Failure analysis of steel ball in the brake operating cylinder of heavy launch vehicle

• Contact stress on the steel ball surface was calculated by finite element method.
• Metallographic and microstructure analysis of steel ball material was conducted.
• Microstructure of the failed ball was much coarser than that of new ball.
• Improper thermal treatment was considered as the reason of steel ball failure.

Steel ball plays as an essential component in the brake operating cylinder assembly. It magnifies the force applied on the raceway promoting the brake of vehicle. In the present work, the failure of steel balls utilized in the brake operating cylinder of heavy launch vehicle has been analyzed. The failure analysis was carried out from two aspects. Firstly, in order to assess the contact strength, the contact stresses of the steel ball under different loading conditions were calculated based on finite element method. On the other hand, metallographic and microstructural analysis of the steel ball material, including the failed ball and the new one, were also conducted on the purpose of investigating the influence of material property. By comparison, it was found that the failures of the steel balls were caused by improper thermal treatment, which induced coarse microstructures and residual stress in the internal part of the steel ball.