Size requirements for a pin-loaded double-edge notch plus crack tension specimen proposed for fracture toughness screening heavy-section alloys were studied. Ranking of eight selected alloys based on the specimen's net strength was compared with that based on the valid plane-strain fracture toughness separately determined. Performance of the specimen was judged on the basis of that comparison.
The specimen's net strength was influenced by three critical specimen dimensions: distance between the crack plane and the loading hole, specimen width, and specimen thickness. Interaction between the stress fields of the crack and the loading holes reduced the net strength, but this effect disappeared as the separation reached a dimension equal to the specimen width. The effects of specimen width and thickness are interrelated and affect the net strength through their influence on the development of the crack-tip plastic zone. Correlation between the net strength of the screening specimen and the plane-strain fracture toughness was enhanced by increasing thickness and decreasing width of the screening specimen.
The work described is intended to form the technical base for the development of a standard fracture toughness screening test method for heavy sections to supplement ASTM E 338 Standard Method of Sharp Notch Tension Testing of High-Strength Sheet Materials. Development of the test method is the responsibility of the ASTM E24.01.02 Task Group on Revision of E 338.