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<p>This study experimentally investigates the impact of mandrel’s working length on cold-expanded 7075 aluminum alloy holed structures subjected to cold expansion. The results show that cold expansion primarily alters the surface morphology around the hole, with more severe deformation occurring at the exit side of the mandrel than at the entry side. Static tensile tests revealed that the failure mode of the strengthened structure is ductile fracture. Further fatigue testing indicated that for 3-mm-thick holed specimens, a 3-mm working length of mandrel maximized the fatigue life, achieving both the highest average and maximum fatigue lives, albeit with the greatest variability. Increasing this parameter to 5&#xa0;mm significantly reduced the variability of the specimens’ fatigue life but also diminished the life gain factor. Additionally, optimal mandrel settings resulted in single-source fatigue crack origins, contrasting with untreated specimens’ multiple sources. The research provides crucial technical guidance for aircraft structure assembly and manufacturing.</p>

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Influence of Mandrel’s Working Length on Fatigue Strengthening Effects in Open-Hole Structures through Cold Expansion

  • 期刊论文

  • 发表日期：

    2025年4月4日

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  • Chushen Li,
  • Jie Wang,
  • Liu Yang,
  • Yangjie Zuo,
  • Qiliang Zhang

摘要

This study experimentally investigates the impact of mandrel’s working length on cold-expanded 7075 aluminum alloy holed structures subjected to cold expansion. The results show that cold expansion primarily alters the surface morphology around the hole, with more severe deformation occurring at the exit side of the mandrel than at the entry side. Static tensile tests revealed that the failure mode of the strengthened structure is ductile fracture. Further fatigue testing indicated that for 3-mm-thick holed specimens, a 3-mm working length of mandrel maximized the fatigue life, achieving both the highest average and maximum fatigue lives, albeit with the greatest variability. Increasing this parameter to 5 mm significantly reduced the variability of the specimens’ fatigue life but also diminished the life gain factor. Additionally, optimal mandrel settings resulted in single-source fatigue crack origins, contrasting with untreated specimens’ multiple sources. The research provides crucial technical guidance for aircraft structure assembly and manufacturing.