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Keywords:

  • 2024 T3 aluminium alloy;
  • hole deburring;
  • metal laminates

ABSTRACT

The results of fatigue and crack propagation tests carried out on dog-bone specimens made of 2024-T3 are described. Two types of specimens were investigated: the first was machined from a 1.27-mm-thick sheet, while the second was machined from a bonded metal-laminated sheet, made of four 0.3-mm-thick layers. Crack propagation tests confirmed the high resistance of metal-laminated sheets to the propagation of fatigue cracks, compared to monolithic sheets, once again. At the same time, standard fatigue tests, carried out up to the final failure of the specimens, demonstrated a comparable fatigue resistance of monolithic and laminated specimens. As a consequence, it can be concluded that fatigue cracks nucleated earlier in the metal-laminated specimens, compared to the monolithic ones, but propagated more slowly. This behaviour was attributed to the presence of sharp edges in the inner laminas of metal-laminated materials which cannot be eliminated by deburring. Additional tests were carried out on monolithic specimens containing burrs and sharp edges at the holes. These specimens were drilled and reamed after stacking and pressing them to form a package. The specimens were fatigue tested without deburring the holes. A decrease in the fatigue resistance was observed. The formation of burrs and sharp edges was additionally promoted by inserting plastic foils between the specimens during the machining operations. Fatigue resistance of these specimens is progressively lower.