eramics like alumina have such high bond strengths that they can theoretically be stretched in tension, elastically, to much higher stresses ... 4 GPa in this case. Unfortunately, most ceramic specimens rarely exhibit their theoretical strength value due to microscopic flaws that are inevitably present in specimens that have been handled, transported, etc. For an alumina specimen, what is the minimum stress at which failure is expected to occur, in MPa, if it features an elliptical surface scratch whose length is 2.43 mm and whose tip radius is 190 nm ?