Abstract
Compact tension (CT) specimen is used to investigate the behavior of fatigue crack growth rate (FCGR) of preheat-treated tungsten inert gas (TIG) welded aluminum alloy (AA2219-T87) on MTS-810. Filler metal used for weld is AA2319. ASTM E399 standard provides a method to convert crack mouth opening displacement (CMOD) data to crack length in CT specimens. Calibration tests are performed to obtain the plots of CMOD versus load and CMOD versus crack ratio (a/W) for different crack lengths in the base metal and the welded metal. Cracks lengths are obtained optically and calculated from CMOD as per ASTM E399. Numerical simulation is used to relate the crack length with CMOD in base metal. Validity of the ASTM standard is verified with the results obtained. Paris curves are plotted and compared for both base metal and welded metal to study the effects of welding on FCGR. It is shown that calculation of crack length through CMOD measurements is not reliable in the case of welded materials. High amount of crack closure exists in welded material, which induces large errors in calculated crack length. The microstructure evolves as a result of the TIG welding. The center of the weld nugget zone consists of dendritic structure followed by recrystallized equiaxed small-sized grains in the heat-affected zone. Grains have elongated structure in the base metal. Due to varying phase conditions and concentration of strengthening particles, a high contrast under optical microscope is clearly observed in different zones of weldment.
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