سجاد برزگرمحمدي

In-service patch welding is frequently used to repair corroded or damaged steel structures. However, the repair welding may adversely affect the long-term mechanical integrity of the structure. Fatigue treatment techniques could reduce such drawbacks. However, the effectiveness of treatment techniques in the case of in-service fillet welded steel patch repairs has not received due attention. This paper deals with the fatigue behavior of fillet welded patch repairs made on normalized A516 GR.70 carbon steel plates. The test specimens received different thermal treatments, including post-weld heat treatment (PWHT), TIG-dressing (TD), and temper bead (TB) welding. The pros and cons of these treatments were eva‎luated through quasi-static tensile tests, high-cycle constant amplitude fatigue testing, microstructural assessments, and hardness measurements. The TD treatment provided the most significant fatigue improvement, owing to beneficial changes it made to the geometry, microstructure and hardness of the weld toe area. The fatigue life and the fatigue-prone locations in the PWHT and TB specimens did not significantly vary from those in the untreated welded specimens. However, there was a reduction of the ultimate tensile strength in the PWHT specimens. The microstructure of the heat-affected zone plus the hardness of the weld toe areas significantly contributed to the fatigue performance. The fatigue lives of the fillet welded patch repairs were also interrelated to the geometrical changes caused in the weld toe by the treatment method. The next part of this research studies the fatigue behavior of fillet welded patch repairs with and without TIG-dressing (TD). Six types of panels were constructed under various in-service cooling conditions. Specimens cut from the main panels were subjected to high-cycle fatigue, hardness, and metallography tests. The fatigue life of the specimens was also predicted using a novel numerical approach. The model incorporated micro-hardness test data from the weldment section. Macrographic and microhardness data were used for the zoning of the weldment section. The harness data were then employed to define the post-weld mechanical properties of the materials in different weldment zones. The fatigue life was estimated using the microhardness data, stress and strain data obtained from the finite element analysis of the specimen, a UVARM subroutine, and several multiaxial fatigue life prediction models. The numerical fatigue life estimations showed reasonable agreement with the experimental data. Both experimental and numerical modeling results proved significant improvements in the fatigue life of the TD specimens. Regardless of the welding conditions/treatments, the best fatigue life estimates were provided by the BMM, SWT, Glinka, and KBM criteria, respectively.

جوشكاري حين بهره‌برداري، گراديان‌هاي حرارتي، عمر خستگي، اتصالات وصله‌اي، المان محدود، معيارهاي خستگي چندمحوره

Patch welding , Fatigue life , Finite element analysis , Fatigue treatment techniques , In-service welding , Thermal gradients

Sajjad Barzegar-Mohammadi

Mohammad Haghpanahi