THE SIGNIFICANCE OF WELD DEFECTS IN SMA COPPER-NICKEL/STEEL PERIMETER WELDS

The excellent antifouling and corrosion-resistant properties of copper-nickel alloy C70600 have led to the idea of using shielded metal arc perimeter welding to sheath steel ship hulls with copper- nickel sheets. In this report, the significance of defects in such copper-nickel/steel welds was studied. Cracks, holes, and slag inclusions were intentionally introduced in welded specimens. These defects were evaluated by fatigue testing the specimens in four- point bending and comparing the results with those from defect-free specimens. Surprisingly, the defective specimens had longer fatigue lives than the defect-free specimens. Finite element analysis was used to show that weld defects increase the compliance of the weld, thus decreasing the stress in the adjoining copper-nickel. Since most failures occurred in the copper-nickel, rather than in the weld metal, it is reasonable to deduce that the defective specimens had longer fatigue lives. An explanation was also given of why the copper-nickel was prone to failure in specimens with defective welds.