Fracture Toughness Testing of Metals

Fracture toughness of metals describes the ability of a metal containing a crack to resist fracture. The linear-elastic fracture toughness of metal is determined from its stress intensity factor ( ) at the point a thin crack in the metal begins to grow and known as KIC. Plastic-elastic fracture toughness of metal is JIC which measures the energy required to grow a thin crack. Fracture toughness of metals is an important measurement for many maintaining a quality product. Welding can result in heat affected zones that are high probability fracture zones. ASTM E1290 test method is a good manufacturing quality control. Determining the right test equipment to meet the requirements of this test will help guarantee accurate measurements. Temperature of a test material will have a significant impact on the fracture toughness. ASTM E1290 outlines the procedure for determining the influences of temperature in the fracture toughness. The geometry of the test specimen is also an important consideration because it can actually affect the measured CTOD values. ASTM E399 measures linear-elastic plane-strain fracture toughness K_Ic of metallic materials. ASTM E 1290 is used to analyze fracture toughness of metals by measuring crack-tip opening displacement in metal that changes from ductile to brittle behavior with decreasing temperature. ASTM E1820 helps determines a metals resistance to fracture from stationary crack, fracture after stable tearing, fracture from the onset of stable tearing, and fracture from sustained stable tearing. ASTM E1820 offers a method from comparing the fracture toughness of materials. The fracture parameters K, J, and CTOD are determined in this test and can be used for material compression. ASTM E399 outlines the specific values regarding the displacement gage, loading fixture design, requirements for individual specimen configurations, and details on procedures for pre-cracking the specimen. ASTM E1820 Fracture toughness machines measure the load applied to the test specimen, the load-line displacement, and the crack-mouth opening displacement. A digital measurement of load versus load-line displacement and load versus crack-mouth opening is also needed. It is also necessary to have a fixture solution that fits with the specific test specimen.