Several novel metal-ceramic composites [1,2] are currently being developed and characterized at Cornell. These composites are produced using in-situ processes, including internal reduction reactions, sol-gel synthesis, and displacement reactions. The processes typically produce fine grained microstructures, whereby the metal and ceramic components are mixed on a size scale of 1 to $10 \mu m$. The in-situ processes also avoid the labor intensive hand layup processes used for some composite systems. Thus it may be possible to automate the processing of the in-situ composites, giving them the potential to be produced economically.
We are, however, far from any kind of production. At present a number of different processing approaches and material combinations are being explored. This exploration includes characterizing material properties, including elastic modulus, hardnesss, strength and fracture toughness. Due to both limitations in the kinetics of the processing and processing equipment and to save on precious material, all of the characterization tests are carried out on very small samples.
For example fracture toughness is measured using 2x2x8mm chevron-notched bend samples[3]. With such small samples, that have maximum load point deflections at fracture on the order of $10$ to $100 \mu m$, sample preparation and instrumentation must be precise. The experimental setup for this test will be described, and the fixturing and instrumentation problems that need to be solved for such small samples will be addressed in this talk. We will also discuss the applicability (or lack of applicability) of the semi-empirical analytic expressions for the stress intensity factors and compliance of small chevron-notched bend samples.
References
[1] E. Ustundag, P. Ret, R. Subramanian, R. Dieckmann,
and S.L. Sass, "In Situ Metal-Ceramic Microsctructures by Partial
Reduction Reactions in the Ni-Al-O System and the Role of ZrO$_2$,"
Mat. Sci. and Engr., A195, (1995), 39.
[2] E.D. Rodeghiero, O.K. Tse, E.P. Giannelis, "Interconnected
Metal Ceramic Composites by Chemical Means," J. of Metals, 26, (1995).
[3] E. Ustundag, E.D. Rodeghiero, H.J. Yoo, and A. T. Zehnder, "Development of a Testing Procedure for Small 3-Point Bend Specimens," in preparation, to be submitted to Acta. Met., (1995).
Acknowledgements This work was supported by the AFOSR
through grant no. F49620-93-1-0235.