On the Fatigue Strength of Welded High-Strength Steel Joints in the As-Welded, Post-Weld-Treated and Repaired Conditions in a Typical Ship Structural Detail
2. Materials and Methods
2.2. Specimens and Welding Preparation
2.3. High-Frequency Mechanical Impact Treatment
2.4. Repair Welding of the Beam Specimens
- Fatigue crack was removed by plasma arc gouging and rotary burr;
- The gouged dent was inspected with the liquid penetrant to ensure that the whole crack was removed before starting repair welding process;
- Tungsten inert gas (TIG) welding was applied to re-melt and re-shape the deepest point of the dent;
- Multipass TIG welding with the consumable of ESAB OK Tigrod 13.09 (⌀2.4 mm) and GMA welding with solid wire of ESAB OK 12.51 (for the EQ47 steel) and 13.29 (for the EQ70 steel) were used to fill the dent;
- In the cope hole details, the weld reinforcement was ground to flush with a lamellar rotary grinder. At the opposite side of the gusset, HFMI treatment was applied.
2.5. Residual Stress Measurements
2.6. Fatigue Testing
2.7. Finite Element Analysis
3.1. Fatigue Tests
3.2. Failure Observations
3.3. Residual Stresses
3.4. Stress Concentrations and Fatigue Assessments Using Structural and Notch Stresses
- Fatigue strength of welded bulkhead stiffener connection prepared with the rutile-cored wire was in line with the detail category of FAT63. The sharp transitions from the base metal to the weld reinforcement were observed, but based on the experimental results, sufficient fatigue strength was found.
- Pre-conditions for the successful HFMI treatment must be confirmed, either using burr grinding or equivalent geometry modifications, or employing solid filler wires. In this study, it was specifically related to the welding quality produced by the rutile-cored wires. With the successful treatment, the results were conservative compared to the design curves, and characteristic (Ps = 97.7%) design fatigue capacity was 173 MPa at two million cycles. In the majority of the HFMI-treated specimens, failures occurred at the weld root or thermally cut edges and, consequently, it can be concluded that HFMI treatment is a viable option to enhance the fatigue performance of welded ship details made of extra-high-strength steels. If HFMI processes are applied, careful attention should be paid on the weld root quality; the gusset end face should be welded without any lack of penetration.
- Repair welding can extend the fatigue life of structural components. In this study, the specimens experienced failures outside the repair-welded regions (mostly from the weld root), and fatigue lives were higher than that of pre-fatigued specimens. In repair welding, it is, thus, important to consider different failure modes from the different crack initiation points.
- With the investigated joint type, a use of the local approaches (structural HS stress method and ENS concept) produced more conservative results than the nominal stress method. Differences in the specimen geometries and load configuration gave different SCFs and can, thus, explain the differences found in the fatigue capacities when using the nominal stress system.
Data Availability Statement
Conflicts of Interest
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|Material ID||Type||fy (MPa)||fu (MPa)||A (%)||KV at −40 °C (J)|
|OK Tubrod 15.17||Typical||544||613||26||124|
|Dual Shield 69||Typical||740||790||20||65|
|OK AristoRod 69 a||Typical||715||805||17||73|
|OK Tubrod 15.17||Typical a||0.05||0.34||1.15||–||–||–||0.96||–|
|Dual Shield 69||Typical a||0.095||0.34||1.25||–||0.4||–||2.8||–|
|OK AristoRod 69||Typical a||0.089||0.53||1.54||0.26||0.24||–||–||–|
|Weld Description||Pass ID||Pos.||U|
|Specimen Type||Material Grade||AW||HFMI||BG+HFMI||Repair-Welded|
|Material Grade||σres (MPa)||FWHM (°)|
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Ahola, A.; Lipiäinen, K.; Lindroos, J.; Koskimäki, M.; Laukia, K.; Björk, T. On the Fatigue Strength of Welded High-Strength Steel Joints in the As-Welded, Post-Weld-Treated and Repaired Conditions in a Typical Ship Structural Detail. J. Mar. Sci. Eng. 2023, 11, 644. https://doi.org/10.3390/jmse11030644
Ahola A, Lipiäinen K, Lindroos J, Koskimäki M, Laukia K, Björk T. On the Fatigue Strength of Welded High-Strength Steel Joints in the As-Welded, Post-Weld-Treated and Repaired Conditions in a Typical Ship Structural Detail. Journal of Marine Science and Engineering. 2023; 11(3):644. https://doi.org/10.3390/jmse11030644Chicago/Turabian Style
Ahola, Antti, Kalle Lipiäinen, Juuso Lindroos, Matti Koskimäki, Kari Laukia, and Timo Björk. 2023. "On the Fatigue Strength of Welded High-Strength Steel Joints in the As-Welded, Post-Weld-Treated and Repaired Conditions in a Typical Ship Structural Detail" Journal of Marine Science and Engineering 11, no. 3: 644. https://doi.org/10.3390/jmse11030644