Shape optimisation to maximise crack initiation time

Article type: Research Article

Authors: Hedia, H.S.

Affiliations: Faculty of Engineering, Mansoura University, Mansoura, Egypt Fax: +20 50 2244 690; E‐mail: [email protected]

Abstract: Most of machine parts, artificial joints and their components used for human body contain fillets, which connects two different diameters or widths. These fillets may cause a failure for these components. So, in this paper an optimisation method is presented which calculates and predicts optimal shape of the longitudinal profile for transition length of a tension bar, which connects two different diameters, using the ANSYS program. This method is applied to maximise the crack initiation time by minimising the fatigue notch factor Kf. A specified program has been developed to calculate the fatigue notch factor using Ansys Parametric Design Language (APDL) which is associated to the ANSYS Package. It was observed that the maximisation of crack initiation time with higher value of the statistical parameter, k, is also a minimisation of stress concentration factor, kt, at the same time. A tension bar with four different transition length, t (t/d=0.333, 0.4167, 0.5 and 0.583) is considered. The crack initiation time of the optimal shape for all cases was increased by 17%, 12%, 9% and 7%, respectively. The stress concentration factor was reduced by 20%, 17%, 15% and 12.5%, respectively.

Keywords: Stress concentration, crack initiation time, von Mises stress, finite element, optimisation

Journal: Bio-Medical Materials and Engineering, vol. 11, no. 4, pp. 293-300, 2001