EFFECT OF WELD DISCONTINUITIES ON FATIGUE OF ALUMINIUM BUTT JOINTS

Transverse and longitudinal GMA welded butt joints in 1/4 in. (6.35mm) thick aluminium alloy 5456 H116 plate were subjected to tensile and fatigue tests to study the advisability of repairing weld discontinuities. It was concluded that: 1) the levels of incomplete penetration and gross porosity present in these specimens did not affect the fatigue strength of reinforcement intact welds. 2) removing the weld reinforcement doubled the lives of sound welds, but greatly reduced the lives of transverse specimens containing incomplete penetration. 3) High residual stresses, such as would be found in actual structures, had more effect on longitudinal joints than on transverse joints. 4) Repaired welds had lives only 40% to 75% those of sound welds, unless the repairs were suitably ground or peened. 5) the discontinuities generally lowered the strengths and elongations of tensile coupons. Although the repaired welds had tensile strengths equivalent to those of sound welds, the restraint of the enlarged weld reinforcement reduced the measured elongation. 6) for relatively short fatigue cracks, insertion of interference bolts in holes at the ends of the cracks produced lives equivalent to those of sound welds. Stoppage holes - even expanded holes - did not delay propagation much. 7) Reinforcement intact repair welding of fatigue cracks was more effective for transverse joints than for longitudinal joints. Moreover, bonded or welded patches were as effective as repair welds for transverse joints.