An investigation of stage I fatigue crack growth in FCC, BCC, and HCP metals

The objectives of this investigation were to 1) determine if Stage I mode or fatigue crack growth could be extended beyond the 45 degree maximum shear plane in metals having a face-centered, body-centered and hexagonal close pack crystal structure; 2) identify the crystallographic planes or crack propagation in Stage I growth in each crystal structure; 3) characterize the fracture surface topography or Stage I growth in each crystal structure. The test material used for this investigation consisted of alpha brass (70% Cu, 30% Zn), Armco iron and commercially pure titanium which are representative of FCC, BCC, and HCP crystal structures respectively. Based upon the results of this investigation it is concluded that: 1. Stage I mode of fatigue crack propagation in FCC, BCC, and HCP metals is not confined to the vicinity of crack initiation. 2. In FCC brass Stage I fatigue crack growth occurs transgranular along the (lll) plane. 3. In BCC Armco iron Stage I Fatigue crack growth occurs inter-granular. 4. In HCP commercially pure titanium Stage I fatigue crack growth occurs transgranular along cleavage planes. 5. The mechanism of Stage I fatigue crack growth in these materials is related more to the decohesion mechanism than to the same mechanism that is responsible for Stage II fatigue crack propagation --Abstract, page ii