Ti 鎔接材의 機械的 特性 및 疲勞크랙 進展擧動에 關한 硏究 = A Study on the Mechanical Properties and the Fatigue Crack Propagation Behavior of Ti Welding Material

국문 초록 (Abstract)

Ti 용접재 시험편을 통하여 용접조건에 따른 기계적 성질 및 피로크랙 진전거동을 각각 비교·검토한 결과 다음과 같은 결론을 얻을 수 있었다.
동일한 용접조건에서 패스 수에 따라 4패스는 7패스와 비교하였을 경우 인장강도가 10%정도 높게 나타났고, 연신율은 30%종도 감소함을 알 수 있었다. 또한 실딩가스량이 많고, 용접 후 자연냉각 시간간격이 길수록 인장강도는 높게 나타났고, 연신율은 감소하였다.
충격 흡수에너지값은 4패스는 7패스에 비해 50%정도 감소하였으나, 실딩가스량이 많을수록 높게 나타났다. 또한 경도값은 패스 수가 적을수록 높게 나타났으며, 용접 후 자연냉각 시간간격에는 비슷하였으나 용접 후 자연냉각 시간간격이 적은 것은 조금 감소하였다.
초기크랙 진전속도는 Bond부, 용착부, HAZ, 온도영향부 순으로 느리게 나타났으나, 피로수명은 Bond부, HAZ부, 용착부, 온도영향부 순으로 높게 나타났다.

다국어 초록 (Multilingual Abstract)

The purpose of this thesis was to investigate the welding characteristics and the fatigue crack propagation behavior of titanium commonly using power station, aircraft and ship. The experimented material was TIG welded in order to look over the characteristics according to the notch position and compare with other materials.
We compared and reviewed the fatigue crack propagation behavior of nonwelded base metal and welded specimens having different notch position to evaluate the fatigue crack propagation behavior by welding condition.
The tensile strength and elongation of the 4 pass welded specimens was shown about 10% and 30% higher than those of the 7 pass welded specimens at the same welding conditions. Also, the more shield gas and the lower natural cooling time, the higher tensile strength but the lower elongation.
The absorption energy of the 4 pass welded specimens, was decreased about 50% more than that of the 7 pass welded specimens, and the more shield gas, the higher impact absorption energy value. The higher hardness, the lower pass, but the natural cooling time almost had no relation to the hardness.
The fatigue life was shown higher as following the order, boundary zone > HAZ > welding zone > base metal. Especially the fatigue life of boundary zone notched specimen was shown 700% higher than that of base metal.