Ti합금 용접재의 용접 특성 및 피로크랙 진전속도 평가법

Abstract

The objective of this paper was investigation the welding characteristic and the propagation behavior of fatigue crack of titanium which is used materials of power station, aircraft, ship etc. We welded them on many different welding conditions, after we cut samples to a fixed size by a mechanical process. Then we compared and reviewed the result of mechanical characters. We compared residual stress distribution in the perfect restraint welding condition with it in the nonrestraint welding condition in frames of industrial field. This theory is not yet scientifically established. 1. The tensile strength and elongation of the 4 pass welding were shown about 15% and 38% more than that of the 7 pass welding, and the more shield gas and welding interval, the higher tensile strength and elongation. 2. The impact absorption energy value of the 4 pass welding was shown about 45% more than that of the 7 pass welding the more shield gas, the higher impact absorption energy value, the higher hardness, the lower impact absorption energy value, but welding interval had no relation to the impact absorption energy value. 3. The welding residual stress in restraint is much higher than the weldin residual stress in nonrestraint. In case of restraint welding, the tensile residual stress of y-D change to the compressive residual stress at 60mm from welding bead. In case of nonrestraint welding, it change to compressive residual stress rapidly at 15㎜ from welding bead. 4. The suitable measuring gap was 0.3～0.7 mm having no effect on the calculation method of crack propagation rate which was disagreed little bit with D. F. Ostergaard's study from the ΔP and ΔK constant test result 5. Putting these error evaluation of test results together with CCT and CT specimens, it was thinkable that the range of measuring interval was appropriate 0.067～0.014 regardless of the specimen types showing the minimum error for fatigue test. 6. The material constant gained f개m experiment of these materials apply to the assumed equation of fatigue crack propagation speed by Nisitani. In the result of a fatigue life's estimate, it accord with a low error about 6% regardless of notch position and load ratio.