Cold Expansion Process with Multiple Balls-Numerical Simulation and Comparison with Single Ball and Tapered Mandrels

Area of Science:

• Materials Science
• Mechanical Engineering
• Aerospace Engineering

Background:

• Cold expansion technology enhances fatigue life in aeronautics by inducing compressive residual hoop stresses.
• Tapered mandrels are standard, while ball mandrels are often rejected due to non-conforming stress distributions.

Purpose of the Study:

• To investigate a novel cold expansion method using multiple balls with incremental interference.
• To compare the effectiveness of this new method against single-ball and tapered mandrels.

Main Methods:

• Finite element method (FEM) simulations were developed to model the cold expansion process.
• Experimental tests were conducted to validate the FEM models.
• Residual hoop stresses from multiple-ball, single-ball, and tapered mandrel simulations were compared.

Main Results:

• The use of three incremental balls significantly reduced the magnitude of non-conforming residual hoop stresses.
• The detrimental zone of these stresses was also reduced.
• The novel multi-ball method showed improved stress distribution compared to single-ball and tapered mandrels.

Conclusions:

• The multi-ball cold expansion technique offers a promising alternative for enhancing fatigue life in aeronautical applications.
• This method effectively mitigates the drawbacks associated with non-conforming residual stresses from simpler mandrel designs.