Dynamic Behavior of a Boron Carbide-Aluminum Cermet: Experiments and Observations

Abstract

Experimental techniques to study and characterize the dynamic behavior of ceramics and ceramic composites are described. A new technique based on the split Hopkinson pressure bar is used to obtain the deformation and failure characteristics of brittle materials at moderately high strain rates. A normal plate impact recovery technique is used to study the evolution of damage under controlled loading conditions and understand the micromechanisms of damage in materials. The normal plate impact recovery technique has the advantage of applying sufficiently high stress levels to initiate damage and yet providing controlled amounts of energy input to avoid catastrophic failure of the material. Hence, the samples can be recovered intact and evaluated for damage using standard characterization techniques such as microscopy and ultrasonics. The damage assessment in the material together with the real-time interferometric measurements serves as a powerful experimental procedure to study processes such as damage initiation, damage evolution, and the failure modes of very hard and brittle ceramics and ceramic composites under stress wave loading. Results are presented for a boron carbide aluminum cermet, a ceramic composite and the role of its microstructure on the failure mechanisms is studied. The cermet exhibits high strength and large strain to failure, in comparison to monolithic ceramics. The basic failure mechanisms in the cermet appear to be axial microcracking due to compression, and transverse cracking generated by compression release and by tension. The cracks are also found to be bridged by ductile aluminum or intermetallics, which together with the microcracking could possibly increase the toughness of the cermet at high loading rates.

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