Determination of fracture and fatigue behaviours of 4340 steel

---

Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2015

Öğrenci: GÖKÇE ŞEN

Eş Danışman: BİLGEHAN ÖGEL, RIZA GÜRBÜZ

Özet:

In this study both the characteristic and mechanical properties of received modified AISI 4340 steel -generally used in aeronautical and defense applications- has been examined. Mode I Fracture toughness (KIC) tests have been conducted with two different directional specimens of RL and LR. Fatigue crack growth behaviors of directional specimens are compared and discussed at three different positive stress ratios (R) which are 0.1, 0.3 and 0.5 under constant amplitude loading. Walker equation is used to perform fatigue life calculations and the evaluation of test results for tensile loading. On the next step, the modified steel specimens are subjected to fully reversed stress cycle (R= -1) and the Paris-Erdogan law has been applied to all achieved data. The difference in the production of modified AISI 4340 steel (M4340) steps are correlated with the results and compared with commercial AISI 4340 steel theoretical information. The obtained measurements show that the M4340 steel has higher hardness and toughness compared to standard AISI 4340 steel.