Optimal re-design of helical springs using fuzzy design and FEM

The aim of this paper is to present results of using fundamental machine element design principles into re-designing optimally heavy duty springs used in terrain machinery and in industry. Use of standard procedures often results in recurring fatigue fracture failures. This reveals need for correcting also the present standards. Main causes of failures are the local bending due to eccentric highly impact force application at squared and ground ends and wearing away of the shot peening protection. Optimum design of the spring is obtained. Goals are minimisation of wire volume, space restriction, desired spring rate, avoidance of surging frequency and achieving reliably long fatigue life. Conclusions are verified by using full 3D solid FEM analysis with MSC Nastran by which the stresses and also strains, deformations and natural frequencies and modes are obtained.