Session: 03-02-01 Fatigue Performance and Testing

Paper Number: 125415

125415 - Effects of Needle Peening on Fatigue Strength of Aluminum Alloy Welded Joint Containing a Surface Defect 

High value-added ships such as LNG carriers are expected to be used for long periods of time beyond their standard design life while ensuring tank reliability. Fatigue cracks can occur in aged tanks due to repeated long-term exposure to dynamic stresses such as thermal loads and sloshing loads. Therefore, cracks are detected by nondestructive testing and repaired as necessary. However, nondestructive testing has detection limits, and standard nondestructive testing methods are said to be unable to detect defects less than 1 mm in depth.

In the author's previous studies, fatigue strength of stainless steel and high tensile steel welded joints containing a semicircular surface defect with depths of 1 mm exhibited high fatigue strength by needle peening (NP); fatigue strength were equal to those of peened specimens without a slit via needle peening (NP).

If similar results can be obtained for aluminum alloy welded joint, it would be effective from the viewpoint of reducing the number of future repair points for pressure vessels such as LNG tanks.

In the present study, the effects of NP on the fatigue strength of an aluminum alloy welded joint containing an artificial semicircular slit on the weld toe were investigated. 

Axial fatigue tests were conducted at a stress ratio of R = 0.05 for NP-treated welded specimens with and without a slit. 

The fatigue strength at 2 million cycles of all specimens increased by 11%–100% due to the NP treatment. Furthermore, NP-treated specimens with slit depths of a = 1.0 mm exhibited high fatigue strength that were equal to those of NP-treated specimens without a slit.

Therefore, a semicircular slit of less than a = 1.0 mm could be rendered harmless through NP treatment.

This result indicates that the reliability of aluminum alloy welded joints can be significantly improved via NP for surface defects with depths that are less than 1 mm, which are not detected through non-destructive inspection.

Presenting Author: Ryutaro Fueki National Maritime Research Institute, Japan

Presenting Author Biography: Ryutaro Fueki is a researcher at National Maritime Research Institute, Japan.
He has a Ph.D. in engineering from the Yokohama National University, Japan.
He specializes in metal fatigue and fracture mechanics and is particularly active in research on improving the fatigue strength of welded joints.

Authors:

Ryutaro Fueki National Maritime Research Institute, Japan