage onset and accumulation in both CVI[22] and MI-CVI matrices[23]. These works were successful in determining a correlation between electrical resistance increase and stressdependent transverse matrix cracking.…”

Stochastic Virtual Tests for High-Temperature Ceramic Matrix Composites

“…Such measurements include those via optical microscopy (108)(109)(110)(111)(112)(113), scanning electron microscopy (114-119), speckle interferometry (120)(121)(122), acoustic waves (123)(124)(125), and electrical resistance (126,127). Most of these measurements were at room temperature; only a few studies tackled in situ measurements at high temperatures (e.g., References 114 and 128).…”