Anomalous Defects and Dynamic Failure of Armor Ceramics

Abstract

The ballistic performance of state‐of‐the‐art silicon carbide armor material can exhibit a fairly wide variability in certain test configurations, which, it is proposed, may be due to the presence of large (>0.1 mm), rare defects, termed, herein, “anomalous” defects. SiC rubble resulting from ballistic tests was examined, as were quasi‐static test samples. Ballistic fragment fracture surfaces revealed large carbonaceous defects that seemed to affect fracture path and mode. Low‐strength biaxial flexure samples demonstrated similar defects (>0.1 mm) as failure origins. Carbonaceous defects similar in appearance but smaller in size were also found at the fracture origins of SiC bend bars. Frequently, alumina inclusions were found within the carbonaceous discontinuities. These alumina inclusions may cause the graphitic regions to form during sintering. The random distribution of such large, rare carbonaceous discontinuities from sample‐to‐sample, as well as batch‐to‐batch variability, may explain high ballistic variability for SiC armor ceramics.

Quantitative analysis of inclusion distributions in hot pressed silicon carbide

“…In view of this result, the idea of anomalous defects warrants reexamination [18]. The original hypothesis was that the anomalous defects have an inordinate influence on ballistic performance due to their significant stress concentration [18].…”

“…The original hypothesis was that the anomalous defects have an inordinate influence on ballistic performance due to their significant stress concentration [18]. While no specific size criteria was established, the larger (>60 mm) defects observed should be considered very severe flaws as they are much larger than the SiCeN grains (w3e5 mm).…”

“…While previous work did find defects on the silicon carbide fragments [18], more rigorous analysis is required to accomplish these goals. In the current work, rubble obtained from large hotpressed SiC tiles that failed under highly dynamic loading conditions were examined.…”

A practical and systematic review of Weibull statistics for reporting strengths of dental materials

“…Danzer et al[18,19,20] have done similar derivations with more generalized flaw size distributions and have reached the same conclusions. Subsequent work, including painstaking measurement of flaw sizes and constructing distributions, has confirmed the power law function for the distribution of large crack sizes and hence the theoretical basis for the Weibull approach [21,22,23]. In other words, a reasonable power law distribution for large flaw sizes, classical fracture mechanics analysis and weakest link theory leads directly to the Weibull strength distribution.…”

Ultrasonic Evaluation of High‐Density Silicon Carbide Ceramics

“…These features may have been the result of carbon inclusions deposited during CVD processing because carbon has a lower velocity than the bulk material and is commonly found as a defect in SiC. 12 Although the extended tail region in sample B increased its standard deviation as compared with sample A, sample C showed the highest standard deviation due to a large overall TOF difference from thickness variations and individual features of higher TOF.…”