Fatigue Life Prediction Method for Self Piercing Rivets Considering Crack Propagation 2019-01-0531
This paper describes the numerical prediction method for fatigue strength of Self Piercing Rivets (SPRs) using fracture mechanics. Recently, high strength steels and non-ferrous metals are adopted to the light weight automotive body. Many kinds of joining are proposed for the multi material bodies. It is important to predict fatigue lives of these joints using the numerical simulation. However, the fatigue strength of joints is related to sheet thickness, base materials, and loading conditions. Therefore, a large number of coupon tests are necessary to determine the S-N curve for the fatigue life prediction of joints in the automotive body. To reduce the amount of coupon tests, the numerical simulation will be efficient for obtaining the S-N curve of joints instead of coupon tests. The fatigue fracture process consists of two stages, the small crack initiation and the crack growth. There are many studies about the crack growth estimation method using stress intensity factor. However, they cannot predict the crack initiation life. On the other hand, the fatigue life prediction method using the stress intensity factor based on Re-tensile Plastic zone Generating Load (RPG Load) can give us not only crack growth life but also the crack initiation life. The efficient of the fatigue life prediction method based on RPG load has been reported for the welding. However, no prediction methods based on RPG load have been reported for mechanical joints. In this paper, a fatigue life prediction method enhanced for the mechanical joints based on RPG load is proposed. Numerical results of SPR are compared with the S-N curves obtained from fatigue tests, and proposed methodology is considered to be efficient for predicting S-N curves.