SEDL / STP / STP1172-EB / STP24716S

Using Chevron-Notch, Short-Bar Specimens for Measuring the Fracture Toughness of a Martensitic Stainless Steel at High Hardness

Marschall, CW
Senior research scientist and researcher, Battelle, Columbus, OH

Held, PR
Senior research scientist and researcher, Battelle, Columbus, OH

Dolan, FJ
Deputy division chief, Engineering Physics, NASA, Marshall Space Flight Center, Huntsville, AL

Pages: 13    Published: Jan 1992

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Abstract

Fracture toughness tests were conducted at room temperature and at – 196°C on a martensitic stainless steel that had been quenched and tempered to a hardness of Rockwell C 61-63. The fracture toughness specimens were chevron-notch, short-bar specimens for which B was 12.7 mm and W was 25.4 mm. Tests were conducted in accordance with ASTM Test Method for Plane-Strain (Chevron Notch) Fracture Toughness of Metallic Materials (E 1304-89).

Five tests were conducted at each temperature, and each test produced a valid K^Iv result. Test results were unusually reproducible for plane-strain fracture toughness tests; the standard deviation for room temperature tests was approximately ±5% and for -196°C tests was approximately ±2% of the mean value of K^Iv.

For comparison with the chevron-notch test results, three standard K^Ic tests were conducted on fatigue-precracked compact (tension) specimens at room temperature. The tests were conducted in accordance with ASTM Test Method for Plane-Strain Fracture Toughness of Metallic Materials (E 399). As was the case for the K^Iv tests, the KIc tests produced very reproducible results: the standard deviation for three tests was approximately ±2% of the mean value. However, it was found that the mean K^Iv values for this high-hardness steel were approximately 18% greater than the mean K^Ic values. That result confirms the warning included in ASTM E 1304 that K^Ic values may be larger than K^Ic values in some materials.