Abstract
Scalelike marks are usually observed in the fracture surface of a Si3N4 specimen tensioned to fracture at 20°C and 500°C. They are the regularly shaped marks, ellipselike and parabolalike ones along with other irregularly shaped marks. The regularly shaped marks are carefully observed and analyzed in the same manner of defining an ellipselike mark (both ends closed mark, BECM) and a parabolalike mark (one end opened mark, OEOM) observed in unsaturated polyester resins (UP) and PMMA, as reported previously. the marks in a smooth specimen are mostly the OEOMs where the crack velocity often reached about 4500m/s at maximum and the BECMs are dominated in the fracture surface of a single edge-notched tensile specimen in which the crack velocity reached the maximum value that is less than the above. The variation of the marks and the mechanism of forming these marks seem to be the same with the cases in UP and PMMA, and they are discussed in detail from the points of fracture strength and the crack velocity change. The shapes of the marks are approximated by the equation of fracture surface marks.
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