MSE Colloquium: Gregory Morscher, Use of Acoustic Emission and Electrical Resistance to Determine Matrix Cracking and Crack Growth in Advanced Ceramic Matrix Composite Systems

Associate Professor, Mechanical Engineering Department, The University of Akron

All dates for this event occur in the past.

264 MacQuigg Labs
105 W. Woodruff Ave.
Columbus, OH 43210
United States

Abstract

Ceramic matrix composites are fast becoming enabling materials for advanced commercial jet engines. The damage development in SiC/SiC composites is a critical factor in understanding this class of material’s mechanical and ultimately long-life behavior. Therefore, it is essential to develop techniques capable of monitoring damage in order to better understand material performance during critical lab tests as well as for future use as inspection techniques of flight hardware. Two techniques are of special interest and tailor made for SiC fiber-reinforced ceramic matrix composites: acoustic emission and electrical resistance. Two examples will be given where both of these techniques are employed. First, matrix cracking was determined due to tensile stress for pre-preg SiC/SiC composites consisting of Hi-Nicalon Type S fibers, a BN interphase and Si-SiC matrix. Three of different laminate architectures were studied: unidirectional, [90/0]2s and [0/90]2s. Matrix cracking was monitored during tensile testing using acoustic emission (AE) and electrical resistance (ER). The numbers of cracks for the different composite architectures were determined for different stress/strain exposures by polishing lengths of tested composites. The AE and ER results were analyzed with respect to the cracking behavior within the different plys of the different composite architectures and used to estimate stress-dependence for matrix cracking. The stress-dependent cracking results were then used in conjunction with micromechanics approaches to model the stress-strain behavior for the different composites. Second, the use of these two techniques was used to estimate crack growth in a wedge DCB interlaminar fracture toughness test. The method uses acoustic emission to determine crack initiation and electrical resistance to monitor crack growth for melt-infiltrated woven SiC/SiC composites at room temperature, with the goal of doing the same at high temperature. In situ optical measurements of crack growth in addition to micro-CT post-inspection were used to validate and calibrate the resistance method. The estimated crack length was in excellent agreement with the measured crack length in the three considered specimen geometries. Preliminary estimates of Mode I energy release rate were also provided.

Bio

Gregory Morscher has worked in the area of high temperature materials and composites for over twenty five years. Before joining the University of Akron, he was previously affiliated with NASA Glenn (formerly Lewis) research center as a research engineer (CWRU) and then senior research scientist (OAI). He has concentrated primarily on the understanding and improvement of SiC-based composites as well as NDE techniques for the purpose damage assessment and monitoring. He studied the high temperature creep properties of ceramic fibers and developed a simple bend stress relaxation test to evaluate relative creep properties of ceramic fibers. He has also made considerable contributions to the improvement of BN interphases for the purpose of improving the intermediate temperature capability of SiC/SiC composites in oxidizing environments. Dr. Morscher has used non-destructive techniques such as acoustic emission and electrical resistance during room and high temperature testing as a monitor and measure of the amount of matrix cracking and other forms of damage that occurs as a function of stress, time, and environment (oxidation). This has served as the basis for modeling stress-strain behavior of SiC/SiC composites for different woven architectures and led to the development of intermediate and high temperature stress-rupture models for SiC/BN/SiC composites in air as a function of stress, time, and accumulated damage. More recently, he has focused on the effect of fiber-architecture and matrix-type on time-dependent mechanical behavior at high temperatures (> 1200 degrees C) as well as joining ceramic composites to metals. In addition, he has applied acoustic emission to other material systems (e.g., polymer matrix composites and metal oxide scale spallation), other structures (e.g., foam/core structures and integrated structures), and Stirling engines. He received his B.S. degree in Ceramic Engineering at The Ohio State University in 1986 and his M.S. degree in Materials Science and Engineering at Case Western Reserve University in 1989. Later, he received his Ph.D. degree in Materials Science and Engineering at Case Western Reserve University in 2000, while working as a Research Associate at NASA Glenn. Dr. Morscher has authored or coauthored over 100 publications in refereed journals or proceedings and has been a frequent contributor to NASA Glenn’s annual Research and Technology Reports. He has received several OAI achievement awards, two NASA Tech Brief awards, two NASA Turning Goals into Reality awards, the 2004 NASA Public Service Medal and the Richard M. Fulrath Award from the American Ceramic Society in 2005.