Fatigue propagation behavior and interaction mechanism of internal multiple cracks for 6082-T6 aluminum alloy joints

This study elucidates the fatigue propagation behavior and interaction mechanism of internal multiple cracks in 6082-T6 aluminum alloy butt joints using experiments and finite element analysis (FEA). The fatigue propagation process of coplanar double cracks includes three distinct stages: single crack growth, crack fusion, and post-fusion propagation. For coplanar cracks with unequal sizes, larger spacing delays fusion and improves fatigue performance; a 4.0 mm spacing increases fatigue life by 36 % compared to 0.5 mm. Under fixed spacings, greater size disparities shift the fusion point toward the smaller crack. The BS7910 standard's equivalent single-crack model (spacing S = 0.5 mm) underestimates fatigue life by 15 % relative to actual coplanar cracks. ABAQUS-FRANC3D based analysis predicts coplanar double-crack propagation life with approximately 8 % deviation from ultrasonic phased array measurements. For non-coplanar cracks within 0.5 mm spacing, coupled stress fields accelerate crack propagation, reducing fatigue life by up to 40 %. In contrast, non-coplanar cracks spaced between 0.5 mm and 4.0 mm exhibit mutual suppression effect, enhancing fatigue resistance. When the spacing exceeds 4.0 mm, fatigue life stabilizes.