Determination of fracture toughness and fatigue crack growth rate using circumferentially cracked round bar specimens of Al2014T651

Fracture toughness (KIC) and fatigue crack growth rate (FCGR) are the important material properties in fracture mechanics. ASTM-E399 and ASTM-E647 are the standards for determination of KIC and FCGR of metallic materials. These standards recommend the use of compact tension (CT) or single edge notched bend (SENB) test specimens. Literature review indicates that CT or SENB specimens are complex in nature, difficult to manufacture, require typical fixtures for loading during experimentation and the test procedures using CT or SENB are time consuming and cumbersome. An alternate specimen geometry which can overcome the above said drawbacks is needed by the industry which can be used as standard test specimen geometry. This research work explains use of circumferentially cracked round bar (CCRB) specimens of high strength Al2014T651 alloy for determination of KIC and FCGR. The pre-cracked round bar specimen was loaded in tensile in a universal testing machine and pulled till failure. Using suitable stress intensity factor equations the fracture toughness can be calculated. In case of crack growth test, the pre-cracked round bar specimen is allowed to rotate under fatigue load. The ratio of length of crack propagated to the number of cycles to failure was the crack growth rate. The SEM analysis of fractured surfaces was also done. The results are comparable with the values reported in the literature obtained by using standard test specimens. There are numerous advantages of using round bar specimen in KIC and FCGR tests. It is concluded that, the methodology of determination of fracture toughness and fatigue crack growth rate using CCRB specimens is relatively simple, reliable, fast and economical. CCRB specimen may be recommended as a standard test specimen for fracture toughness as well as crack growth tests.