PSI - Issue 19

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Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000 – 000 Structural Integrity Procedia 00 (2019) 000 – 000

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Procedia Structural Integrity 19 (2019) 423–432

Fatigue Design 2019 Enhancements of a Stress-Based Approach for Fatigue Life Estimation of Multi-Material Connections Joined by Self-Piercing Rivets and Adhesive Fatigue Design 2019 Enhancements of a Stress-Based Approach for Fatigue Life Estimation of Multi-Material Connections Joined by Self-Piercing Rivets and Adhesive

Jan Presse a *, Boris Künkler a , Thorsten Michler a Opel Automobile GmbH - Vehicle CAE, 65423 Rüsselsheim am Main, Germany Jan Presse a *, Boris Künkler a , Thorsten Michler a Opel Automobile GmbH - Vehicle CAE, 65423 Rüsselsheim am Main, Germany

Abstract Abstract

Due to the continuously reduced emission targets from legislation, lightweight constructions are getting more and more important for car manufactures. One way to reduce weight is the use of multi-material design for the body in white where new joining technologies, such as self-piercing rivets (SPRs) need to be considered instead of spot welding. Since both spot welds and SPRs are local circular joints, it appears reasonable to adapt and modify existing methods for spot welds to estimate the fatigue life of SPRs. These established methods typically use calculated radial stresses at the joint from inner forces (derived from FEM) and compare them to an SN-curve. Instead of comparing to a regression of calculated stress values, the presented method uses measured material specific SN-curves for this purpose. These curves contain the stresses of the materials at a notch, oriented on the rivet diameters. A modification of parameters in the stress calculation leads to a significant reduction of scattering in the comparison of simulated and tested fatigue life values. In addition to this method, an approach for the estimation of fatigue life of adhesively bonded joints was adapted. This method considers an effective stress value, which is evaluated either on a critical distance to the notch or is calculated as average over a defined path. Additional requirements during the development of the new method were the reduction of tests and a small complexity of the required FE-models to enable fast and still accurate fatigue life estimation on full vehicle level. Due to the contin ously reduced emission targets from legislation, lightweight constructions are getting more and more important for car manufacture . One way to reduce weight is the use f multi-material design for the body in white where new joining technologies, such as self-piercing rivets (SPRs) need to be c nsidered i stead of spot welding. Since both spot welds and SPRs are local circular joints, it appears reasonable to adapt and modify existing meth ds for spot welds to estimat the fatigue life of SPRs. These established methods typically use calculated radial stresses at the joint from inner forc s ( erived from FEM) an compare th m to an SN-curve. Instead of comparing to a regression of calculated stress values, the presented method uses measured m terial specific SN-curves for this purpose. These curves c ntain the stresses of the materials at a notch, oriented on the rivet diameters. A modification of parameters in the stress calculation leads to a significant reduction of scatterin in the compari on of simulated and tested fatigue life values. In ad ition to this method, an approach for the estimation of fatigue life of adhesively b nded joints was a apted. This metho co siders an effective stress value, which is evaluated either on a critical distance to t notch or is calculate as average over a defined path. Additional requirements during the development of the new method were the redu tion of tests and a small complexity of the required FE-models to enable fast and still accurate fatigue life estimation on full vehicle level.

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers.

Keywords: hybrid joined connections, multi-material connections, fatigue strength, SPR, adhesively bonded, fatigue assessment concepts Keywords: hybrid joined connections, multi-material connections, fatigue strength, SPR, adhesively bonded, fatigue assessment concepts

* Corresponding author. Tel.: +49-6142-7-76546 E-mail address: jan.presse@opel-vauxhall.com * Correspon ing author. Tel.: +49-6142-7-76546 E-mail address: jan.presse@opel-vauxhall.com

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers.

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 10.1016/j.prostr.2019.12.046