A combined true stress-strain data-generating testing technique, and method for determining unknown loads applied in compression to relatively thin, metallic and ring-shaped test specimens by means of flat die platen members. Both the die friction component .DELTA.D of the total applied load and the percent deformation .DELTA.T, or true strain of the ring specimen, as well as the unknown compression load, may be determined respectively from the change in shape or inside diameter and thickness of the deformed specimen. From a plot between the previously computed deformation, .DELTA.T, or true strain, and die friction component, .DELTA.D, the ratio between the total pressure applied to the specimen and the true flow stress may be computed from the total pressure required to overcome the previously found die friction component, .DELTA.D. A true stress-strain curve may be plotted from values found in testing a number of specimens under various loads, and the load being applied may be found, when the basic flow behavior of the material under test is known.
BACKGROUND OF THE INVENTION
The present application is a continuation-in-part application of applicants' copending patent application, Ser. No. 64,536 filed Aug. 14, 1970, and entitled "A New Method of Determining a Compression True Stress-Strain Curve." The latter application was abandoned on Oct. 6, 1971 .
A novel test specimen configuration and modified ring test method for determining the fracture toughness, K.sub.Ic, using rock core is disclosed. The use of a truncated hollow cylindrical specimen under compressive load avoids the development of a large process zone (microcracked region) during testing, thus allowing accurate fracture toughness measurements on subsized specimens. Results using soft sandstones and Indiana limestone validate the procedure.
