What Is Fracture Toughness Testing?

Fracture toughness is an indication of the amount of stress required to propagate a preexisting flaw. It is a very important material property since the occurrence of flaws is not completely avoidable in the processing, fabrication, or service of a material/component.

The KIC test or K1C test is used to determine the fracture toughness of metals. The testing consists of fracturing and failing a specimen of a specified geometry that has had a sharp defect or fatigue precrack built into it. bO the compact tension (CT) and 3 point bend specimens are most commonly used in the testing with the CT specimen is being the most widely used geometry for the testing.


The fracture test is carried out in displacement control at a constant rate of increase of stress intensity while recording load and crack opening displacement data, until the specimen breaks. A Crack Opening Displacement gage is used to measure the Crack opening displacement. Knife edge fixtures are affixed to the specimen to accommodate the gauge sizes.


For CT specimen, we recommend that you send us samples of 60 mm x 62.5 mm x 12.5 mm (Thickness). For SENB,  our recommended sample size is 55 mm x 5 mm x 10 mm.


The Crack Tip Opening Displacement or CTOD Test measures the resistance of a material to the propagation of a crack. Accurate measurement of the opening is a pre-requisite for the test. The actual test is performed by using a 3 point bend specimen and accurately measuring the amount of crack opening using a CTOD extensometer.