Failure Analysis And Evaluation Of A Low-alloyed Steel And Its Welding Metal

The inevitable defects in the welded ship increase the ship's brittle fracture tendency. On the other hand, the ships always support the dynamic loading while in service. And the defect sensitivity of the structural steel will increases with the loading rate, these will be harmful to the safety of the ship.The rapid development of the Fracture Mechanics establishes the academic foundation of the safety assessment of structures containing defects and improves the development of the fitness for purpose. R6 is the typical assessment method adopting the J rule and failure assessment diagram (FAD) technique in the standards for check and accept. The integrity of structures containing defects was used to assess the safety of the shipbuilding steel and welding in the static and dynamic loading in this thesis, and assess the failure mode of the structure according to the SC figure simultaneously. The main results are as follows.1. In the condition of static loading, there are similar fracture properties and enough abilities suffering load in steel 907A and its welding metal, and the plastic failure or elastic-plastic failure mode is presented in both them, as a consequence, the storage of plasticity and toughness is enough and the security is satisfactory.2. In the condition of dynamic loading, there is still enough suffering loading ability, the elastic-plastic failure mode is presented, the storage of plasticity and toughness is enough, and service safety is satisfactory in steel 907A. On the contrary, the service ability of welding metal lost severely and failure in the mode of brittle fracture, appearing inadaptability with dynamic loading.3. The SC values corresponding to failure point of 907A steel and welding metalincreased obviously with the increase of the loading rate from k = 10⁰ MPa(m/s)^1/2to K = 10⁷MPa(m/s)^1/2. What the SC values of base metal increased with increase of loading rate indicates that even though the plastic deformation within the elastic-plastic fracture process decrease, the brittle fracture mode will not appear. And yet, What the SC values of welding metal increase with increase of loading rate indicate that the fracture mode is changed from elastic-plastic fracture to brittle fracture. Surely, more attention should be paid on the latter one.