Suspension ball joints from the automotive industry are considered as safety critical parts. The quality management assigned to these parts is significantly important. Suspension ball joints (ball pin and plastic socket) allow the articulation of the wheel around its vertical axis and manage the movement of the suspension of vehicles. These operating conditions generate a cyclic loading causing then damage in the ball joints and a reduction in their lifetimes. Thus, different major failure causes should be analyzed in order to warrant that the parts do not exhibit early deterioration. Thereby, due to the contact confinement in the ball joint, some authors use the combination of finite element modelling and the modification of the ball socket surface due to his interaction with the ball pin to evaluate the wear in the running phase of the ball joint. To achieve the same objective, Peyruseigt has developed an analytical method to evaluate the pressure field in ball joints resulting from a mechanical solicitation in aeronautic applications. Concerning tribological behavior at the ball pin/plastic socket interface (usually carbon based steel / POM), an evaluation of the friction coefficient at different temperature, sliding speed and shape geometry using different tribometers has been performed. In addition, the identified phenomena that causes wear in POM/Carbon based steel is resulting from the abrasive and adhesive contacts. To predict the wear rate of POM/Carbon based steel, Shih-Shyn has used the modified Archard's law by discretization of the wear law to evaluate the wear accumulation (height) in a local mesh.

In the present study, the ball joint is composed of carbon steel based ball stud (42CrMoS4) and a polymer based ball socket (polyoxymethylene) which form the tribological system. Both components are moving each other when the ball joint rotates and tilts around its static position. In order to optimize the ball joint interface, the probability of the ball joint failure has been analyzed. An analytical model has been developed to estimate the sliding distance and the pressure field on the ball socket using different material behaviors from rigid body to elastoplastic. The results show the location of some critical zones at the contact interface . A correlation with experimental observations (SEM and optical micrographs) has been carried out to validate the model. Furthermore, tribological tests have been performed with and without lubrication in order to evaluate the friction coefficient and the wear rate for different loads and different sliding speeds, representative of the global movement of the ball joint during its life. The linear reciprocating test has been preferred to the pin on disk methodology, this is due to the fact that the ball joint is preferably used alternatively during its life. Thus, the evaluation of the friction coefficient has been done in the range of frequency and the load as in the real solicitation of the ball joint. Coupling the wear rate, the pressure field and the sliding distance field of the socket, the wear resulting from the mechanical solicitation has been estimated. Some real tests on ball joint have been then carried out to compare the real and predicted wear fields. This data can be used to optimize the product design and the process of validation/acceptance criteria.