PSI - Issue 75

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ScienceDirect

Procedia Structural Integrity 75 (2025) 538–545 Structural Integrity Procedia 00 (2025) 000–000 Structural Integrity Procedia 00 (2025) 000–000

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© 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under the responsibility of Dr Fabien Lefebvre with at least 2 reviewers per paper © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the Fatigue Design 2025 organizers. Keywords: fatigue assessment; spot-weld; structural stress; notch stress; multiaxial loading Abstract This paper proposes a multi-scale approach to account for additional Mode II / III loading using structural stresses. Two parametric models, one with shell elements and one with solid elements, are used to set up a high number of macro- and meso-scale models from which the correlation between forces and moments and local notch stresses at spot weld is evaluated. To reduce the computa tional e ff ort in practical application, a machine learning model is trained from the results of both models to estimates notch stresses (solid element) from nodal forces (shell element). This model can be used to reliably assess spot weld fatigue performance in full body analyses. © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the Fatigue Design 2025 organizers. Keywords: fatigue assessment; spot-weld; structural stress; notch stress; multiaxial loading Fatigue Design 2025 (FatDes 2025) Advanced Machine Learning-Based Durability Assessment of Spot Welds Addressing Mode II and III Loading Jo¨rg Baumgartner a , Philipp Ro¨melt b a Fraunhofer LBF, Institute for Structural Durability and System Reliability, Bartningstr. 47, 64289 Darmstadt, Germany b Noa ffi liation Abstract This paper proposes a multi-scale approach to account for additional Mode II / III loading using structural stresses. Two parametric models, one with shell elements and one with solid elements, are used to set up a high number of macro- and meso-scale models from which the correlation between forces and moments and local notch stresses at spot weld is evaluated. To reduce the computa tional e ff ort in practical application, a machine learning model is trained from the results of both models to estimates notch stresses (solid element) from nodal forces (shell element). This model can be used to reliably assess spot weld fatigue performance in full body analyses. Fatigue Design 2025 (FatDes 2025) Advanced Machine Learning-Based Durability Assessment of Spot Welds Addressing Mode II and III Loading Jo¨rg Baumgartner a , Philipp Ro¨melt b a Fraunhofer LBF, Institute for Structural Durability and System Reliability, Bartningstr. 47, 64289 Darmstadt, Germany b Noa ffi liation

1. Introduction 1. Introduction

Spot welds are the main joining elements of the body-in-white. Depending on the complexity of the structure, around 2000 – 5000 spot welds are present [13]. The majority of these joints is cyclically loaded; therefore, these spot welds need to exhibit high reliability over the lifetime of the vehicle. For over 30 years, numerical assessment approaches exist to estimate the fatigue strength of spot weld. They can be subdivided in structural and notch stress approaches as well as approaches that use fracture mechanics. The most commonly used approaches have been developed to reliably predict crack initiation under mainly Mode I loading conditions, i.e., a ”peeling” combined with ”shear” is present. This is the case for standard overlap specimens under a global shear loading, since secondary bending moments are induced due to the eccentricity. This limitation can lead to Spot welds are the main joining elements of the body-in-white. Depending on the complexity of the structure, around 2000 – 5000 spot welds are present [13]. The majority of these joints is cyclically loaded; therefore, these spot welds need to exhibit high reliability over the lifetime of the vehicle. For over 30 years, numerical assessment approaches exist to estimate the fatigue strength of spot weld. They can be subdivided in structural and notch stress approaches as well as approaches that use fracture mechanics. The most commonly used approaches have been developed to reliably predict crack initiation under mainly Mode I loading conditions, i.e., a ”peeling” combined with ”shear” is present. This is the case for standard overlap specimens under a global shear loading, since secondary bending moments are induced due to the eccentricity. This limitation can lead to

∗ Corresponding author. Tel.: + 49-6151-705-474. E-mail address: joerg.baumgartner@lbf.fraunhofer.de ∗ Corresponding author. Tel.: + 49-6151-705-474. E-mail address: joerg.baumgartner@lbf.fraunhofer.de

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under the responsibility of Dr Fabien Lefebvre with at least 2 reviewers per paper 10.1016/j.prostr.2025.11.054 2210-7843 © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the Fatigue Design 2025 organizers. 2210-7843 © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the Fatigue Design 2025 organizers.